36 replies to this topic

[Fred.R]

Hi after looking at images of older race cars alot of them seem to be equiped with Girling AR calipers, when were AR brake calipers first used? is there more than one version? does any one know what the quality of the repro ones are like?

Cheers
Fred

[Peter Morley]

There are 3 sizes AR, BR & CR, with AR being the smallest, plus the NR which is smaller again and has fittings for a handbrake and was used on the rear of things like Lotus Elevens & Elites.
There are different versions of the AR - the first version has triangular pad retaining plates and external piping, later versions have spring clip pad retainers and internal piping - I think the last version was the Mk 3.
Plus a wider later version for vented discs.

They must have been available by 1957 when Connaughts were fitted with them rather than their original Dunlops (actually the Connaught's used BRs on the front and ARs on the rear).
People like Lotus and Cooper started using them around that time as well.

As for the quality of the reproductions there are several people who make them - some have a dull dark grey finish and don't look right (but are no doubt made of some far higher spec. material), others are the correct silver colour and are visually identical.

Some have been made to use original pistons and seals, but I've seen others that use a modern piston/seal of similar size (but easier to find) and even some NRs with metric threads...

As for using them, when a restorer lost an AR on one of my cars he fitted a new copy and I didn't notice until it was pointed out and it worked exactly as expected.

[Lotus11Register]

This is the later version, without external lines.

[Lotus11Register]

And this is the outside face. I've been told this appears to be an AR made in the late 1960s. What types of cars was this type fitted to?

[BT 35-8]

2.0'' ARs are fitted to just about everything in the mid - late 1960s and early 1970s , Brabhams , Lotus , ETC.
I own a BT35 Brabham , fronts are Girling AR s rears are a smaller version in 1 and 11/16'' size [ 1.687'']
Lotus 23s used AR fronts NR rears , Coopers use them .
Why buy reproductions when you can buy new ones from the same Girling people that are still making them.

Bryan Miller.

[Paul Hamilton]

The problem with the early AR calipers with external piping is their tendancy to flex in high stess situations and allow tapered pad wear with obviously detrimental consequences if the pads are not replaced VERY frequently or regularly ground flat. Its a problem I have been dealing with for almost 40 years with my Elfin 600 F2 car and, although my Elfin has never used any of the later model ARs with internal piping or the modern replicas, they all look a bit meatier and, from my observation of their performance on other cars, it seems to me that they don't have the problem or at least not to the same extent.

I was interested to read of Peter Morley's experience with the performance of the modern replacement as it could indicate either that:
1. He was replacing one of the later internally piped versions which would be more likely to perform in line with the modern replacement ; or
2. The car to which the replacement was fitted was an older one which does not generate as much braking power as a late 60's open wheeler and therefore has never experienced the flexing problem.

Its interesting to observe the corelation between brake specifications and tyre development over the years. I am sure that the ARs would have been perfectly adequate in the early 60s but by 1968 when my Elfin was built their adequacy was being tested because of vastly enhanced grip levels and by the time of the early 70s when wings and slicks accelerated the grip equation they were becoming inadequate on a front line single seater and were replaced, at least on the front, by larger and stiffer 4 piston calipers.

Any comment Peter? What type of car was your one corner replacement fitted to?

[Ray Bell]

As can be seen from Jay's side-on picture, the 'frame' of the caliper, the part of the casting that holds it together during braking, is cohesive to past the centreline of the piston...

This means that, provided the alloy has sufficient integrity, the caliper shouldn't spread. The problem with this is that it limits disc size, as larger diameter discs will naturally have to go further into the caliper than would be permitted by the relief shown. This would weaken the structure and allow spreading.

I recall clearly when Frank Matich was developing the Lotus 19B how he remarked that going to bigger discs measurably improved braking. His comment was intended to question why, if you can lock a wheel with a smaller disc, you won't lock the wheel while stopping harder with the larger ones.

So he must have had calipers that either suited the larger disc or relieved the regular Girling units to give clearance. Was there a range of disc diameter provisions in these calipers?

[Peter Morley]

Quote

Originally posted by Paul Hamilton
The problem with the early AR calipers with external piping is their tendancy to flex in high stess situations and allow tapered pad wear with obviously detrimental consequences if the pads are not replaced VERY frequently or regularly ground flat. Its a problem I have been dealing with for almost 40 years with my Elfin 600 F2 car and, although my Elfin has never used any of the later model ARs with internal piping or the modern replicas, they all look a bit meatier and, from my observation of their performance on other cars, it seems to me that they don't have the problem or at least not to the same extent.

I was interested to read of Peter Morley's experience with the performance of the modern replacement as it could indicate either that:
1. He was replacing one of the later internally piped versions which would be more likely to perform in line with the modern replacement ; or
2. The car to which the replacement was fitted was an older one which does not generate as much braking power as a late 60's open wheeler and therefore has never experienced the flexing problem.

Its interesting to observe the corelation between brake specifications and tyre development over the years. I am sure that the ARs would have been perfectly adequate in the early 60s but by 1968 when my Elfin was built their adequacy was being tested because of vastly enhanced grip levels and by the time of the early 70s when wings and slicks accelerated the grip equation they were becoming inadequate on a front line single seater and were replaced, at least on the front, by larger and stiffer 4 piston calipers.

Any comment Peter? What type of car was your one corner replacement fitted to?

Paul

It was an early external pipe version, fitted on a 1961 Emeryson F1 car - a 1½ liter car with narrow wheels, with as you say limited braking power.

I'd never heard of the calliper flexing problem and a lot of early 70s F2 cars used ARs without problem, but they were presumably the internally piped versions by that time.

Have you considered that maybe the problem is in the calliper and/or disc mounting, flexing of the upright (or calliper mounting lugs) and/or stub axle could cause the problems you describe?

What you are sugesting would be a design weakness that would affect originals as well as replicas (unless the replica has been modified in which case it isn't a replica or really acceptable), actually calling it a design weakness is probably unfair since they worked perfectly well on the cars they were designed for, by the time your Elfin was made things had moved on and presumably it should have been built with different callipers (or BRs?).

I just came across an early AR in the garage will photograph it later for comparison with the later one in Jay's photographs.

Peter

[Peter Morley]

Here are some photos of an early AR (missing the pad retainers) and a later (wide slot, vented disc) version.
The early one is dated 10 7 / 66 (10th July 1966 for those who use strange date formats!).

To answer Jay's question his calliper is a later one, it would have fitted things like early 70s F2 cars - if he looks carefully he might even find a date stamp on it somewhere - it should be interchangeable with the early version.

[Paul Hamilton]

Peter, your photos provide an interesting direct comparison which, I think, demonstrates my point that the later internally piped ARs were 'meatier' in the bridge area across the top of the caliper which would therefore make them more resistant to the flexing I have experienced.

Over the years I have indeed taken steps to stiffen the stub axles and caliper mounts with positive results in eliminating pad knock off but no impact at all on the tapered wear problem. The pattern of the wear on each pad seems to clearly confirm that the calipers are flexing and, as I like to maintain the car in as original a specification as possible, I have long since accepted the issue and simply regularly grind the pads flat and replace them quite frequently - sometimes between races at meetings on circuits such as Mallala which have particularly heavy braking requirements. Provided it is maintained in that way the Elfin's braking performance is at least the equal of similar late 60s cars. I know that other people using the early model ARs on cars from this period have had similar issues and I have always presumed that the flexing problem was one of the reasons for development of the internally piped version.

I agree that the problem should not be seen as a design deficiency in the context of the intended original application of the AR caliper as it only becomes evident when suspension, tyre and aerodynamic changes increase grip to a point where the calipers are no longer up to the job. It is interesting to note that in my long experience with this car there has been a direct corelation between the scale of the problem and the remainder of the car's specification. When I used the 600 with wings and slicks in the early 70's the problem was at its worst. It reduced significantly when I brought the car back into action and started historic racing in the mid 80s using Dunlop CR65s similar to those which would have been used back in 1968 and I suspect that, when the car was run originally with CR65s which would have been a bit harder that those now available, it may not have been much of an issue at all. In recent times since we have been using Avons on this type of car in Australia it has again become more of an issue as they have much more grip and have shortened braking distances appreciably. Its all pretty logical really and simply highlights the manner in which technical progress in one area often raises problems in another - an issue of great significance in the late 60s / early 70s when there was a great deal of technical change in a relatively short period.

[John Brundage]

I too have seen the tapered brake pads from the calipers flexing. The driver of one car that has this problem complained that he had to press harder and harder on the pedal as the race evolved. I am trying different compound brake pads to see if the car can slow with reduced pedal pressure and thereby reduce the flex of the caliper and resultant tapered pads. We shall see in a month if this works.

[Peter Morley]

Quote

Originally posted by Paul Hamilton
Peter, your photos provide an interesting direct comparison which, I think, demonstrates my point that the later internally piped ARs were 'meatier' in the bridge area across the top of the caliper which would therefore make them more resistant to the flexing I have experienced.

It is hard to see from the photos but the thickness of the top part of the bridge area is much thinner on the earlier ones - where it is machined flat and level with the tops of the pads for the pad retainers - the rest is of similar thickness.
I wonder if that was deliberate when they introduced spring clips, for quicker pad changes, or just a lucky bonus.

With your tapered pad wear does it happen on both pads or mainly the outer one?
Given the calliper mount is less likely to move I would expect a flexing calliper to bend on the outside (assuming you don't have floating discs).

[Paul Hamilton]

[QUOTE]
originally posted by Peter Morley
'With your tapered pad wear does it happen on both pads or mainly the outer one?
Given the calliper mount is less likely to move I would expect a flexing calliper to bend on the outside (assuming you don't have floating discs).'

Yes Peter the tapered wear is much more pronounced on the outer pad which, as you have rightly suggested, supports my contention that the calipers are flexing. That is what I was referring to when I mentioned the wear pattern on each pad. It also tends to confirm that both the caliper mount and the suspension upright that it is mounted on are quite stiff and that flex in that area is not the issue.

I am firmly of the view that the flexing is a simple product of hydraulic line pressures moving beyond those expected when the calipers were first used on cars with lesser grip capabilities. In that context it will be interesting to hear whether John Brundage's experiment with softer pad compounds makes much difference for him. While it should certainly help I suspect it will not overcome the demands created by the increased grip available as, in the short historic events we now contest, I am already using much softer pads than I did in former times but the problem is still there.

[Peter Morley]

Paul
That certainly sounds like a calliper issue.
I've no idea what has happened to the circuits in Australia over the years but in europe they tend to have gained chicanes and tighter corners to slow cars down, one effect of this is that brakes can be used a lot more than when our cars were designed. That could also have an effect on your problem - the changes in speed required being higher now which, as you say, requires more braking effort which is pushing the callipers beyond their design.
Also when the cars were new it is likely that they changed pads every race (Which would have been a lot longer than most historic races) so they weren't as badly affected as you are.
I'm sure there are some modern pad materials with a higher coefficient of friction that will require less brake pressure, finding the right one could be a solution.
It could be an interesting (albeit expensive) exercise to try some of the later ARs on your car to see if that reduces the wear issue - especially if your callipers are 30+ years old and have been flexing for so long, that could lead to fatigue issues.
Peter

[Paul Hamilton]

For the most part, Peter, the circuits now used in historic events here in Australia remain pretty much unchanged in layout from the way they were when I was competing back in the late 60s / early 70s and, fortunately the newer circuits which have come on the scene such as Eastern Creek are not blighted by Tilke like chicanes etc. The braking demands on the car are no greater now but the races are shorter which must help. Its difficult to draw a valid comparison on the extent of the flexing now compared to what it was back then because of changes in pad material, tyres and other specification changes bearing on the grip level but, in general, the frequency of pad changes remains pretty much the same. Grinding pads flat and replacing them regularly has been part of my routine maintenance of this car for more than 35 years!! I don't think that there is a fatigue factor here which might have agravated the problem and, if I did have reason to suspect that, I would almost certainly replace the calipers.

Over the years I have already tried a few different pad materials and would not like to go any softer than those I now use so I don't see that as a likely solution.

Regardless of any fatigue motive, it would be interesting to replace the calipers anyway simply to see if the later version is in fact better and that idea has periodically crossed my mind. It would, as you say, be expensive and, more importantly from my perspective, it would reduce the cars originality which would be sad particularly when these early externally piped calipers are so visually distinctive. The current calipers are date stamped 1967 and are original to the car which has a pretty fair history in SE Asian and Oz events of the period so, apart from the occasional bleat about the problem such as I have aired in recent posts here, I am happy to accept tapered pad wear as one of the burdens of ownership of a car which, overall, continues to give me great satisfaction. I well recall the great impression it made on me when I first drove it at Oran Park in 1973 and it still gives me great pleasure whenever I get the opportunity to step behind the wheel.

[Peter Morley]

At least changing callipers is a reversible process and you would still have the originals so swapping them would have no long term effect on the car's originality.
And if it did solve the pad wear problem they might eventually pay for themselves!
I'd be interested to hear the results if you did try it.

[xkssFrankOpalka]

At Indy I saw AR calipers used and the extenal bridge pipes were fiberglased to the body of the caliper, perhaps a broken pipe had happened. I usually shim the caliber bracket to the spindle, amazing how much out of line they are. The brakes are much improved.

[johnny yuma]

When Holdens got discbrakes in 1965 most I've seen were Girling stamped with stainless steel clip and internal piping.I had done many thousands of miles in several models up to 1972--even 350 Monaros and XU1s had the same brakes--but for street use never saw the distorted pad wear, till I raced an old holden sports sedan on slicks,although I never got brake fade pulling up the 1040kg from 110 mph at Oran Park.Not that the braking or cornering g-forces would be anything like Paul Hamilton's car !

2005, a competitor at ECR in a Sunbeam Tiger (Alpine V8) destroyed almost-new pads on the Saturday at an Eastern Creek historic,ditto a Canadian I met at Timaru historics in February has the Tiger brakes as an Achilles heel for race stresses.These have identical brakes to the 65-72 Holdens.

The faster Group N© XU1 Toranas now often use old Volvo twin-pot calipers which bolt straight in and clear the 13 inch wheels.I guess most of us remember the almost-brakeless status of the heavy 327/350 Monaros in the Bathurst 500.Nothing like racing to reveal deficiencies !!

[Ray Bell]

They were cast iron, Johnny...

These ARs were all aluminium castings.

[johnny yuma]

I should have known that. Hang on,I DID KNOW THAT ! I'll just go now....but it does seem maybe it is the hydraulic pressure spreading the calipers causing the off-square wear on the pads,not knock-off due to cornering forces distorting adjacent components.Do you end up with a pair of mirror-image off-square pads (caliper spread)or a pair of parallel off-square (cornering distortions) and does it change on clockwise or counterclockwise-dominated circuits?

[Paul Hamilton]

[QUOTE] originally posted by Johnny Yuma
Do you end up with a pair of mirror-image off-square pads (caliper spread)or a pair of parallel off-square (cornering distortions) and does it change on clockwise or counterclockwise-dominated circuits?

My experience , Johnny, is that the pads wear in a 'mirror image' fashion but with the taper more pronounced on the outer pad than the inner which is better supported by the caliper mounting. Its purely a braking issue and circuit direction or corner orientation makes no difference.

[John Brundage]

[QUOTE]Originally posted by Paul Hamilton
[QUOTE]
originally posted by Peter Morley
'With your tapered pad wear does it happen on both pads or mainly the outer one?
Given the calliper mount is less likely to move I would expect a flexing calliper to bend on the outside (assuming you don't have floating discs).'

Yes Peter the tapered wear is much more pronounced on the outer pad which, as you have rightly suggested, supports my contention that the calipers are flexing. That is what I was referring to when I mentioned the wear pattern on each pad. It also tends to confirm that both the caliper mount and the suspension upright that it is mounted on are quite stiff and that flex in that area is not the issue.

I am firmly of the view that the flexing is a simple product of hydraulic line pressures moving beyond those expected when the calipers were first used on cars with lesser grip capabilities. In that context it will be interesting to hear whether John Brundage's experiment with softer pad compounds makes much difference for him. While it should certainly help I suspect it will not overcome the demands created by the increased grip available as, in the short historic events we now contest, I am already using much softer pads than I did in former times but the problem is still there. [/QUOTE]

Preliminary reports on the compound change from the driver are positive. He was able to get on the brakes hard with no change in brake pedal feel that was associated with the other compound that was worn to a taper. The previous compound was all heat and no braking, which caused the driver to push harder, calipers to flex and pads to wear at an angle. I will do a visual check later this week.

[Mogens Christensen]

Hey,

Are there anybody here in this forum, who can help us, please.

My problem is our restauration of my Wolverine CanAm racingcar from 1965.
We want to drive racing with this car all over the world, but it is only possible if we can show FIA in France some paperwork, data and so about this brakecalibre with type Girling AR and especially year for production.

Best regards

Mogens Christensen

[CLR]

In an earlier posting, I think it was Peter M who talked of repro Ar and Nr's.

Well in the UK some are Forged magnesium and some are cast mag.

As I understand things, the forged items would seem to offer a stiffer caliper.
Kevin Whittle

[Kale]

Hello

I have two pairs of Girling Calipers
A set of Aluminium Calipers - stamped 64320805 and a set of steel calipers sta,ped 64327863
From whar car come this parts ( Racecar ? )

[Peter Leversedge]

I had a Griling Caliper on my sprintcar in the late 80's. If I remember correctly it was a AP, had internal piping, two pistons, looked like some of the capilers in the photos. It was mounted inboard on the left rear, it worked ok and the pad wear was even.
It fell off in a race once and apart. It was mounted to an aluminium with UNC bolts threaded into the bracket and the bolts worked loose. I discovered with that car that any UNC bolts threaded into aluminum worked loose when the track was "heavy". UNF was ok. Hence I put lock nut on all UNC bolts with lock wire and had no more trouble. Any one have the same trouble?

[Lee Nicolle]

Peter Leversedge, on Dec 15 2011, 10:18, said:

I had a Griling Caliper on my sprintcar in the late 80's. If I remember correctly it was a AP, had internal piping, two pistons, looked like some of the capilers in the photos. It was mounted inboard on the left rear, it worked ok and the pad wear was even.
It fell off in a race once and apart. It was mounted to an aluminium with UNC bolts threaded into the bracket and the bolts worked loose. I discovered with that car that any UNC bolts threaded into aluminum worked loose when the track was "heavy". UNF was ok. Hence I put lock nut on all UNC bolts with lock wire and had no more trouble. Any one have the same trouble?

Surprisingly a lot of modern cars use metric coarse bolts on callipers.Though screwed into cast iron or steel. And I have seen them loose too though why I do not know. Personally I would never bolt a callper on threaded into alloy.

Personally I have always used unf bolts on that sort of hardware with no problems.

And Peter I have seen a rotor explode in that position on a sprinter. The driver was very lucky to get away with minor cuts to his nether regions but the seat was destroyed. It was one of those stupid scalloped lightweight rotors that dont seem to be around these days.

[Peter Morley]

Mogens Christensen, on Apr 24 2009, 12:56, said:

Hey,

Are there anybody here in this forum, who can help us, please.

My problem is our restauration of my Wolverine CanAm racingcar from 1965.
We want to drive racing with this car all over the world, but it is only possible if we can show FIA in France some paperwork, data and so about this brakecalibre with type Girling AR and especially year for production.

Best regards

Mogens Christensen

Hi

The AR, BR & CR calipers all existed in the late 1950s, they were fitted to cars like Lotus 11, 18 and Lister Jaguar, you should easily find some photos of such cars with them fitted which will prove to the FIA that they existed before 1965 (which the FIA should really know).

I suspect your problem is to prove exactly which types of brakes were fitted to your car originally?
If so it is a typically stupid FIA problem, since these calipers were easily available and probably the most common that were being used at the time.
The FIA probably want to 'make sure' that you have not improved the car from its original specification, which is really stupid because the only thing worse would be drum brakes which no one would have been using on such a car and most of the other disc brakes available at the time would have been bigger/better like the Girling 4 piston callipers fitted to cars like Lola T70s.

Good luck
Peter

[Peter Leversedge]

Lee
Re Caliper Mounting, I would not mount one myself threaded into alloy but that was the way it was done when I got the car
Peter

[ianrand]

While were discussing AR, BR, CR Girling calipers: Has anyone here ever removed the large plug from the side of the caliper? I have a CR caliper that leaks around the plug and thought I'd ask what to expect as far as the type of internal seal, torque to remove/re-install plug, etc. Thanks.

[horizon]

Ian,
yes, I've removed the plugs from a couple of Calipers. Not something you really "want" to do, but if it's leaking.....
The treads are very fine. use some gentle heat and a good tight fixture. There was a seal in one caliper and not the other.I got lucky ....twice, the treads were okay. I used a dab of locite to reassemble after every thing was super clean.


Good luck

[ianrand]

Thank you for the info re removing the large plug. I feel better about attempting the repair now. I assume the threads are RH?

[plannerpower]

Re coarse -v- fine threads; coarse threads are generally stronger, especially in cast iron, aluminium etc.

There is a greater amount of material in each thread engaged at the thread pitch diameter.

Fine threads can sometimes be stronger if the parent material itself is very strong but coarse seems to win in "ordinary" materials.

The downside of coarse threads, as described, is their greater tendency to loosen and a locking device is a good idea.

I seem to remember a story that either Chapman or Duckworth believed that a properly-designed threaded fastener requires no locking device and the Lotus 49 was initially built on that principle.

On-track experience soon prompted the fitting of locking devices to certain key fasteners.

Edited by plannerpower, 17 December 2011 - 00:21.

[Lee Nicolle]

plannerpower, on Dec 17 2011, 01:11, said:

Re coarse -v- fine threads; coarse threads are generally stronger, especially in cast iron, aluminium etc.

There is a greater amount of material in each thread engaged at the thread pitch diameter.

Fine threads can sometimes be stronger if the parent material itself is very strong but coarse seems to win in "ordinary" materials.

The downside of coarse threads, as described, is their greater tendency to loosen and a locking device is a good idea.

I seem to remember a story that either Chapman or Duckworth believed that a properly-designed threaded fastener requires no locking device and the Lotus 49 was initially built on that principle.

On-track experience soon prompted the fitting of locking devices to certain key fasteners.

With callipers most are bolted to the upright using NC or fine other threads. But tapping fine threads into alloy and to a lesser extent cast iron is not a good idea as the material 'strips' out. That in hindsight is why I am seeing more coarse threads into uprights or callipers, as they are [high grade] cast iron. And these bolts are generally loctited in, or on Falcons lock wired.

[carlt]

Does anyone know what max disc diameter can be used with an AR caliper

cheers

[SJ Lambert]

Peter Morley, on 15 Dec 2011 - 12:42, said:

Hi

The AR, BR & CR calipers all existed in the late 1950s, they were fitted to cars like Lotus 11, 18 and Lister Jaguar, you should easily find some photos of such cars with them fitted which will prove to the FIA that they existed before 1965 (which the FIA should really know).

I suspect your problem is to prove exactly which types of brakes were fitted to your car originally?
If so it is a typically stupid FIA problem, since these calipers were easily available and probably the most common that were being used at the time.
The FIA probably want to 'make sure' that you have not improved the car from its original specification, which is really stupid because the only thing worse would be drum brakes which no one would have been using on such a car and most of the other disc brakes available at the time would have been bigger/better like the Girling 4 piston callipers fitted to cars like Lola T70s.

Good luck
Peter

 

 

At least a couple of the ones on my Mono are date stamped 1964 

[terry mcgrath]

I have a pair of these possibly for sale including a copy of workshop manual/specification sheet etc for them

terry

tmcgrath@bigpond.com