8 replies to this topic

[davo]

Having been enjoying some time with the "Grand Prix Legends" game over the Christmas break I think I have now understood how a traditional clutch pack and ramps slip limiting diff works. Within the game at least as of 1967 all the teams were using these diffs.

My question is what other diffs have been used over the intervening time? There a lots of alternatives currently in use in road cars but within F1 I only know of:

Brabham/BMW using a Weisman which was a form of locking diff - simple, light, and fully open on zero power, fully locked on any power.

and what is used currently which is computer controlled hydraulics/clutch pack to mimic whatever the team wants.

[Ray Bell]

This is one of the areas where not much information filters through to the common man. However, in the late fifties and early sixties the most common was the pawl-arrangement type of LSD made by ZF and (under licence, I think) by Hewland.
A confrontation between the Lago Talbot of Doug Whiteford and the Maybach Special of Stan Jones (Alan's daddy) in the early fifties was resolved in favour of the hybrid because it had a limited slip diff from a 1920s (Studebaker?) truck.
On the circuit involved, that would have really counted.

[Ian McKean]

This is a really interesting subject and it is unfortunate that very little info is released these days.

But I am intrigued by the comments from Ray Bell about the limited slip diff from a 1920s (Studebaker?) truck in Stan Jones Maybach special and also by the inference that the Lago Talbot had no LSD.

My knowledge of LSD's in motor sport is that the ZF LSD was introduced by Auto Union in 1936 and of course that was the year that Bernd Rosemeyer was European Champion. Mercedes only installed a LSD in 1937, and in that year they were back on top.

I would have thought that everyone including Lago Talbot would have had LSD's by 1949/50.
Also, I wonder what people did before? Surely a locked diff (i.e. no diff) would have been better than a conventional diff in racing? Some early cars such as the GN and Frazer Nash of the twenties and thirties had chain drive with no differential. They used a narrower rear track to minimise the need for a diffential effect on tight corners.

Also my own experience tells me that for racing no diff at all would be better than a diff with no LSD. I remember a ride in a full-race Lotus Anglia with a locked up diff in about 1965. Only driven slowly on tight corners were you aware that it was reluctant to turn. Karts (I used to race a gearbox kart) handle fine with no diff. People used to drop bronze weld in between two teeth only on the diff planet gears so that the diff worked for nearly a revolution of one driving wheel before locking.

I remember reading somewhere that the Porsche 917 was raced (maybe just occasionally) with no diff instead of a LSD. Can anyone provide more info on this?

Lastly, if Dr Porsche came up with this idea for the 1936 Auto Union, how come it was on a Studebaker truck in the 1920's?

Ian

[This message has been edited by Ian McKean (edited 01-23-2000).]

[Ray Bell]

I'll check it out, but that's what I read in the report on the 1950 Woodside meeting, where Jones beat Whiteford because he had superior traction.
Now, Woodside, that was about two miles from Lobethal, and it had a doosy of a narrow bridge at the base of a steep hill, all on a gentle curve, of course! and a railway line that crossed the main straight diagonally...

[desmo]

I read in R&T that diffs are run fully locked nowadays. That was a few years ago, though.

[BRG]

I am no engineer, especially when it comes to gears and diffs, but I know the effects of different diffs from experience.

I thought there were two sorts of mechanical LSDs - the ZF type (dog and pawls, whatever they are) and the Salisbury type (using plates). I had the former on my Capri 3000 and it was a bitch at slow speeds, clanking and jerking and generally scaring old ladies. But give it some welly and it worked smoothly and well. The Salisbury type is more civilized and is the sort that I think was fitted as original equipment on certain road cars (my Toyota Corolla GT Coupe had one, for instance). But how modern F1 and World Rally Car electronic/hydraulic diffs work, heaven knows.

As to the effects, well, the more locked the diff is, the better the straight line traction, but there are other problems. A highly loaded LSD can cause terminal understeer unless you enter corners right off the power - otherwise, it simply pushes the car straight on (or rather, off). I experienced this on a rally once where the driver had just fitted an LSD to his Mk1 Cortina GT and it took time to get used to turning in off the throttle and then burying it. So we visited the scenery several times, before he got the knack.

An LSD or a locked diff can help to steer a (rear wheel drive) car on the throttle, particularly useful on gravel rally stages . For rallying, the slow-in, fast-out approach is fine, but for modern racing, drivers often go into corners still on part-throttle and brake into the apex. With a full locked diff, you would be in the gravel traps, I suspect. You do need some slip which is why LSDs were developed and why they can be given different degrees of preset to suit the car and its use.

These days it is all a really black art. But there must still be advantages in having a degree of slip in the diff sometimes, otherwise it would be locked diffs all round in motorsport. I guess the secret of modern racing diffs is that they can vary from unlocked to locked through degrees of slip limitation depending on what is required at exactly that moment.




------------------
BRG

[tak]

There is also an interesting family of "torque biasing" differentials, that are capable of biasing more torque the the wheel with more traction. The "Gleason Torsen" and "Quaife" (spelling) differentials are two examples. They work extremely well, but are too expensive for everyday autos and too heavy for F1! I've seen Quaife's availble for Golf's, and I know the 3rd gen Rx-7 used a Torsen. I think Audi might still use a Torsen for the center differential in their Quattro's.

[Jonathan]

Would this topic be better suited placed in the Technology Forum ?

I think some of the early 1980ies Brabham F1 Cars were rumoured to be using a TORSEN (or was it a Weisman ?) differential.

I know my Subaru uses a "viscous coupling" centre-differential that works really well. I suppose this same technology could work on the rear-diff as well.

The interesting thing about a viscous coupling is that there are only cetain synthetic fluids that can be used. These fluids have an interesting property of "thickening" as they get warmer. (The more slipage that occurs, the hotter the fluid gets, and the harder it becomes for slipage to continue).

I think Jeep / American Motors Corp pioneered this in the early 1970ies under the name of "Quadra-Track".

I am not sure how much of a performance penalty I pay for this, however. I know the Subaru Rally cars use some form of an electro-mechanical clutch in place of a Centre-Diff.


[This message has been edited by Jonathan (edited 02-10-2000).]

[Ray Bell]

Brabhams definitely used a Weismann, that was well reported. But I wonder at how simple they might have been - the Bob Jane Monaro had one and when Phil Ward bought it he had a problem. It would drive and then not drive, and he said it was too tricky to fix and he had to send it to the States. Bob Jane said you had to be a genius to figure them out as well.