5 replies to this topic

[mariner]

Reading the kit car thread has made me think about checking my brake line pressures.

Two reasons I can think of to do it

a) to see if the pedal assy (Tilton in my case) is really putting through the line pressures I calculated.

b) To see how the brake balance may actually be split front/rear.

BUT some questions if anybody knows the answers

1) Do you have to use two gauges and read off both front and rear at the same time to be realistic?

2) Is it best to fit the gauges to the bleed nipples ( and thus save a full re bleed) or do they have to go onto the hose outlets?

3) I have ASSUMED a 0.40 co -efficient of friction for the pads in my calcualtions. I got this from some Performance Friction data as I am using PF pads. Is this realisitc or is all the line pressure stuff second order versus knowing the right pad co efficients?

4) Lastly does anyone know of a source for a 0 - 1000 psi gause suitable fro this testing?

Any help greatly appreciated.

[McGuire]

If you want to go with a mechanical pressure gauge, the various performance brake suppliers sell a little kit with a gauge and a set of adapters that screw into the bleeder port on the caliper. Just found this one for 50 bucks USD...

http://www.ssbrakes....Gauge Kit&year=

Or you can just make up your own from shop junk without too much trouble. It's just a gauge and some fittings, big deal. ABS can require more elaborate gauge setups but I assume that is not what we have here.

Personally, I have always found it useful to check both front and rear pressure, just to verify the brake bias or proportioning valve picture. There is usually no special need to have two gauges to check both ends simultaneously, it's just easier & quicker.

Another cool little tool I have found useful is the Kent-Moore pedal effort gauge. Attaches to the brake pedal and reads foot effort in lbs. I have had mine for over 25 years. J-28662 from Kent-Moore, which is now part of SPX. I just checked and it costs 400 bucks now, wow. I think I remember paying something like $70.

Of course now you have the option to do it all electronically with pressure sensors. Useful in your more exotic dynamic scenarios, driving around pumping data into a laptop or PDA.

[McGuire]

Some short-track racers run front and rear brake pressure gauges permanently installed on their cars. Over the course of a 50-lap feature they may run the brake bias all the way out in either direction and it is easy to get lost, especially when they are trying to drive at the same time. These gauges are teed right into the master cylinder outlets to simplify plumbing. You can get the gauges and panel from Longacre, Speedway, or any of the other oval-track supply houses.

Many drag racers use a dash pressure gauge in the front brake circuit because they run a holding device ("line lock") to prevent creep at the starting line. They will pump up the brakes to max pressure and then lock it with an electrically-operated valve in the front brake circuit. When it is time to go they hit the switch as they release the clutch. These gauges are sold by Autometer etc.

[exFSAE]

Pad friction coefficient *can* vary wildly with temperature. Hence pad fade. Some manufacturers will post up friction versus temperature.

Probably not a bad idea to use temperature paint on the rotors and stickers on the calipers to see how hot they get.

If you want to test brake pressure.. depends on what you have available. In-line pressure sensors are nice. I'd have one front, and one rear. They are pricey, for sure. And it had better be able to read to at least 1ksi.

[McGuire]

$80 here.

http://www.longacrer...id=774&catid=18

[exFSAE]

Cool. Didn't know Longacre made em for that cheap!