Excessive Brake Pedal Travel

Adams,

The rod length I found changed slightly when I installed the new master ... i don't remember if i lengthened it r shortened it to bring the pedal up. Again if memory serves me correctly its taking the 2 nuts off on the master and turning the rod ... it took me two try's to get it where I wanted the pedal.

Ron

Adams,

Are you saying that the pedal is lower than before at rest and then it travels to far OR, is the pedal in the correct location at rest and then travels to far?

The rod length will not fix the latter. I have a stock master I could measure if need be...

Scott

Did you bench bleed the master before install? That is important. It gets all the internal passages of the new master full of fluid before you connect it to the system.

http://www.superchevy.com/tech...9sc_bench/index.html

if the pedal travels too far, the rod needs to be longer. a rod that is too long would possibly cause the brakes to drag, but it will not increase pedal travel.

the new rod length will be dependent upon which master cylinder PI Motorsports sold you; i.e. is it an OEM style replacement master, a GM master, a Ford master, etc.

I would expect Jerry at PI Motorsports to have an answer for you.

I would draw a picture to detail how to deduce the rod length, except I'm on the road working from a laptop.

-G

Rod length should not affect the stroke of the pedal, only change the position of the pedal, or create a certain amount of free pedal movement before it starts pushing the piston.
So, does the pedal have a low position before it starts to move?
Is it level with the clutch pedal?
If your pedal is starting at a high position & the pushrod is too short then the pedal will have no resistance for the first part of its stroke & then after a short amount of stroke you will start to feel pedal pressure.
If the pedal is high & the there is no slack in the pedal & there is pressure for the full stroke.
Then it could be the master cylinder bore is too small.
A small bore master cylinder will create a light pedal, requires little effort, but it will be a long stroke.
A larger master cylinder bore will do the opposite, it will be a hard pedal & have very little stroke & require more effort from the driver.
Regards,
Tony.

Wow, this is the most awesome board on the internet. Thanks, thanks...

1. Brake pedal position seems fine, even with clutch. Basically 'normal'.

2. Pedal travel until brakes grab is too far. It is a fully firm pedal.

3. I did NOT bench bleed, but we pressurized and vacuumed 3 cans of Valvoline synthetic through the entire system to 'correct' that oversight. We hope. Again, pedal has no squish, just too much travel.

Does that help?

I replaced mine a couple of months ago with what is probably the same master cylinder from PI, stock looking although larger overall and a larger bore. I had to fabricate a locknut for the rod because the threads were too loose unlike the stock setup but that was easy. I purposely set the rod length long and assembled the system but did not tighten it down so I could feel where the rod bottomed out. I used a feeler gauge between the MS and brake booster to determine the rod length overage. From there I removed the MS and using a caliper and the Factory manual recommendation for free play I set the lenght. It worked the first time! What a made a big difference though was the new Porterfield brake pads. I ordered the R4-S fronts and the grippier R4-1 for the rears. The car stops now!

Steve

quote:

Originally posted by A Hudson:
Wow, this is the most awesome board on the internet. Thanks, thanks...

1. Brake pedal position seems fine, even with clutch. Basically 'normal'.

2. Pedal travel until brakes grab is too far. It is a fully firm pedal.

3. I did NOT bench bleed, but we pressurized and vacuumed 3 cans of Valvoline synthetic through the entire system to 'correct' that oversight. We hope. Again, pedal has no squish, just too much travel.

Does that help?

Well, too much pedal travel, presuming that the mechanicals have no issues, is a symptom that there is not enough pressure being produced by the master and one of the reasons is...ta da...you need to bench bleed the master.

Why some master cylinders are so sensitive to this and others not...beats me, but it's true.

If you decide to do that, you might want to measure the diameter of the bore of the master while it is out.

My stock Pantera master is 30mm or ruffly 1-1/8". If yours is smaller, that is also an explanation of why there is more travel and less inherent pressure in the master.

I am a believer in going larger then stock because it adds feel to the pedal and reduces the overall travel to maximum.

My '68 GT350 has what the vintage racers call the "Mustang Trans-Am Brakes".

The master is sourced from an F250 of the era and get this, it is a 1-5/16" bore. (1.315" diameter). I love the feel. I haven't met anyone who thinks the pedal is too hard. Everyone loves it.

According to many who sell brake kits though, it is way too big, and I won't have the leg strength to work it. They recommend no larger then 1-1/8" bore for RACING brakes. Know what? Poppycock. Don't you believe it.

Bigger is way better.

BIG UPDATE:

I've had more going on that need be this spring, and just got back on the car.

1) The man(Joe H. PI member) who bought my master cylinder sent me PERFECT measurements from my old master cylinder. Turns out 4.86" from body of master to end of piston was what I needed. About 1/4 of turns to adjust.

2) Plus, I bench bled the master. A little messy but got it.

Put it back together, bled the brakes. MAN O MAN I have brakes again.

Thanks all for you input.