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Softish Brake Pedal When Engine Running.

BASHO
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BASHO Mentor

BASHO

Posted
Posted

Just bled the brakes on my R34GTT , all good, pedal as hard as nuts till I start the engine then the pedal gets a softish feel at the top of its travel.

The brakes work fine.

WTF am I doing wrong ?

It's not as though I've never bled brakes before and this is shitting me no end I've bled the farkers out twice just to be sure I had it right the first time.

Any ideas anyone.

:cool:

MrStabby Grand Master

MrStabby

Posted
Posted

The only diff with the engine on is that the booster is helping put force on the master cylinder. So nothing will change in the hydraulics. Are you saying its worse than before you bled them?

paulR32gtr Mentor

paulR32gtr

Posted
Posted

To be honest I have found the procedure in the 32 GTR manual to be not as effective as a different method - how are you bleeding them?

I suffered from a lot of ineffective travel at the start of pedal in, brakes still worked fine.

Rather than pulsing the brakes with the bleeder screw open as the manual says to do, I get my assistant to push and hold the brake pedal hard while I quickly open and close the bleeder screw. Do this until no bubbles come out before moving on to the next, make sure you bleed in the right order - RR, RL, FR, FL and dont forget the ABS in the right order.

My pedal is now quite solid since switching to this method.

  • 2 years later...
Hanaldo Grand Master

Hanaldo

Posted
Posted

Right, just going to bump this thread as I'm currently experiencing the same issue. I have bled my brakes twice and have got clear fluid coming out at all four corners with no air bubbles. Peddal is solid when the engine is off, but as soon as you fire up the engine the pedal goes to the floor. Mick_o mentioned he had the same issue when he fitted Alcon calipers to his car, and it turned out to be the ABS unit needing to be bled. This makes sense in my case, as I had to remove the brake lines from the BMC when I was removing my head, so air would have got into the lines before the ABS unit.

Now what I want to know, is can I bleed the ABS module without the service tool to cycle it? Mick said he bled his in the same way as normal, by cracking the lines off and pumping until no air came out. But his is an R33, are R34's the same? Another method I have heard is to take the car for a drive and keep hitting the brakes hard to activate the ABS, then re-bleed everything? I'm not too keen on that method for obvious safety reasons. Any other ideas?

Also, is it necessary to follow the 'procedure' for bleeding brakes? Ie. RR, RL, FR, FL? I did mine the opposite way, RL, RR, FR, FL; will that not work properly?

Hanaldo Grand Master

Hanaldo

Posted
Posted

bleed all brakes on all cars from longest brake line to shortest, have you tried bleeding the brakes with the engine running so the abs is active and solinoids are open?

Yes, no luck. It just stays spongy. I think I'll give it a go just bleeding it as Mick has done, worst case it just doesn't work.

Mick, did you bleed the lines from the BMC in any specific order? I'm not sure how the ABS module looks internally, so not sure whether it's better to bleed one line before another or all at the same time, etc. etc?

Missileman Veteran

Missileman

Posted
Posted

Sometimes you can get a bubble stuck behind the piston, connect a clear tube to the bleed nipple and tie it up so it remains in a vertical position, loosen the nipple and then push back the piston, you will see a bubble or two rise up the tube, close the nipple and rinse and repeat.

Hanaldo Grand Master

Hanaldo

Posted
Posted

Sometimes you can get a bubble stuck behind the piston, connect a clear tube to the bleed nipple and tie it up so it remains in a vertical position, loosen the nipple and then push back the piston, you will see a bubble or two rise up the tube, close the nipple and rinse and repeat.

But that wouldn't explain why it only does it with the engine running.

Mick_o Grand Master

Mick_o

Posted
Posted

Yes, no luck. It just stays spongy. I think I'll give it a go just bleeding it as Mick has done, worst case it just doesn't work.

Mick, did you bleed the lines from the BMC in any specific order? I'm not sure how the ABS module looks internally, so not sure whether it's better to bleed one line before another or all at the same time, etc

. etc?

No specific order Marty pretty sure I only cracked the 1 line going into the unit and yeah I done the abs last

Missileman Veteran

Missileman

Posted
Posted

if there is only a small amount of it might only be able to be felt when the booster is operating..? Bleeding brakes the oldfashioned way is a little risky, pushing the master cylinder piston all the way in past the point where it normally sits can cause the seal to leak.

air or seal damage....

air in the abs???

Sinista32 Grand Master

Sinista32

Posted
Posted

I found multiple issues on mine after a caliper upgrade and new rotors.

1. Calipers put on wrong side/upside down.

2. Bleeding order wasn't followed. -> Furthest away to closest.

3. ABS unit wasn't bled !!

4. BMS Stopper to remove the brake pedal travel from flexing fire wall

5. Stone gaurds getting in the way

6. Brake bias adjusted

Hope this helps

ACT Brakes :verymad:

and I took it to get a power bleeder on the job

scandyflick Grand Master

scandyflick

Posted
Posted

My guess is booster. I've experienced similar troubles the whole time I've owned my current car. I've bled and re-bled the system, had it power bled, replaced lines, replaced and rebuilt all calipers, and replaced the master cylinder with no noticeable effect.

It wasn't until I borrowed a booster canister off a mate's GTR that they started working properly.

I've now replaced the booster, haven't had the opportunity to even start it yet to see if it's made any difference yet...

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