Excessive brake pedal travel HELP PLEASE

[scooby seb]

Evening guys, long story but I've got excessive brake pedal travel and can't sort it

I did a trackday at snetterton last June, it was probably one of the hottest days last year and on the last session my brake pedal dropped, I still had brakes but pedal was almost on the floor, I was running yellow stuff pads and dot 5.1 fluid, I just assumed I had boiled the fluid. Then I was doing an activity day with car limits at north Weald, so changed the fluid to castrol react srf ( snapped the bleed nipple on the nsf caliper in the process so that was swapped for a recon one) but still not a great pedal.

Then booked cadwell in sept and decided to fit carbon tech front pads and rebuilt the caliper carriers and on fitment found the new caliper was leaking on one of the Pistons so this was changed under warranty, but still not a great pedal.

Then booked brands in December and on checking the car over before hand found the rear pads were shot ( OK on the outside pad but the inners were on the limit) so changed them thinking this could of been the trouble but still not a great pedal.

So I've bitten the bullet and rebuilt the master cylinder, changed the servo, changed the proportion valve, two refurbed rear calipers from Bigg red and reblead the system from the master cylinder then the proportion valve then all 4 corners, guess what still the same, when I first fitted the braided lines and the master cylinder stopper it had a lovely pedal, not a lot of travel and great feel and feed back from it, the brakes still work fine but the pedal just feels horrible now.

Just seeing if anyone has any pointers or tips or if I've missed something??

Cheers Scott

[stuMR2lee]

Hi Scott,

Things to check in this order : condition of front caliper pistons, vacuum test for leaks (many brake problems are caused by tiny leaks), pedal height. When refitting the rears I assume you bled them first, then pumped out the pistons to set them up, before re-connecting handbrake cables.

Everything else you seem to have covered.

[scooby seb]

Hi Scott,

Things to check in this order : condition of front caliper pistons, vacuum test for leaks (many brake problems are caused by tiny leaks), pedal height. When refitting the rears I assume you bled them first, then pumped out the pistons to set them up, before re-connecting handbrake cables.

Everything else you seem to have covered.

Hi, cheers for that, one front caliper a pagid new/recon unit, the other is working fine (Pistons not seized and moving freely), not vacuumed the system but no leaks anywhere,checked front to rear, pedal height is level with the clutch pedal but higher than the throttle pedal???

I fitted the rear calipers, then bleed the master cylinder, then the proportion valve so the rear calipers may of been pumped out before I got to the rears to bleed them?? I hadn't adjusted the rear calipers/piston as I don't run the hand brake, but I just went out and adjusted them as wood sport have suggested, wind the piston back then out 180 BUT I had to wind mine out 360 to get a snug fit on the rear calipers???????

Just can't understand how I've changed pretty much the hole system less the lines and there's no difference what so ever, I'm starting to think that something was binding or seized before giving it a nice solid pedal and suddenly freed off and this horrible pedal is the norm????

[stuMR2lee]

No need to wind back 180 degrees. Just a little bit to line up the notch will do. You don't connect handbrake cables at all?

I'd recommend vacuuming the system. Several times we've had issues and it's often due to tiny air leaks on the bleed nipples. Not enough to see fluid easily/immediately but enough to let in air. Ptfe tape wouldn't hurt.

Worth trying the feel of another MR2 to compare. Although not modern car standards mine seem pretty good. BGB gives recommended pedal heights. Even a minor adjustment may help.

Edit: if you had to wind your pistons out 360 to get a snug fit then that could certainly have affected your pedal feel. I usually just wind them in when changing pads, then out just a little to align cut out on piston to notch on caliper/brake pad. Once they are initially bled I then pump the pedal as much as necessary for the pistons to self adjust and take up the slack. The aim is that under normal braking the piston only has to move a fraction.

Go round all 4 calipers 2 or 3 times.

[scooby seb]

Ok cool, I'll give the vacuum bleeding a try, do you use an air fed vacuum bleeder or a hand pump one??

No I leave the hand brake cables disconnect as the car is for track use only.

Cheers Scott

[SonicSW20]

Yeah, there's no need to wind out 180 degrees or any amount at all. This isn't mentioned in the BGB at all. Stu has a hand pumped vacuum bleeder, works really well.

Bleeding the system does take patience. I've always had to go round several times to get a good bleed, and I've never been able to get a good bleed with a one man bleed kit. It gets most of it, but has always benefited from a traditional two man bleed (build pressure, hold, open nipple, allow some flow, close nipple, release pressure).

[stuMR2lee]

As Gareth says. Mine is as Mityvac but I'm sure an eBay one would be fine. I try and pull a vacuum on each bleed nipple (when they are closed). If it doesn't hold vacuum then it's somewhere to start looking. Sometimes the seal isn't great due to the age of these calipers. The ptfe tape and new bleed nipples are worth a go. We've had a bit of fun in the past bleeding MR2 brakes! It's amazing how easy they are to bleed when all fully functioning.

[pbmr2]

got a cheap ebay hand pump just to do this job. going to fit the brakes tomorrow so i'll report back how useful it was.

[stuMR2lee]

Useful tool to have regardless. Make sure the caliper banjo bolts are torqued to around 30Nm. Surprising how often tightening them by guess work often isn't sufficient for a perfect seal.

[pbmr2]

good tip, cheers.

[scooby seb]

Quick update, I had the race mechanic at work check the car over, he confirmed its not air in the system as you can't pump the pedal up, he checked over the hole system and said everything is working as should be, he said it feels like the servo is over vacuuming, we took the one way valve out of the vacuum pipe and that's working fine, we disconnected the vacuum pipe and tried it, biting point was much higher but the pedal was solid.
So fitted an restrictor into into the vacuum pipe and made them about 85% better.
I did a trackday at Cadwell with it like that last Friday and could feel what the brakes where doing again so made it easier to push the car but still no fault found just really masked the problem.
Don't get me wrong the brakes were great even with a low pedal it was just hard to feel what the brakes were doing.
I think next winters project will be rip the oe servo and master cylinder and fit an after market pedal box???

[scooby seb]

Quick update, I had the race mechanic at work check the car over, he confirmed its not air in the system as you can't pump the pedal up, he checked over the hole system and said everything is working as should be, he said it feels like the servo is over vacuuming, we took the one way valve out of the vacuum pipe and that's working fine, we disconnected the vacuum pipe and tried it, biting point was much higher but the pedal was solid.
So fitted an restrictor into into the vacuum pipe and made them about 85% better.
I did a trackday at Cadwell with it like that last Friday and could feel what the brakes where doing again so made it easier to push the car but still no fault found just really masked the problem.
Don't get me wrong the brakes were great even with a low pedal it was just hard to feel what the brakes were doing.
I think next winters project will be rip the oe servo and master cylinder and fit an after market pedal box???

[stuMR2lee]

As you've ruled out faults I'd try raising the brake pedal height just a little. I've done this in the past and it's made a big difference to pedal feel.