Excess brake pedal travel

[mister bridger]

My mk1 is suffering from excess brake travel unless I "double dip" the pedal to take up the slack, so to speak. It's not spongy so don't think there's air in the system and they pull up well enough for what they are (7" Cooper discs on front, single circuit , tin can master cylinder). No difference with handbrake on and the rear drums are adjusted properly. Master cylinder is only a couple of years old, discs less than a year and calipers had new pistons and seals at the same time. Any ideas?

[rich@minispares.com]

front calipers on upside down?

[mister bridger]

No, definitely not as I bled them successfully initially and this has only become noticable recently

[swifty]

Maybe you need to fit the smaller bore rear wheel cylinders . Less fluid transfer so should bring the pedal up ..... Ken

[Craig]

How old are the flex hoses ??

Craig

[ivor badger 2]

Does the excess travel appear only when driving the car? As in, the excess travel disappears when trying the brakes when stationary.

Just read your query elsewhere. Stuck pad or caliper piston.

[Rusty old S]

I had this happen recently, bleed ,adjust rears, handbrake on ,rebleed, jack up front bleed, give up , took for MOT failed on brake light switch .bearing in mind it was under a year old and second one as well, back home found rusty old sixties one in garage, wire brushed, up filled master to top covered neck with clingfilm refitted cap, changed swich fitted wires now working lights, and had full pedal (and MOT) without bleeding to my surprise . My only explanation that the Chinese switch had failed and possibly inside there is some type of miniature diaphragm that punctures or similar which then compresses the trapped air thus causing one small pump to full pedal . I should have cut it in half to look but was binned before I thought it about it, so check your brake lights. R.O.S.

[Lord Croker]

Swifty, your idea is perfectly logical, but without an adjustable pressure reducing valve, the back brakes would probably not be up to MOT standards. (I've tried it! )
What I am going to say next will seem totally 'way out' & I'm sure there will be many people come along & tell me this doesn't happen, I would have said the same if it hadn't happened to me, twice.
I had exactly the same problem on my Cooper S about 20 years ago, I was needing a lot more pedal travel for no apparent reason. After a lot of work, new flexi-pipes etc. no air in the system, I discovered that when I released the brake pedal, the caliper pistons were moving back into the caliper, only by about 25 thou, but multiply that by 4 & that's quite a lot of fluid in relation to pedal travel. I am sure this is because the seals were very tight on the pistons & were deflecting slightly & then pulling the pistons back slightly. I rebuilt a pair of modified Metro 4-pots for my current Mini & the same thing happened. If you want to go with this, mister bridger, (promise I will only blow the doors off! ) jack the front of the car up, depress the brake pedal a couple of times, release & see if you can move the pads at all between caliper piston & disc, the movement should be virtually un-noticeable, if they wobble back & forth you have the same problem as I had. Having said all that I never found a solution to the problem but I was told by a former Mini Miglia Champion that this is much more likely to happen with stainless steel pistons, he always insisted on the original chrome ones. I put my drums back on - much less trouble!

[1071 S]

Pedal pump up is a classic sign of air...I'd give it all a good bleed before looking for more exotic problems...

Cheers, Ian

[swifty]

Another way to get a good pedal is to pump the pedal up and lodge a bit of wood or / screwdriver or other on to the seat frame or crossmember , thus leaving pressure overnight . In the morning , hey presto , full pedal ....... Ken

[mister bridger]

Thanks all, some useful suggestions there. I no longer have a hydraulic brake light switch as I got fed up with them failing so have fitted a push button type behind the pedal, so that's not going to be the issue. I DO have stainless steel pistons, made by an engineer friend so it's possible that may be the issue. Will try bleeding again but it doesn't really feel like air in the system as the pedal comes back up instantly with an initial dab, and there is no spongy feel. Not sure how the method of holding the pedal with a piece of wood could cure the problem but I will certainly try it before dismantling everything else. I'll let you know how I get on.

[mascher]

If the brakes are firm on the second pump then it most likely isn't air and this procedure may help you isolate the cause. Adjust the rear brakes so they are firmly locked. Try the pedal and see if they are improved. If they are then the problem is in the rear brake adjustment. If they are not then the problem is in the front brakes. The only way I know of for the front brakes to do this is for the rotors to knock back the pads and pistons but this would only happen when you're driving.

Bad flex hoses can fail is unusual ways so they can't be discounted as a problem.

Hope this helps.

Kelley

[JohnA]

If you're still on rubber hoses get somebody to sit in the car and using pipe clamp to isolate each brake and check the change in travel, if you use more than one clamp you can blank off front or rear. This should tell you if your calipers are the problem.

[davidmuir]

definitely try the 'wedged down pedal overnight' route.............this is/was a common fix on motorcycles to get the pistons to slowly protrude past the seals/dust excluder on the caliper!(both rear footbrake & front handlebar lever).

[gs.davies]

I had similar on a mk2 Golf GTi. Turned out to be a loose hub nut (!)

The hub had too much plays allowed the disc to move around whisky pushing the calipers Pistons back in...

[mister bridger]

TBH all I've had time to do is try the "wedge down the pedal" route and no improvement. Loose hub nut wouldn't have this effect when stationary, surely? Pretty sure it's sticking pistons so will try to work up the enthusiasm to go out there in the cold and have them all apart.

[mister bridger]

If the brakes are firm on the second pump then it most likely isn't air

Kelley

I totally agreed with this statement but, on inspection there seemed to be no sign of pad knock off. A mate came round this morning and we decided to bleed the brakes anyway - and it is utterly transformed! Rock solid pedal and a joy to drive again. The moral is: don't be too quick to discount the easy fix!
Thanks for all your input chaps.

[swifty]

The reason that I suggested the wedge the pedal overnight route is because it will slowly push any trapped air out ...... Ken

[andy1071]

I may have missed this reading through, but has nobody mentioned worn fork-end / pedal hole / clevis pin on the pedal?
(although I agree that air in the system is the most likely cause)

Lord Coker, it is actually a design feature that the seals pull the piston back slightly when pressure is released. -This is so that the pads don't drag on the disc. (the seal groove is slightly tapered -it took a lot of development to get this right!).

The Metro calipers will do the same.
If your original calipers were pulling back too much, then there was something wrong somewhere with the seals and/or pistons.

ALSO, one of the design problems with the vertical master cylinder, is that any degradation of the seals (age / wear) and they can 'gulp' air past the secondary seal. -Thus you have a really hard time to fully bleed the system, as you are always adding air...!
(Another reason to pump the pedal slowly when bleeding...)

[nick@dunsdale]

If you're still on rubber hoses get somebody to sit in the car and using pipe clamp to isolate each brake and check the change in travel, if you use more than one clamp you can blank off front or rear. This should tell you if your calipers are the problem.

This is what i would try as well i would clamp both front, try pedal, then try both rear. if you have someone in the car get them to hold the pressure and release the clamps, the pedal will sink a little anyway, but should there be a lot of sink you have found the problem area.

Hopefully find out witch end of the car the problem is with.

Then clamp the problem end one at a time or it may be both at the same end, i have had this problem on a few of my mini's years ago, for me it was usually air, and it was a bugger to get that illusive tiny bit of air out lol.