Excessive brake pedal travel

[MikeyB1]

Hello folks, need some ideas please. Yesterday fitted new discs and Mintex pads. Had a hell of a job to fit the pads, the pistons on one side required a lot of force to push them back into the caliper. First test drive the car pulled very hard to the right, so back home, stripped out LH pads and pushed the brake pedal. The inner piston struggled to move but when it did....what a mess, it was badly rusted. This was obviously why it was difficult to push in when fitting the pads. Despite having reconditioned many calipers over the years, I concluded that this amount of corrosion would have probably made the caliper bores beyond redemption. Rang Moss...new calipers arrived this morning at 9am. Fitted these and bled the system. Now car stops in a straight line BUT, pedal is to the floor! Damn disconcerting but a couple of pumps (there's a lot of clearance twixt pads and discs) sees the pedal to the top and rock hard. Read all the posts. Pad "knock off" is a non-starter as this happens even when sitting still. The Workshop Manuals all state that this is what the Restrictor prevents, and there is one fitted, but whether it has any innards or not, I have yet to check. M /cyl is the correct size, but could this be the problem. Might it be sucking the fluid back, and thereby pulling the pads too far back?. I didn't have this problem before I changed everything but I suspect that the rusty pistons wouldn't have returned very far anyway! Any suggestions gratefully received. Cheers, Mike.

[RogerH]

Hi Mike,

there was a post in the last 6 months on here describing exactly your problem.

 

It would appear that the Moss caliper uses a rather hard rubber for the caliper piston seals.

These pull the piston back to where they started - rather than staying at their furthest projection.

 

It may be possible to fit a repair set of seals that may be softer.

 

Roger

[MikeyB1]

I obviously missed that post Roger. Thanks, I thought I'd read them all!

[RogerH]

Hi Mike,

have a read here https://www.tr-register.co.uk/forums/index.php?/topic/64144-bleedin-brakes/?hl=%2Bdifficulty+%2Bbleeding&do=findComment&comment=556843

 

Roger

[MikeyB1]

Just occurred to me Roger, I presume you must be referring to the dust seals, rather than the fluid seals. In which case it begs the question "who can supply alternatives?" I would have thought that they can't be many different manufacturers. The new calipers use the clip on type of dust seals rather than the bellows type, as fitted to my old calipers. If they are interchangeable perhaps these would be better.

[RogerH]

Hi Mike,

yes, I believe it is the dust seals.

You could ask somebody like Revington. They seem to know their stuff.

 

Roger

[MikeyB1]

Thanks for pointing me to the post Roger....food for thought. Must admit I'm a tad reluctant to ask Revingtons as I didnt purchase the calipers from them. Will keep it in mind however. Mike.

[RogerH]

Hi Mike,

how about reporting back to Moss and asking if their repair kits are more pliable.

 

Roger

 

PS - how about removing the dust seals to see if that cures the problem

Edited May 22, 2018 by RogerH

[MikeyB1]

How is it possible to read someones mind via a forum? I've just been contemplating the easiest way to strip off the dust seals with the minimum of disassembly! Also looking at part numbers for the different types of piston, seals etc. I still have the old calipers so will compare fittings for both seals tomorrow. Cheers Roger.

[RogerH]

.....and what will the lottery numbers be............

 

 

Roger

[RobG]

Normally when you release brake pressure the piston will retract just enough to clear the turning disk and any little warp.

The pads will still feel tight if pulled or wiggled.

If the pistons are retracting all the way back, surely the pads would feel loose if pulled or shaken.

 

Just an idea.

 

RobG

[harrytr5]

Moss new calipers

The cure I learnt from others was, remove the disc pads, fit back old worn ones or in my case reduced thickness of 12mm ply the same shape as the pads.pump up the brake pedal and place a length of timber between the seat and brake pedal holding it down firmly and leave over night or two.I left mine over two nights.The idea was to alter the memory of the seals and their pull back.

Strange but it did work in my case and has done for the past 170 miles or so.

Try it.

Regards Harry

[MikeyB1]

RobG...the pads are loose. This morning I checked the gaps between pads and discs, these were, in thous, 31,21,26 and 21 so in total nearly 1/10".

 

I've considered doubling up on the anti-squeal shims at 16 thou each they would eliminate most of the gap, but as the pads bed in this will increase again, although perhaps as has been mentioned before the seals should be a little more pliable by then.

 

Harry, thanks, that's certainly worth a try. By late last night I had decided to replace the M/cyl so that everything hydraulic would be in A1 condition. If this doesn't do the trick ( I'm wondering if the current one isn't pushing as much fluid as it should) I'll certainly try your trick.

 

Worth mentioning.....adjusted the rear brakes, they only moved one flat on the adjusters so this had no effect.

New M/cyl due tomorrow a.m. Stay tuned folks. Mike.

[PYU940F]

I read somewhere that this is due to the poor quality of the piston seals and cure maybe/sometimes is to bleed the brakes with the anti-squeal shims removed. Then re-insert the shims. Apparently you have to be "forceful" in getting the pistons far enough in to get the pads and shims back in, but it can be done. All to do with seal roll back (or lack of it.??) or something else just as technical

[stuart]

RobG...the pads are loose. This morning I checked the gaps between pads and discs, these were, in thous, 31,21,26 and 21 so in total nearly 1/10".

 

I've considered doubling up on the anti-squeal shims at 16 thou each they would eliminate most of the gap, but as the pads bed in this will increase again, although perhaps as has been mentioned before the seals should be a little more pliable by then.

 

Harry, thanks, that's certainly worth a try. By late last night I had decided to replace the M/cyl so that everything hydraulic would be in A1 condition. If this doesn't do the trick ( I'm wondering if the current one isn't pushing as much fluid as it should) I'll certainly try your trick.

 

Worth mentioning.....adjusted the rear brakes, they only moved one flat on the adjusters so this had no effect.

New M/cyl due tomorrow a.m. Stay tuned folks. Mike.

Check the length of the pushrod on the new M/cylinder as some are too short and that definitely wont help pedal travel!

Stuart.

[MikeyB1]

Update time folks.

Stuart, push rod same length as original.

Problem now solved. I fitted a new M/cyl, so now had new hydraulics throughout the front end. Without trying the brakes at all I placed 10mm spacers in the calipers instead of the brake pads and as per Harry's sugestion held the brake pedal down with a length of timber braced against the seat. I left this nearly 2 days. The dust seals were well and truly stretched. Took the wood out and replaced the pads and shims. Hey presto.....brake pedal hard and up to the top of it's travel. Brilliant. Only problem now.....horrendous squeal, but that's in another post. Thanks for all the suggestions folks. Mike.

[stuart]

Update time folks.

Stuart, push rod same length as original.

Problem now solved. I fitted a new M/cyl, so now had new hydraulics throughout the front end. Without trying the brakes at all I placed 10mm spacers in the calipers instead of the brake pads and as per Harry's sugestion held the brake pedal down with a length of timber braced against the seat. I left this nearly 2 days. The dust seals were well and truly stretched. Took the wood out and replaced the pads and shims. Hey presto.....brake pedal hard and up to the top of it's travel. Brilliant. Only problem now.....horrendous squeal, but that's in another post. Thanks for all the suggestions folks. Mike.

That could also have just bled the last of the air out, Pumping the brakes up and then jamming the pedal down overnight to cure long travel/spongy brakes is a well known cure all. Whatever its good that you have sorted it out now.

Stuart.

[Swissmaxie]

On 5/28/2018 at 8:51 PM, MikeyB1 said:

Update time folks.

Stuart, push rod same length as original.

Problem now solved. I fitted a new M/cyl, so now had new hydraulics throughout the front end. Without trying the brakes at all I placed 10mm spacers in the calipers instead of the brake pads and as per Harry's sugestion held the brake pedal down with a length of timber braced against the seat. I left this nearly 2 days. The dust seals were well and truly stretched. Took the wood out and replaced the pads and shims. Hey presto.....brake pedal hard and up to the top of it's travel. Brilliant. Only problem now.....horrendous squeal, but that's in another post. Thanks for all the suggestions folks. Mike.

Thanks for the thread. Fitted new calipers to my MGB and got the same problem. Will try the cure tomorrow.

[rogerowen]

Have the same. Just completely renewed all hydraulics  (from Rimmer Bros). Could not get to a point in bleeding without air showing, although I can't find any leaks. Long pedal travel - but not hitting the floor. Took to friendly local Garage (Classic Car savvy), and they thought all ok (after a little tighten up of rear adjusters now new shoes a little more centred). Suggested that we all get too used to modern car servo brakes. 

[david ferry]

I’d have suggested send them back and buy properly reconditioned ones....... 

David