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JPD

Brake pedal travel

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At my last MOT I had an informal advisory that my brake pedal travel was too long. I'd finished a complete restoration of the car in 2016, during which I'd fitted new brake pipes, new repro calipers and cylinders. I also fitted new discs, pads and shoes. To try to sort out the pedal travel over the last few months I've:

  • bled and re-bled the brakes several times
  • taken some slack out of the m/cyl push rod
  • swapped the repro m/cyl for my original, now fully remanufactured
  • re-checked the rear brakes and re-adjusted them
  • tightened the wheel bearings one flat per side

All this helped, but the pedal was still variable - sometimes it had short travel and was firm, sometimes it had a longer travel and felt soggy.

My last resort was the brake calipers. I had always noticed that the LH pads had a bit more slack against the discs that the RH side, and also the LH side often squeaked when driving, which I could stop by pressing the pedal, but it would come back again a while later. Even though mine were new repro ones, I decided to send my original calipers away for complete remanufacture.

I fitted the LH one first, as that was the one that I suspected was causing the problem. Hey presto, the pedal is now consistently firm with a consistent short travel. I'll fit the RH one as well, as that may improve things even further.  

Just thought I'd post this for interest, and see if anyone else has had similar experiences with the repro ones? Note that the repro ones had the circlip holding the piston seal in place, the remanufactured ones have the larger push fit seals with no circlip. The car is a 67 4A

Jeff

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Common causes of long pedal include :

poorly adjusted front wheel bearings

poorly adjusted rear brake shoes

silicone brake fluid

pad knock back 

you seem to have most of these covered !

what fluid are you using Jeff, and do you have standard front axles?

regards

steve

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Hi Jeff,

something that has come up in the last year or so with new calipers.

The seals appear to be quite stiff.

When you apply the brakes the pads should only just come off. However the stiff seals are dragging the pistons back too far - similar to pad knock back.

There are a couple of cures. The easiest one that has been posted here is to apply the brakes and jam the pedal down and leave for 24 Hrs.

This allows the seals to go back to their rest position with the pistons extended.

 

Roger

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I'm using DOT 4 fluid Steve, - I'd read too many bad reports about the silicon fluid that it put me off! All the front suspension is standard.

I'd read on the forum about the rubber seal problem Roger, and did try jamming the pedal down for 24 hours, using old pads that were a bit thinner than my newer ones. It worked for a short while, but the pedal soon went back to its old tricks again, so didn't solve the problem. In my mind I've certainly put the problem down to the rubber seals - it's could be the smaller circlip type seals that are the problem, may be in conjunction with the type of rubber used on the repro calipers

Jeff

Edited by JPD

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I had a very similar problem for months- long travel, soft pedal etc - eventually tracked it down to the amount of travel in the master cylinder area. Solved by purchasing an adjustable master cylinder pushrod from Revington TR. Now I have a hard pedal which is much more confidence-building- even with silicone fluid, which many say gives a spongy feel and longer pedal travel. Not so now.

James

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You said it's variable, sometimes longer travel than others.

I would suspect the small seal at the end of the master cylinder. This seal blocks the reservoir supply at initial movement of brake pedal, allowing pressure to build in the mcyl. If this seal is damaged or if the sealing surface compromised then it leaks for a while as the pedal moves...giving long pedal.

I had this...it was worse when hot...took a long time to find that this tiny seal (about 1/4 inch dia) had a split and performed worse as it got hot.

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If a car does not get a great deal of regular use, one disc brake piston may jam. This means that, when the brakes are applied, the opposing piston has to do all the work and in so doing the assembly (calliper and disc) will be pushed sideways as the brakes are applied. The driver will find that the pedal has to travel further.

It’s not difficult to discover this problem as, having removed the front wheels, one pad will be loose (not skimming the disc).

To rectify the situation, remove the loose pad and push the piston back into the calliper (beware overflow from the master cylinder!).

Insert lever with thickness less than that of the disc pad (e.g. a tyre lever), then pump the brake pedal until it goes firm.  Push the piston back again and repeat the procedure a few times more until the piston moves freely.

Re-insert the disc pad and pump the brake pedal to get a firm response.

Ian Cornish

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Just to close this one out, I ended up sending both my original callipers to Past Parts for re-manufacture. They got out the seized pistons, gave the caliper bodies a complete clean up, new pistons, seals etc. These have been on the car for 4 months/ 1500 miles and the pedal has always been firm with consistent short travel.

The moral or the story is, as ever, always refurbish original items rather than buying repro parts

The repro ones will go in the spares bin. If I rebuild them with better rubbers they might be ok.

Jeff 

Edited by JPD

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1 hour ago, JPD said:

Just to close this one out, I ended up sending both my original callipers to Past Parts for re-manufacture. They got out the seized pistons, gave the caliper bodies a complete clean up, new pistons, seals etc. These have been on the car for 4 months/ 1500 miles and the pedal has always been firm with consistent short travel.

The moral or the story is, as ever, always refurbish original items rather than buying repro parts

The repro ones will go in the spares bin. If I rebuild them with better rubbers they might be ok.

Jeff 

Hi Jeff,

I have read many accounts of NEW repro calipers having long/soft pedal ravel. I have just experienced this over the last couple of days.

Original calipers but using the TRW rebuild seals.

Today I fished the old seals out of the dustbin an d refitted then - problem solved.

I now need to locate a source of seals that work correctly out of the box.

 

Roger

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I got new seals & pistons for my 3 from the TR shop. a bit tricky to fit, but have given no trouble in 6 years

Bob.

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Hi Bob,

it may be that you bought your parts before the problem started.  I think it was reported on here 3 or 4 years ago.

Can you remember if the seals came in a TRW packet.

 

Roger

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2 hours ago, RogerH said:

Hi Bob,

it may be that you bought your parts before the problem started.  I think it was reported on here 3 or 4 years ago.

Can you remember if the seals came in a TRW packet.

 

Roger

Sorry, cannot remember who made them.

Bob.

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If anybody has a new repro calliper not fitted I would be interested to know if you take out the piston and the seal, what is the shape of the groove that the seal fits in.

I'm sure on the originals the seal groove is not square cut slot at its base, but slightly not the same depth at each side of the bottom of the groove this then gives the square seal a pinching action on one side of the seal to the piston.

It would interesting to know if the slot for the seal on the repro ones is like this, or perhaps they have  made the slot with a square cut bottom of the groove.

Sorry this is a bit difficult to write, but would be interesting if the profile of the slot is the same on the repro one to the originals, its much easier to cut a square slot than a tapered one, just a machining error or a copy misunderstanding.

Hope that understandable?

John

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