MOT Failure Excessive Brake pedal travel

[keithforst99]

Hi any body got any ideas car failed the MOT handbrake and excessive travel on the footbrake. I have bleed the hydraulics, servo check valve working, servo is holding vacuum. Handbrake was an easy fix, not sure what to try next .

Keith

[greyV8pete]

Re: MOT Failure Excessive Brake pedal travel

If the brakes were working correctly in the past I would first suspect excessive travel of the brake pistons front or rear before shoes / pads contact with the drums / discs. Usually a rear drum issue if any auto adjusters are not working correctly. If a recent fault I would suspect possible incorrect master cylinder diameter during recent replacement? Peter.

[martinclan56]

Re: MOT Failure Excessive Brake pedal travel

You could also check the play in the pedal before it activates the servo. My Sportster had a threaded adjuster for this.
Cheers Robin

[Patrick]

Re: MOT Failure Excessive Brake pedal travel

On the original servo/adapter supplied by Marlin (E30 sportster) with single diaphragm servo there is an adapter plate which means the brake pedal didnt work until 1/2 down. Robin has this adapter made for me. Check if you have one of these and it's out of adjustment or if you don't have one at all this makes a huge difference.



and in place:



I have since upgraded to a dual diaphragm servo as part of a group buy many years ago, this is a bit different:

https://www.msportster.co.uk/2012/10/07/brake-servo-upgrade/

https://www.msportster.co.uk/2012/11/11/servo-upgrade-complete/

I also swapped my pads from Jurid to ATE which improves the inital brake bite a lot.

[Ye Ol Ripper]

Re: MOT Failure Excessive Brake pedal travel

What is the rear brake set up , is it disc or drums and what car was it originally off?

[keithforst99]

Re: MOT Failure Excessive Brake pedal travel

Hi and thanks for the replies.
The car is E36 based disc brakes all round with a with a 7 in. dual diaphragm servo, all callipers are relatively new. The is an adjustment to be had on the pedal but the brakes have gone from being excellent to poor while the car has been garaged over the lookdowns. Adjustment on the pedal looks to all most impossible to do as there is little to no room to swing a spanner, although I am having another attempt at this today. All four callipers are working correctly and although the servo seems to be holding vacuum I now suspect that it could the problem.
Cheers Keith

[greyV8pete]

Re: MOT Failure Excessive Brake pedal travel

Hi and thanks for the replies.
The car is E36 based disc brakes all round with a with a 7 in. dual diaphragm servo, all callipers are relatively new. The is an adjustment to be had on the pedal but the brakes have gone from being excellent to poor while the car has been garaged over the lookdowns. Adjustment on the pedal looks to all most impossible to do as there is little to no room to swing a spanner, although I am having another attempt at this today. All four callipers are working correctly and although the servo seems to be holding vacuum I now suspect that it could the problem.
Cheers Keith

As well as the comments in the posts above, bear in mind the following when working on the dual servo.
1) The pedal push rod must NOT be adjusted unless the clevis (or rose joint if fitted) is disconnected from the pedal. Attempts to turn the push rod itself will irreparably damage the diaphragm inside the servo unit.
Push rod adjustment can usually only be achieved when the servo is removed from the bulkhead. It is only really adjusted on assembly to get the pedal at the correct height. It should not need to be adjusted afterwards.
2) The vacuum non return valve connector on the servo body must NOT be removed! The yellow label around the valve carries this warning.
3) Some users of the dual servo experienced problems with the brakes locking on. Fitting a Land Rover pedal return spring cured that.


Finally check the handbrake is adjusted exactly as per the workshop manual for the donor vehicle. Over tightening the cable adjuster on some cars can prevent the auto adjusters working as the operating lever needs to return fully to the stop. Peter.

[Ye Ol Ripper]

Re: MOT Failure Excessive Brake pedal travel

Hi Keith
As its using E36 parts ,just to rule this possibility out , does your car have ABS and 2 electrical switches fitted to the underside master cylinder like on the later E46 models?

When you were bleeding the brakes did you start bleeding the cylinder furthest from the master cylinder?

In addition to possibly still having some air in the hydraulic system, make sure none of the callipers are leaking either from the piston seals or the bleed nipples.
It is not unknown for even a new calliper to be faulty.

If your rear brakes have a set of shoes inside the brake discs (as many earlier BMW and Mercedes of that era did) . Then the correct procedure to adjust the hand brake is always to adjust up at the disc first and do the handbrake cable last.

If you remove 1 wheel stud and shine a torch through the hole and the adjuster iirc used to be at 11 or 1 o'clock (depending on which side your working on). There was a toothed wheel you turn to move the shoes out with a flat screwdriver until the shoe just touches lightly on the discs inner drum.

That will have no bearing on the excessive brake pedal travel though , just the handbrake.

In addition to the other Marlin Specific advice for your set up you could also:

1)Check all brake lines front to rear in case there is a brake fluid weep.

2)Play in wheel bearings can effectively push the piston back into the calliper causing excessive brake pedal travel , however if that was the case, I would hope the mot tester spotted that.
But nevertheless worth checking again now.

[dogoncrazy]

Re: MOT Failure Excessive Brake pedal travel

Does the pedal travel decrease /feel improve if you 'pump' the pedal ?

[keithforst99]

Re: MOT Failure Excessive Brake pedal travel

Hi All,

I have spent a couple of days in the garage, managed to remove the servo as it was the only way I could make any adjustment on the pedal. All back much less travel in the pedal now although I am not 100% satisfied with brakes. The problem was one of travel pumping the brakes made no difference, I have done all the usual tests no leaks anywhere on the system, if you press hard on the pedal it does not move. The car has been up on on the scissor jack engine running in gear rear brakes working, front bakes locking the front wheels on a short run around the estate. The servo / master cylinder set is identical to the one on Patrick's car. All callipers where new in 2019, new pads etc . I am still not convinced the servo is functioning fully, tests have shown it is holding vacuum. I am going to bleed the system again tomorrow and get it back to the garage for a re test and see what happens. Worst outcome it fails if so I will have to order a new servo and maybe master cylinder from the USA ( Not A 100% sure if the master cylinder is an import or not) Cheers for advice offered .Keith

[greyV8pete]

Re: MOT Failure Excessive Brake pedal travel

The master cylinder will be Sierra (two versions / different flange hole centres/ look for ID numbers on the casting) or BMC so sourced in UK. If there is no servo vacuum leak (check this by listening with a rubber pipe in the footwell next to the servo) then I doubt if the servo is faulty. Check carefully the clearance between the servo plunger shown in post 3&4 above. Aim for no more than .020” (0.5mm in new money) and check the small locknut is tight. Excessive clearance here will give a much larger pedal travel. Peter.

[keithforst99]

Re: MOT Failure Excessive Brake pedal travel

Hi All, Pleased to say the car passed it's MOT . After adjustments to the servo I bleed the brake system so new fluid all round. Brakes better than they have ever been. The handbrake issue came about after I moved the guide tubes to stop the prop catching under hard acceleration .Handbrake now functioning correctly and the prop doesn't catch anymore so a result. All help appreciated. Cheers Keith

[greyV8pete]

Re: MOT Failure Excessive Brake pedal travel

Good result then! Now to enjoy driving it!

[Patrick]

Re: MOT Failure Excessive Brake pedal travel

Nice, glad you got it through the MOT!