Brake pedal adjustment

[Tanz]

I have a fair bit of 'slack' in my brake pedal movement. i.e. You have to move the pedal a distance before it engages with the master cylinder. With the instrument cluster removed, I can see the 'push rod' that passes through the bulkhead moves as soon I move the brake pedal - no slack at the pedal end, but it is a while before I feel any resistance. The brakes work OK and for the record the master cylinder was professionally rebuilt a few months ago and I have bleed the system twice since then.
Could it be a problem between the servo and the master cylinder? Is there an adjustment I can make?

[Tanz]

May have found the answer by searching

viewtopic.php?f=7&t=8360&p=61946&hilit= ... ent#p61946

[soldave]

Just done that myself after having the servo rebuilt. Only done one short drive since but made a big difference. Just be sure that you don't have any preload on the master cylinder when everything is warmed up.

[Pete Boole]

If you take the clevis pin out of the brake pedal/pushrod you should be able to tell fairly easily how much clearance there is between the pushrod and the servo "piston" - when the pedal is fully back there should be a few thou clearance. The article you found above is about the clearance between the same servo piston and the master cylinder piston. Again you need a few thou clearance. It is vital that there is no preload on the master cylinder piston as Soldave says - this will lead to the brakes binding.

Pete

[Tanz]

Thanks for the very useful replies chaps. Will let you know how I get on. Perhaps take a few pictures and this could be a 'how to' for future owners.

[TonyL]

Yes please, Tanz. A "How To" with pictures would be very welcome.

I think my excess travel is <10mm, but it's quite annoying. I'm adding this fix to my to do list.

[Tanz]

So removed the instrument cluster this morning and was pleasantly surprised to see access to the brake pedal clevis pin was excellent. Not something you can usually say about anything to do with the pedal box. Clevis pin and adjusting nut arrowed.




Pushing the rod, I could feel that there was only a small amount of play. Also with the pin in place and watching the rod while I pressed gently with my foot, I could feel there was very little play so the problem must be at the master cylinder end.
Used some bungs to minimise fluid loss.


The 'rod' sticks out about 8mm


The depth of the 'hole' from the flange face is 29.5mm so does that mean the rod has to move 21.5mm before acting on the master cylinder?


My problem now is how to adjust it. Is the knurled nut a lock nut? If so I can't move it. Refuses to move.

[Pete Boole]

No - the pushrod has to move the depth of the piston cavity minus the amount the snout of the master cylinder is recessed into the servo - ISTR ~ 7/8". The knurled section of the pushrod grips the end piece (with the hexagon on it) but they should turn against each other. The knurled part needs to be held - the factory must have a special tool because although the end bit has the 7mm hex the knurled part is neither 8mm or 9mm. Anyway - that is how it is adjusted - hold the knurled part and turn the hex.

Pete

[Tanz]

OK thanks Pete
I'm a bit nervous of shearing the end off as it's very tight. As you say 8mm is too small and 9mm too big plus it's recessed so you need an off set ring spanner anyway. This should be a simple thing to do I will have another go

[bash]

Ive got a picture somewhere of the adjuster, I will dig it out later and post it. If you get it too cose on clearance you might find the brakes start binding slightly after a short drive but you just need to back the clearance off very slightly if that happens. Watch this space.

Bash

[Tanz]

Got it moving. Guess it's the first time it's been adjusted since 1988.
Used this to grip the knurled end by holding it at an angle, not ideal - a bit brutal but it worked and didn't mess up the knurled bit Once the 7mm screw was moving it was quite easy to adjust.



Tried to be clever by measuring the piston cavity, and the snout of the master cylinder housing and came to a figure of how much the push rod should stick out of the servo. Not easy to measure accurately but ended up with a figure of 7.7 mm which was about where it was. So then decided to screw the adjuster out so it was too far out. Offered the master cylinder up to the servo and there was a gap between master cylinder and servo, so clearly too far out. Then I just kept backing off the adjuster until the master cylinder was flush with the servo then backed it off a little bit more. Have put it all back together now - just need to bleed the brakes but rain stopped play.

Would be interested to see the picture of the adjuster Bash

[TonyL]

Well done. It sounds like you're almost there with this job. I look forward to your report on the test drive.

[bash]

Its just a bolt with knob on the end... Anyway, the clearance should be about 0.6 to 0.65mm engine off and vacuum released. DONT press the brake pedal when doing any of this with the master cylinder off, it will bugger the servo. Dont ask me how that could be measured without some plastigauge but basically the clearance is low. Its a while since I did mine but basically I put some tippex on the end and after adjusting it until it touched by lots of fitting and removing I then backed it off one turn. This seemed to work.

Good luck

Bash

[Pete Boole]

You can get special tools to measure the clearance.

Pete

[Tanz]

Bash - I also did the Tippex thing. As long as the pedal is improved and the brakes don't bind I'm happy.

Question - I bled the brakes last Saturday. As only a small amount of air has got into where I removed the pipes and put bungs in the holes - can I get away with just bleeding the front brakes to get rid of the air?