Humbug
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 posted on 24/8/08 at 09:39 PM |
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Brake pedal not fully returning
I have noticed that my brake pedal (floor mounted, 2 master cylinder setup with bias bar) does not fully return after I have braked. It doesn't
seem to affect the braking itself, which is fine, but it definitely doesn't return fully, leaving the brakes slightly on. I know this because if
I stop on a gentle slope and take my foot off the brake pedal, it holds even without the handbrake on. If I pull back the brake pedal with my foot,
the car starts to roll.
Any ideas as to:
a) cause?
b) solution?
I have seen some other threads about fitting return springs, but the setup I
have got means it would be difficult to fit anything without dismantling the whole pedal box - even then, I can't see exactly how and where a
spring could be fitted. Also, it wasn't always like this, though I'm not exactly sure when it started.
Thanks for any advice
Simon
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dmac
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| posted on 24/8/08 at 09:42 PM |
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Do you have remote mounted reservoirs? if so, check for kinks or tight bends in the connecting hoses that might stop the fluid returning from the
calipers.
Duncan
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allanbirt
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| posted on 24/8/08 at 09:49 PM |
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check the bolt or pin that runs through
pedal could be a bit tight had same problem on my mk once
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Humbug
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| posted on 24/8/08 at 10:05 PM |
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The pivot of the pedal is the bias bar... I suppose that the bush thingy which the bias bar goes through might need greasing... the car has been on
the road for 3 years. Worth a try, anyway.
btw, the brake pedal really is at an angle to the vertical - the bush/pivot is horizontal, but the pedal has been welded on a bit skewiff (ST pedal
box, NTDWM  )
The remote reservoir is connected by proper hose to a t-piece going to the master cylinders. Nothing has changed in that area... maybe the flexi hoses
to the front brakes have stretched/kinked? They are braided, so would have expected them to be OK. Thoughts?
Keep 'em coming!
Simon
 
Rescued attachment Pedals.JPG
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Johnmor
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| posted on 24/8/08 at 10:30 PM |
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I had exactly the same problem, after removing everything and messing around for ages including replacing both calipers I discovered it was the
adjustment of the pushrods on the end of the cylinder pistons. They were extended to far out , I had insuficient play to allow for caliper piston
return. So things were ok when the brakes were cold but the more I used them the worse it got until the brkes were smoking on the last trip.
Ensure there is enough slack so that the piston can fully return when the brakes are released. I left around 3-4mm of movment before any effective
braking takestakes place.
Hope this helps.
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Humbug
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| posted on 25/8/08 at 09:25 AM |
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Thanks again... I will try greasing the pivot first. If that doesn't help, how do you adjust the pushrods?
I would like to avoid having to dismantle the pedals if possible, because to get the bias bar out I have to remove the clutch pedal, and to do that I
have to extract ther clutch pivot out through a hole in the tunnel panel  .
If it is the pushrods, why would it only have started to happen a year or more after the car was built???
Simon
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rusty nuts
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| posted on 25/8/08 at 09:38 AM |
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Do you have a positive stop on the brake pedal to stop it returning too far?? If not then it's unlikely to be push rod length. If it has got a
stop then you should be able to slacken off lock nut on each push rod and screw pushrod into the clevis which will have the effect of shortening push
rods. Might also be worth checking that the breather in the reservoir cap is not blocked, ? As pads wear fluid level will drop, unlikely but it could
be holding a vacuum Partial seizure of pedals ?
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Humbug
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| posted on 25/8/08 at 09:46 AM |
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No positive stop... also, thinking about it, the problem is not that there is slack in the pedal per se, but that the pedal not returning fully leaves
the brakes slightly on.
I have greased the bush bearing
Will check the reservoir
Could be brake calipers partially binding and not fully disengaging?
Would bleeding the system (for the nth time) help?
Simon
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rusty nuts
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| posted on 25/8/08 at 09:59 AM |
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The fact that you can pull the pedal back and the brakes release doesn't point to sticking calipers IMHO
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Humbug
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| posted on 25/8/08 at 10:49 AM |
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Update:
I just went and jacked up each front wheel in turn:
- with the brake pedal pulled right back, each wheel spins freely
- with the brake pedal in the position it returns to on its own, each wheel drags on the disc.
So, unless by chance both of the front calipers are partially seized at the same time, it looks like something else...
...any other ideas what?
Cheers,
Simon
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ginger ninja
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| posted on 25/8/08 at 01:00 PM |
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looking at your picture, I would doubt that the bias bar bush would be causing the binding of the pedal. Its still worth checking though, but more
likely to be the pedal pivot at the bottom of the picture. When pressure is released from my pedal, the pedal feels very free and easy to move,
almost rattles on the pivot bolt.
If all else fails, I've fitted a return spring simply to the brake pedal which also doubles to operate the brake light switch, Ill post photo if
you think this may help.
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Humbug
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| posted on 25/8/08 at 01:12 PM |
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quote:
Originally posted by ginger ninja
looking at your picture, I would doubt that the bias bar bush would be causing the binding of the pedal. Its still worth checking though, but more
likely to be the pedal pivot at the bottom of the picture. When pressure is released from my pedal, the pedal feels very free and easy to move,
almost rattles on the pivot bolt.
If all else fails, I've fitted a return spring simply to the brake pedal which also doubles to operate the brake light switch, Ill post photo if
you think this may help.
Yes, please. I would be interested in seeing how you've fitted a return spring. Ta
Simon
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