samwilliams
|
| posted on 18/11/05 at 11:27 AM |
|
|
Brakes going wrong
Sorry for the vague subject, but I don't know much more myself!
Last night when driving along (it was very cold, don't know if that is what caused it), the brakes started to gradually stick on. The brake
pedal felt completely solid.
Once I'd pulled over and left it for a bit, you could push down a few times on the brake pedal, and they'd release a bit, but gradually go
back within a couple of seconds. After a little bit more of waiting, it gradually went away, enough for me to get where I was going, but it was still
alternating between being fine, and then the brake pedal would feel a huge amount firmer (and with no give at the start at all).
Ended up going home on the back of a breakdown van, by which point they'd pretty much released.
Only got the car on saturday and, from what I understand, it hadn't done a lot over the past year. Does anyone have any suggestions as to what
was going wrong and, more importantly, how to fix it? (sorry for the basicness of my questions. If you've seen any of my other threads,
you'd know that I'm a bit of a beginner!)
Thanks
Sam
|
|
|
|
|
britishtrident
|
| posted on 18/11/05 at 11:33 AM |
|
|
Very simple; the piston in the mastercylinder isn't coming back far enough to let normal fluid expansion vent back to the reservoir as result
a hydraulic lock forms and the hydraulic pressure builds up more as the brakes warm up.
Problem is either pedal sticking/maladjusted pedal stop or the mushroom end of the pedal pushrod(s) are too fat.
If you have a servo (!) then it could the push rod stub on the mastercylinder side of the servo needs adjusted in 1-2 mm.
[Edited on 18/11/05 by britishtrident]
|
|
|
DarrenW
|
| posted on 18/11/05 at 11:49 AM |
|
|
Hi Sam - following from your starting thread i thought id ask if you fully understand what BT is saying?
I dont know what system you car has but i will try and explain mine.
Brake pedal is hinged close to floor. About 2 inches up there is a u-shaped 'saddle' attached to it. From this u saddle there is a
threaded bar. The other end of the threaded bar acts directly onto the end of the brake master cylinder. As you push the pedal you in turn directly
push the master cylinder plunger. There needs to be slight clearance between the end of the threaded bar and the start of the MC plunger. The reason
for this is explained by BritishTrident above (brakes warm up, fluid expands, if oil cannot go anywhere it basically starts to push brakes on which
get hotter etc etc viscious circle) The clearance allows the brakes to fully disengage and give the fluid expansion somewhere to go.
Some brake systems use a servo (most road cars) which works slightly differently. Some kit cars use a twin cylinder brake pedal box - basically one
pedal puhes two cylinders (one for front brakes, one for back brakes). Same theory as above but the bias can be fine tuned bewtween front and back
(race car stylee).
Did you notice any of the brakes getting hot?
Common problem, easy to fix apart from pedal access being tight.
|
|
|
samwilliams
|
| posted on 18/11/05 at 12:11 PM |
|
|
Thanks for the replies. Just going out now, so will have a play later. A couple of things that probably won't change what you've suggested
is wrong with it, but thought I should ask anyway:
I'd driven a fair distance (a few hundred miles) without any problem before this started to happen. Could it be the cold making if worse, or
could that mean it's a different problem?
Also, when the brakes are working normally, there's quite a bit of movement before the brakes actually start to work. Would what you're
suggesting only occur if there was normally not enough free movement?
Thanks
Sam
|
|
|
Peteff
|
| posted on 18/11/05 at 12:14 PM |
|
|
You could space the master cylinder out a bit with a few washers between the flange and the mount if you have no adjustment on the pushrod just to
check if it cures the problem.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
|
|
|
samwilliams
|
| posted on 18/11/05 at 07:27 PM |
|
|
Gone out and had a look and a fiddle, and not quite sure what to adjust. I've put a couple of pictures in my photo archive of the right bits (I
hope!), so if anyone could do me a pretty picture or something, that'd be wonderful!
Is it normal for this to just start happening after having been fine before?
Thank you very much.
Sam
|
|
|
samwilliams
|
| posted on 18/11/05 at 09:44 PM |
|
|
Anyone?!
I've been out seeing what I can do, but I can't work out how to adjust the push rod. I don't know what you can tell from the
pictures, but the brake pedal can't go any further back due to a stopping thing (that's my technical term for it) that is completely
unadjustable by the looks of things. I can't work out how to turn the push-rod to adjust the length. I'm stuck!
Sam
(I'm hoping that someone can make me look like a complete fool now, by suggesting something blatantly obvious that I've overlooked. Go on,
you know you want to!)
|
|
|
Peteff
|
| posted on 18/11/05 at 11:37 PM |
|
|
It looks like all the adjustment has been used up. I'd be tempted to take the pushrod out and cut 1/2"ish off the other end to get some
adjustment back. That way you'll be able to fit a locknut to it as well.
[Edited on 18/11/05 by Peteff]
 
Rescued attachment pushrod.jpg
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
|
|
|
Baldrick
|
| posted on 19/11/05 at 05:51 AM |
|
|
I agree with all the above - this happened to me too. also after having used the car for a while. When it locks up can you get hold of the pedal and
manually pull it back? Does this release the brakes? It only needs a very light pressure on the master push rod to cause the problem. I cured mine by
fitting a return spring on the pedal to ensure it came all the way off when I took my foot off - never had the problem again. The suggestions re.
adjusting the pushrod & spacing the master cyl. are all equally good but I kind of get the feeling you're not too confident and playing with
the brakes might not be the best place to start. Your local garage will probably be happy to help - make a change from all the boring tin boxes.
Mine set up all the timing & carbs etc. on his whizzy computer thingy for a couple of pints in the local. (afterwards!).
[Edited on 19/11/05 by Baldrick]
|
|
|
samwilliams
|
| posted on 19/11/05 at 01:14 PM |
|
|
Thanks for the diagram and other bits. I had a feeling it was probably that, and it doesn't have any more room to be adjusted. It's going
to be looked at by someone who knows a lot more than me on wednesday, so hopefully we can sort it out then!
Sam
|
|
|
