rear brakes won't adjust up

S

Sekrap53

New Member
I've replaced all 4 discs, both front calipers, offside rear caliper and over hauled the nearside rear. I've bled the system 3 times by the usual method, and there is no more air coming out of the nipples. I've raised the car on a jack and confirmed that the front brakes work on both front wheels, but neither of the back brakes lock up with either the foot brake or the handbrake and neither piston moves.Is bleeding the brakes using the conventional method sufficient, bearing mind that I have completely drained the whole system. Or would I need to pressure bleed it?
I have been raising and lowering the handbrake expecting the back brakes to adjust up.When you engage the handbrake, on the first 4 clicks the nearside caliper rocker arm begins to swivel with each click but the offside doesn't start moving until click 5, by the time the handbrake is fully up which is about click 10 neither brakes are engaged enough to grip the disc. The nearside rocker arm has rotated about 90% of its travel but the offside has only travelled about 60%, if that. I'm as sure as I can be that I have reassembled the handbrake linkage correctly when I replaced the calipers. I confirmed that the handbrake rocker arms were ratcheting and moving the pistons out correctly on both calipers before I installed them on the car. Is there some form of adjustment somewhere to ensure that both handbrake rocker arms begin moving together (assuming that that is what should happen) on the first click of the handbrake?.
Due to the expected rusty bolts, and waiting for parts, I have been on this job for weeks. I've got to the stage of wanting to throw spanners up the garage. Any advice or suggestions would be very much appreciated.
 
I'd guess that the most likely problem is that you have the handbrake cable adjusted too tightly. The ratchet mechanism needs to fully disengage in order to take a fresh bite, so any tension remaining in the cable with the handbrake released will disable the self adjusting.

Try that to begin with, then if you aren't making progrss we'll give you some tips on how to preset the adjustment so that pads and discs are withinn sight of each other to start with. But you'll want to do the cable first, because the latter techniques involves having the discs out.... The adjustment per activation of the handbrake is very small indeed, so some patience is required.

Hope that helps

Chris
 
I'd agree about the cable adjustment, with the handbrake off, the quadrants on the calipers should be right back on their stops, if they aren't then back off the cable adjustment until they are, after that I'd forget about using the handbrake (or footbrake) to adjust them up, and I'd get the handbrake linkage removed from the calipers and diff and out of the way, and the discs removed, and then set them up by operating the quadrants manually until the disc will just slide in with the calipers at rest.
 
Thanks for that fellas, the quadrants are fully off, there isn't a problem with an over tight handbrake cable it is the complete opposite. I had disconnected the handbrake linkage and moved the offside quadrant by hand from stop to stop. This action did not move the piston out which I assumed it would. I have since removed the pads from the offside caliper and managed to partially rotate the piston by hand, that has taken up some of the gap but the inner pad is still a little sloppy, unlike the nearside. When you turn the quadrant by hand and hold it in the brakes fully on position it does cause the pads to grip the disc but not with enough force to stop the wheel from rotating.
As far as adjusting the handbrake cable is concerned, where is the adjuster nut, is it under the car under the front gater or is it accessed from inside.
 
Sekrap53 said:
I had disconnected the handbrake linkage and moved the offside quadrant by hand from stop to stop. This action did not move the piston out which I assumed it would.
Click to expand...

The caliper isn't working in that case.

Sekrap53 said:
As far as adjusting the handbrake cable is concerned, where is the adjuster nut, is it under the car under the front gater or is it accessed from inside.
Click to expand...

The cable adjuster is on the transmission tunnel. above the propshaft, just forward of the pinion crossmember.
 
I take it you mean the threaded section with 2 x 9/16th nuts half way along the under side of the car where the cable disappears into the outer sheathing and then on to the rear calipers and not, under the rubber gater at the front of the cable by the gearbox, where the cable disappears up onto the handbrake. If you mean those two 9/16th nuts then I did start turning them, thinking that they were the adjusters, but they didn't seem to have any effect on the cable tightness.
 
Have you checked to see that the pad can slide. I have refitted pads which had shims before but the would not slide so brakes would work or adjust.

Colin
 
Sekrap53 said:
This action did not move the piston out which I assumed it would.
Click to expand...
With mine the pistons will come out visibly given a full turn of the quadrant, ie. 1-2mm, and return ever so slightly less each time as the ratchet slowly turns the rotating sleeve inside it. If you look closely, does it not move at all? If not something has fallen out of position inside and there will be no braking as Harvey says. If it does but doesn't seem to pick up the "slack" and you absolutely can't hear or feel the ratchet clicking, then the ratchet is half an iota out of whack and it simply won't self-adjust. There's tales here of random serial disassemblies with no discernible changes made until refitting and they suddenly work.

I also found that if the offside caliper doesn't have the little spring on it keeping the handbrake actuator arm close to the caliper cap ... the action on that caliper is slightly impeded... I noticed when working the handbrake mech, ref. your 90/60 pct. travel although the difference seems greater than I had. Once you know that both ratchets work and the pistons move, set up the pads as per Harvey's method - driveshafts disconnected so the discs can be slipped in and out while you set up the pads at the calipers manually. The adjuster by the propshaft should make all the difference necessary, but if the cable is very slack the limited access means it'll take a lot of fiddling to get it tight.
 
Hi.

As an alternative to removing the discs when adjusting the ratchets up in increments, i have found that removing just the outer pad when adjusting the caliper up and periodically sliding it back in until the pad to disc clearance is acceptable. This avoids the hassle of removing the driveshafts and is more accurate especially if there is a wear/corrosion ridge on the edge of the disc. Other than that, the procedure remains the same as previously posted.

Glen. :twisted:
 
I must admit to being a little confuzzled at this thread.

I rebuilt my calipers, then a few months later when putting Sparky back on the road (after bleeding the brakes) I pumped the footbrake a few times and pulled the handbrake up a few times and it all worked.

The handbrake and foot brake both passed the MOT and both continue to work flawlessly to this day.

Is this not how it is supposed to work?

Richard
 
I'm glad I'm not the only one Richard, I understand the principle of getting the initial setting spot on by removing the disc/pad, but surely once you start using them, they will just return to the standard gapping each time a new ratchet click is reached ?
 
Well I've had this car a long time and because of infrequent use I've messed with the rear calipers on quite a few occasions, most recently a month or so ago for the MOT, as one of the adjusters had stuck. All I've ever needed to do was just ratchet up the quadrants until it went tight, disks and pads all in situ. Handbrake efficiency was 31% which is pretty damn good for any rear disk handbrake setup, and definitely the stuff of dreams for a inboard disk jag. The handbrake was coming on in perhaps 4 or 5 clicks of the lever.

As for removing the outer pad, my experience on my own car is, once the adjustment is getting close, there's no way that pad will slide out, as there is a slight recess in the pad, which engages with a similar shape in the caliper itself. It could be the other way round, but there is definitely something which stops the pad sliding out in the manner described.

Although they are a bit fiddly to get to, I do have a soft-spot for these calipers as I find the mechanism quite fascinating. Its true that if you watch the mechanism operating when the caliper is off the car, then the pad actuating piston does move in and out a bit. But, thats only a side effect of there being no back pressure on the mechanism, in that condition there is nothing to push back against the S-spring so the whole assembly moves out a bit, due to mechanical backlash. But once the pad is pushed up against the disk, the ratchet mechanism just keeps on rotating the toothed wheel. Each time the handbrake is applied, any excess travel on the handbrake mechanism allows the pawl to click over the tooth on the ratch wheel. When the handbrake is released the pawl then pulls the wheel round by one tooth, and this being attached to the threaded shaft in the centre of the piston, pushes the latter out a little bit further.

In true Wallace and Grommit style, its a "cracking contraption"!
 
When you operate the quadrant with the caliper off, you hear the clicks as the pawl goes past the point where it will adjust the caliper. You get 3 or 4 clicks for each full movement of the quadrant IIRC. Each time the quadrant is moved when it's on the car it tries to apply the brake by moving the cup but if it's too far away it moves far enough to click and ajust. The problem is that with the disc in place, eventually the cup comes out and touches the disc before the caliper can adjust, so although the hand brake will hold (if you're lucky) by removing the disc you'll get to the point where the pad is close to the disc at rest, which you can't do with the disc in place. There is loads more adjustment available between the point where you can't get any more with the disc in place, and the point where the disc won't slide back in once it's been removed and adjusted that way.
Any rear discs that have a wear ridge should be binned anyway. Passing the MOT readings just means you've reached their standard, you can do far better. I like to get them so that they are totally free when the handbrake is off (obviously) and the handbrake is fully on in about 4 clicks. As with all disc hand brakes you can pull harder but you just start bending things.
 
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