So, after the brakes seizing on the way to MOT last Saturday, I had a read of the archives and found that you need some slack in the brake pedal to ensure that the master cylinder can return fully. I've adjusted my m/c push rods and that problem seems to be solved now. There is still quite a lot of drag from the brakes though.

I've measured it with a torque wrench - with callipers off, it takes 7 ft-lbs to turn the wheels & diff (LSD, in neutral). With one calliper, 10, with both, 14 ft lbs, so a fairly even split. That seems like quite a lot though, it takes it from "can just about turn the disc with one hand" to "requires two hands". (Before adjusting the master cylinder push rod it was "can just about turn it with a wrench on the hub nut, but not with hands on the disc" ). Does this sound OK, or do I still have brake issues? Don't want a repeat of last Saturday's MOT debacle...

[Edited on 9/11/10 by rodgling]

Sounds a bit too much IMO - do they get hot after a run?

No idea - can't really test this as I haven't IVA'd yet. It's on axle stands so I could run it for a bit and see how it goes - will probably give this a try tomorrow night.

why were you going to an MOT if its not IVA's yet?

What brakes are they? Sierra? Front, rear, both? New,used?

Sounds a bit much but a bitmore info would be good.

As Blake said, why are you going for MOT if it's not yet IVA'd. It's not a requirement. If it's just for a check over preIVA then make sure they only go through it but don't actually log it into the MOT system.

They're new Golf callipers at the back and used BMW 3-series callipers at the front (fronts are OK though). New pads, new discs. After winding back the rear callipers by hand there is (just) enough space for the wheel to turn without significant drag from the brakes, but after applying the brakes a few times, they don't retract as far and drag a little bit.

The MOT is a good way to get a legal test-drive in before IVA, and to get someone else to check the car over for things I might have missed. I have to do it at some point, so might as well be before IVA (with an old engine I won't be able to get the 3 year MOT exemption anyway).

[Edited on 10/11/10 by rodgling]

An MOT is not a legal exemption for a test drive of an unregistered car as an MOT is not a prescribed requirement.
The only test you can drive to is the IVA so long as you have the relevant insurance.

I phoned my local DVLA, and eventually got put through to VOSA, who told me that as long as I have insurance, I can drive to MOT without IVA or registration. The guy I spoke to seemed to know about this kind of thing as he didn't have to go away and look it up or anything - he was quite clear about it.

He's wrong (which isn't hard to believe with DVLA). You can only drive to and from a pre-booked, legally required test. MOT isn't legally required for you car.
Once it's been tested then it has to havea test every year from then irrespective of age. So no 3 year exemption which you do get. Old engine has nothing to do with it. First test is 3 years from first registration of the car and has been covered many times on here.

Are your handbrake cables coming fully off? ie. Do the caliper levers come all the way back to thier stops?

Theres a little bit of slack in the handbrake cables when the handbrake is off (1-2mm), so I'm confident it's not that

[Edited on 10/11/10 by rodgling]

If you are sure that its only the back ones dragging, i would disconnect the handbrake from both calipers, at least that will discount the handbrake

If they are still dragging, then the master cylinder is under mild pressure on brakes off, that is it, there is no other explanation and the pushrod is to tight and will need backing off, assuming you are using standard pads/shims etc in standard calipers

What about taking the shims out on all calipers for the moment ?
and while doing that i would be inclined to force the pistons back and forth a few times to check theres no mechanical problems

Regards

Steve

also, it takes 7-10lb to turn the wheels with the calipers off ??

That is wrong, my wheels with pads out, would spin by hand freely, and possibly a hard shove will spin 2-3 times unaided
i doubt you would get any spin

I can pull the handbrake cable back by 1-2 mm at the callipers, when the handbrake is off, and the lever on the caliper stays put, so it's definitely in its fully-back position. I've disconnected the pushrods from the brake pedal, so there is nothing preventing them from coming as far forward as they want - under these conditions there is still some drag from the pads as described.

7 ft-lbs without callipers is what it takes to turn the diff (maybe this is normal for LSD [it's off an E36 328])? It's smooth, just takes a bit of effort to turn. As you say, almost no free spin without pads.

On the fronts a hard shove will get maybe 2 full rotations which seems about right.

Faulty MC? I've wound the pistons in by hand, and there doesn't seem to be an issue there - once fully wound in, and before trying to apply the brakes, the increase in drag over no-calipers is almost nothing. After an application of the brakes, there is additional significant drag, as described.

According to the BMW forums it's normal for the LSD to require quite a bit of force to turn it (more than an open diff), so I think that 7 ft lbs number to rotate just the diff is probably about right. It's the increase that the brakes introduce that is concerning me.

quote:

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Originally posted by adithorp
He's wrong (which isn't hard to believe with DVLA). You can only drive to and from a pre-booked, legally required test. MOT isn't legally required for you car.
Once it's been tested then it has to havea test every year from then irrespective of age. So no 3 year exemption which you do get. Old engine has nothing to do with it. First test is 3 years from first registration of the car and has been covered many times on here.

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Drag in a LSD is normal. You will often feel some slight drag from pads but not a lot. Does the caliper slide freelyon the carier with no pads in. Check the sliders. Can't remember if yours have rubbersin them but if they do, put "redrubber grease" on them and not ordinary grease or copperslip.

You say you have slack at the push rod but is there a return spring on the pedal so it is lifted clear of the rod at rest?

Is there a servo connected ?
Are the pads a tight interferance fit in thge calipers ?

as i i on occasions have had to file of the painted edges on pads to stop them effectivly seizing on, once the peddle has been depressed

Steve

[Edited on 10/11/10 by steve m]

I've tried disconnecting the pushrod from the pedal for testing, so the source of the drag is not pedal return, or handbrake (there's enough slack in the cables). No servo.

I haven't checked the tightness of the pads in the calipers, will do that tonight, and also check the caliper is able to slide freely. I didn't notice the caliper pins sticking before, so I don't think that's an issue.

I think the drag is on the high side, but having idled the car in 5th for five minutes (on axle stands), both discs got only slightly warm to the touch. I will try to get an improvement, but if I can't, I think this is acceptable and will not stop the brakes from working properly.