rodgling
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| posted on 9/11/10 at 10:40 PM |
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brakes dragging
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]
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RazMan
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| posted on 9/11/10 at 11:31 PM |
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Sounds a bit too much IMO - do they get hot after a run?
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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rodgling
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| posted on 9/11/10 at 11:51 PM |
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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.
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blakep82
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| posted on 10/11/10 at 01:26 AM |
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why were you going to an MOT if its not IVA's yet?
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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adithorp
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| posted on 10/11/10 at 08:33 AM |
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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.
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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rodgling
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| posted on 10/11/10 at 09:34 AM |
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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]
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minitici
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| posted on 10/11/10 at 09:54 AM |
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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.
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rodgling
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| posted on 10/11/10 at 10:13 AM |
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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.
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adithorp
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| posted on 10/11/10 at 10:26 AM |
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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?
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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rodgling
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| posted on 10/11/10 at 10:30 AM |
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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]
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steve m
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| posted on 10/11/10 at 11:21 AM |
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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
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steve m
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| posted on 10/11/10 at 11:26 AM |
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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
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rodgling
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| posted on 10/11/10 at 11:35 AM |
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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.
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rodgling
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| posted on 10/11/10 at 11:51 AM |
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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.
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mcerd1
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| posted on 10/11/10 at 12:13 PM |
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quote:
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.
^^ what he said - don't trust what the DVLA tell you unless you've got it in writing
(and thats before you get into the small print of your insurance....)
-
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adithorp
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| posted on 10/11/10 at 12:25 PM |
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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.
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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Dingz
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| posted on 10/11/10 at 05:04 PM |
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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?
Phoned the local ramblers club today, but the bloke who answered just
went on and on.
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steve m
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| posted on 10/11/10 at 05:59 PM |
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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]
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rodgling
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| posted on 11/11/10 at 01:07 PM |
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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.
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