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Author Rear brake lock up
7builder
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Registered: 28th Dec 06
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28th Dec 06 at 18:16   View User's Profile U2U Member Reply With Quote

Evening all, this is my first post on this forum so hopefully you can help me out. My daughter has a bog standard 1.2 8 valve merit corsa B that is locking up the rears under light or heavy braking. This usually happens the first time you brake after the car has been stood for a while but will also do it on other occasions. The other day it happened coming out of a car park at about 5 mph, it's a real death trap. I've read a lot of info on this site about lock up after cars have been lowered but this car is standard. It would also appear that the bias valves dont seem to go faulty so has anyone got any idea what could be causing this problem?
My daughter is learning to drive at the moment and doesn't need this added complication.
Dave A
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Registered: 10th Dec 03
Location: County Durham
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28th Dec 06 at 18:26   View User's Profile U2U Member Reply With Quote

probably a faulty bias valve. as a safety measure until you find the cause for certain just disconnect the spring between the rear beam and the valve and let the compensator valve bracket hang down.
Joe
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Registered: 20th Jun 04
Location: Hesketh Bank, Lancashire
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28th Dec 06 at 18:32   View User's Profile U2U Member Reply With Quote

Check it is'nt seized up too.
gingerob
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Registered: 11th Apr 06
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28th Dec 06 at 19:23   View User's Profile U2U Member Reply With Quote

also check the drums and shoes... could be contaminated.
7builder
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28th Dec 06 at 19:33   View User's Profile U2U Member Reply With Quote

Thanks for the replys everyone. I'll try and get under the car tomorrow foe a look. I was going to have a look today but I'm a bit smashed up at the moment (back, ribs and bicep) and can hardly move. Some idiot talked me into a Dads v Sons rugby match yesterday. The lads play for Bristol Rugby Academy and I feel like I've been in a car crash.
SportBoy
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28th Dec 06 at 19:38   View User's Profile U2U Member Reply With Quote

unlucky
abdus
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28th Dec 06 at 21:47   View User's Profile U2U Member Reply With Quote

quote:
Originally posted by 7builder
Some idiot talked me into a Dads v Sons rugby match yesterday. The lads play for Bristol Rugby Academy and I feel like I've been in a car crash.


mattk
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Registered: 27th Feb 06
Location: St. Helens
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28th Dec 06 at 23:57   View User's Profile U2U Member Reply With Quote

hmmm strange mine has been doing this the past week as well, this bias valve u speak of, what does it look like, what does it do and can it be changed easy??
tom_simes
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Registered: 12th Jan 05
Location: Undy, Newport Drives: Skoda Octavia vRS estate
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29th Dec 06 at 00:30   View Garage View User's Profile U2U Member Reply With Quote

If I'm right, the 1.2 8v don't have a bias spring valve.

When I had my old 1.2, I'm sure I read in my Haynes manual that they are in the rear brake lines on those models.
Kurt
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Registered: 23rd Oct 05
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29th Dec 06 at 00:30   View User's Profile U2U Member Reply With Quote

it sits on the rear cross menbery thing and it looks like a bracket with a spring on it and it tells the rear brakes how much weight is on the rear wheels (but a bit more cleverer)

Edit: pretty sure my 1.2 8v has one

[Edited on 29-12-2006 by kurtofcc]
mattk
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Registered: 27th Feb 06
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29th Dec 06 at 00:53   View User's Profile U2U Member Reply With Quote

will have a look tomorrow
Teknologikal
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Registered: 11th May 06
Location: Cardiff
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29th Dec 06 at 12:08   View User's Profile U2U Member Reply With Quote

Thank god it isn't just me.....went to reverse yesterday and she acted like I'd left the handbrake on I even said to the missus, "I think the brakes have seized".

I put it down to her being idle for so long but since that's 2 other cases in as many days might be summat else
Will_Sport
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Registered: 28th Jun 04
Location: Notts
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29th Dec 06 at 13:24   View User's Profile U2U Member Reply With Quote

as far as i was aware its only like the 1.4/1.6 16v's and the corsavans/combos that have these fitted? (ie the springy valve thing on the rear beam... over on the right hand side btw)
Teknologikal
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Registered: 11th May 06
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29th Dec 06 at 13:43   View User's Profile U2U Member Reply With Quote

Well I yanked up the handbrake then released it again and all was well.....will be keeping my eye on things. I need to change my drums before long anyway so will have a proper look then.
7builder
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Registered: 28th Dec 06
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30th Dec 06 at 13:46   View User's Profile U2U Member Reply With Quote

Well I finally managed to drag my battered carcass under the car for a gander but there is no spring loaded bias adjuster on this model. I followed the brake lines from both rear back plates all the way to the front but couldn't see anything that resembled any sort of bias adjuster. I took the car for a spin (literally) and at 10 mph the car swapped ends when I stamped on the brakes hard. The rears kept locking up for the next few brake applications and then the fronts seemed to come into play, it still feels like the rears want to lock first. I'll have to get the car in the air and check all around but am thinking it might be the master cylinder. Anyone got any other ideas?

I was also surprised on ow heavy the steering had become but I'll do a search on this forum and post elsewhere if I need help.
neil h
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Registered: 28th Sep 06
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30th Dec 06 at 14:48   View User's Profile U2U Member Reply With Quote

right, i've jus had a quick butchers in the haynes manual, and it could be either the bias valve, or your brake shoe linings contaminated.

and as far as the bias valve goes, on the 1.2 there is an individual one for each side of rear braking system. and they are above the axle.
7builder
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Registered: 28th Dec 06
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30th Dec 06 at 15:00   View User's Profile U2U Member Reply With Quote

quote:
Originally posted by neil h
right, i've jus had a quick butchers in the haynes manual, and it could be either the bias valve, or your brake shoe linings contaminated.

and as far as the bias valve goes, on the 1.2 there is an individual one for each side of rear braking system. and they are above the axle.


Hi Neil,

I'll take another look under the car when the rain stops but I couldn't see anything other than metal brake pipe and rubber flexi's. Also if the shoes were contaminated wouldn't that make them less effective, therefore less likely to lock up? The weather is really shitty at the moment but I reckon I'll end up stripping the front and rear brakes completely. Can anyone suggest a supplier I can try for a replacement master cylinder (just incase)?
neil h
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Registered: 28th Sep 06
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30th Dec 06 at 16:14   View User's Profile U2U Member Reply With Quote

thats what i thought bout the shoes aswell, but i've checked the manual again and thats definately what it says.

btw the compensator valves look like a lil metal hose union about 20mm long. one's found just infront of the rear axle, and i think the other one is above the axle, running across to the other brake drum.
CorsAsh
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Registered: 19th Apr 02
Location: Munich
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30th Dec 06 at 16:18   View User's Profile U2U Member Reply With Quote

Daft question perhaps but how are the front brakes? Are they working well?

If the front calipers are seized off or the pads are badly worn, most of the braking force will be at the back and hitting the brake pedal would have a similar effect to yanking the handbrake on... hence the swapping ends malarky.
7builder
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Registered: 28th Dec 06
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30th Dec 06 at 17:00   View User's Profile U2U Member Reply With Quote

quote:
Originally posted by CorsAsh
Daft question perhaps but how are the front brakes? Are they working well?

If the front calipers are seized off or the pads are badly worn, most of the braking force will be at the back and hitting the brake pedal would have a similar effect to yanking the handbrake on... hence the swapping ends malarky.


That's what I was thinking. I have a feeling the fronts might not be working effectively but won't know for sure until I can get at them. If the bias valves are as Neil described then I dont think there will be anything to adjust. I think a complete brake overhaul is in order. If things don't improve after that then I'll take a closer look at the master cylinder.
neil h
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Registered: 28th Sep 06
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30th Dec 06 at 20:19   View User's Profile U2U Member Reply With Quote

think they are adjustable, but only a tiny bit 'cus it looks like you can loosen the nut on one end to make the whole assembly longer/shorter
gingerob
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Registered: 11th Apr 06
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31st Dec 06 at 11:46   View User's Profile U2U Member Reply With Quote

quote:
Originally posted by gingerob
also check the drums and shoes... could be contaminated.


Mine were contaminated with all kinds of shit and kept locking up with hardly any braking.... worth a look....
7builder
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Registered: 28th Dec 06
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31st Dec 06 at 16:59   View User's Profile U2U Member Reply With Quote

Right, I managed to get under the car today and had a closer look at the brakes. I started with the fronts and everything checked out fine. The pistons were moving freely, there was plenty of life left in the pads and the disks were in good order. The OSR drum brake also looked good, handbrake worked fine and the slave cylinder was working correctly. The NSR brake was a different matter. There was no contamination but the shoes had moved from the back plate and had wedged themselves under the lip where the drum edge runs (hard to describe). The ratchet mechanism for the self adjuster was gummed up and not moving freely so I removed it, cleaned the threads with brake cleaner and an M8 tap and die then reassembled with some light oil. I then reassembled the brakes and checked the operation of the hand brake and foot brake. Nothing was siezed and all seemed ok but the self adjuster doesn't work correctly. The little leaver that engages with the adjuster ratchet is not operating correctly (do they ever on drum brakes - I've got a similar problem on a Pug 306) so the slack was not being taken up when the brakes were operated. I messed about with it for a while but in the end I had to adjust manually until I could only just get the drum back on and I could feel the brakes biting. When all was done I took it for a test drive and I think I have sorted the problem. I couldn't get the bac brakes to lock up and the pedal seemed a lot firmer. Before I claim a complete success though I am going to leave it overnight and try again tomorrow as it seems to be worse if the car has been left for a while with the hand brake on. I'm hoping it is sorted now but I'll have to bear in mind that the self adjuster is iffy and remember to occasionally remove the rear drums and manually adjust the brake shoes.

Is it possible to convert to rear disks? I hate drum brakes.

Happy new year everyone.
Jake
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Registered: 24th Jan 05
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31st Dec 06 at 17:06   View User's Profile U2U Member Reply With Quote

yes but you need to get some conversion plates welded onto the axle
7builder
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Registered: 28th Dec 06
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31st Dec 06 at 17:29   View User's Profile U2U Member Reply With Quote

quote:
Originally posted by jake
yes but you need to get some conversion plates welded onto the axle


That's no problem I have a MIG welder and an AC/DC TIG welder sat in my garage. I've seen the plates advertised on a motorsport web site for 25 or there abouts. What disk brakes does that allow you to convert to, Astra GTE's / GSi's?. Do you know of a web site that shows a step by step on how to convert?

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