Snap-off
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| posted on 11/7/08 at 11:05 AM |
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Back wheel lockup before front?
Hi guys,
One of my back wheels locks before the front on heavy breaking. Is there some sort of SVA friendly restrictor valve that I can fit to the rear line to
stop this? Or anything that I can change on the drum?
My setup is:
Sierra master cylinder
Sierra rear drum brakes
Wilwood front calipers.
Thanks.
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Mr Whippy
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| posted on 11/7/08 at 11:08 AM |
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there's various inline adjustable ones, I'd fit it in the engine compartment to keep Mr SVA happy
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BenB
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| posted on 11/7/08 at 11:10 AM |
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Strange that drums are locking up before discs..... Adjustor valves are available... might be worth making sure everything is set up and bedded in
first though. Normally drums are suitably pants to lock up about half and hour after discs have locked.....
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Snap-off
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| posted on 11/7/08 at 11:13 AM |
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quote:
Originally posted by Mr Whippy
there's various inline adjustable ones, I'd fit it in the engine compartment to keep Mr SVA happy
Mr SVA said that it must not be adjustable. He mentioned that there was a restrictor valve fitted in some sierra models in the rear line. Anyone know
anything about it?
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JAG
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| posted on 11/7/08 at 11:14 AM |
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You may also be able to fit smaller bore slave cylinders in the rear drumbrakes.
Take one of your current slave sylinders to your local motor factor and ask. Ford use the same or similar fixings for all thier models,
Fiesta/Focus/Sierra etc... and you may find a smaller cylinder (on both sides) will cure the problem.
Justin
Who is this super hero? Sarge? ...No.
Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!
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JAG
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| posted on 11/7/08 at 11:15 AM |
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The Sierra rear restrictor is a G-Valve and has to be installed at an angle to give the correct level of restriction.
Best to use something else 
Justin
Who is this super hero? Sarge? ...No.
Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!
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Mr Whippy
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| posted on 11/7/08 at 11:19 AM |
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quote:
Originally posted by Snap-off
quote:
Originally posted by Mr Whippy
there's various inline adjustable ones, I'd fit it in the engine compartment to keep Mr SVA happy
Mr SVA said that it must not be adjustable. He mentioned that there was a restrictor valve fitted in some sierra models in the rear line. Anyone know
anything about it?
sure he didn't mean adjustable while driving along? hence putting it in the engine compartment, all brakes are adjustable to some degree, just
normally you don’t fiddle with them when moving.
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gingerprince
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| posted on 11/7/08 at 11:23 AM |
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quote:
Originally posted by Mr Whippy
all brakes are adjustable to some degree, just normally you don’t fiddle with them when moving.
Unless you're a smartarse and you want a different brake balance for turn 3 than you do in turn 8 
I'm not! Though it is useful to twiddle on the early laps of a track day on the fly to get the balance right for the level of grip the circuit
tends to give.
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Snap-off
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| posted on 11/7/08 at 11:23 AM |
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quote:
Originally posted by Mr Whippy
quote:
Originally posted by Snap-off
quote:
Originally posted by Mr Whippy
there's various inline adjustable ones, I'd fit it in the engine compartment to keep Mr SVA happy
Mr SVA said that it must not be adjustable. He mentioned that there was a restrictor valve fitted in some sierra models in the rear line. Anyone know
anything about it?
sure he didn't mean adjustable while driving along? hence putting it in the engine compartment, all brakes are adjustable to some degree, just
normally you don’t fiddle with them when moving.
Sorry, not sure, he just said that the restrictor must not be adjustable.
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whitestu
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| posted on 11/7/08 at 11:27 AM |
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Are you sure the front brakes are OK?
Mine has standard sierra fronts and rear drums with no pressure limiting valve and the fronts always lock first.
As you have Wilwoods I should have thought these would be more powerful than standard brakes and so should lock well before the drums.
Stu
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Mr Whippy
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| posted on 11/7/08 at 11:28 AM |
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I'd double check, think of the bias bar cars that are passing the SVA, all they have to do is pin the adjuster.
how bedded in are the front brakes? They may have slight contamination and will get better with more use.
[Edited on 11/7/08 by Mr Whippy]
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Snap-off
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| posted on 11/7/08 at 11:36 AM |
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quote:
Originally posted by whitestu
Are you sure the front brakes are OK?
Mine has standard sierra fronts and rear drums with no pressure limiting valve and the fronts always lock first.
As you have Wilwoods I should have thought these would be more powerful than standard brakes and so should lock well before the drums.
Stu
I thought that too. I think I will try bleeding the front again and get some miles on the car to bed them in before my re-test.
The car had not really been driven before the test and all the brakes are new.
Thanks guys!
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westf27
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| posted on 11/7/08 at 11:52 AM |
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if your master cylinder is dual circuit have you connected front and rear pipes the correct way round.Mine is the the old escort one and not sure what
the sierra one is like
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will121
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| posted on 11/7/08 at 11:52 AM |
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need to look at the basics first, like may be 1 caliper not operating properly, is you master cylinder set up front/rear or the standard sierra
opposite sides. i think on most fords each section of the master cylinder piston would have been to oposite fron/rear sides with restrictors in the
rear pipe to limit pressure to the rear which may now answer why, have you tried jacking up the front and get someone to apply the brakes a bit at a
time and try and spin the wheels and se if they start to bite at the same time with same force?
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Snap-off
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| posted on 11/7/08 at 12:08 PM |
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quote:
Originally posted by will121
need to look at the basics first, like may be 1 caliper not operating properly, is you master cylinder set up front/rear or the standard sierra
opposite sides. i think on most fords each section of the master cylinder piston would have been to oposite fron/rear sides with restrictors in the
rear pipe to limit pressure to the rear which may now answer why, have you tried jacking up the front and get someone to apply the brakes a bit at a
time and try and spin the wheels and se if they start to bite at the same time with same force?
The brakes were tested on the SVA rolling road for each individual wheel. They all passed. But for some reason when the examiner drove the car to test
they reported one rear locking just before the front. I'm positive that the master cylinder is setup propery.
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mackei23b
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| posted on 11/7/08 at 12:23 PM |
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Hi had my rears lock first as well with a standard sierra master cylinder, that said, I've got cosworth disks on the back.
I used a willwood adjustable bias valve and made a bracket so that a roll pin would lock it off. I passed the SVA OK with this, though it does sound
that your tester is into every detail.
Cheers
Ian
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Paul TigerB6
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| posted on 11/7/08 at 12:45 PM |
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quote:
Originally posted by Snap-off Mr SVA said that it must not be adjustable. He mentioned that there was a restrictor valve fitted in some
sierra models in the rear line. Anyone know anything about it?
Yep - it does absolutely bugger all on the rollers as it relies on the deceleration to restrict the pressure to the rear line. As above i'd
suggest ensuring the front brakes are bedded in and the system is properly bled before inserting a restrictor to the rear which you probably wont need
with drums
[Edited on 11/7/08 by Paul TigerB6]
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britishtrident
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| posted on 11/7/08 at 01:57 PM |
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Bleeding the brakes won't fix it.
If only one rear is locking it points to corner weights try jacking the springs up just a little at that corner.
If you want to fit a pressure reducing valve in the rear brake line either fit a Fiat Uno or Fiat Ritmo/Starda or Lada Riva one (very cheap from
Brakes International) or go to the scrappies and get one off an early Mondeo without ABS -- it is bolted straight on the master cylinder outlet but
remember to cut through the pipe and take the tube fitting with it.
[Edited on 11/7/08 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
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