Stott
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| posted on 3/11/10 at 10:09 PM |
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Front vs rear lockup - sierra brakes
How many of you have used the std sierra disc/drum master cylinder setup, without a pressure reducing valve, and have found the fronts lock before the
rears?
I have sierra m/c, servo, 240 discs and 9" drums (or the bigger of the 2 available whatever they were) and am wondering whether to bother with a
pressure valve of sorts before I plumb the rear brakes.
Car is a Robin Hood S3 and will prob weigh a tad short of 700kg at a guess.
Thanks in advance, Stott
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mookaloid
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| posted on 3/11/10 at 10:18 PM |
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I don't think you will need a pressure reducing valve for drums - even the bigger ones.
The fronts should lock before the rears.
cheers
Mooky
"That thing you're thinking - it wont be that."
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handyandy
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| posted on 3/11/10 at 10:21 PM |
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I,m running the same setup as you, I haven,t fitted a pressure valve, & my brakes feel fine,
its taken a couple of drives to "bed in" the new discs & pads, feels great now.
cheers
andy
ps, sorry, no servo on mine, just the same brakes as you( std sierra discs/drums)
[Edited on 3/11/10 by handyandy]
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Stott
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| posted on 3/11/10 at 10:23 PM |
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Thanks for the info, HandyAndy - do your fronts lock first?
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handyandy
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| posted on 3/11/10 at 10:39 PM |
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quote:
Originally posted by Stott
Thanks for the info, HandyAndy - do your fronts lock first?
Yes, but I haven,t really used the brakes in "mega" anger yet, but yes the fronts lock first.
In all honesty its quite hard to lock them up, as the car comes to a halt nicely controlled, in a straight line etc.
My car is approx 530kgs & I weigh 71kgs...if that makes a difference.
cheers
andy
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snapper
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| posted on 4/11/10 at 07:14 AM |
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for IVA and MOT fronts have to lock up first.
If rears lock up first it's a failure.
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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whitestu
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| posted on 4/11/10 at 08:08 AM |
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I had the same setup and the fronts locked first every time.
Is your problem that the rears lock first?
Stu
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interestedparty
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| posted on 4/11/10 at 08:20 AM |
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It's perfectly possible to be in a situation where, at heavy pedal pressure, the fronts lock first, but, at light pedal pressure, the rears lock
first.
Actual wheel lock up at light pedal pressure would be unlikely except on a slippery road, but that's why the IVA brake test checks through a
whole range of pedal pressures.
Best advice is to use good quality brake pads such as Mintex, and make sure the brakes are well bedded in.
As some day it may happen that a victim must be found,
I've got a little list-- I've got a little list
Of society offenders who might well be underground,
And who never would be missed-- who never would be missed!
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AdrianH
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| posted on 4/11/10 at 08:25 AM |
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Mine would lock up on the fronts first, but the new brake balance test meantI failed at 2 of the 5 testing points, set up was the same with sierra
disks on front and 9 inch drums on back. yes it will matter about the weight and distribution of the car for IVA test. I had 53/47 split front to
back or thereabout.
I swapped the rear slave cylinders for a slightly smaller escort one and ended up with closer to a 70/30 split for braking effort.
unfortunately the setup can not be tested on MOT rollers unless you measure pedal pressure.
If it helps have a read of my IVA fail sheet.
http://www.tamarisktechnicals.com/pages/iva.html
They would not provide the figures to me once I passed.
Adrian
Why do I have to make the tools to finish the job? More time then money.
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Stott
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| posted on 4/11/10 at 07:45 PM |
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Thanks for that everyone, I'm aware of the rules and all that, cheers though Paul.
Adrian: my rear cyls are listed on brakes international as 20.6, this is also the case for the 1.8cvh, what cyls did you have that were 22.22? or did
you mean the master cyl was 22.2?
My master is 22.0 diam according to their site
I've just had a look at your spreadsheet and I guess the weights are going to be similar so I put in that my orig cyl is 20.6 and new cyl 19.05
and it's made the 5 boxes true at the end of it.
The car is still on stands at the moment and I'm about to pipe the rear brakes but I wanted to try safeguard myself against the balance test at
IVA as it's expensive at £90 a retest so I thought I'd ask what people have found. Assuming I passed the rest of it I be pretty pi55ed if
it failed because of £12 worth of wheel cylinders! 
It might be worth me sticking a pair of those mk2 escort 19.05 ones in before I pipe and bleed it all, at least it would be a step in the right
direction and it's never going to be as easy to change them as it is now.
What do you think?
Cheers for the link BTW, very good
Stott
[Edited on 4/11/10 by Stott]
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AdrianH
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| posted on 4/11/10 at 10:52 PM |
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Hi stott sorry for the long time to reply.
The local motor factors put the donor registration into their database and came back with the 22.2 mm cylinders., so that was what I originally
fitted. Still have them. You could always try and make the foot gauge and take the car to an MOT brake roller test and try to do your own checks or
even fit a pressure gauge on the brake line?
Which ever the way you go I wish you success.
Adrian
[Edited on 5-11-10 by AdrianH]
Why do I have to make the tools to finish the job? More time then money.
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Stott
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| posted on 4/11/10 at 11:17 PM |
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Ok thanks for all your help. I have a feeling I'll end up with problems at IVA if I leave it as is. I'll probably end up fitting smaler
bore wheel cyls just to err on the side of caution, and it's not going to knock loads off the rear brake efficiency and also it will save me
thinking about pressure reducing valves. Plus it's cheap and easier to do before I pipe and bleed it.
Thanks again
Stott
[Edited on 4/11/10 by Stott]
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