Scuzzle
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| posted on 12/2/15 at 04:44 PM |
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Rear Caliper Lock up
Ever since I fitted my 4 pot calipers when I press the brakes firmly my OSR caliper locks up almost straight away,it never did this when the XR2
calipers were fitted. I have the restricting valves that screw into the master cylinder to reduce rear brake pressure and the NSR one is fine just
the drivers side is too sharp.
Does anyone have any ideas why this is happening now or how to go about curing it.  Like I say it was fine on the XR calipers and has only started
this since fitting the 4 pots. It's the Sierra Cosworth rear calipers. Cheers
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onenastyviper
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| posted on 12/2/15 at 05:13 PM |
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Restrictor valves plugged in the right ports?
"If I knew what I was doing then it wouldn't be called research would it?...duh!"
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CNHSS1
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| posted on 12/2/15 at 05:20 PM |
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possibly corner weighting out, and the extra braking of the fancy 4 pots is showing it up??
"Racing is life, everything else, before or after, is just waiting"---Steve McQueen
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Scuzzle
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| posted on 12/2/15 at 05:40 PM |
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It's a Mondeo master cylinder I'm using and the restrictor valves are different thread sizes so you can't really go wrong. I
thought it might be because I now have Ferodo DS250 pads up front and cheap £12 ones on the rear. It is odd how it was fine with XR2 calipers on the
front but now I've fitted the Wilwood 4 pots the OSR is locking up way too easily.
[Edited on 12/2/15 by Scuzzle]
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CNHSS1
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| posted on 12/2/15 at 05:49 PM |
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have you worked out the difference in piston area from the xr2 to wilwoods? could just be that you need to change your Rr mastercylinder size assuming
2 m/cyls for the braking?
summat like this (2sec google) may help work out if its piston size issue
cheers
CNH
[Edited on 12/2/15 by CNHSS1]
"Racing is life, everything else, before or after, is just waiting"---Steve McQueen
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Scuzzle
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| posted on 12/2/15 at 06:06 PM |
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I worked it out and it should be OK, I'm using the 31.8mm, I just can't figure out why it's the OSR only, the NSR is fine. When I
ran the XR calipers I could jump on the pedal and it would stop evenly now the OSR lock up far too easily every time.
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rdodger
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| posted on 12/2/15 at 06:39 PM |
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The OSR isn't seized is it?
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britishtrident
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| posted on 12/2/15 at 06:55 PM |
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Corner weights are the first port of call. The stiffer the car is sprung the more critical detting the corner weights becomes. However if you stop the
offside rear loving it increase the tendency for the near side rear to lock.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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Scuzzle
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| posted on 12/2/15 at 07:25 PM |
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The OSR is not seized, it turns freely however it's always that side I've had issues with. I used to run adjustable in-line bias adjusters
but I gave up on them as they were always leaking or holding pressure, when I binned them and went to the pressure valves in the master cylinder
things got much better.
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garyt
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| posted on 12/2/15 at 09:15 PM |
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if any were seized or binding it is the nsr to check obviously the osr is working fine.
also could be with the increased braking efficiency on the front it is lightening the rear almost like bunny hopping allowing the rear to lock
abruptly as the load lightens under braking. In your post you said when "pressed firmly"
Check the nsr for any piston binding seizure, check statically with rear jacked up , pedal pressed osr locked is the nsr?. once the rear axle
imbalance is sorted then work on the front rear balance
had a similar problem when we messed about with mini's and the problem was the one not locking
Good luck gary
[Edited on 12/2/15 by garyt]
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MikeRJ
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| posted on 13/2/15 at 01:01 PM |
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Maybe one of the pressure limiting valves isn't sealing correctly. If you swap the valves and the problem moves to the other side then
you've found the problem, though a bit of a pain to have to re-bleed.
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DW100
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| posted on 13/2/15 at 03:27 PM |
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The issue will be down to weight transfer under braking. I'm still using XR brakes on my Zetec powered Mk1 Fiesta hillclimber and using sticky
Avon slicks. I have a couple of pictures of the rear wheels off the ground under heavy braking. With mine having no interior, perspex windows and
glass fibre tailgate the weight distribution is 80/20 front to rear.
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Scuzzle
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| posted on 13/2/15 at 04:53 PM |
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Thanks guys, I think I will bin the Mondeo limiting valves and invest in a decent adjustable valve setup, I had some previously and one leaked from
new and the other held pressure on but they were cheaper ones so I suppose it's a case of you get what you pay for.
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