locosaki
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| posted on 17/6/08 at 09:43 PM |
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Braking problems
Hi all,
Had my car on the brake rollers this evening to try and get the bias set up,We tried adjusting the bias bar but it seemed to make no real difference,I
have set the bias up as per rally design site as it's there stuff I'm using.
The figures from the rollers were as follows
OSF 124
NSF 155
OSR 130
NSR 157
I took the car along the road for a test(we began to doubt rollers) When I just lightly pressed the braked pedal the NSF would lock up with no real
pressure applied.Didn't have the back locking up at all !!!
The master cylinders I have are as follows
Front 0.625
Rear 0.700
The clevis that the bias runs through appears to be correctly fitted too,I.E Doesn't appear to be jamming.
Any ideas would be appreciated.
Oh and to top matters off the oil pipe going to the cooler blew on the way home !!!!
Hopefully no damage,had to walk away or I might of done something I would regret !!!!
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The Great Fandango
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| posted on 17/6/08 at 09:47 PM |
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You do know the system's meant to be adjustable front to back and not left to right?
PS: Only kiddin' with ya
He Who Dies With The Most Toys Dies The Happiest
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locosaki
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| posted on 17/6/08 at 09:54 PM |
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ha ha,
Really !!!
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Bigheppy
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| posted on 17/6/08 at 10:01 PM |
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quote:
Originally posted by The Great Fandango
You do know the system's meant to be adjustable front to back and not left to right?
PS: Only kiddin' with ya
Might be worth checking that both fronts are connected to one brake cylinder and both rears to the other.
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locosaki
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| posted on 17/6/08 at 10:04 PM |
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Yeah,I checked all the obvious things tonight thats whats got me beat,I even tried bleeding the system again just incase there was some air causing
the imbalance
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joneh
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| posted on 17/6/08 at 10:09 PM |
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Looks like a NASCAR for going round bends....
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locosaki
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| posted on 17/6/08 at 10:20 PM |
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Ha ha,
I've maybe found a use for it now then,I thought I was saving it for bon fire night too !!!
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ReMan
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| posted on 17/6/08 at 10:26 PM |
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OK so say the brake are set about right, have they been bedded in?
then...
What about your tire pressures?
Spring and shock settings?
Stiff suspension bushes?
Corner weights?
Front to rear ride height?
My o/s front locked up until I'd got the whole package about right
[Edited on 17/6/08 by ReMan]
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locosaki
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| posted on 17/6/08 at 10:40 PM |
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Hi ReMan,
They are bedded in but your point on suspension set up could be a good call,Would I be better getting the suspension etc set up before going much
further in your opinion ????
Tire pressures are set at 16psi front/18 psi rear
Shocks are set just below medium/275 lb springs on front/rear unsure
New wishbone bushes/existing shock bushes used
corner weights.... I have no idea if I'm honest,I don't know anyone local that has the equipment !!!!
Front 110mm
Rear 140 mm
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ReMan
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| posted on 17/6/08 at 11:05 PM |
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Looking again I think the difference may just be too great side to side , sorry can't tell you whats causing it though ?
Don't worry about corner weights, but imho your springs are going to be too hard on the front with a ZX10, but it still is'nt the problem,
all your other bits are about right i'd say in a non pro way 
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britishtrident
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| posted on 18/6/08 at 06:28 AM |
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First of all you can't set brake bias up on a roller tester it just won't give sensible results.
Secondly your car will have a weight bias towards the rear so using a 0.625" front and 0.7" rear master cylinder combination
dosen't really make sense.
You want either the same sized cylinder on both circuits or 0.7" front and 0.625" on the rear.
[Edited on 18/6/08 by britishtrident]
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procomp
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| posted on 18/6/08 at 07:11 AM |
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Hi as said above with just a driver in a car you will have a rear bias of weight somewhere around 3-6 % and you will be heavy on the drivers side by
2-3 %. This causes the NSF to be light loaded causing problems that you are encountering.
Once all the obvious symptoms have been looked at. If no particular problems found then it is usually a corner weighting setup that is required to
correct this problem. It is one of the most common problems with brakes locking up on one side only at the front.
A Corner weight setup should cost no more that £30 from a professional setup who have the equipment.
Cheers Matt
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ReMan
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| posted on 18/6/08 at 07:48 AM |
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When I first read the post I read that NSF and NSF were 124 and 130, ie near enough!
I think unless the brake rollers are really duff the readings of 124 vs 155 are still a concern. Likewise the back shows a similar variance.
What about the handbrake, did this indicate the same variance?
The road test then goes to prove this to some extent.
So as per mine and the last post, there will be a benefit getting the car set up, but if the rollers are correct I would still be concerned about the
brakes, can you test them with a known good car?
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locosaki
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| posted on 18/6/08 at 08:15 PM |
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Thanks for the help guys,I'm sure when I bought the master cylinders I was told to put the smaller to the front,I've no knowledge on this
and just took the word of the supplier,I think going by the info I have now I will swap the M/C over and see what like from there.
How would I go about setting the bias bar up if I can't use the rollers ?
[Edited on 18/6/08 by locosaki]
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britishtrident
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| posted on 18/6/08 at 08:36 PM |
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Testing the brakes on a roller tester will only prove that they work or they don't. The SVA brake test is slightly different because they use
the "shoe" to measure pedal pressure.
While the figures don't seem make any sense what is clear is that the car has problems with the front-rear balance of effort in the brake
system, so before looking for other problems the first step must be to sort that out, then move on to corner weights and spring rates.
So looking at what we know -
(1) We know the brake system comes from a car that is slightly nose heavy.
(2) We know a BEC Locost should be tail heavy -- more so than most Seven style cars.
(3) We know with the current set we don't have enough rear brakes and too much front bias.
(4) We know the current master cylinder setup gives more hydraulic pressure to the front brakes than the rears.
Proposed Plan of Action
(1) Check the hand brake cable tension adjustment isn't preventing the rear brakes from working fully.
To do this slacken the handbrake cable tension right back and pump the brake pedal half a dozen times, only then tension the cable so the handbrake
bights roughly halfway up the ratchet.
(2) Swap the master cylinders over (this may give too much rear bias) or to be more sure of being SVA friendly order another 0.625" master
cylinder and fit the same ize on both front and rear circuits.
(3) Adjust the brake bias bar so the pivot bearing is central.
(4) Roadtest --- (driveway test) for locking rears.
After that we start looking for corner weight issues.
[Edited on 18/6/08 by britishtrident]
[Edited on 20/6/08 by britishtrident]
[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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locosaki
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| posted on 18/6/08 at 08:45 PM |
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Thanks for the info,very much appreciated.
I did infact check the hand brake last night to ensure the shoes were not causing any issues,I have just left the tension off the cable at the
minute.
I'm going to order another M/C from Rally Design (0.625)
When I was adjusting the bias bar,Am I right in saying it screws out further on one side than it does the other ???
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britishtrident
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| posted on 18/6/08 at 08:49 PM |
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Setting up the bias by road test is simple but requires caution it has been covered a few times.
Do a couple of dummy runs to get the feel of the pedal before the first test, gradually build up the pedal pressure. Test is best done with the car
running in a slight curve --- be aware if the rears lock completely the back end can come out in the blink of an eye.
The most important point is for road use only test on god dry surface at quite low speed , start with what you think is a little too much
front brakes and only adjust one turn at a time .
When you find the balance point where the rear brakes just start to lock at the same pedal pressure as the fronts back off the adjustment two full
turns towards the front.
You can then retest at a slightly higher speed --- only adjust the balance if you have too much rear brake bias if the fronts are still lock just
before the rears leave the adjustment alone.
[Edited on 18/6/08 by britishtrident]
[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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ReMan
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| posted on 18/6/08 at 11:04 PM |
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Hang on!
What about the side to side imbalance ?
If it does exist it may be serious and it has nothing to do with cylinder size or the bias bar or front/rear weight distribution, still think this
need eliminating or proving out
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britishtrident
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| posted on 19/6/08 at 10:09 AM |
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quote:
Originally posted by ReMan
Hang on!
What about the side to side imbalance ?
If it does exist it may be serious and it has nothing to do with cylinder size or the bias bar or front/rear weight distribution, still think this
need eliminating or proving out
I strongly suspect the roller test results have two readings swapped over by mistake --- the two rear wheels are not locking under test so corner
weights don't have any effect on the brake test readings for the rear axle.
Once the master cylinder problem is sorted I would expect readings of close to 160 from all 4 wheels.
However very light cars can give odd results on roller test, particularly if stiffly sprung.
[Edited on 19/6/08 by britishtrident]
[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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locosaki
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| posted on 23/6/08 at 09:28 PM |
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Well I have got the brake balance from side to side fixed now,Problem lay with the pistons on the nsf,I had 1 working piston the other 3 were not
moving/returning,After a little clean up the pistons do seem to be working and the brake pedal has more feel to it.Just to do the front/back bias now
!!!
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britishtrident
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| posted on 24/6/08 at 06:53 PM |
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If you have 4 pots on the front you might need the 0.7" master cylinder on the front circuit to get a balance ----
Personally if I was starting afresh I would go for standard Sierra front calipers and see if was possible to use MGTF rears.
[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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