Sierra
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| posted on 30/5/13 at 08:42 PM |
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Brake setup
I've finally finished fitting my obp pedal box, fitted the bias bar and bled the brakes. I took it for a quick drive yesterday and the brakes
didn't seem to work very well. Today I went back with a fresh head and adjusted the threads on the cylinders so they both only go in the clevis
by about 15mm. Took it for another drive and this time the brakes worked very well and for the first time since owning it the wheels locked up (only
front left though)
What's the best setup and which wheels should lock up first, front or rear?
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Ben_Copeland
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| posted on 30/5/13 at 08:43 PM |
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Locking the rears up is bad, the fronts must lock first.
Ben
Locost Map on Google Maps
Z20LET Astra Turbo, into a Haynes
Roadster
Enter Your Details Here
http://www.facebook.com/EquinoxProducts for all your bodywork needs!
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Wheels244
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| posted on 30/5/13 at 08:44 PM |
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Front
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Sierra
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| posted on 30/5/13 at 09:06 PM |
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Thanks so does that mean when looking at the push rods the rear one will be longer as more of the front ones screwed in the clevis. Also what's
the reason for the right front locking but not front left
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Ben_Copeland
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| posted on 30/5/13 at 09:19 PM |
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http://www.obpltd.com/wordpress/?p=191
Worth a read..
Ben
Locost Map on Google Maps
Z20LET Astra Turbo, into a Haynes
Roadster
Enter Your Details Here
http://www.facebook.com/EquinoxProducts for all your bodywork needs!
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Sierra
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| posted on 30/5/13 at 09:32 PM |
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Many thanks that's helped and answered the question that front push rod should be 5mm longer than rear but what about the full length of push
rod, or is that just to determine how far forward or back you won't the pedal itself?
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britishtrident
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| posted on 30/5/13 at 09:43 PM |
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quote:
Originally posted by Sierra
Many thanks that's helped and answered the question that front push rod should be 5mm longer than rear but what about the full length of push
rod, or is that just to determine how far forward or back you won't the pedal itself?
Here be dragons !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Very very important the master cylinder pistons are allowed by the pushrods to come back fully against the stop washers at the end of the cylinder,
if they don't the brakes will bind when the brake temperature increases. After a mile or so they will so solidly the car will come to a halt.
If you have more travel in one circuit than the other deal with it properly.
The reason why one front wheel is locking before the other is down to corner weights.
[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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Sierra
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| posted on 30/5/13 at 09:56 PM |
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Sorry I'm new to this and just got a bit confused. By coming back do you mean when the pedal returns back when released because surely it will
always fully return as the thread is on the clevis end or do you mean when pedal is pushed that the push rod goes all the way into the cylinder.
The first time I fully threaded both push rods resulting in a very soft pedal that hit the bulkhead and didn't brake where as now only threaded
abit into clevis pedal is stiffer and brakes
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Daddylonglegs
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| posted on 30/5/13 at 10:41 PM |
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quote:
Originally posted by britishtrident
Here be dragons !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Very very important the master cylinder pistons are allowed by the pushrods to come back fully against the stop washers at the end of the cylinder,
if they don't the brakes will bind when the brake temperature increases. After a mile or so they will so solidly the car will come to a
halt.
I have a straight forward single pedal/MC system, but believe him when he says they will lock up!! Don't ask me how I know 
It looks like the Midget is winning at the moment......
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Sierra
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| posted on 30/5/13 at 11:16 PM |
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I don't have a stop on my brake pedal so surely it'll just come forward and stop when push rods are fully out. I've got the obp
cylinders with the rubber boot over the pushrods
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britishtrident
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| posted on 31/5/13 at 07:20 AM |
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The master cylinders have a recuperating port (on some types a recuperating valve) that links the fluid in the cylinder bore to the reservoir
allowing top up fluid into the master cylinder bore and excess fluid to vent back to the reservoir. The recuperating port is only open when the
master cylinder piston is fully back in its' rest position hard against the stop washer. If the piston is even 1mm from stop it can close the
port.
When the brakes are used the fluid temperature in the calliper increases and the fluid expands. Unless the piston in the master cylinder can come
fully back to its rest position hard against the stop washer the fluid cannot return from the cylinder bore back to the reservoir. As a result if
the expansion of the fluid isn't vented back to the reservoir the pressure in the system increases and the brakes start to drag causing more
expansion and more drag from the brakes.
A lot of Locosters builders have had this problem and had their car grind to a halt with the brakes locked solid the first time the brakes were
used in anger, one builder was so convinced it wasn't the brakes but thought it was the rear axle seizing and changed the complete axle not
once but twice.
Jacking out the push rods on one or both master cylinders should only be done with great care to check the master cylinder pistons return fully
home, the pedal should also have a return spring.
If one circuit has excess pedal it should be tracked down, usually on cars with Sierra rear discs it is either air trapped in the rear calliper or
the self-adjuster for the handbrake not operating.
Brake bias bars only work best if the balance point adjustment puts the balance bearing close to the centre position, if when adjusted the
balance point is skewed to one side then ideally this should be fixed by changing the bore of one of the master cylinders.
[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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Sierra
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| posted on 31/5/13 at 10:14 AM |
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Thanks for explaining everything. I think I'm going to double check the the pushrods do fully return before anything. Might also look into
fitting a spring to clutch and brake pedal but for now they return fine
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