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One wheel always locking before the other

Shocks, Springs, Brakes, Frame, Body Work, etc

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BirdMan
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Re: One wheel always locking before the other

Post by BirdMan »

Dual reservoir mstr cyl? Is the front wheels feed line from mstr cyl teed to each wheel equal in length lines and hoses?
Dale C.
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Re: One wheel always locking before the other

Post by David Redszus »

enigma57 wrote: Tue Apr 06, 2021 4:31 am Just a thought...... In this situation, what about adjustable proportioning valves for each wheel? Then experiment and fine tune until you have even braking with the car weighted to suit track conditions.

Good luck,

Harry
Brake force proportioning valves are only used at the rear to balance hydraulic pressure under hard braking.

Front brake line pressures are determined by the driver applied pedal force.
David Redszus
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Re: One wheel always locking before the other

Post by David Redszus »

I'm baffled why the lighter side front runs hotter without ballast though. I cant get my head around that one.
We have encountered a similar problem on occasion. The problem was found to be a dragging brake pad due to the
use of a circular cross section caliper piston O ring. Unlike a square section O ring, the circular ring did not withdraw
the piston when the pedal was unloaded. But the drag was intermittent and not easy to diagnose.

Also, we have sometimes found brake pads that hang up in the caliper and cause drag.
AC sports
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Re: One wheel always locking before the other

Post by AC sports »

BirdMan wrote: Tue Apr 06, 2021 10:50 am Dual reservoir mstr cyl? Is the front wheels feed line from mstr cyl teed to each wheel equal in length lines and hoses?
Dual reservoir on drivers side. Hard line to within a foot of the caliper then flexi line.
Obviously drivers side is a shorter run....longer run to the passenger side that locks up.
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Re: One wheel always locking before the other

Post by AC sports »

David Redszus wrote: Tue Apr 06, 2021 11:29 am
I'm baffled why the lighter side front runs hotter without ballast though. I cant get my head around that one.
We have encountered a similar problem on occasion. The problem was found to be a dragging brake pad due to the
use of a circular cross section caliper piston O ring. Unlike a square section O ring, the circular ring did not withdraw
the piston when the pedal was unloaded. But the drag was intermittent and not easy to diagnose.

Also, we have sometimes found brake pads that hang up in the caliper and cause drag.
Caliper seals are square section and the calipers do visibly retract an equal amount, checked by feelers. No idea if this is consistent though....it could well be hanging up under stress.
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Re: One wheel always locking before the other

Post by enigma57 »

David Redszus wrote: Tue Apr 06, 2021 11:21 am
enigma57 wrote: Tue Apr 06, 2021 4:31 am Just a thought...... In this situation, what about adjustable proportioning valves for each wheel? Then experiment and fine tune until you have even braking with the car weighted to suit track conditions.

Good luck,

Harry
Brake force proportioning valves are only used at the rear to balance hydraulic pressure under hard braking.

Front brake line pressures are determined by the driver applied pedal force.
:D I know, David. Just thinking outside the box here. If rules require the OEM calipers and they are as good as they can be made to work but still result in uneven braking, individual manually adjustable proportioning valves at all 4 corners to fine tune and equalize braking seemed worth trying.

Just a thought,

Harry
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Re: One wheel always locking before the other

Post by David Redszus »

enigma57 wrote: Wed Apr 07, 2021 2:00 am
David Redszus wrote: Tue Apr 06, 2021 11:21 am
enigma57 wrote: Tue Apr 06, 2021 4:31 am Just a thought...... In this situation, what about adjustable proportioning valves for each wheel? Then experiment and fine tune until you have even braking with the car weighted to suit track conditions.

Good luck,

Harry
Brake force proportioning valves are only used at the rear to balance hydraulic pressure under hard braking.

Front brake line pressures are determined by the driver applied pedal force.
:D I know, David. Just thinking outside the box here. If rules require the OEM calipers and they are as good as they can be made to work but still result in uneven braking, individual manually adjustable proportioning valves at all 4 corners to fine tune and equalize braking seemed worth trying.

Just a thought,

Harry
After pressure testing about a dozen prop valves, I found the knee of the curve point and pressure slope to be very inconsistent. Inconsistent meaning that each model had its own characteristics and readings varied even within a single model. Prop valves must be carefully selected. The lever type were the worst of all and should be carefully pressure tested before use.

Once upon a time, a brake pressure accumulator was installed to dampen and smooth line pressure pulses.
I don't know what happened to them.

Our solution for brake optimization for race cars is to retrofit an ABS system, with all relevant data going into
a data logger.
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Re: One wheel always locking before the other

Post by dannobee »

Sounds like it's not a hydraulic problem at this point, since everything's been replaced. If you're running a spacer to even the ride heights, then for sure I'd scale it and see how much cross weight you have. Also, since in the beginning you mentioned that it might be a suspension problem, any difference in anti-dive left to right should be measured. Especially if the car has been in a collision and the unibody or frame was twisted. Might be time to break out the frame/body specs and start measuring stuff.
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Re: One wheel always locking before the other

Post by Geoff2 »

I think it has to be a hyd problem.....or some type of binding within the caliper/disc.

Do not see how weight distribution can be the problem because the brake heat comes from the friction of the pads/disc. That friction comes from the hyd pressure in the system & should be the same side-to-side if it is working correctly.
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Re: One wheel always locking before the other

Post by AC sports »

Geoff2 wrote: Thu Apr 08, 2021 4:27 am I think it has to be a hyd problem.....or some type of binding within the caliper/disc.

Do not see how weight distribution can be the problem because the brake heat comes from the friction of the pads/disc. That friction comes from the hyd pressure in the system & should be the same side-to-side if it is working correctly.
I'm with you here.....but when I loaded up the lighter side brakes worked more consistently and evenly. Temps were within 10*c whereas before, around 40*c after a couple of applications. The car is used mainly for short hillclimb, so brakes dont really get hammered.
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Re: One wheel always locking before the other

Post by AC sports »

I followed the hard line coming from the side that has the tendency to lock up and found this.... looks like some sort of joiner maybe? Could this be the issue I wonder now. That caliper does bleed nicely though,
20210103_121112.jpg
no noticable restriction.
You do not have the required permissions to view the files attached to this post.
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Re: One wheel always locking before the other

Post by chimpvalet »

If it's the hex shaped bit you refer to is it possibly one of those pressure retention gadgets with an internal spring-loaded check valve? The intent of these appears to be keeping pedal travel within range but I view this as suspect and potentially troublesome. The hotter state of the one corner stands out for analysis, indicates brake dragging as others have observed. Have you applied a touch of anti-seize on the sliders?
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Re: One wheel always locking before the other

Post by dannobee »

David, could that be a residual pressure check valve? If so, that could be his problem. Why the heck would someone put one on a disc brake car?
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Re: One wheel always locking before the other

Post by chimpvalet »

Perhaps someone who did not understand what causes long pedal travel? Examples: flex-y caliper brackets, loose wheel bearings.
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Re: One wheel always locking before the other

Post by emsvitil »

I agree with the residual pressure valve theory.

Any possibility that there were drum brakes in the rear and that was for them at some point?
Ed
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