One wheel brake lockup? - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 16 Old 10-17-2005, 12:23 PM Thread Starter
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One wheel brake lockup?

I've got an '85 mustang coupe (track-only) with a Bullitt brake conversion on it-- running PFZ pads and Goodyear Gatorback tires.

Since I've started tracking it (6 weekends/~1000 miles), it's had a slight problem with locking up the passenger side front wheel. This past weekend, at VIR-Full, this problem seemed to get significantly worse. I couldn't seem to use the brakes to their full potential, especially going into turn 1. I had to start braking at the 5 marker, and do what I considered really slow braking to avoid it to lockup and even then it would still potentially lock-up. Eventually, I ended up locking it up hard and flatspotting a tire really bad.

I'm trying to figure out why the passenger side front appears to be the only one locking up or the one that locks up first. A person in the paddock suggested that the I rebuild the calipers, because there could be grud in the piston that doesn't allow proper actuation. I do plan on doing this winter, but is there anything else that could be causing this? I don't want to end up killing another tire because of it-- especially when I'm thinking of getting proper track tires soon.

Thanks,
Anthony

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post #2 of 16 Old 10-17-2005, 01:11 PM
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Air in the other line, flex in the other hose, sticky caliper(s). Or trying to brake hard and turn left at the same time.

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post #3 of 16 Old 10-17-2005, 02:03 PM
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post #4 of 16 Old 10-17-2005, 03:42 PM Thread Starter
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Originally Posted by MFE
Air in the other line, flex in the other hose, sticky caliper(s).
I bleed before every event and the brake pedal is already solid, so I don't think there's air in there. Both front lines are new stainless steel braided, I hope there's no flexing in there. The sticky caliper would be fixed via the rebuild, right? Or is there another place, that would cause it to stick?

However, one thing I was trying to remember was how the brakes lines are routed from the stock proportioning valve. I'll have to trace the lines, but if I screwed up the routing and have one of the fronts and the rear line coming from the same port, would that cause this kind of problem?

[OUOTE]Or trying to brake hard and turn left at the same time.[/QUOTE]
Turn one at VIR is a right-hander. And I typically try to brake in a straight line.
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post #5 of 16 Old 10-18-2005, 11:00 AM
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Fat bastard in left seat creating more load on the left tire?

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post #6 of 16 Old 10-18-2005, 11:01 AM
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post #7 of 16 Old 10-18-2005, 01:45 PM Thread Starter
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Originally Posted by ScarSnake
Fat bastard in left seat creating more load on the left tire?
You calling me fat!? Truth be known, I am a big guy-- both in height and weight, so it is a possibility. But it still happens even with an instructor in the car. (Not to mention the fact, that when I installed my Kirkey seat, I have it set way back so I'm pretty sure my weight is more rearward than forward.)

When inspecting the car yesterday, I noticed the pass. brake's top dust boot is pretty much 3/4 gone (It's had a smaller melt in it since the first time out.) So, I'll definitely be rebuilding the calipers. Also, I traced the lines-- they're routed correctly, so that possiblity is out. Since, I'm done with events for the year, I'll have a while to figure it out.
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post #8 of 16 Old 10-18-2005, 04:15 PM
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I remember a discussion about this on a mailing list a couple of years ago. Someone was having the same problem and it turned out a lot of people were experiencing the same thing. After putting pressure gauges on the lines he noticed that the passenger's side front caliper was receiving more pressure than the driver's side. If you look at how the brakes are plumbed, the passenger's side front and rear go through the distribution block. The driver's side front doesnt. From my understanding the engineers designed some inequality in the front brakes as a safety measure. This is so that one front wheel will lock up before the other. This way there is still one wheel that has some control. I dont know if this is entirely true, but it does seem to make some sense. Also like said above, generally the passenger's side has less weight.

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post #9 of 16 Old 10-19-2005, 09:53 AM
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After putting pressure gauges on the lines he noticed that the passenger's side front caliper was receiving more pressure than the driver's side.
If this is true, how can it be cured. I am tired of flatspotting (driver needs some tunig as well) my pass. front tires. Last auto-x, after one good lock up, I was leaving marks at nearly every braking zone on the course. Gave me good reference points though.

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post #10 of 16 Old 10-19-2005, 12:23 PM Thread Starter
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Quote:
Originally Posted by Oktavius
If you look at how the brakes are plumbed, the passenger's side front and rear go through the distribution block. The driver's side front doesnt.
It's not this way on my car. Both fronts come from the distribution block. Driver's Front comes from the rear of the block, while the passenger front comes from the bottom, rear of the block. (Similar to some pictures I've seen of the M2300K kit.) Maybe they changed something in later years.

In that configuration, I don't see how the pressures could be different. Unless they used different diameter lines between passenger/drivers side. Perhaps I'll just replumb the system over this winter-- I've been wanting to move the adjustable proportioning valve to the inside anyway.

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post #11 of 16 Old 10-19-2005, 12:38 PM
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It happens, and is a problem with brake line routing.

Stock, They try to have right-front along with rears on one line (sort'a).

Basically, you have to T-off the front lines, and separate from the rears. Split the M/C into a "true" font/rear setup.

Been there, done that, and now fixed it!!!

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post #12 of 16 Old 10-19-2005, 01:02 PM Thread Starter
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So let me see if I understand the way you fixed it. Take one port from the M/C to a T-fitting. Then connect both front-lines to the T-fitting. Then take the other port of the M/C to the adjustable proportioning valve and off to the 'T' fitting on the rearend. Therefore, the stock distribution block goes away completely? Does it matter which port of the M/C gets connected to the front or the rear?

Thanks.
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post #13 of 16 Old 10-19-2005, 01:36 PM
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Basically, yes.

Dont have the schematics here, but that is about right. I believe the M/C port closer to the firewall is the front brakes.

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post #14 of 16 Old 10-20-2005, 05:02 PM
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3/2 port conversion.

All bleeding stops eventually.
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post #15 of 16 Old 10-21-2005, 04:23 PM
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You might throw the car on a set of scales and check the corner weights, especially the comparison of the cross weights. If the cross weights are off, you will tend to lock one front side (the lighter number). Also, if you flat spot a tire, it will continue to find the flat spot again and again, making efficient braking virtually impossible. If you've been locking up the same tire over several events, it's not going to get any better...

With a stock style suspension (non-coil over), adjusting the cross weights is a challenge. You'd likely need to shim the springs or something, or physically move weight around.

I don't believe there is any "imbalance" left-to-right designed into the brakes. If the brake line routing is in its stock configuration, I'd not mess with it. Making sure brake lines and calipers are all in good shape wouldn't hurt. Inspect the slider pins are moving freely and the piston is retracting properly.

Good luck-

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post #16 of 16 Old 10-21-2005, 05:43 PM
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I have coil-overs up front. Do I adjust until what weights balance? Lower the heavy corner, right?

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