Help fixing a front brake bias problem
 

OK since I purchased the car I have had a problem with the front right locking up under heavy braking. This is not to say that the car is stopping fast, before the tires locks up, it stops about as fast as my 3800lb truck. Under normal driving no problems and it doesn't wander or pull to a side under braking. The same type of tires are on both sides (I think, I'll have to check the tread wear/load rating, but they are both nitto.)
Things I have done to try to fix it:
alignment,
bleed brakes (by myself),
vacuum sucked to bleed brakes (it worked like the title "sucked", air kept getting in around the bleed valve),
swapped to SS brake lines
changed from DOT5 to DOT4,
bleed brakes (with wife helping),
bleed brakes (with car knowledgable friend helping),
verified tire pressure matching side to side,
dropped tire pressure in right front for testing,
changed brake pads (and made sure the pistons were freely moving),
tested with a guy weighing 300+ pounds sitting shotgun (trying to see if is was my weight causing the problem)


I bleed the brakes by starting with the back right wheel, then left rear, front right, front left. I do about 5 pumps then refill keeping the level high.

I can't figure out what else to do...

Thanks up front,
Rob

Just a thought, is the LEFT side to weak and the RIGHT side is fine?

It could be. I have checked each side equally as far as piston movement, SS lines, bleeding. I don't know what else I can check.

This is very tough to get a handle on all right. I just didn't think it was a good idea to focus 100% on the right, when the left might be the problem.

...I'm still thinking of possible diagnostic steps...

How about swapping pads right to left? Hmmm, changed brake pads all ready, hmmmm

Sound like you covered a possible defect in the brake lines all ready.

I'd check each caliper on the dirt car as a routine maintenance procedure with on of these:

http://www.autoanything.com/brakes/61A3154A0A0.aspx

http://www.irvansmith.com/scart/quic...term=LON-44144

Might also be a weak spring.

Wow, that looks like a great tool Scott. Heck I think I'll buy the gauge itself just to check for the heck of it.

So, say you find out the left or right front is getting more or less pressure? Then what? Not as easy as setting bias front to rear.

Scott, so I guess I need to buy two gauges so I can actively compare with a buddy? Then what, swap out the master?

Rick, What spring are you talking about? the main suspension spring is new (1500 miles) and I had the same problem when the stock springs were installed. I didn't mension it in the troubleshooting cus I didn't think of it and I didn't upgrade springs because of the brakes.

Not sure if he means coil-over-shock springs or not, but if it's only under hard braking and the calipers and pads and brake system in general, are known to be good, a spring adj might be the answer. Mind you, I've never seen it...although that's with stock car suspension set-ups, not the typical unequal Cobra front suspension.

The 300lb guy probably will not make a difference as the driver's side is weak compared to the passenger side which is strong. Plus most of the weight transfers to the front during braking, so the 300 lbs is almost negligable.

All in all, with anything like that, it has always been my experience that it is a brake component problem. In your case, more likely the driver's side is weak vs the passenger side being overly strong.

Second, is bleeding. You definately need help (and the wife is perfect for this, as well as helping install an intake manifold, cleaning parts, removing old gaskets, etc, etc.). At wheel....open bleeder a bit. In driver's seat...push down on brake and HOLD it.....At wheel, close bleeder screw......tell driver to let up brake. Repeat a lot, especially when doing rear brakes first. It is imperative that the wheel man with the wrench YELL a lot to make sure driver operates brakes in the appropriate manner. Subsequent to this, flowers, chocolates and dinner at a restaurant helps.

Now you got me thinking... The ride height is even, but I have never weight balanced to see if the left and right have the same static weight load. So say the weight balance is off, I would have to go up on the driver side or down on the passanger side, right? I don't have scales, what do most guys use? maybe I should just give the coil over a twist or two on the height and see if it changes the brakes.

Getting access to a set of scales is tricky all right. AND they need to be perfectly level to get the best reading.

Needless to say some bathroom scales won't cut it. :)

If you have just a few miles on the new pads, take them out and examine the contact pattern. It is possible you have a caliper bracket that is not parallel to the brake rotor. this would reduce the contact area and clamping effectiveness.

Did you sand and clean the rotors when you changed the pads? If not it might be a good idea. One rotor could have some glazing or pad transfer.

Keep us posted.

I will check the pads but I thik they will have too many miles to show any signs. I didn't sand the rotors prior to the pad swap but they only had ~300 miles on them and had not been broken as they still showed orginial machining marks. There is no shimmy in the wheel so I think the rotors are running true.

I'd set the balance bar full front and compare left to right. Then do the same for the rear. Never used it to actually adjust F-R bias. The brake lines were always getting smashed by rocks... hard to tell by looking at them if they were good, so I'd check pressure one corner at a time while someone applied the brake.

Air anywhere in the front system will affect both calipers.

Good advise to check the pads. Wouldn't hurt to lap them on sandpaper too while they're out.

Rob,
You have covered alot of possibles with out success so have you checked the rubber brake lines to each wheel for possible deteriation /dry rot where as the line could be colapsing and not leaking fluid. just another suggestion pleas lets us know final cure

BONOS

I have replaced the brake lines to SS lines and there was no change

I had the same issues on my car after a big brake install, and went through the same shakedowns also. When I grabbed a light and compared both calipers carefully, I had installed and centered one caliper with one less shim on the bottom than the top. This was all it took to pull to the right(right caliper cocked). It still pulled a little after the fix until I rebedded the brakes.

Hope this helps.

R

I only briefly breezed thru these postings---as Scottj said get pressure guage--

If the pressure is equal---you need to check to see if the calipers are exactly the same area pistons

another biggie I saw in your post was the switch from dot 5 to dot 4 fluid--with that you have ruined all the seals and o rings in your system---

Please explain? I know the two aren't compatible so I flushed the system (pushed a lot of DOT 4 through and then did it again a few days later). I've never seen documentation where if you have used one you can never switch to another.

On a similar note it did the same thing with the DOT 5 ;)

Check the sizes of the rotors, calipers and the pressure---If---the rotors are the same(size, thickness, material) the calipers are the same( size, not type or brand) and the pressure is equal----the brakes should stop the same-----

bounce the corners of the car to see if the left front is stiffer than the right, and also if the right rear is stiffer than the left ---

The dot 4 fluid will not flush out dot 5 even if you pumped 50 gallons thru it----