HELP: FRONT BRAKES

[chip]

Brakes were pulling hard to the left, locking the left front wheel. We flushed the whole system, replaced on suspect tie rod end, bled the brakes, replaced both complete front calipers and discs, put new brake master cylinder in, switched front brake lines (to rule out one line being clogged) and during the road test STILL locked up the left front wheel just as it did before!

All this money and work and NO improvement. ANY suggestions would be appreciated. cb [img]images/icons/frown.gif[/img]

[Ron Earp]

Chip,

hold up! Did you do all of these things at the same time, or in some particular order? If in order, then that might help some of us help. There has to be some method to your troubleshooting and I think that will help all of us try and help you.

Ron

[David Morton]

Chip,
One thought may be to check the wheel geometry on both sides. Toe in and camber combined with tracking may exarcerbate braking problems. Additionally check the tyres are from the same batch or supplier.
A harder tyre obviously will lock up sooner
- ammonia will soften up a tyre. Provided
you have the same hysteresis characteristics
on each tyre, and given all the things you have done so far and the geometry is correct,
you may have a damper/spring poundage problem. I think we'd all love to know the fix?
Dave M
[img]images/icons/confused.gif[/img]

[Frank Catt]

Chip, have you checked the corner weights of your car? If one wheel is being carried by the other three on a very stiff chassis setup because of incorrect suspension settings then the lightly loaded wheel will tend to lock up first. This is critical on pure race cars and just might be your problem, Frank

[Bill Bayard]

Chip,

Did you check the inline metering block,

between the master cylinder and brake lines?

Bill

[ April 13, 2003: Message edited by: Bill Bayard ]

[Trevor Jones]

Even differences in front tyre pressures can cause brakes to pull in one direction or the other, and corner weight was mentioned in a previous post.

[Mark Clapp]

Not knowing what master cylinder you're using, I'd suggest rechecking the plumbing. My car's cylinder was misplumbed when I got it and had the fronts and rears mixed together. Took a while to sort it out.

[chip]

Ron: Yes, we did all these changes at once: figured we do all these things while we had the front end apart.

Appreciate all the ideas. Will check all them and post results.

ANY suggestions/ideas welcomed! cb

[Howard Jones]

For not too much money you can get a inline brake pressure gauge and see what is really going on. Test on level ground. You don't need to move the car just apply the brakes and record the gauge reading at each caliper. Make the reading at the calpier port so as to include the flexline in each reading. The front two should have almost the same pressure applied to both calipers as should the rear two within a few % of each other. Front to rear pressure readings should not be the same depending on the proportioning valve setting. You will only need one gauge but you will need to do them one at a time. Use the same brake peddle presure for each test. Something like broom handle cut to lenght and wedged against the brake peddle the same way each time. This process will take awhile but will yield some useful data. Just a thought if you have a brake bias bar or something else like a adjustable proportioning valve check that you don't have the lines mixed up. Also how hard are you braking when you have this lock up thing. Low speed easy braking lockup is more than likely a brake system problem. If it works at low speed/low brake effort but fails at high speed/ high brake effort I think it could be related to suspension setup. Good luck.

[ April 16, 2003: Message edited by: Howard Jones ]

[chip]

Howard: Great diagnostic tool! This has been drivig 3 of us crazy! Where can we get such a gauge? NAPA? Auto Zone? We will try this. chip

[Howard Jones]

Any pressure gauge made for fluid and up to about 2000lbs will work. you will have to mate it to a "T" fitting with one end going to the caliper and the other with the brake line attached, gauge in the middle. Since most of these cars have An3 or An4 braided lines along with the fitting to the calipers you can start by looking at a Earl's catalog, 310-606-1602, to get a catalog. This is a very good scorce for AN fittings infomation. Lots of aplication stuff, how to etc. You can get a dual brake pressure test gauge setup Part number 44140 $69.00 from Longacre racing www.longacreracing.com or you can make your own from parts you get locally. Big heavy equip. repair/supply places have a lot of this stuff also. Cat. dealer?
good luck
What kind of brakes, car, do you have?

[ April 18, 2003: Message edited by: Howard Jones ]

[Trevor Jones]

Another way to check the front brake balance without taking the brake lines apart is to use a torque wrench on a tightened lug nut (without the wheel on). Make sure the torque wrench is always pointing radially towards hub center then apply pressure to the brake pedal until it takes about 60ft-lbs to rotate the disc. (any more and you may stretch or break the stud). With the same pedal pressure or ideally with a 2nd friend and another wrench, simultaneously check the other front disc for torque needed to rotate this disc. (You'll have to rotate this one in the opposite direction). Although this method will not give you the balance at very high braking pressures, it does give you an indication if something is starting to go wrong at lower pedal pressures (sticking piston or whatever.)and you can do both sides simultaneously with a couple of friends.

If you do try this make sure the guys on the wrenches have stopped pulling on the wrenches before you let up on the pedal, or you will be treated to the sight of two friends spinning across the workshop floor.

[Robert Logan]

chip,

MoTeC have a pressure transducer which can be plugged into their dash and with one connected to all callipers than the differential pressure could be monitored and faults assessed.

This sort of information gathering is available to most race teams and the technology can also be accessed by us mere mortals. Remember that unless you ask you will never get !!!!

Best wishes,

Robert

[chip]

We replaced the fron brake lines with stailess lines and have had a great improvement. Still pulls a little to left, even when wheel is centered. Next: front end shop for an alinment. we did so much, nort sure what did it but much improved. Thanks foe all the help. Will reort back results. cb