I have a 72' big block that is starting to do something really strange, and it seems to be getting worse.

When you apply the brakes, it will pull hard left, then goes right, and then weakens a little bit and tries to go left again. It will finally settle a little once it does this, and you roll to a stop.

Where would you start with looking into this? I bleed the brakes before the last drive, but it didn't seem to help much.

Thanks,
Rob


[Modified by RLH, 9:17 AM 10/17/2002]

 

If you havent replaced the brake lines to the calipers I would start by doing that. However, sounds like a proportining(sorry about the spelling) valve. I would still check out the rest of the brake system first.

 

First place to look is the flexible lines to the calipers. It sounds like you have one that has deteriorated and is collapsing on you. The lines collapse on the inside, it is not seen visually. What happens is under pressure the fluid goes through the line, but when you release the brakes, it does not come back through soon enough. Because it doesn't, when you apply the brakes again, it will grab much sooner than the other side because it already has pressure on the caliper. If this is the case, you should replace ASAP because the caliper will end up grabbing the rotor and holding on even when you release the brakes, thus heating up the caliper, the rotor, and the pads. This is a common problem with the flex lines. Replace these and you should be all set. Hope this helps. :seeya

 

Chuck and Torcher, thanks, I'll check those first and probably replace them. :cheers:

Thanks for the help,
Rob

 

The above tips are good but from your description you step on the brakes and the car goes left, then right and then tries to go left again? - I would look at the steering system not the brakes.

Usually brakes pull in one direction due to differentiall braking force on the various corners of the car, but I have never experienced brake pressure varying at each corner of the car under constant pedal pressure.

If you have some sloppy connections in the steering then not oly braking forces but irregularities in the road surface and the tires even could cause some wandering on braking.

At least thats my guess :cheers: good luck, let us know what you find.

 

And for the near-worst case scenario:

I had the same problem a real long time ago on my '72. It started gradually as a slight pull to the right under braking. It was getting worse the more I drove the car over a couple of weeks. It would move to the right, back into line, back to the right. I checked everything in the steering and brakes even to the point of replacing the pads thinking that I must have some grease or fluid contamination. I also replaced the front wheel bearings in hopes of finding a solution to my ever worsening problem. I took it to the alignment shop. No difference.

Very shortly after I had exhausted myself throwing money at the problem in hopes that it would go away, I detected what felt like a tire rubbing on the fender. I looked and sure enough, there was a little paint worn off the front of the passenger-side fender lip. Humm, odd to day the least. I figured the caster must be way out of whack to do that and that could account for the bizzar handling under braking. So, back to the alignment shop for another look. Everything was within spec and out the door I went, no closer to having a solution.

I was determined to find out what was going on since everything in the steering and brakes was fine and I had ruled out the usual suspects. So I went through the frontend top to bottom and BINGO! The lower control arm bracket had broken its weld. The more the suspension moved under braking force, the more it bent the bracket, the worse the handling under braking got. I re-bent the bracket into position and re-welded it back to the frame. I also put a couple spot welds in the lower rail for security. End of story. Problem solved. That was about 15 years ago.

 

The prop valves will only modulate front to rear, its does nothing to control side to side.

 

Usually those "left / right darting under braking" problems are associated with the old drum brakes when wet.......which happened frequently with my old Camaros ('67-'68)....

Proportioning valve, severely 'scarred' or warped rotors, pads down to the metal, or very, very dirty brake fluid all contribute to these problems.... :smash:

Pull the wheels & check your rotors & pads first ......then pop the cover on the master cyl. to check the fluid (should be 'clear' golden in color) ....then get back with us to see what's "wrong" before spending mucho $$$ replacing this & that. ;)

 

Lots of good ideas here, but I also think it sounds more like a steering/alignment issue than a brake line problem. However, replace the flex lines first, as they are easy. Then check for worn or loose ball joints, tie-rod ends, idler arm, or rag joint. Finally check the alignment specs, especially front AND rear toe settings. GL.