TedH

Agree. sounds like suspension (ball joint, trailing arm bushings).

ajrothm

WOW... never thought of that. I'll take a good look around under it tomorrow. It has 157k miles on it so....anything is possible. Absolutely no rust anywhere though. Its been a Houston car since new.

I'm half way temped to buy that brake pressure measuring tool. That would definitely determine if I have good brake pressures to each corner.... If I had equal pressures, then I would know for sure its not the brakes and some weird chasis problem.

Trailing arms were just rebuilt by Tracdogg back in 2010. Only have about 10k miles on them. That's with Tom's Diffs HD big bearing upgrade and 31 spline axle flange. I SERIOUSLY doubt its anything with the trailing arms causing this hard pull when braking. When acceleration hard, the car goes dead straight.

c69vete

One more thing to have checked. A couple of years ago, I had a similar problem on my 69. It started pulling to the right when I hit the brakes. I thought it was either brakes or suspension wear so I took it back to the local shop that did the front end alignment to have it checked out. They said all of the specs were where they were supposed to be, but said the right front tire was delaminating. It looked OK from the outside, but a new set of front tires and all was good again.

hotrodnick

Kid Vette

I had a problem with mine pulling to the left when I first hit the brakes. I finally discovered the problem when mounting my new Wilwood calipers.

I noticed the right caliper wasn't mounted parallel with the rotor. I thought the mounting bracket was bent and started trying to bend it back in shape. Finally I noticed that the top bracket bolt wasn't pulling the bracket all the way in tight against the knuckle.

Turns out the knuckle wasn't tapped deep enough for the bolt (probably from the factory) and it was bottoming out. Tapped the hole deeper and the problem was solved.

ajrothm

Wow... Both of these are some crazy causes for pulling when braking. Thanks for the ideas. I am due for some new front tires as these are about 9 years old. I am actually buying a new set before my trip in July.

This will be an easy test, swap front tires from side to side and see if the pull changes. I'll do that test after I test the new caliper and rotor swap.

Thanks for the ideas!

Rebelrob

Let it be known that yer car pulls wheel stands at the track.

ajrothm

LOL... Maybe all that heavy iron upfront tweaked the frame or something..LOL

ajrothm

Round 4

Bled the front brakes after the new left caliper and rotor swap (side to side). Also checked out the lower control arm bolts (TIGHT) and frame brackets they bolt to, no cracks, no rust, looks normal.

No visual air bubbles after bleeding, had pretty firm pedal, went for a drive...First couple light stops, it pulls to the LEFT! WTF? (its NEVER pulled to the left). Pulled out of the neighborhood, got up to 40 mph, stopped a few times, back to the same old crap...Pulling right.

So I keep doing some stops...it seems to be getting worse....The lightest input of brakes has it pulling the steering wheel to the right along with the car. Some harder stops REALLY had it swapping lanes and at this point, its locking up the right rear wheel..(never did this before).

Hands off the wheel braking

I could just about dance the steering wheel around by stabbing the brakes.

Round 5

So I come home, decide to try to swap the front tires from side to side...Didn't expect much but it was easy so I did that. Brakes are plenty hot, it did seem that the right side was hotter then the left...Even the lug nuts were hotter on the right.

I go drive the car, same crap, still pulling (as expected). So I keep doing stops, panic stops, short stabs of brake etc etc... Got the brakes REALLY hot, then I could smell brake lining material burning.... Ironically, the stops started getting slightly straighter.


I continue with this nonsense, occasionally getting the right rear to lock up and the front still pulling some but its getting better. I do this for about another 5 miles... By the time I got home, it was stopping about 95% straight, even under hard braking.

Last stop test, it almost felt like the right rear brake starts to grab first, then the left front comes in after and settles it down and stopping straight.

Is it fixed? I SERIOUSLY doubt it. BUT, atleast I know its NOT rotors, its NOT tires, its NOT chasis related.... Definitely something in the brake system...Either air getting back in the system after a while, proportioning valve acting up etc etc... It seems to get better after a bunch of heat goes in them... But those first few stops getting to that point are doozies...

I'm gonna let it cool, drive it to work tonight and test again... Maybe its been a freakish air in the system problem that doesn't work out with pressure bleeding or 2 person bleeding.

BKbroiler

Keep an eye on that thing tonight while its parked at work.
Good luck with those brakes - I can't add anything.

70BBvert

Are you running rubber brake lines? Take a close look for a damaged line that may be swelling under pressure.

Jim

blk79nj

I read this post yesterday, and was thinking...

My daughter had a Pontiac Gran Am that was doing the opposite. When lightly pushing the brakes, it would pull left, and when you pressed harder it would go straight.

It ended up being the rubber brake line on the right front. So basically, the line was kinked or something, and when pressing lightly the fluid couldn't pass through. When pressing heavy it could. So, if it is going straight in light braking, I don't think it's a line problem.

I kind of agree with premiss that a caliper is not lined up correctly, or there is a stuck piston somewhere that causes a caliper to not make even pressure on a rotor. Might be ok when pressing lightly, but gets worse as you press the brakes. My guess is that if it's pulling right, it's the left front caliper.

ajrothm

It has new stainless braided lines, and I'm on the 3rd new left caliper in a month. I would hope I didn't have 3 bad calipers in a row. One of which was on my car since 06', the other 2 are new O Reilys calipers. Not sure about the caliper alignment. I mean it just bolts to the bracket on the spindle, there is no adjustment. I am leaning towards the proportioning valve or hard line with some kind of pluggage.... Now that it seems to be intermitten, or atleast different its gonna be harder to pinpoint.. Its definitely something dynamic, moving...

wcsinx

I don't think it's intermittent. I think you're just getting fade on whichever side is working harder. Thus it starts to balance out when the effectiveness of the good side drops to the level of the bad side.

Based on everything else you've done, I too would suspect you have a blockage in a hard line or the prop valve. The prop. valve indeed is only intended to operate front to back, but that doesn't mean it isn't gunked up somehow. Since it's the front, it wouldn't be too hard to temporarily run new hardlines around the engine bay bubba-style just tee-d directly off the MC port. And if that fixes it, then correctly install new lines. ...just a thought

Gale Banks 80'

I know this has been brought up before in other posts but I will bring it up again. When there are many good Corvette Vendors offering rebuilt parts why are we buying parts from a local auto parts store ? You have gone threw 3 Calipers in the last month, Really? Your talking about squirting oil from a Caliper you must of got last week. I got re sleeved Calipers from VB&P and run Silicone Fluid and I have had no issues in 30 Years. Yes 30 Years. Ask the Parts counter guy what the Micron finish is on the Stainless Sleeve and see what kind of re action You get. Are You aware that there are a couple of different Master Cylinder bore sizes for the C3 ? Which one did the Computer at the local store recommend ? Was it the Camaro one, Impala, Truck ? If You have warped Rotors it causes the Pistons to suck Air into the system. Probably the leading cause of pulling Brakes. Yet we still have not herd what the Rotor run out is ? How many Shims did it take to get them to run true? It sounds as though You are able to get the brakes hot and that some may be hotter than others but by how much ? An inferred Temp Gun will instantly tell You if one Rotor is hot and another not and by how much. Radial Tires are intended to be run in one direction and can not be switched from side to side.

gungatim

some proportioning valve info....(just converted a chevelle to 4 wheel disc and hand to diagnose a problem so had this info at the ready)

"Combination valve: In normal braking, the poppet piston is held in a relaxed position by a large pressure spring. The poppet valve is held against its retainer by a light return spring, and fluid passes freely through the valve to the rear brakes.

In heavy braking, master cylinder pressure can reach a valve’s crack-point. The pressure applied to the 2 different areas of the poppet piston creates unequal forces. That moves the poppet piston against the large pressure spring. This action holds the conical section of the valve against the seat, which limits the pressure increase to the rear brakes.

As greater pedal force increases pressure in the master cylinder, fluid pressure rises on the smaller end of the piston. This combines with the force of the pressure spring to overcome the lower pressure now on the larger end. This forces the piston back, clear of the poppet valve.

The increased pressure now acts on the larger end of the poppet piston and again forces the piston forward to contact the valve.

When the pedal is released, the pressure of the rear brake fluid unseats the poppet valve, letting fluid return to the master cylinder. The pressure spring now returns the poppet piston to its relaxed position.

Should the front brake system fail, the warning lamp spool moves forward, taking the poppet valve with it. Pressure in the rear brakes rises and the piston moves forward but it can’t seal on the valve.

Should the rear brake system fail, the warning lamp spool will move backwards to activate the warning light. The proportioning valve doesn’t operate in this situation."

also have this: (wow, did I read that right? 1/16" id of the flexble hose? seems awfully small. any little piece of rust could clog)

ajrothm

Thanks for the post! I'll study up on that proportioning valve tonight. Good info!!

zwede

gungatim: Your text on combination valves does not apply as no C3 had a combination valve. Those are for disc/drum cars.

Your scanned text from SSBC is correct (we have a distribution block).

ajrothm

Ok... The deal with the part store calipers... (and the prequel to this thread)

Back in 10', I installed some stainless/O-ring calipers all around from Lonestar caliper. A couple months ago on a Friday night before a car show, I see a left rear caliper leaking pretty good. I had a car show to attend that Saturday and no time to order/ship a new caliper from Lonestar Caliper. In a pinch, I called around locally and O Reilys had a caliper in stock, 5 mins from my house.. I decided to give it a try and it worked great.

Two months later, this brake pulling to the right crap started... I figured it was just another of my high dollar Lonestar calipers crapping out... So back to O Reilys I go and get two new front calipers and new Wagner ceramic pads. A month goes by and I thought the pulling problem was solved until last weekend when I was racing and got on the brakes and the car yanked hard to the right. That's at the start of this very thread. When swapping rotors from side to side to test, I was monkeying around trying to compress the pistons in the driver front caliper and it started leaking, so I went and swapped it out...Maybe I caused the failure trying to compress the pistons...Not sure. But other then the pulling problem, I have had no issues with O Reily calipers...

If I DO determine my pulling problem to be calipers, I will put Wilwood D8s on it... however, I do not think this is a caliper problem.



Oh and its still pulling to the right, not near as bad as it was, but slightly...and I don't trust it. Next week, I'll pull the proportioning valve off and clean it out, at the same time I'll install a new MC just because, bleed the whole system again and see where it ends up.

I've got to get this thing stopping correctly, consistently before I head out on a 3k mile trip to the Tail of the Dragon.

The battle rages on...

BLUE1972

I would double check the brake lines for a crushed line or a restricted / swelling rubber flex / SS hose as a start.

If it's pulling right then then usually the left brake is weak. assuming a brake issue. This could be a partially blocked line .. something like a rust issue internally, a crush on the brake line or a partial blockage in the line.

This may sound far out, check the threads on the tie rods and the idler arm mount for play. Years ago I found a tie rod end with stripped threads. It drove everyone nuts trying to find the issue. We kept one front wheel on the ground and shoved the other - the rod end moved.. I should have noticed the uneven tire ware but....

Hope you find the issue....