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Re: Right front wheel locking up on braking
Posted by: Jonathan Knapp ()
Date: December 29, 2019 03:59PM

Right front brake drum is out of round. You said they looked fine, but you can't see out of round. I had this problem on my autocross car (back when when I first put it together and it still had drum brakes).

Jonathan Knapp
Now in Martins Ferry, OH
'66 Corsa Autocrosser

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Re: Right front wheel locking up on braking
Posted by: TerribleTed ()
Date: December 29, 2019 05:25PM

The adjusters might not be the exact correct part. Some perfectly functional adjusters are longer than others. I was under the impression you changed all 4 wheel cylinders and there was a leak right after. I misreadsmiling smiley

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Avid Corvair hobbiest since 1984.
I have personally performed ground up restoration on over 20 Corvairs.
I currently work full time at restoring and repairing Corvairs.
Located in the Atlanta Georgia area.
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Re: Right front wheel locking up on braking
Posted by: FL103Dave ()
Date: December 29, 2019 05:32PM

Also look at the wheel bearing seals for grease leaking. I have seen this cause brake lock in the past

Dave

Naples, Florida
1968 Monza Coupe 140 4 Speed, Quick Steer, HD Suspension, Tele Wheel - My Dad bought new in Jan 1968 - 265,000 miles
1974 Corvette - 350 Auto.
2016 Cadillac ATS-V
2003 Harley-Davidson Road King

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Re: Right front wheel locking up on braking
Posted by: rowin4 ()
Date: December 29, 2019 08:25PM

My 63 right front wheel locks up. It's the front left hose. Just because it looks new or is new doesn't always make it work properly. Also as stated above the master cylinder that has to big of a bore will cause a hard peddle.

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Re: Right front wheel locking up on braking
Posted by: JimBrandberg ()
Date: December 30, 2019 06:13AM

You can usually tell if the hoses are flowing freely when bleeding the brakes.

Rock hard pedal and good fluid flow when bleeding along with no movement of the brakes is often a stuck wheel cylinder.

Just trying to return to the basics.

Also in reply to above comments, I am under the impression that all other things being equal, a larger MC bore would cause a softer pedal and a smaller MC bore would cause a firmer pedal.

Jim Brandberg
Isanti, MN
CorvairRepair.com



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Re: Right front wheel locking up on braking
Posted by: RexJohnson ()
Date: December 30, 2019 10:19AM

A larger MC bore makes it harder to push and a smaller bore is easier to push. With everything equal in the bigger bore you are trying to push more fluid thru the same size hole with the same leverage of the pedal.

RJ tools
Salem,Oregon

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Re: Right front wheel locking up on braking
Posted by: Gold ()
Date: December 30, 2019 11:04AM

I received my latest Corvair in March. It had received a complete brake job, hoses, shoes , wheel cylinders From clarks. It only had 200 miles on them. It would pull to the left. I determined that the original drums were no good. Although they had been turned they were out of round.Replaced drums with new shoes. Its all good now!

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Re: Right front wheel locking up on braking
Posted by: JimBrandberg ()
Date: December 30, 2019 07:35PM

I believe the rule of thumb is all other things being equal, a smaller MC bore will feel firmer at the pedal.
You can't push more fluid through the same size hole no matter what the cylinder size before the hole is. A smaller cylinder will feel firmer because there is less fluid being compressed before the hole. Also you can only push as much fluid through the hole as what is being accepted on the other side.
Maybe we just have different language. I'm saying softer and firmer, you're saying easier to push and harder to push.

A MC bore that is too small may not have enough volume to do the job, especially in a dual MC when one half fails and the pedal stroke goes very long.

I suppose this is not germain to the brake locking up problem at hand but I can't help myself.

Jim Brandberg
Isanti, MN
CorvairRepair.com



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Re: Right front wheel locking up on braking
Posted by: MattNall ()
Date: December 30, 2019 08:13PM

Sarge also complains of WEAK brakes.... no stopping power...

This happens when the MC Boree is too large..

Remember the Sintered Metallic shoes ? Came with a SMALLER 7/8" MC


With Auto adjusters I've never had a problem with an otherwise stock LM.

MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Right front wheel locking up on braking
Posted by: Jonathan Knapp ()
Date: January 01, 2020 08:40PM

You guys are passing by the fundamentals of hydraulics with your language. If you apply (for ease of example) 100 lbs. of force to a brake master cylinder piston whose total surface area is 1 sq. in. (BTW, a 1" bore does not have a surface area of 1 sq. in.) then the pressure in the system is 100 lbs. per square inch.

If you apply 100 lbs. of force to a brake master cylinder piston whose total surface area is 1/2 sq. in., then the pressure in the system is 200 lbs. per square inch.

Therefore, all other components being unchanged, the smaller master cylinder generates more braking force at the brake for an equal amount of force applied at the pedal.

Interestingly, it works the opposite way at the wheel cylinder. 100 psi in the system will generate 100 lbs of force pushing out on the brake shoe if the wheel cylinder piston is 1 sq. in. If the wheel cylinder's piston is 1/2 sq. in. the resulting force pushing out on the brake shoe will be 100/2 or 50 lbs.

Hydraulics are force multipliers or force dividers, depending on the size of the cylinders. Smaller master cylinders and larger wheel cylinders give greater braking force for an equal amount of force input. Larger master cylinders and smaller wheel cylinders give lesser braking force for an equal amount of force input.

Because stock Corvair brakes overbrake in the back, this is why performance enthusiasts bore out the stock 7/8" front wheel cylinders to 15/16" and rebuild them with rear wheel cylinder pistons, seals, and boots. It generates more braking force at the front to balance out the overbraking at the rear.

Jonathan Knapp
Now in Martins Ferry, OH
'66 Corsa Autocrosser

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Re: Right front wheel locking up on braking
Posted by: rowin4 ()
Date: January 01, 2020 08:54PM

Well that explains the whole thing in plain english. Thank you sir.

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Re: Right front wheel locking up on braking
Posted by: aircooledairhead ()
Date: January 14, 2020 08:01AM

Heading up to my son's to work on the problem.
Thanks to all of the good suggestions, here's my plan.

First, I'll check the wheel bearing seals, check wheel cylinders for excess fluid inside rubber cups and ascertain that the brake master cylinder is 1 inch diameter. I believe all will be OK. Prior to replacing shoes and wheel cylinders braking effort was poor, with hard pedal, but no pulling, so I think brake drums are OK.

All 4 wheels bled easily and the car showed no sign of a sticking brake. As soon as I released the pedal all braking action ceased including at the wheel that was locking up so I believe the hoses are OK.

Then,

1. Change the shoes on the right front wheel (one that is locking up). The wheel cylinder on this wheel was leaking (prior to replacement) and some fluid definitely got on the shoes (darker color), though they seemed dry to the touch.

2. If problem persists, change hoses on front left and right sides and see if problem moves to other side. If so, replace bad hose.

3. If hoses are OK, put straps on both sets of front shoes and have son depress pedal to make certain both new wheel cylinders are functioning. If so, test back wheels.

4. If necessary, I'll switch the front brake drums from left to right to check for out of round, though the lack of pulling prior to replacing all of the parts leads me to believe that won't be an issue.

I'm haunted by Matt's comment that one wheel is braking properly. In spite of the logic above, my intuition says he's right.

Thanks again for all of the great suggestions. I'll update after I get back. Can't believe I'm stuck on brakes! Thought reseal, replacing heater hoses, cleaning up heater box, hooking up vacuum line to Corsa dash, etc., would be the challenges.

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Re: Fixed! -- Right front wheel locking up on braking
Posted by: aircooledairhead ()
Date: January 18, 2020 06:20PM

Again, thanks for all of the suggestions!
I had installed new linings but left the old wheel cylinders in. The right front wheel brake shoes looked wet but felt dry to the touch. The wheel cylinder was leaking.

I then put new wheel cylinders in and the car pulled hard to the right. Upon disassembly the right front brake shoes had black goo on them. I used brake cleaner to remove most of the goo and then sanded the shoes with 100 grit sandpaper. Brake drum and backing plate were cleaned along with ascertaining that new cylinder was not leaking. Everything was reassembled.

No more pulling! Brake pedal is still hard but car stops well, just with lots of pressure on pedal. It was suggested that the master cylinder PO installed might be larger than 1" diameter cylinder. There were no markings on the cylinder so it is hard to tell if it is too large. That is definitely a possibility.

Spent the rest of my time at my son's adjusting the steering box, replacing a jury rigged clutch return spring, adjusting the carbs and linkage, replacing the accelerator return spring, duct taping a gap in one heater hose (all will eventually be replaced) and installing the grommet where the fuel and electrical lines pass through the sheetmetal. Also discovered no cotter pin on pin through shifter where it enters transmission. Installed one and couldn't get reverse. Will research posts on here I know I've read before to figure out what adjustments to make.

Next major effort will be to start resealing all the leaks at differential and engine. Also need to check compression as there is enough blowby to push a bit of oil out the dipstick tube. If compression is low, it will get new rings and honed cylinders. I'll also clean the flashing off the cooling fins.

Car has been driven about 75 miles with no oil consumption and oil is still clean, so that is a plus. (65 140 HP Monza 4 spd coupe). The left carb still isn't perfect, but the engine pulls strongly. Tach on Corsa dash works, but reads 400 RPM high.

So much to do, But it now goes, stops and steers! And drinks lots of premium gas!

Thanks again for all of the great suggestions!

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Re: Fixed! -- Right front wheel locking up on braking
Posted by: MattNall ()
Date: January 18, 2020 06:50PM

We knew you'd get it! Now have some fun!

MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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