Seized brakes - seeking a little advice

[shed7]

After a morning spent by the side of a freeway with seized, smoking brakes, hoping you guys might have a little advice. Running for 20 mins 40-70mph when I felt the drag (feels like loss of power), downshift and it tightens more. Pull over and we are seized solid, immovable. Heat and light smoke coming off all four wheels. Brake pedal solid. After 30 minutes the car is drivable again (we trucked it back anyway), pedal has a spongy-feel and brakes are weak.

Car is '68 SWB 912, running 2.7RS spec motor and '73 master cylinder/discs with portafield pads. It was shipped from UK recently, so spent 10 weeks or so sitting in various ports/container. My amateur diagnosis says calipers may be out of alignment, with friction building heat as I run until the brakes start to seize. But could be the master cylinder or block in the lines (Goodrich braided lines fitted a couple of years back)...

The car is back in my garage and before I get stuck in I thought I'd seek some sage 'Early S' advice...

Many thanks in advance
Neil

[davep]

It sounds like some rubber lines are acting as one-way valves thus locking the brakes on, or the calipers are seized. Even the parking brake could be seized.

[EA911]

How are the hard brake lines? I had a similar problem when I first bought my car and it turned out that one of the hard brake lines had a kink on it stopping the fluid from releasing the pistons.

Pull the wheel and remove the calipers to check for seized pistons or pits/rust on the pistons.

[Allen Henderson]

It sounds like some rubber lines are acting as one-way valves thus locking the brakes on, or the calipers are seized. Even the parking brake could be seized.

+1. Before you do anything else, replace those lines and bleed the brakes. Thanks.


-Allen-

[304065]

Well, before you start replacing anything, first get the car up on jackstands and securely supported so it doesn't fall.

Next, with the wheels on and the car in neutral, try spinning each wheel. Do you hear grinding? Do you feel resistance? If the pistons have seized in their bores you will definitely feel drag. That's the biggest diagnostic step by far.

Next, pull off the wheels and look at the rotors for any obvious signs such as metal-to-metal contact. Do you see excessive brake dust, as in everything is black? Another telltale sign of sticking calipers.

Next: remove the hairpins, knock out the retaining pins and pull out the pads. Carefully note which is the inboard and which is the outboard side.

What is the pad thickness? Could someone have unknowingly fitted the wrong pads? In the later cars, the Carrera pad is thicker than the earlier pad.

Next: can you get the pistons to retract at all? There are some nice brake piston tools on the market, can you borrow or fab something like this? I hate to tell you to use a prybar wrapped in duct tape to move the piston back, I have used the handle of a rubber mallet in an emergency on the track, you put it in and turn it sideways to push the pistons back.

What you are trying to figure out before tearing the whole brake system apart is where is the source of the trouble.

Does your car have the original single circuit master cylinder or was it upgraded to a dual circuit? If upgraded, was it done exactly right, following the way the factory did it in '68? If unclear ask us and I will post the diagram of the 68 system.

Hope this helps, some photos of your starting point would be great.

[Neunelfer]

Goodrich braided lines fitted a couple of years back

If they're braided lines they probably won't suffer the "bloated line" fate.

Running for 20 mins 40-70mph when I felt the drag

If it happened after running for 20 minutes, I'd guess that you have a sticking piston somewhere in the system. Calipers don't get mis-aligned. I'd simply look for the smoking gun or... brake pad(s) in this case. I'm guessing it heated up the fluid in the system and expanded causing them to drag & lock.

How do the calipers look? Rebuilt recently? Might be fluid grunge or sticking knockback mechanism's.

[Allen Henderson]

If they're braided lines they probably won't suffer the "bloated line" fate.



If it happened after running for 20 minutes, I'd guess that you have a sticking piston somewhere in the system. Calipers don't get mis-aligned. I'd simply look for the smoking gun or... brake pad(s) in this case. I'm guessing it heated up the fluid in the system and expanded causing them to drag & lock.

How do the calipers look? Rebuilt recently? Might be fluid grunge or sticking knockback mechanism's.

I agree probably not the brake lines and probably not the calipers since they are all locking up. Check the MC, is the brake pedal sticking or was the MC rebuilt..sounds like a problem with it. Thanks.

-Allen-

[Neunelfer]

Yup... if it's all four, look at a MC problem. Maybe bad pedal cluster bushings causing the pedal to stick??

[shed7]

Guys, big thank you for the advice (a fine welcome for a Brit newbie

Got dragged away yesterday so will get the car on stands on work through some of the tips above. Stay tuned...

[Allen Henderson]

Physically with your hand pull the brake pedal and see if it moves a meaningful amount and stays put..if so Ipso facto = MC. Thanks.

-Allen-