Brake locking up and strange pedal feel!!!!

[1glaserfwd]

Well long story short engine spun a balance shaft bearing last september. I pulled everything out washed and painted the engine bay and built a stroker motor and got the car running last saturday! Number one problem is after I drove it about 5 minutes I could tell the car was being held back, the brakes locked up solid!! Luckily I had some pliars I broke the bleeder on the RF caliper and it let go. So I limped home using the e brake.

Thinking I had a bad caliper I got another one installed it and bled all four wheels. I noticed when bleeding the LR caliper and RF caliper would never get a steady stream of fluid and the brake pedal would only go half way down while bleeding. The other two had a good stream and the pedal would travel all the way down.

So I went for another drive and again in about 3 miles it started grabbing and locked up. This time I broke the master cyl nut loose and it let go. Also I noticed the pedal when the engine is running feels real strange, the first 2 inches feel like nothing then it gets stiff and it jerks when braking, basically its all or nothing!! I am suspecting the proportioning valve where all the lines go in and go there seperate ways. Strange that the LF and RR bleed fine and pedal goes down and the other two do not. Any help would be greatly appreciated, I am trying to get this engine broke in and this is a real PITA!!

 

[5150DSM]

I think you're on the right track. Sounds like the proportioning valve.

 

[ACM]

Before you drive the car, check that none of the brakes are stuck on (including the parking brake).
Drive the car - does one or more brake start locking up ? If yes, you have the bleed/vent hole block in the master cylinder for that circuit - my guess is that the RF/LR circuit's blocked, based on your description.

As the fluid heats up it needs somewhere to go - that's typically back into the master cylinder via the bleed hole. The master cylinder has two independent circuits built in, they operate diagonally opposite calipers - two pistons, two bleed holes, two output ports. Race cars split front to rear, street cars split diagonally. You can strip & clean your existing master cylinder or replace it with a new one.

 

[streetraceboi]

Did you happen to remove all the emissions when you had the motor out? Sometimes the brake booster hose running to the back of the intake gets overlooked. And in some occasions when removing the emissions for some reason, makes the brakes lock up if the stock check valve isnt there in line with the hose, or was replaced in the past. You might want to check that....it could be a possibility

Another way is do to a boost leak test, if the check valve is missing you will have a big boost leak at the brake pedal area

 

[ACM]

Brake booster/hose problems will affect both hydraulic circuits equally, not just one circuit on it's own.

The problem almost certainly lies within one of the hydraulic circuits, and since the RF/LR circuit is exhibiting heat-lock and bleeding problems, that's the logical place to start. It's possible the prop valve could be involved, but all the symptoms point to a piece of debris blocking the master cylinder bleed port for that circuit.

 

[5150DSM]

Booster is not the problem. ACM has it nailed. Master could definitely be the issue but in my experience the pedal will be spongy on full application with a bad circuit in the master. I lean toward prop valve because of the lock-up issue and the poor fluid flow to the diagonal circuits without fluid flowing back into the reservoir. (Unless I missed that somewhere) IMHO, if it were a master, you would see a fluid level rise in the reservoir on application, whereas the prop valve will increase pressure to the other circuit without back-flow.

 

[1glaserfwd]

Before you drive the car, check that none of the brakes are stuck on (including the parking brake).
Drive the car - does one or more brake start locking up ? If yes, you have the bleed/vent hole block in the master cylinder for that circuit - my guess is that the RF/LR circuit's blocked, based on your description.

As the fluid heats up it needs somewhere to go - that's typically back into the master cylinder via the bleed hole. The master cylinder has two independent circuits built in, they operate diagonally opposite calipers - two pistons, two bleed holes, two output ports. Race cars split front to rear, street cars split diagonally. You can strip & clean your existing master cylinder or replace it with a new one.

You nailed it bro it was the master. After this post it all made very good sense and I have not read or found a single situation with the prop valve being bad I went for it and its fixed. Thanks for your input I love when people who know what there saying post its very helpful!