Derping brakes...

[Ferret]

I think the brakes on my car hate me. LOL

I bled the entire brake system (with different methods) and I'm almost sure that there isn't any air trapped inside.

Problem: the brake pedal is hard to press after bleeding the entire system, but as soon as the booster works with the engine switched on, the pedal gets soft and travels all the way down and the car is hard to stop (feels like a manual brake) at speeds above 15MpH. Got to jump with both feet on it. Anything slower is a perfect imediat stop. While bleeding I noticed that the rear calipers move a lot, indicating they get a lot of pressure, but the front calipers barely move. My guess here is that the front does not get enough pressure due to a wrong master cylinder. Anyone got a clue about this one? Here's some tech about the setup:

- SSBC Master Cylinder A0476, 1" bore, 1.75" stroke
- SSBC Front Disc Brakes A181, double piston caliper (per piston: size 1.5", area 1.77 sq-inch)
- SSBC Rear Disc Brakes A127, single piston caliper (per piston size 1.77", area 2.46 sq-inch)
- Brake Booster and Pedal are stock

Any advice is welcome!

 

[pontiacgp]

What residual valves are you using?. With disk brakes if you don't use at least a 3 lbs residual valve the piston in the caliper will retract and you'll have alot of pedal travel. Also did you bench bleed the master?

 

[clean8485]

Since you've changed much of your braking system over to aftermarket parts, probably your best bet would be to get in touch with SSBC, and see if they have any kind of technical help or insights for you. The 2 things that I would look at would be the brake booster-first, is it compatible with the SSBC master cylinder? Some A/G body cars have a single diaphram booster, and some have a double diaphram booster. Does the SSBC system require a specific booster to work properly? Secondly, is your booster working properly? Shut the engine off, then pump the brakes 4-5 times to exhaust all of the vacuum out of the booster, then hold your foot on the brake pedal and start the engine. The brake pedal should drop closer to the floor. If it doesn't, then you have a booster issue. The other item that I'd look at is the combination/proportioning valve. since you've switched over to 4 wheel disc brakes using aftermarket parts, is there a specific proportioning valve required for your system? You mention that there seems to be lower hydraulic pressure at the front wheels. Maybe you need an adjustable proportioning valve. As I said before, I'd start by contacting SSBC and talking with them. Hope this helps.

 

[Ferret]

What residual valves are you using?. With disk brakes if you don't use at least a 3 lbs residual valve the piston in the caliper will retract and you'll have alot of pedal travel. Also did you bench bleed the master?

Benchbleeding wass the first thing I did, as it was required by the installation manual. I checked a few sites on the web and they all tell me that there's no need for a residual valve in a disc/disc brake system as long as the master cylinder is positioned higher than the brake calipers. This article explains it better than all the info I gathered on the web: http://www.thebrakeman.com/valvetechi

Since you've changed much of your braking system over to aftermarket parts, probably your best bet would be to get in touch with SSBC, and see if they have any kind of technical help or insights for you. The 2 things that I would look at would be the brake booster-first, is it compatible with the SSBC master cylinder? Some A/G body cars have a single diaphram booster, and some have a double diaphram booster. Does the SSBC system require a specific booster to work properly? Secondly, is your booster working properly? Shut the engine off, then pump the brakes 4-5 times to exhaust all of the vacuum out of the booster, then hold your foot on the brake pedal and start the engine. The brake pedal should drop closer to the floor. If it doesn't, then you have a booster issue. The other item that I'd look at is the combination/proportioning valve. since you've switched over to 4 wheel disc brakes using aftermarket parts, is there a specific proportioning valve required for your system? You mention that there seems to be lower hydraulic pressure at the front wheels. Maybe you need an adjustable proportioning valve. As I said before, I'd start by contacting SSBC and talking with them. Hope this helps.

I checked and the booster works perfect. The adjustable proportioning valve is in place, working too, but the master brake cylinder is the wrong one (from what I digged up on information).

I mailed SSBC but I think these guys will never again sell me a product of theirs. Told them about the brake setup (everything on the car no was made by them) and the answer was one sentence: "you have a master cylinder designed for manual brakes, not power brakes, so go back to a stock master cylinder" Sounds fair if it's that easy and will solve the problems. I searched Summit Racing, Jegg's and Rock-Auto and they all offer different stock master brake cylinders for both, manual and power brakes on my car, but also with different bore sizes. Checked back with SSBC to determine what bore size would be best, 0,94" or 0.875" and they replied: "there is no choice, go back to stock". Dudes, great help -.- at least could have told me more info about what exactly I shoudl buy, especially since I gave them the links to all the stock master cylinders offered for my car.

Right now I got an 1" bore size. The only thing I know for sure is that the other SSBC master cylinder had previously installed was 1.25" and thus too large. The brake pedal felt like steel but without any stopping power, even with the power booster working.

 

[pontiacgp]

What residual valves are you using?. With disk brakes if you don't use at least a 3 lbs residual valve the piston in the caliper will retract and you'll have alot of pedal travel. Also did you bench bleed the master?

Benchbleeding wass the first thing I did, as it was required by the installation manual. I checked a few sites on the web and they all tell me that there's no need for a residual valve in a disc/disc brake system as long as the master cylinder is positioned higher than the brake calipers. This article explains it better than all the info I gathered on the web: http://www.thebrakeman.com/valvetechi

In the article it says in most cases a residual valve is not needed if the master is higher than the brakes. If you have excessive pedal travel then it sounds like you need a residual valve. Also manual brakes on these cars work great.

 

[clean8485]

Did you hang onto your old original master cylinder? Are there any ID numbers or markings on it that would help you determine the bore size? If you look up the part number for your original application (i.e. your car), there should only be one correct replacement part number. Good luck with your project.

 

[Ferret]

I FOUND THE ISSUE!!!

The replacement hoses I ordered from Raybestos were supposed to be NEW. Well, they weren't: bent & expanded under the pressure of the fluid. Checked the printing on the hoses and they were made in 1993... Great, I got sold old crap that doesn't hold any pressure. No wonder the brakes don't work... Well, I'll never again order anything from Raybestos.

 

[Fox80]

That's to bad as I read down your thread I was thinking hoses, my car acted like that when I got it I changed all three hoses and it stops great. Well at least you got it fixed

 

[Ferret]

That's to bad as I read down your thread I was thinking hoses, my car acted like that when I got it I changed all three hoses and it stops great. Well at least you got it fixed

Looks like I'm not the only one who had such issues ^^ what 3 hoses were involved in your car? front, rear or axle to body? 🙂

 

[Fox80]

The two rubber hoses from the frame to the caliper then the one that goes from the frame to the rear axle housing, and trust me if your car is rusty that one can be a mother$@%#*+ to get off, luckily on my car it came right out