Brake Pressure Problem.. Any Experts

[obengston]

I have a 68 Camaro with the factory power disc/drum set-up. I just recently added a Moser rear end with disc brakes (SSBC brakes). I called SSBC and they said I should be able to use the set up I had. I have all new stainless brake lines front to rear, and new rubber flex lines in the front. The front is the factory 4 piston disc brakes. I have lost all pressure. I also changed the M/C with a new one (stock), but still can't build pressure. I bench bleed the M/C and started at the right rear trying to bleed, but can't seem to build pressure up. The pedal goes to the floor. I believe the proporting valve may be leaking. Could that be my issue? I have sent for a new one. The distribution block seems to be good (but I don't know if that can have anything to do with it. The distribution block is just below the M/C, and the proportiong block is to the right of that. If I pump the brake really fast after about a second pressure/air will push back up into the Master cylinder from the front part of it, which I believe is the part that runs to the proportioning block. I could be wrong on the name I'm calling it a proportioning block, but I have seen sites that list it as a hold off valve (may be the same just worded different. Any suggestions????

Thanks

[a67]

Be sure to remove the residual pressure check valve from the former drum side of the M/C. It is located behind the brass seat for the line. Can pull the seat, the valve (spring and rubber cup) can then be removed and the seat pressed back in.

In the '67 Firebird FSM, which may be a little different then a '68 Camaro, the distribution block is just that along with the pressure differential switch for the dash light.

The piece behind it is the metering valve. With a disc/disc system it needs to be removed.

If there is a proportioning value, most likely it is located on the frame rail under the drivers seat area. If there it should also be removed.

Then an adjustable proportioning valve installed in the line to the rear.


Once the re-plumbing is completed start again with bleeding the M/C. My guess is the lack of pressure is from the M/C not being fully bled.

Use the tubes back to the reservoir method in a vise. Make sure that the M/C is level and that it is given full strokes. Both pistons need to be bottomed out in the bores. Take your time and when applying and releasing the pressure on the M/C piston, GO SLOW.

Tap on the M/C casting with the plastic end of a heavy screwdriver. Then bled it some more. This will knock any bubbles clinging to the sides loose.

Before re-installing the M/C, close all bleeders on the calipers. Make sure that all re-plumbing has been completed. Then connect the lines to the M/C first then bolt it up. This is so that the least amount of fluid is lost.

Then fill the M/C with fluid and set the cap on top.

Open a front caliper bleeder and let gravity fill it. Close the bleeder.

Can tap on the caliper as it is bleed fluid out with the hanlde of a heavy screwdriver. This again will knock any bubbles clinging to the walls loose.

Now to the other front bleeder and do the same. Check the fliud level in the M/C at regular intervals.

Back of car, do the same. Open a bleeder and let gravity fill it. Then the other rear caliper.

At this time you can then further bleed via pressure or by the vacuum method. Although it may not be required as the gravity bled should do the trick.

Bob.

[obengston]

How do you pull the seat from the M/C, and that will be on the M/C where the rear line connects correct. Also the distribution block is located below the M/C , but the proportioning valve I was talking about is located just to the right of that and attached to the M/C with a bracket also called ahold off valve I believ. Are you saying take that off the car? And install a adjustable proprtioning valve? I believe the proportioning or hold off valve I have delays pressure to the front brakes so pressure would go to the rear drums originally, but not 100% sure.

[a67]

Can thread a small machine screw, some use a sheet metal screw, into the hole in the brass seat. Then use two flat-blade screw drivers opposite each other under the screw head and pry straight out. Doesn't take much force to pull them out.

A metering valve is also referred to as a hold off valve. Which is completely different then a proportioning valve.

A disc/disc system does not need a metering valve. And one should not be in the system. They are only required in a disc/drum system.

Whether your car has a proportioning valve was dependent upon whether GM thought it required one or not. In the '67 Firebirds it had to do with which particular engine was used or if there was A/C in the vehicle.

The issue is, whether there is one there or not, the front to rear brake balance may be way off. There is a possibility that it is OK. But this is something that you will need to find out once you drive the vehicle again.

Bob.

[obengston]

Well I finally got pressure to all the brakes. Remember I installed a rearend that had SSBC disc brakes on it. The front is the factory 4 piston disc brakes. About 3 hours with a suction on all the lines. But now I have problems stopping. The brake pedal seem to be hard, and slows down not lock up. (it is factory power brakes). I checked my vacuum only about 8-10. So I ordered a electric vacuum pump from SSBC ($270 ugg). I installed it and it runs the shuts off only for a minute the starts running again (this is without me touching the brakes). I drove it, and when I hit the brakes the 1st push seems to work good, but then becomes hard again and slows the car. So I'm thinking the problem may be the Power Booster not holding vacuum good once the brake is engaged. Any opinions. I ordered a replacement booster yesterday, will see when it gets here in a couple of days. If it fixes the problem I'm going to try it without the electric vacuum. If it works looks like I will be selling a pump. Anyway Just wanted to see if anyone had any opinions. Also I do have a new master cylinder as well (factory replcement for disc brakes).

[Apogee]

You might have a booster issue, or it could just be a faulty vacuum check valve. Most new boosters include a new check valve, so either way you should be covered. Your vacuum levels are poor, so even with an accumulator added to increase the volume, I think you'll still need some sort of auxiliary vacuum pump, but it can't hurt to try it again without. Either that or convert to Hydro-boost or manual is always an option.

Tobin
KORE3

[obengston]

I put a vacuum pump on it from SSBC. It would have one good pedal then go hard again. I think the booster may be bad and let to much vacuum escape. I just put a new booster on tonight and it helped without the vacuum pump. I now think I may have a bad head gasket. Valve cover inside is milky. Checked dipstick can't tell. Tomm I will drain oil and see. And the hits keep on coming. New engine on top of all. MAN. I wonder if that can cause me to lose vacumm some??