disc conversion problems

[d.c.]

Hi All,
Got a 69 charger in the shop for a client/friend. Did a disc conversion on it from SSBC the car was originally a power drum. pedal feels is good but I cannot seem to get enough line pressure to stop the car. SSBC supplied a m/c that has a 1 and 1/32 bore. Here's what we have done thus far: Had a low vac condition and hooked up a electric vac pump direct to the booster with no change. Verified 20 inches of vac with gauge. Replaced booster with a dual 8 and 3/4 inch and no improvment. Installed a m/c from a 73 dart disc drum car with a bore size of 15/16ths. Slight improvement but not enough to drive the car safely. Bleed many times and no changes. Removed the stock dist. block and replaced with a direct tee circiut for the fronts and a straight coupler into the prop valve from the master and out to the rears.No Change. Linkage and pushrod clearance checks out. I have left a 1/16th to 1/32nd clearance. SSBC techs say to go back to the original booster and their master. I can't see this helping since it is a single booster and a larger bore combo. I am about to go to the parts store and buy a hydroboost system from an astro and get some lines made up and be done with it. Any ideas?

[Gorilla]

I would look for an issue with the brake lines. Are they all new? Did you reuse any sections of old lines? Does it pull when you brake?

[406 Q-ship]

Upfront I am not real up on Mopar braking systems. Does the brake pedal have a second hole in it? Sometimes on GMs there is a second hole for power or non power brake cars and that will effect pedal travel and leverage ratio. The higher up the pedal the more pressure it will put to the master cylinder. If it were my car I would look at a 7/8 bore m/c but becareful because a smaller m/c will move less fluid and might not move enough to work the front calipers properly. I hope this helps.

[claytonisbob]

Are you using the stock proportioning valve?

[Apogee]

First, I would say that if you have a caliper guage kit, use it and let us know what you're getting for pressures. If not, it's a great investement and should be considered mandatory for shops doing aftermarket brake installations IMHO.

Pads maybe? We had a weird instance where a customer was running PFC pads from Autozone and had similar issues to yours, however this customer was running Hydro-boost and getting plenty of pressure at the calipers per the gauge kit he bought. Turned out the pads were pre-glazed from the manufacturing burnish process, which turned a respectable coefficient of friction rating pad into what felt like an ice cube sliding across glass. I don't know if you can get some cheapie NAO pads locally for your SSBC calipers, but it could be worth a shot. Worst case scenario is that it doesn't fix the problem and you can rule out one more thing that it isn't.

Tobin
KORE3

[NOGO]

First, I would say that if you have a caliper guage kit, use it and let us know what you're getting for pressures. If not, it's a great investement and should be considered mandatory for shops doing aftermarket brake installations IMHO.

Pads maybe? We had a weird instance where a customer was running PFC pads from Autozone and had similar issues to yours, however this customer was running Hydro-boost and getting plenty of pressure at the calipers per the gauge kit he bought. Turned out the pads were pre-glazed from the manufacturing burnish process, which turned a respectable coefficient of friction rating pad into what felt like an ice cube sliding across glass. I don't know if you can get some cheapie NAO pads locally for your SSBC calipers, but it could be worth a shot. Worst case scenario is that it doesn't fix the problem and you can rule out one more thing that it isn't.

Tobin
KORE3

x2

In my experience the SSBC pads are JUNK!

[d.c.]

sorry for the delay. As luck would have it I went on vacation in the middle of this. I pulled the new booster put the stock one back in and then pulled the ssbc adjustable bias valve. this made an appreciable difference. Hooked up a vac pump direct to this setup and got no change. I think we have a pad issue. The car stops o.k. now, but not like it should. I think I am going to put a few miles on it to try to get the pad to seat properly and then go to a new pad if things don't get better.