1967 Mustang with 1989 5.0 drive train (motor and AOD)
Originally the car was a 4 wheel power drum car, I change this to a power from disc and rear drum car. Now here is the problem, I HAVE NO POWER ASSIST! Here is what I have done and changed to no avail:
1. Power booster 1st rebuild original, no help
2. Replaced booster with period correct one, no help
3. Replaced master with period correct one, on help
4. Changed pedal to period correct one, no help
5. Checked booster vacuum (17.5 PSI)
6. Add vacuum pump to check, (23 PSI) still no boost
7. Checked PSI at Calipers (1000 Psi front) and (700 PSI rear)
8. Checked proportion value, not tripped to front or rear
9. Front disc are four piston from SSSBrake older 1990’s
Looks like everything checks out. The only thing I would say is (and this is a stretch) but check and make sure you have period correct length pushrod on the master and booster. I went thru two master cyls thinking they were bad before I realized my rod was too long and piston in the master cyl was shoved too far forward from the start. might be worth looking into?
Is the check valve in the booster good ? It is inside the plastic piece that pushes into the booster ,the vacumm hose attaches to it . you should be able to blow through it one way but not the other if it is good . And Yes, check the push rod length it could be wrong .
I was just talking with a friend of mine ,i am not sure what brand your booster is , but he was telling me that he had the SSB booster brand new and it did not work .He sent it in for a replacement and the replacement didn't work . Another friend was telling me the same thing . Mick , the first friend, found a little shop in Orange Cali. called ABS .He stopped in a talked with the owner and found out the shop is building a new unit .
Mick bought it and put it on his 66 convrt. and says it fixed everything
Mick was having the same trouble you are having .I dont have a number for the shop but i will try to get it from Mick ,he said the unit was a lot cheaper and clears his clutch cable for his 5 speed .The only problem he had with it is the lines come out on the wrong side of the aluminum master cylinder ,that he fixed with braided brake line .
Everybody on this forum will be smarter when the problem gets cured! I once saw a car with a old hose that would collapse shut [with engine running] when he put on the brake . it had no assist and it really takes alot of pedal to stop car. my 71 booster bolts directly to firewall, i have noticed older mustangs have some mounting bracket instead is their a possibility you have a drum brake pedal that could have a different pedal ratio? i have heard of this but dont know if its a mustang thing .