Headsup for Brake Proportioning valve booster problems

[71chevc10]

Just an FYI
My brakes didnt function well my rear brakes not activating and hard brake pedal.
I chased my tail on my brake system replacing booster, master cylinder wheel cylinders proportioning valve. I checked vacuum at the carb which was 18 which is spec for the booster.
after doing all this and no change in braking I looked at the vacuum t on the manifold and the inlet was undersized I replaced it with the correct size inlet and my brakes are great.
I hope this helps someone else if they are trying to find the problem that I had

[robs71]

The bright side is you have a fairly new brake system and isn't it a good feeling when you figured out the issue??Good job and thanks for the info..sometimes it is the simple things we miss when diagnosing an issue..

[71chevc10]

LOL i was at it for a month chasing my tail
glad its over

[NorCalC20LWB]

Deja Vu for me, same issue here. Have replaced booster, MC, Prop valve, rear shoes/brake cylinders, front pads/calipers. Better, but still feels like a very hard pedal. Could you elaborate on the T fitting and what the correct size should be?

[GASoline71]

I think the main thing you learned was diagnose first... then throw parts at it!

Gary

[71chevc10]

Originally Posted by NorCalC20LWB

Deja Vu for me, same issue here. Have replaced booster, MC, Prop valve, rear shoes/brake cylinders, front pads/calipers. Better, but still feels like a very hard pedal. Could you elaborate on the T fitting and what the correct size should be?

I found this fitting on amazon
The Right Stuff Detailing IMF68RS '68 - '69 3/8 Thread, 2 Ports (Rally Sport) - Intake Manifold Fitting
I used pipe sealant on the threads
And i used 11/32 gates Vacuum hose with it to the booster

[71chevc10]

Originally Posted by GASoline71

I think the main thing you learned was diagnose first... then throw parts at it!

Gary

I had to find the solution myself as i took it to an ASE certified mechanic and he couldnt figure it out

[NorCalC20LWB]

Thanks for the link to the fitting, however looking at mine the vacuum hose comes straight out of the back of the carb, no T fitting.

[GASoline71]

Personally I wouldn't use a T-fitting for the line that runs to the Brake Booster. Factory had a line right from the carb or manifold to the booster. You want FULL vacuum to that booster and nothing else on the circuit robbing any vacuum from it.

Gary

[71chevc10]

It worked for me for this problem

[burnin oil]

The prop valve is the other big headache I have run across on a Dodge. Rebuilt the rear brakes and upgraded the wheel cylinders to a 40+% increase in stopping power. Replaced the front rotors, pads, and calipers. Each time it got better but still horrible brakes. This was a 95 Dodge diesel and it had brakes worse than my old beater 76 chevy blazer. Finally said to hell with it and yanked the ABS and prop valve out and replaced it with a 70s GM valve, new from Summit, for under $100. After that you could lock them down and get whip lash! Initially troubleshooting wasn't needed as I was replacing parts that were wore out but once everything was replaced that I scratched my head. Went from mash and pray to be easy on the pedal.

[Voodoo556]

I happen to know a guy that swapped both the front axle and rear axle to 1 tons with 4 wheel disc brakes.
Ordered a booster, master cylinder and proportioning valve for disc/disc.
Had decent front brakes but zero rear brakes.
Spent weeks trying to figure it out, must of bled the system 100 times (ok not 100 but 15-20) and finally broke down and trailered the truck to a shop in town.

Upon picking up the truck he asked "so what was the problem with the brakes"? Answer "um, you had the lines going into the proportioning valve backwards, front brakes were in the rear brake position and vice versa".

Needless to say this guy felt pretty stupid and suggested to the manager of the shop that they lie to him next time and make up some complicated highly involved problem that only the most skilled brake ninja would be able to decipher.

I gladly paid my bill and now have operational brakes both front and rear