Details: 1970 Challenger 440 6 Pack - 4 speed
Factory Dana Rear Axle with 10" drums (New brakes & Drums)
Using DOT5 Synthetic Brake Fluid so it won't damage my paint.
New after market front disc brakes (SSBC)
New Power booster & master cylinder & new brake lines
Both brass proportioning valves are new.
Adjusters are backed all the way off (maximum slack)...Still have the problem.




Background
On the maiden voyage, I was driving down the highway and at speeds over 30-40 I started to feel a vibration that I thought was driveshaft or rear end.... (it wasn't)

I hit my brakes and slowed down a bit then I pressed in the clutch to shift, I felt the car lunge forward like the brakes were still being pressed...and I had to give it much more gas just to keep going.

It felt like the brakes were being applied harder and harder and after stopping on the side of the road I noticed that my rear brakes were hot.
I let them cool down and drove the car back home.
IT was not a fun drive...felt like the rear brakes were being pressed hard all the way home.

I jacked up the car and took off the rear drums so I could see all of the drum brake inter-workings.

No damage and the brakes looked like they were installed correctly.

With the wheels and drums off, I performed the following test so I could see what was happening when I pressed the brake pedal.

Whenever the brake pedal was pressed, the drum brake pads expanded like they should, but when the pedal was released...the brakes never returned to the normal position... They stay expanded. This is causing my brakes to lock up.

The return springs are working and trying to return the brakes to the normal position, but the wheel cylinders will not release the pressure in the line until I open the bleeder and release some pressure.

Any suggestions ?

There are known issues with the new proportioning valves.. And it sounds like your the next victim...

I appreciate the feedback.

This is my 2nd rear proportioning valve. The 1st one leaked at the little nipple....this new one I thought was going to be ok...but now seems like it could be bad also.

Is it possible to bypass the rear proportioning valve and go straight to the master cylinder with my main rear brake line or will that also cause too much pressure and no relief when I let off the brakes ?

This is getting old.

Thanks Again

Took awhile to find this thread but...

https://board.moparts.org/ubbthreads/showflat.php?Cat=0&Number=6836227&Main=6835825

Very good post...
I go online and buy a PV from Fine Lines.

Thankfully, I was able to stop the damage before things got too hot. Just a little discoloration.

Thanks !

is it possible you switched the brake lines ---on the master cylinder the rear line goes to the front brakes---the front line goes to the rear brakes---the master cylinder is proportioned 70 front 30 rear----the brass fitting is only a residual pressure for the rear drums----front brakes dont need any residual---bob

the front disc brakes only need 2 inch pounds of column pressure-- so if the master cylinder is mounted on the firewall it has enough column pressure---if you had a hot rod with the master mounted on the frame rail you would need that 2 inch pound residual valve to hold the pads close enough to the rotor to work----- the rear drums need 12 inch pounds to hold the shoes out to the drum so they have to have that to actually press against the drum---that brass splitter lets the disc brake go straight through and the rear has the residual valve built in----if you bought an adjustable residual like a wilwood you have to open the front all the way (wasted money) and the rear has to restricted ----bob

Bob.. It the rear brakes that are holding to much pressure....

I understand it is just the rear---but there are several things that can happen if everything was replaced---front and rear lines get switched---front and rear residual is different---thought other guys might like to know----it would be interesting to know if the fronts are working at all or normally----or if the system installed is after market--bob

Arn't the front and rear fittings different so they can't get switched up at the MC?

Its probally the prop valve and the fix is to swap the top piston from a OEM valve. The same thing happened to my 71 Charger after swappin in a new reproduction valve a few years back. I actually talked to the owner of Fine Lines at Carlisle after I saw the same defective valves on his table for sale and showed him the problem. This was around 2005 and Im sure he fixed them and has since made some improvements to make the valves more correct lookin. The problem is that others are still selling the same defective valves to this day. If I remember correctly you can spot the bad ones by trying to blow air through the top fitting and if you cant, it may be one of the bad ones. I showed some pics as well in a older post.

yes the front and rear are different(on the master)---but if everything is new we dont know exactly what was done---if the lines are stock why replace the residual valve/line splitter? if you replace it because its bad thats one thing but if its just because its shiny then i guess the lines may be shiny now too-----and just remember when this post started we were told everything was new---BOB

well i reread his post and he states the lines are new along with all the other parts---if he bent/flared and fitted the lines it is possible the front and rear are switched--and i have seen it happen when everything is new that logically it looks like the front goes to the front and the rear to the rear and therein is the rub---- the modern mopar master cylinder is set up 70/30 without an external portioning valve when you plug in a wilwood portioning valve in any direction(front or rear) all you are doing is restricting the flow----now for the drum brake setup the residual valve is critical because without it you couldnt stop your car unless your name is fred and barney----bob

If I missed this already, sorry, but I had this issue with my 64 Polara a few years ago and it turned out to be the inside of the rubber line down to the rear axle was collapsing. After I replaced it my rear brakes stopped dragging.

You could have swapped the rear brake shoes 'front to rear'. There are 2 different sized friction material.
The shoe with the smaller lining should be on the frontside while the brakeshoe with more lining should be mounted on the rear part of the brake backing plate.

If you swapped them they could be self-energizing too much now perhaps.

It might also be the rear hose, if it's failing internally it could be acting as a check valve.

You will probably have to release pressure at the frame side of the hose to see, if it's there then release pressure at the output of the prop valve, if it's there then release pressure at eh input to the prop valve, if it's there then it is a M/C issue.