Imperial With Rear Drum Conversion - Brakes Sticking?

1975.Imperial

Member
Joined
May 2, 2022
Messages
105
Reaction score
128
Location
Ontario, Canada
Hello all, all 4 of my '75 Imperial's brakes are dragging and I need some help troubleshooting before I spend even more money on this problem. Please keep in mind that this is my first project vehicle and that I'm only 19 so this is a learning experience for me, I'm also currently at school and don't have regular access to my car so I might take a while to test anything on it.

Like I said, all 4 corners are sticking on, making it very difficult to turn the wheels by hand, after a while, they do become pretty easy to turn. This has been happening since I owned the car, even when it had its original disc rears. The car can go and stop under its own power. So far, I've replaced front callipers, pads, and soft lines, as well as rear wheel cylinders, hardware, shoes, and soft line. Now I'm thinking that the problem's either in the master cylinder or the proportioning valve. While I was bleeding the brakes there was a noticeable sucking force from the master cylinder when the pedal was released which lead me to believe that it was good, I'm however not sure how strong that force should be. I've kept the stock, 4-wheel disc, proportioning valve so I'm not sure if that would potentially cause a problem, I'd imagine that if it did it'd only cause a problem for either the fronts or the rears, not both. I've also kept the stock master and booster, I've ordered a new New Yorker master but it uses 4 studs to mount to the booster whereas my current booster is only a 2 stud for the unique Imperial master.
Right now I see myself having to either find a used brake booster or proportioning valve from a drum-rear Chrysler, which leads me to another question, are all drum-rear boosters the same from '74-'78? Rock auto, for example, lists their (discontinued) booster as exclusive for '74/'75, and '76-'78 is not on their compatibility list.

Thank you all in advance, and again, I'm coming into this with no real-world experience except for a degree from the University of Youtube so any insight is appreciated

IMG_1580 2.JPG
 
Since all 4 wheels are dragging, it sounds like you have a problem with the master cylinder not releasing after pressure is removed from the brake pedal. Usually this condition is caused by the travel rod from the brake booster being adjusted too long. Try backing off the 4 mounting bolts for the master cylinder about 1/8". Now jack up one wheel to see if it will turn freely. If the wheel turns freely, the travel rod is adjusted too long. Remove the master cylinder, the travel rod has an acorn nut on the end, this is used to adjust the length of the travel rod. Turn the acorn nut clockwise to shorten the length of the rod. Usually about one turn will shorten the rod enough to allow proper release of the master cylinder (you will need to restrain the rod from turning inside the booster, usually there is a flat spot on the rod to attach a tool for this purpose.) Reattach the master cylinder to the booster and check the brake function.

Dave
 
Last edited:
Since all 4 wheels are dragging, it sounds like you have a problem with the master cylinder not releasing after pressure is removed from the brake pedal. Usually this condition is caused by the travel rod from the brake booster being adjusted too lung. Try backing off the 4 mounting bolts for the master cylinder about 1/8". Now jack up one wheel to see if it will turn freely. If the wheel turns freely, the travel rod is adjusted too long. Remove the master cylinder, the travel rod has an acorn nut on the end, this is used to adjust the length of the travel rod. Turn the acorn nut clockwise to shorten the length of the rod. Usually about one turn will shorten the rod enough to allow proper release of the master cylinder (you will need to restrain the rod from turning inside the booster, usually there is a flat spot on the rod to attach a tool for this purpose.) Reattach the master cylinder to the booster and check the brake function.

Dave
Thank you, I'll try that out this weekend. It'd be really nice if that was it
 
is the proportioning valve different on the 4 wheel disc setup compared to the disc/drum ?
 
is the proportioning valve different on the 4 wheel disc setup compared to the disc/drum ?
I'm not sure about that, all the other components related to the rears are different and I could see there being a difference in the pressure discs need over drums. I haven't actually looked into it at all though
 
I'm not sure about that, all the other components related to the rears are different and I could see there being a difference in the pressure discs need over drums. I haven't actually looked into it at all though
Quit the youboob research and get an FSM... you can learn a lot from the information in there, including proportioning valve function.
 
Since I made this thread, I haven't been able to work on the Imperial in much depth due to school, I'm home now for a weeklong break and plan on getting as much done on this car as I can.

An update on the brake sticking issue, I was wrong with a large portion of my original diagnosis. Only the front brakes seem to be sticking, and they stick hard, they also don't release at all, after practically a month of sitting untouched, the brakes were still stuck on. Also to note, I can only remember this issue starting after I did the original conversion

I tried unbolting the master from the booster, no difference. I removed the callipers from the disc and compressed the piston, while compressing (with the cap off the master), some brake fluid shot out of the top of the master. The callipers stayed expanded until I reinstalled and pressed the pedal multiple times, at which point they stuck again.

So far I've determined that it's not the callipers (they're new, old ones did the same), it's not the soft lines (they're new, old ones did the same), it's not the booster or an incorrectly adjusted travel rod (problem persisted while disconnected from the booster), I'm unsure if it could be the master (there was a sucking force while bleeding the brakes, which would indicate a good master, but maybe a seal has swelled up, I'm not sure), and I'm still unsure if using a disc/disc proportioning valve on a disc/drum system would cause this to happen.

Jeff, I can't find a section in the FSM on converting rear discs to drums and this seems to be a conversion specific issue
 
Back
Top