HELP! Brakes Dragging After OEM Disc Conversion

[TeamPontiac79 12]

Hey folks, I'm having a difficult time with my "new" brakes; 70 spindles on a 69. My car had power drum from the factory, so now it has power disc. Problem is the rears seem to be dragging more and more as I drive. The pedal also becomes harder and harder until it applies immediately upon being touched without hardly moving. Once it cools off for a while all is well again. I checked the rears yesterday, and found everything visually in good shape except one anchor pin was bent. Straightened it out, and backed out the adjustment slightly on both wheels. No leakage from cylinders, but I didn't take them apart to see the insides. The rear brakes were redone about 6 years ago, but the car has seen little use.

 

I had the brakes installed by a Mustang specialty shop in Bensalem, Pa, along with all new brake lines, hoses, master, and a new correct proportioning valve.

 

From the research I've done, it seems that the pushrod length is a likely culprit, but it could also be bad wheel cylinders? Again, I had this setup professionally installed, but that doesn't mean mistakes weren't made. I just need to be careful qith taking it back because these guys aren't cheap if it turns out to be additional work instead of a mistake on their part.

 

Highway driving seems not to really effect it, but stop and go causes them to drag, slowly getting worse until I don't need the brakes to stop while parallel parking.

 

Any thoughts? I'm supposed to be taking the car on a long road trip late next week, so I have to get this sorted out asap, as well as a few other bugs...

[barnett468 418]

are the rears drums?

 

if they are drums they are possubky adjusted too tight or the shoes sare installed incorrectly . . the shorter one ir the one with the beveled edge on top goes in front.

 

i would check the clearance between the master rod and the master cylinder . . the clearance is around .015 - .040 with the smaller clearance being better.

 

the fluid may not be returning either for some reason.

[TeamPontiac79 12]

Yes, rears are original drums, untouched during front disc conversion and were working properly before. I've been sitting around doing research for a couple hours, and it seems all evidence points to the pushrod being adjusted too long. I'm going to check it as soon as the weather is agreeable enough, which right now looks like Saturday.

[Rsanter 152]

Have you talked with them?

They should at least talk about possible issues with you for free

 

Bob

[69NC 21]

For drum brakes there is a residual pressure valve that is usually in the distribution block, which may have been replaced by a portioning valve to adjust between the disks on frint and the drums in hte rear.  I would also check for this.  Also if you had drums in the front andother thing to check is if they did change out to remove the residual pressure valve form the front. If not, then the fronts may be what are draging as disks do not need any residual pressure.

[TeamPontiac79 12]

The drum/drum brake distribution/proportioning valve was replaced with a brand new high quality repro disc/drums combo valve. I don't think that would be the problem in this case. I was going for a full on factory setup so as to avoid issues in the future.

[TeamPontiac79 12]

Bob, I haven't talked with them. In truth, I have found communicating with them to be a most frustrating chore. These guys don't seem to have a concept of a budget or of what's right and wrong. I don't think I want to go back even if it was their fault. I wish I felt differently, but the more I think back on this and previous dealings with them, the more strongly I feel I don't want to take my car there again.

[SA69mach 39]

Are you sure you have the correct disc/drum master cylinder?

 

Can you post a picture of your master and booster in place. Ford setup is larger rear reservoir, which is for the front disc brakes, with a smaller front reservoir, for the rear drums. check you have the correct lines attached to the appropriate reservoirs.

 

Check the rear flex lines (hoses) Both the feed lines to the drum and the flex line to the block on the diff. Collapsed lines or worn fittings may cause a problem with brake fluid return, which can cause binding.

 

Check for any damage dings or kinks in the hard line from reservoir under the car, down to the flex line.

 

check for heat in both sides, see if the binding is occurring with both sides.

[TeamPontiac79 12]

Hi All, the problem turned out to be the booster push rod was adjusted too long. I had hoped that my professional installer would not have made a mistake like that, but that's life I guess. Car seems to be stopping good now. Thanks for the advice.

[1969_Mach1 333]

are the rears drums?

 

if they are drums they are possubky adjusted too tight or the shoes sare installed incorrectly . . the shorter one ir the one with the beveled edge on top goes in front.

 

i would check the clearance between the master rod and the master cylinder . . the clearance is around .015 - .040 with the smaller clearance being better.

 

the fluid may not be returning either for some reason.

 

If you haven't done so, check the items barnett468 mentioned.  I have had both occur at different times a long time ago in high school causing your issues.  Rear drum brakes initially adjusted too tight and they just got tighter and slightly burned the new linings.  And, on another incident I adjusted the master cylinder push rod slightly too long and the brakes would drag after driving the car a while.

[TeamPontiac79 12]

Yep, all other suggested things have been or already were checked. The entire brake system is essentially new including steel lines and hoses. I've put a few trips on her already since adjusting the push rod, and no problems noted. The pushrod was adjusted long enough that it was pushing on the master as it was being installed. I don't know how these guys made a mistake like that, but they did. She's stopping good now.