More troubles with new master cylinder

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Walker434

Walker434

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I ordered a new dr drift 1 15/16 master cylinder for my 71 Dart. Manual drum brakes on all 4 corners. Had a really rough time bleeding brakes after install but finally got all the air out. Now, after some test drives my rear brakes get way too tight, so bad the drivers side was smoking. After looking into it, I thought maybe the self adjusters weren't working right so yesterday I removed them, manually adjusted the rears and took it for a drive. After a short drive I could tell the rear brakes were Not releasing correctly.

I was so stumped I called my Dad to come look for some help. He says the rear shoes aren't returning to the the anchor pin which makes him think the master cylinder isn't letting the brake fluid return to the MC. Does that make sense to you guys? Anyone else had this issue? I'm going to call Cass at Dr Diff today but just thought I'd see if anyone has any other ideas. Thanks in advance for any help.
 
I had bought the adjustable push rod from Cass as well as master. When I installed the adjustable push rod I had it extended too far not letting the brakes release. Your push rod may not be backing off and not allowing the brakes to release.
 
lilnoah said:
I had bought the adjustable push rod from Cass as well as master. When I installed the adjustable push rod I had it extended too far not letting the brakes release. Your push rod may not be backing off and not allowing the brakes to release.
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I am running my original push rod. So you are saying I may need to order the adjustable one from Dr. Diff? Thanks for the quick reply by the way.
 
Another member recently discovered his brake lamp switch adjustment was preventing the master/push rod full return. Adjustable rod wasn't required. Only finding the bolt where that switch bracket adjusts was the cure.
 
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First check your brake pedal to see why it can't return and let your brakes loose. It could be brake switch. It only takes a fraction to allow your brakes to release.
 
If the push rod is putting any pressure on the back of the master cylinder piston your brakes will run hot (stay engaged). I had the same problem until someone suggested that I remove the master cylinder and make sure that there was at least 1/32" between the push rod and the piston. It can be less than 1/32" but it shouldn't touch.

treblig
 
Another issue to check, and I know this from personal experience, make sure that little rubber ring on the brake rod is fully inserted into the end of the master cylinder piston. I thought mine was but it was only partially inserted making my brake pedal look normal but holding the piston in just enough to keep pressure on the rear brakes. I had to pull the MC and used KY Jelly on the rubber (no pun intended) and it slipped right in (that's what she said)!
 
mopardude62 said:
Another issue to check, and I know this from personal experience, make sure that little rubber ring on the brake rod is fully inserted into the end of the master cylinder piston. I thought mine was but it was only partially inserted making my brake pedal look normal but holding the piston in just enough to keep pressure on the rear brakes. I had to pull the MC and used KY Jelly on the rubber (no pun intended) and it slipped right in (that's what she said)!
Click to expand...

Ha! Another use for my KY Jelly! Okay thanks for the replies. I'm going to check into these things this week when it get time. Thanks FABO, I'll post back the results when I figure out what's wrong.
 
Know this... If you go under the dash, separate the rod from the pedal and pull that rod hard enough... you might pull the master cylinder apart ( this was seen in a recent thread too ). In most cases there's nothing more than a sheet metal finger/keeper holding the spool valve in the master cylinder. Combine significant pull with the internal return spring already applying some pressure against that finger/keeper. So anyway IF the rod with rubber ring was fully seated at the workbench, or even kicked in with the pedal, it's not likely the problem and pulling there can become a different larger problem. Good luck with it
 
Many people have reported similar, and not just w/ Dr Diff MC's. Indeed, I think they just sell the 1980's Dodge truck MC that you could buy at any auto parts, plus the 2-4 adapter plate. The brake lamp pedal switch should not prevent the pedal from moving fully back. Loosen or remove the switch while installing the MC. The pedal should be pushed back to where the MC wants to stop. That will expose the fill ports for both F & R, thus giving no resting pressure and thus no lock-up like you are experiencing. The only reason you should need an adjustable pedal rod is if you don't like where the pedal sits. View photos to see where it should sit relative to the accelerator pedal. Of course, if you drive w/ 2 feet (recommended today w/ an automatic), the pedals don't need to align.
 
Found my problem and it had nothing to do with the master cylinder. My dumb *** didn't replace my rear brake hose when installed my 8 3/4 rear a few years ago. Hose was the original 1971 unit. $15 replacement hose and its fixed.
 
That too. In old hoses, chunks of rubber or flaps come loose internally and can act like a check valve. Old hoses can also rupture. Not here, but have read of it on a M-B forum.
 
FWIW, my master cylinders are NOT the common 1 1/8" bore truck units.

In fact, I'm the ONLY source for aluminum 15/16" bore manual brake master cylinders. These are my own product.
 
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