1970 Road Runner with Power Disc Front Brakes Locked

[Dragon Slayer]

Working through my recently acquired 1970 Road Runner. It came with Factory Power assist disc brakes on the front. Look all original. The rear was upgraded to a Dana 60 so it has the 11 inch Drums. Despite 2 successful test drives before purchase, the car locked up after unloading from the trailer and trying to put in the garage. Wouldn't budge. Jacked the front end an know both front brakes were locked. Not sure about rear. Did not clear after sitting for 2 hrs. So I bled about 1/2 to 1 oz off the front passenger caliper and every thing released. I know I have to get into all 4 wheels to inspect, etc... Curious if this is a master cylinder type issue, or the distribution valve/proportioner? G

 

[68GTX440]

Has the M/C been replaced?
If so or you are not sure pull the brake line off the master cylinder for the front brakes. Look inside and see if you have a brass insert. If you do pull it out and check again.

Working through my recently acquired 1970 Road Runner. It came with Factory Power assist disc brakes on the front. Look all original. The rear was upgraded to a Dana 60 so it has the 11 inch Drums. Despite 2 successful test drives before purchase, the car locked up after unloading from the trailer and trying to put in the garage. Wouldn't budge. Jacked the front end an know both front brakes were locked. Not sure about rear. Did not clear after sitting for 2 hrs. So I bled about 1/2 to 1 oz off the front passenger caliper and every thing released. I know I have to get into all 4 wheels to inspect, etc... Curious if this is a master cylinder type issue, or the distribution valve/proportioner? G

 

[Dragon Slayer]

Ok, Have worked through this some more. Bleed back brakes and they look relatively new with Wagner Lockheed wheel cylinders that also look new. No automatic adjusters on this, but they are the 11" drums on a DANA 60 that the casting and date codes indicate a 1969 B body. When I got to the front, the reservoir had a milky appearance, and realizing the cap had swelled up, I immediately sucked the fluid out of the front. The owner said he topped off the front. It must not have been brake fluid. I than bleed the front passenger. It was hard to get fluid out, but I did. When I moved to the driver wheel, I could not get fluid out except a small amount. The pedal is rock solid even if I start the car and draw vacuum. Rotors are hard to turn until I cracked the bleed valve. So I decided to pull Master Cylinder after draining fluid. It is an original Bendix with cast # 2226821 with a 019 B date code? Once the master cylinder is off, the pedal had more travel, which at least told me I didn't have a mechanical issue with pedal. The master cylinder piston can be compressed, but it did not return full, unless I pressed down and released fast to get it to snap back. I guess the MC may not have returned and pressure was locked on. At this point I have new front brake lines, hoses and valves coming along with a new Centrix Master Cylinder. Where can I get a rebuild kit for the Bendix MC? How does the piston come out on this model. I removed the plug, do I need to remove the brass fittings in the outlet ports? Thanks in advance. G

 

[68GTX440]

Here is some diagrams for you. Hope this helps.

 

[Dragon Slayer]

Thank you. I did get the piston out. After I realized it was stuck I was able to push and release quickly to get it to pop out partially. Used ring pliers that open to grip internal of plunger and pull out. So how about a rebuild kit for this, and sources? It is 1.125" bore. G

 

[68GTX440]

Have you tried Napa? Do yo have an old brick and mortar mom and pops parts store in your area?

 

[Dragon Slayer]

Yes, Tried NAPA, O' Reilly, AA, AZ, PartsGeek, Rockport, Bendix site, centric site and about 100 pages of google searches. Closest I have found is a 1" bore kit. Seems that most are moving away from MC rebuild kits since the remanufactured or even new are a few dollars more. Hoping some one had an old Bendix or Mopar catalog with part numbers, or a source for kits/seals. Without a specific part number hard to even tell if the stuff on ebay will work. G

 

[AMX364]

The oil that was added to the brake fluid does bad things to rubber seals. Might also have to replace brake valve also, but I would wait and see if that item is needed. Rear brakes seem to be OK, so it appears to be only the disc brake side needs work.

Good luck on your hunt!

 

[mobileparts]

That master cylinder kit has NOT been packaged by any company now in over ten years.... I have about 7 or 8 of those kits remaining and will have them with me at Chryslers @ Carlisle..... are you going???? I have the master cylinder --- brand new --- and those last 7 or 8 kits --- a rebuilt OEM MOPAR master cylinder is worth considerably more than my reproduction / aftermarket BRAND NEW!!!!!!!!!!!!!
Call me --- Craig -- 516 - 485 - 1935... New York...... will be at h107 - H108 at Chryslers @ Carlisle......

 

[Meep-Meep]

My 71 Ford truck had the same issue and it turned out the hold off valve in the front brake line was acting like a check valve.

 

[Dragon Slayer]

Thanks guys. At this point I have new brake lines and hoses and the 3 valve set installed. Also replacing calipers. The passenger side is definitely stuck and I found corrosion and gunk inside when I popped the piston out. Still finding all original parts with KH markings and date codes on the valve set. This has been a interesting learning experience. Craig I will give you a call. G