1972 Dodge m300, seems like back brakes aren't working.

[Winnebago Man]

Hello everyone,

It would appear that everybody is having trouble with there brakes right now haha. I don't want this to turn into a disk drum debate, I am quite ok with the drum brakes for my purpose.

When I got my 1972 Winnebago brave it was sitting for years and it had no brakes. I replaced the master cylinder first and bled the system. I went for a short drive and the pedal was very high and it stopped well. On the way back into the driveway it blew out a rear wheel cylinder. After that I replaced all of the wheel cylinders, hoses, hardware, and shoes. I adjusted the shoes properly and then bled the system again. This time the pedal sits much lower when applied than before. I bled the system again and went for another drive and it is the same. It does not feel spongy and there should be no air in the system. It stops quite well again, but it does feel like only the front brakes are working. There are dirt roads where my RV is and when you touch the brakes at a low speed the fronts lock up and it actually slide forward a few inches, and the front end totally nose dives, It does not seem like suspension. I know there is a combination valve on the frame that has the piece that closes off some brake pressure to the front or back in the event of brake failure. I could still bleed the back brakes fine so it doesn't make much sense to me. The return springs were broken on some of the shoes when I pulled the drums off. Possibly the would affect the height of the pedal before? It would be so nice to know how far the pedal was supposed to go down before to have a reference.
I hope this makes some sense. I have given everything a once over but I am kinda at a loss. Maybe someone with a similar model could tell me how far there brake pedal moves when it is applied.

Thank you
-Gavin

[Rickf1985]

Broken springs would make the pedal lower if anything because the shoes would not retract all the way. It sounds to me like you got the wrong wheel cylinders and they are a larger size than the old ones. Larger size requires more fluid hence the lower pedal. You say they are not spongy so that rules out air in the system. You also replaced the master cylinder, if the piston in the master cylinder is smaller than original then that will also give you a lower pedal.

[Winnebago Man]

Hello Rick, first thing I thought was the back wheel cylinders were incorrect also. I just looked up the part specs of what I bought again and It looks like I have the correct parts. When I bought the parts I cross referenced the original Dodge part numbers and this is what the specs say in the Dodge service manual. Those are the same with what I got.
The rig is not near me, but I need to double check again now that those rear shoes are adjusted properly.

Thank you.

Master cylinder bore: 1.125
Front wheel cylinders: 1.125
Rear wheel cylinders: 1.06

[Preese]

Gavin,
You did not mention adjusting the M300 rear brakes either manually or by backing up multiple times to re-set them.  Try that?  My self brake system rebuild effort worked for while (about half way down to apply max braking) but had to later take it to a local professional, turned out an rear drum adjuster had broken.  They fixed and now system works very nice, but just as always with drums stay about 10 car lengths behind (and I love my truck horn upgrade).
Paul

[Oz]

Yeah, totally forgot about that backing up thing.  First time I read about it, I did it and there was an immediate improvement!

[Winnebago Man]

Hello everyone. Problem solved, sometimes you over look the simplest things. I got to work on the winnebago the other day. It was the adjustment of the shoes on the rear brakes. When I did the brake job I though I had it close when I put it back together, but both of the back drums took many turns of the adjuster to get a good ajustment. The brake pedal sits about 2 inches higher now when depressed. I will do a final ajustment on all of the drums when I get it on the road.
Thank you for the help!

[Oz]

Awesome! Gotta love it when what seems like it might be a major project turns out to be a simple fix.