Dodge RM400 brake job pointers..?

[Old Man Powell]

Gonna dive into the brakes tomorrow. Did a lot of research here and got a lot of good info. Right now the brakes are squishy and definitely not up to par. They do come up if I pump them but obviously not in the condition they should be. When I first checked the brakes one side of the reservoir was pretty much empty but the other wasn't bad. So, of course I have air in the lines. And even more of a "of course," both of the front bleed valves are frozen and stripped. I'll deal with that. I have sprayed them plus the rear bleed valves with PB Blaster several times over the last 4 days. I have ideas for getting them loose but am always open to more suggestions.

Assuming I get all the bleeders working, I will bleed the entire system. I have yet to find the bleeders on the two boosters but I will find them. If I have problems getting them open will I still see improvements by bleeding all the other "components?" Will it be a "moot point," so to speak?

Next will be front pads. No idea how old they are so will look for cracks. They do seem to bite just fine. Rotors luckily look wonderful. Not a single "ridge" of any sort on either one. I see absolutely no reason to mess with them.

I'm assuming I have a leaking wheel cylinder, or four, which is why the reservoir was down. But I know it could be other things like the boosters. Geoff at ATP is out for a two week vacation. I caught him the day he was leaving so i didn't order any parts then. For the time being we are going to jack up the rear end... listen for anything frightful... spin the wheel and make sure the brakes are at least engaging. Maybe even pull the "plugs" off the back and see if I can adjust myself. Without new grease seals on hand I'm not gonna tear into the actual brakes themselves.

I did a quick check of all the vacuum lines and brake lines and everything appears good. i was actually imnpressed with the vacuum lines... no cracking or dry rot at all. Will perform more indept look tomorrow.

Any other suggestions or pointers?

[Stripe]

Have you gone through Daves' Place?  http://dave78chieftain.zxq.net/DodgeRBrake.html

[legomybago]

Was it the rear system that was really low or dry in the MC? How long did the house just sit?? Brake wheel cylinders go to crap from sitting. EVERYONE SHOULD GO OUT AND PUMP THERE BRAKES ATLEAST ONCE A MONTH IF NOT EVERY COUPLE WEEKS, JUST TO KEEP THE SYSTEM UP. Not sure what Hydrovacs you have, but the bleeder is usually on top, about midship. I've always had great luck using a 6-point 1/4" drive socket to brake tight bleed zurks loose (wrenches can strip them easily)..If that socket strips the zurk, then you have issues...break out the small good pair of vice grips!

[DaveVA78Chieftain]

From my site: http://dave78chieftain.zxq.net/M500_73-75-RM400.html

This picture also applies to your M500 (RM400)


Your can see the bleeder valve on the booster on the left side


Service manual drawing (Page 5-52):


Dave

[legomybago]

Nice Pics Dave..

Those hydrovacs are another source for break issues too..they sit and collect moisture, then pit and rust.

Something to always remember with a hydrovac is: If you have "power" brakes, then your booster is working fine...but they can leak brake fluid into the inside of there vacuum diaphram housing, making for "mystery brake fluid loss" out of your MC. Always bleed the hydrovacs before bleeding your wheel cylinders..

[Oz]

If you bleed only part of the system, you may see some improvement, but you may see none, if there's air in the other components.  From the sounds of it though, "squishy" would generally say the fluid is old (will be very brown when you bleed the brakes) and you may have some air in the lines.  To start, just purge the whole system and replace all the fluid with new.  It takes some time, but the results are incredible!

Be sure not to let the fluid go too low in the reservoir or you'll be starting all over again.

[Old Man Powell]

Found the bleeders for both boosters. One is going to be a pain... it's practically against a cross member. Got both sprayed down. I did the test of pressing on the peddle and then starting the engine. Luckily the brake peddle went down like it sounds like it is supposed to do. Feeling a little better! Hope i'm not being overly optimistic but I really think about 90% of my problem is old fluid and air in the line. I'm sure I'll be replacing some wheel cylinders soon though.

Again, rotors look awesome and the front pads still have one season driving left, best I can tell without diffing into the front.

I have backed Rooster up a few times and hit the brakes. You can feel the thing rock back like the rear brakes are working... just not real well! I will try manually adjusting after bleeding. Luckily the rear bleeders are in great shape... have not been rounded. May be a different story once I try breaking them loose. Of course there is not enough room to get a socket on them. Looks like I'll be using my dad's brake/hydraulic wrenches.

Question... the part of the MC that was empty was the back reservoir... the smaller one. Is that for the back brakes? I know it's backwards, so to speak, from a typical MC in a car (basically rotated 180 degrees) but it has always been my experience that the "front" reservoir, the smaller one, is for the front brake. Is this the opposite... which say the wheel cylinders are in fact leaking.

Know what I mean Vern?

[DaveVA78Chieftain]

Again, from my site (http://dave78chieftain.zxq.net/MCBendixDual.html)

The residual valve shown on this diagram is required to maintain light hydraulic pressure in the rear wheel drum brake hydraulic system to keep the wheel cylinder piston cups sealed against the piston bore during "off brake" periods.

Dave

[Old Man Powell]

Okay... so Rooster now has brakes. Was able to bleed the entire system, including the boosters which I was afraid I wouldn't be able to do. Definitely removed some old, nasty fluid and a lot of air bubbles.

Now, when I hit the brake peddle it does go down quite a bit before the brakes "engage," but once they do enggage I have some serious stopping power. If I pump the brake one time I have the same stopping power but the peddle does not have to go down as far. So, same stopping power, just less peddle travel.

The only thing I noticed is that when I let go of the peddle after being at a stop, it takes a fraction of a second for the brakes to let go even when the peddle is all the way up. Should I be concerned?

I noticed the front seal of the master cylinder, the seal around the rod, is seeping a little fluid so I will replace the master cylinder. Also, the front lines to both calipers need replaced. Not cracked but definitely erroding.

When I back up and hit the brakes there is no doubt the back brakes are working... the front end comes up and you immediately stop!

Other than the very, very minor seepage around the master cylnder seal I saw no signs of leaks. I even cheacked the vacuum lines for the booster and saw no fluid "blow by" what so ever. I was very pleased with that. I am still going to assume it's a wheel cylinder. Other than the new master cylinder, brake line and some new front pads, I don't see the need to do anything else aqt the moment. I will contiue to mmonitor the fluid level and check for leaks. And of course be concious of the brakes themselves. I'm thinking next year new wheel cylinders and shoes. Thoughts?

Once finished with the brakes I changed the 4-5 year old oil in the engine and generator. While doing that my neighbor got on the roof and looked at the A/C capacitors. Said the "start up" capacitor is definitely shot. The other was fine. He has already found a replacement one made by the same complany online. Woo hoo!

Of course, after changing the oil I fired the engine up and waited for the oil pressure to come up. Nothing! The wire to the sensor was off. Put a new conncetor on it cause the old was shot and the wire was corroded. Well, still nothing. I know it worked before. However, no idea if it stopped right before I changed the oil or when. Engine is fine.. no knocks or running cool. Oil pump is pumping. It's always something!

[legomybago]

Sounds like you still have some air in the system with your peddle action. Did you get the rears adjusted? The dragging brake should be looked at.

[DaveVA78Chieftain]

Now, when I hit the brake peddle it does go down quite a bit before the brakes "engage," but once they do enggage I have some serious stopping power.

Brakes should begin to engage within an inch of peddle travel.  If not then either there is still air in the line or the peddle may need adjustment

Dragging brake may be:
Rusty caliper runway
Front rubber hose starting to deteriate such that a section has dropping down like a flap valve resulting in slow return of fluid to booster master cylinder.
Booster binding up not allowing vacuum to bleed off.
Binding rear brakes
Rear Brakes not adjusted properly

Dave

[Old Man Powell]

We didn't try manually adjusting the brakes. Sounds like I should. Once I get the new master cylinder and front lines I will re-bleed entire system and try manually adjusting rear brakes. Thanks for the info guys!

Would you agree the booster are working correctly from the info I provided? I was really worried about that! They seem fine. Passed the test of putting pressure on pedal and starting engine. Bleed fine too.

I wonder if I still have air in the system due to one of the master sylinder reservoirs going dry, so to speak, when I first checked the level before bringing it home. While bleeding system (there was 3 of us) the person in charge of checking the maste cylinder level accicdentally let the reversvoir empty all the way a couple of times... D'oh! To properly bleed the system we should have started with the master cylinder. I fgured I was going to replace it so I didn't really want to mess with it at the time. Always learning from my mistakes!

[Old Man Powell]

Sorry Dave... just re-read your reply. I skippedm right over where you said a booster might be binding up. Any suggestions on how to tell if that is the casuse of the problem?

[DaveVA78Chieftain]

Running reservoir dry while bleeding only means air gets in the line.  I would not expect any damage from it
Other than watching how a brake assembly reacts I am not sure.

With a dual booster setup it can sometimes be daunting to identify if the issue is in front or year system.  Here is an isolation process for that if you need it.
Brake Troubleshooting Guide

Dave