Rear Brake Trouble

[70NewY’ER]

Hello all. I have a '68 Newport with drum brakes all around. 2 3/4" up front and 2 1/2" in the rear. I had the brakes redone about a year ago. New master, wheel cylinders, hoses, shoes, hardware, wheel bearings, etc. I noticed that whenever I would take the car out for a drive, the rear drums got wayyy too hot (about 300 degrees F. on both). So, I figured maybe the problem was related to the proportioning valve, so I found an NOS P.V. on Hiltop Auto Parts and replaced the old one. Brakes still got hot in the rear. After that I thought it could be the drums and shoes, so I replaced them. Shoes are from Powerstop, and the drums are from Raybestos. Still very hot. The wheel bearings don't seem to be getting hot either. The major heat is coming from the shoes and the drums. I thought of everything and can't seem to figure out the problem. Not even my local mechanic can figure it out. Could the master cylinder be absorbing some engine heat and causing problems? Bent axle and/or flange? I have the car registered for the upcoming Chryslers at Carlisle event and I'd like to get this sorted out before going. I'm not an expert so any help on the matter would be greatly appreciated. Thank you!!

 

[Boydsdodge]

Check your master cylinder push rod depth, are the shoes installed correctly? Not reversed.
Have the drums been turned to be true?

 

[Big_John]

First, there is no proportioning valve in a '68 Chrysler. So, if you paid someone to replace a proportioning valve, or they told you that was the problem, find someone else to work on your cars. There is a "safety switch" that both lines run into that lights the brake light on the dash if the front or rear hydraulic lines should break.

As far as your problem, was the rear brake hose replaced? My money is on the hose is old or damaged and restricting flow back to the master cylinder. Even if new, that can happen if the hose gets stretched or otherwise damaged. Another possibility is the master cylinder push rod is adjusted incorrectly, being too deep in the MC and not letting it release.

 

[Big_John]

While I'm not going to suggest buying from this guy, he has some good videos.

 

['66 Fury I]

Big John covered my ideas (and more), but I would add the parking brake. If it is not releasing completely, it could allow the self adjusters to over-adjust. Lindsay

 

[CBODY67]

ONLY power disc front/drum brakes rear cars have proportioning (or similar) valves. Drum brake cars do the proportioning between the front and rear with a combination of master cyl bore diameter, wheel cyl bore diameters, brake shoe width differences, and a few other things related top "hydraulic mechanics" dynamics.

Common to both drum and power disc brake cars is the pressure bias switch which causes the "BRAKE" light to illuminate when one end's brake fluid is lost, making the switch go "off-center".

Other than what @Big_John mentioned, I might suspect that with the commonality of the heat, that possibly a good place to look might be the rear brake shoe adjustment itself. Especially on the rear brakes where the wheels will not manually spin as easily as the front wheel can in checking to see if the linings are dragging or not. Which is where a brake drum/brake lining caliper might come in handy, for the initial adjustment.

Also check the parking brake cable adjustment AND to ensure that until the parking brake pedal makes a few clicks bEFORE the rear brakes start to apply that way.

IF all of those things check out fine, then look at the fluid level in that end of the master cyl AND the condition of the rubber diaphram on the master cyl's top. It should be flat and normal. IF it has swelled and expanded, they some "foreign liquid" might have possibly found its way into that end of the master cyl. Which THEN means a flush and replacement of the affected wheel cyls, hoses, and maybe even the master cyl itself.

Check the simple things first, if nothing found there, then go deeper.

Please keep us posted on your progress,
CBODY67

 

[70NewY’ER]

Boydsdodge, I had the original drums cut to true recently but I opted to go with new drums that I ordered about a week ago. Shoes are, to my knowledge, installed correctly (shoe with more material faces the rear, shoe with less faces the front). I haven't checked the push rod. I will have to read my manual for the specifications. Thanks for the tip. Big_John, I replaced the rear brake hose twice with the same results, but who knows with these chinese parts. Also, I think I have my terminology mixed up here. I had the distribution block replaced up front, not the proportioning valve. My apologies. If I'm still wrong, please let me know. I'll leave a picture to show everyone what I'm referring to:

It's not a picture of my car, but it's a good general representation. As for the parking brake, I had it readjusted a little while back and was told it wasn't causing any dragging. I will dig a little deeper and see how to adjust it on my own. I'm going to readjust the shoes tomorrow, so hopefully that fixes everything. I definitely could've adjusted them incorrectly. I will also check the condition of the master cylinder/fluid level and see what's up with that. I do have a spare in the event that it went bad. Hopefully I'll have some updates sometime tomorrow or the next day. Thanks for all of the info everyone!

 

[mrfury68]

Make sure the self adjusters are on the appropriate side. If not, your brake shoes will be adjusting out as you drive.

 

[70NewY’ER]

Make sure the self adjusters are on the appropriate side. If not, your brake shoes will be adjusting out as you drive.

I believe they are. I’ll show some pictures to confirm:

 

[halifaxhops]

I would make sure when they are adjusted, they do not drag on the drums. Bet @mobileparts has the answer.

 

[rags]

e-brake lever on the right side is in the applied position. gap between shoe and lever in picture. lever on the left side is released, lever is behind the shoe. return springs could be wrapped around the stop a little better!

 

[Big_John]

e-brake lever on the right side is in the applied position. gap between shoe and lever in picture. lever on the left side is released, lever is behind the shoe. return springs could be wrapped around the stop a little better!

^This^.

 

[70NewY’ER]

e-brake lever on the right side is in the applied position. gap between shoe and lever in picture. lever on the left side is released, lever is behind the shoe. return springs could be wrapped around the stop a little better!

Interesting. Looks like I’ll have to loosen that side up a bit. Never done it before so it’ll be a learning experience. Shouldn’t be too hard. I struggled to get those springs on that darn stop! I noticed that both of the wheel cylinders were acting as if they were slightly applied while trying to put the springs back on. Is that normal?

 

[rags]

Is that normal?

yes, they'll retract.

Looks like I’ll have to loosen that side up a bit.

more a matter of a frozen brake cable.

I struggled to get those springs on that darn stop!

do yourself a big favor and get a pair of these snap-on brake pliers:

 

[70NewY’ER]

yes, they'll retract.

more a matter of a frozen brake cable.

do yourself a big favor and get a pair of these snap-on brake pliers:View attachment 595781

That tool looks very handy. I’ll have to get one for next time. Is there a way to free up a frozen cable? If not, I’m assuming to just replace it. I’m not sure where I read this (shop manual maybe), but is it true that the front cable is a different adjustment from the rear 2?

 

[rags]

front cable is a different adjustment from the rear 2?

it's one system of cables. the one adjustment is for the e-brake system. back it off so the e-brake levers in the drums are completely retracted. put the drums on. do the service brake adjustment, then the e-brake adjustment. apply the e-brake a couple of times to center the shoes in the drum, then recheck the service brake adjustment. don't go nuts over tightening service brake adjustment.

Is there a way to free up a frozen cable?

not beyond the range of possibility, but how desperate are you? just **** can it. check both. the other could be frozen solid in the retracted position.

That tool looks very handy.

normally i would never recommend snap-on hand tools due to the price, but that one's worth every cent. check the second hand market. puts that brake assy. together in minute.

 

[rags]

Is that normal?

wanted to point out that the wheel cyls. retracting easily indicates that fluid is returning to the master cyl. in turn that means the brake pedal/booster is releasing properly.

 

[70NewY’ER]

it's one system of cables. the one adjustment is for the e-brake system. back it off so the e-brake levers in the drums are completely retracted. put the drums on. do the service brake adjustment, then the e-brake adjustment. apply the e-brake a couple of times to center the shoes in the drum, then recheck the service brake adjustment. don't go nuts over tightening service brake adjustment.

not beyond the range of possibility, but how desperate are you? just **** can it. check both. the other could be frozen solid in the retracted position.

normally i would never recommend snap-on hand tools due to the price, but that one's worth every cent. check the second hand market. puts that brake assy. together in minute.

Ok cool I’ll have to give that a shot. If they’re stuck I can always just replace them. I didn’t know they were readily available so that’s nice. I’ll start there and see if that fixes the problem

 

[70NewY’ER]

UPDATE:
I took the car over to the mechanic shop and he found a slight bend in the passenger rear axle shaft. That would probably be the cause of my problems. I will still give some attention to the older parking brake cables/adjustments just to be safe. I’ve been looking at a set of Nitro axle shafts and bearings. Does anyone have a brand that they trust more?

 

[USSMOPAR]

Your mechanic needs help
The brake shoe springs are very worn out!!!!!!!!!! REPLACE
The emergency brake adjustment is critical Pay attention!
It's not the prop valve unless it's leaking
When the drums are cut the shoes have to be arced on a special fixture to match the radius of the drum. The lining material should be a modern material not asbestos.
Do not listen to the curmudgeons when it comes to lining materials