Overheating rear end

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63valiant

63valiant

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Hey all, I have what I think is an odd problem. Back in '92 I swapped in a 7.25 axle from a '66 V8 Valiant into my slant six '63 Valiant.
It turned out the hubs on both sides were bent, not real bad, but if you put it up on jacks and ran it you could see noticeable run out.

In the years since then I picked up another 7.25 out of a '66 V8 Valiant with straight hubs/shafts. Recently I finally got around to working on it. Instead of swapping the entire axle I opted to swap just the shafts as it would give me a chance to put the 9" brakes back on. Both V8 cars had 10" brakes, and 10 on the rear with 9 on the front kind of sucked, lol

Everything seemed to go smoothly, no issues with swapping them out and I only reused the 9" drums. Shoes, hardware, master and wheel cylinders, all new.
The problem I'm having is the rear brakes are running really hot. Even melted one of the plugs for the star wheel. So I figure the brakes are dragging, jack it up, no drag, they freewheel nicely. Wheel bearings have no excess slack in them, fluid level is fine, e-brake cable has plenty of slack in it, I did put the primary shoes in the proper position. Everything checks out good, but they get hot. Pulled the drums off again, everything checks out fine. The brakes release after applying, car rolls well after coming to a stop.
RS rim is hot, LS rim is hot to where it almost burns to touch it, that's the side that melted the plug. Front ones feel fine, no abnormal temps noted.

Today I drive the car for about 30-40 minutes then I take the temp gun to the wheels. The outside of the wheels, not the drums themselves. Both fronts are just past 100 degrees and feel okay to the touch.
LR was 185 and really hot to touch
RR was 166 and hot to touch

LR axle tube was 113 and warm to touch, RR was cool to touch @ 100 even. Differential was at 132.

Going by these results obviously the heat is being generated in the brake/bearing areas since they are much hotter than the attached parts. Does anyone have any ideas what's going on here?

For extra data the front brakes aren't as new, but had been replaced in the recent past and are also adjusted properly. 9" drum in the front too.

TIA for any input
 
Ima thinkin.

In the meantime,
Are your rear tires and wheels matched in size?, and
what are your tire pressure back there? and
have you done a 4-wheel alignment to make sure both of the rear wheels are parallel to the centerline of the car? and
Ok my brain is waking up
You said;
"I only reused the 9" drums. Shoes, hardware, master and wheel cylinders, all new."
My guess is that you also swapped on, the 9" backing plates.
You didn't mention unusual noise, so my guess is that the sides of the shoes are NOT rubbing on the drums, as if
the shoes were the wrong width, or
the backing plates were the wrong offset,
or the axle "hubs" were too short, or
Somehow the axles went in, too deep into the tubes.
or simplest of all, the drums are just shaped wrong.
 
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I had the same type issue after my 8 3/4 swap.

  • Do you have power brakes?
  • I assume this did not happen with the old not true axles
All of your temps are not that outrageous but being different side to side is concerning. BUT if one side was working better than the other... (air in the line, shoes not adjusted enough)


Next time,

drive for 5-10 minutes somewhere you can stop without using the brake (and try not using the brake along the way) like a slight uphill coast to a stop and
  1. measure the housing right behind where the backing plate attaches IE where the bearing sits in the housing on both sides
  2. measure the drum its self both sides, pick a spot the same on both sides
  3. measure the center of the axle visible with the hubcaps off

Some odd things that can happen

  1. the housing is bent up / down OR fore / aft.
  2. the bearings should not rotate completely freely, they are sealed bearings and are permanently lubed. if they are dry or damaged that will generate a lot of heat
  3. when you insert the axles do they seat fully or do the nuts pull them in? if there was an issue with axle length you might be pinching the bearing so to speak

in my case the shoes were 10" (new) while my drums were at or slightly over max, the adjusters would work fine but would end up too tight. I put the old shoes back in and everything is good now.
 
Oh yes, sorry, I did skip over the backing plate. I swapped in the 9" ones when I swapped the shafts.
Stock 13" rims, 34 psi. No alignment. No power brakes, stock single pot MC.
No unusual noises, no rubbing of any parts inside the drums. Shafts and bearings slid easily into place when installed.
This problem did not exist with the old setup. I bled the brakes with a pressure bleeder and pedal feels good, but I suppose there's no guarantee that the bleeding is 100%
I wonder if the bearings are dried out? I didn't know these were sealed bearings, I had assumed they got some oil from the tube, but didn't really pay much attention.
Sounds like an easy next step would be to swap the drums out and see if the hotter side moves with the drum to narrow it down any.
Thanks for the tips guys, gives me more to check out, I'll keep at it
 
If the brakes got hot enough to melt the star wheel rubber, I very much doubt that was caused by 'hot' brgs. They would have seized up &/or be extremely noisy.
 
Imagine there is air in the rear system, close to a heat source; could that air expand enough to energize the wc's?
We know that drum brakes are self energizing. So, If the front shoe moves out enough to catch on the spinning drum, it could drive the rear one into the drum, just enough to drag.
By the time you get the corner jacked up, to check it, the air might have cooled, the w/c retracted, and you'd never catch it.
I mean just throwing stuff out there.

Easy test is to back off the rear adjusters so there is no possibility of dragging.
If you suspect air, I imagine a good place to look for it, is in the crossover line where the fluid goes uphill over the differential.

When I was younger, I would clamp the rear flex hose. But, if the line is old, it can come apart inside and act like a slow-release check-valve. That actually happened to me once on a front caliper. Sat on the side of the road for a bit, the brake released, and I drove straight home. The point is, that I don't clamp the flex hoses any more.

To accurately check for air, in hard cases, what I have done in the past, is to remove all the drums, and all the shoes, then C-clamp all the w/c's in such a manner that the pistons cannot come out. Thus the pedal, when you step on it, is high and hard, like a rock . Two or three rapid stomps on the pedal, should bring the pedal even higher. When you take your foot off the pedal, and wait for a few seconds, the fluid will return to the reservoir, and the pedal drop to normal height. There should not be any sponginess in the pedal.

I'm not saying that you need to go thru this procedure ..... yet. Because it is so time consuming, it's kindof a last resort. But, it is definitive. I've never had to do a drum/drum car; it's always been disc/drum, or disc/disc dual M/C system, in my line of work.
In your case, since the front is normal, and you have a single power-piston in the M/C, I imagine doing just the rear, might be sufficient.

One more thing worth mentioning;
is that hard lines sometimes rust from the inside, from moisture accumulation, and the rust forms in the lowest part of the system. I have seen that rust pocket also act like time-release check-valve. In my case, the M/C had enough hydraulic pressure, to push the fluid out, but the return springs were slow to return it thru the restrictive rust pocket. I my case, I just cut the bad section out, and stabbed in a jumper, all properly double-flared of course.
You can see this in action by removing the rear drums, ONE atta time, and watching the action while a helper slowly presses and releases the pedal. The normal action should be smooth and retraction as fast as application.

and finally, what if the front brakes are not braking, and the rears are doing all the work?
 
Still working on this, so bizarre to be having a difficult problem with such a simplistic system.
I have swapped drums from side to side, no change
Checked the drums, they are well within spec and do not appear warped.
Confirmed it is a brake issue, removed the rear brake hose and capped it off and drove around for a while, rear hubs stayed dead cold to the touch. Hooked the rears back up again, hot brakes returned.
Swapped out the shoes on the left side for some gently used ones of a different brand from another car, no change.
Brake adjustment is fine, ebrake is not too tight, in fact it's too loose, lol
I can spin the wheels freely, hit the brakes, release, and the wheels spin freely again, so they're not dragging.
Thanks for all of the suggestions guys, I think my next line of attack is to flush the system, put fresh fluid in, and give it a good bleeding again. Not really sure what to do beyond that.
 
Check that the adjusters are on the correct side. And that the primary and secondary are correct too
 
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