bizzare brake issue

Hello folks,
I have an interesting problem I have never experienced that has me stumped. Hoping someone may have experienced this and knows a solution.

Background info: 1974 CJ5, 11x2 manual drums all the way around. I have re plumbed the entire system. New master cylinder. New drums. New shoes. New front slaves. Aftermarket stainless braided hoses.

The last few days, after driving, my rear drums get HOT. Like blister your finger hot. So much that I can feel it slowing the N/A diesel with it's whopping 50-60HP way down, even at street speeds. First thought was star wheel out of adjustment. Let them cool, jacked rear up. Both wheels spin freely. If anything, a bit on the loose side of adjustment with almost no drag. Spin tires, and they lock up immediately when pressing pedal. Jacked up front, same thing. Spin free, stop immediately. Little drag.

When first assembled and driving, front pass would lock first. Adjusted, been fine until like I said the last week or so.

Kinda at a loss, and worried about having to replace an unavailable proportioning valve, which would mean re plumbing my nearly new system only a month into service.

Side note: Found a rare Kelly Safari Full Cab mounted on a '68 or older CJ6 at the local pick your part. Needs complete resto, some rot on doors and tub mounting flange areas, but in very good shape for age and in the rust belt. And, $140. Metal work this week, and need to source wiper motors/system. But absolutely love it. Only downside was adding almost 200 lbs to a already slow vehicle. Working on turbo'ing it

 

"I have re plumbed the entire system."

Maybe an incompatible parts mix-up? Is there a non-return valve somewhere in the system, or the brake master cylinder? Those are needed for discs but inappropriate for drums.

 

The Proportioning valve is a stock one, the nicer of the two I had from my CJ and the parts '74.
The master cyl. is from O'rielly I believe. Front port had "front" cast into it, so plumbed that way.
I had it mocked up differently, thats why the lines cross.

As I mentioned, when I first started driving it, the front passenger drum would lock first.



I REALLY wish I could figure out how to upload pics here and not links to pics.

 

If the brake return springs are installed correctly there job is to pull the shoes away from the drums..........in most cases a 10 lb. residual valve should be in the system to counteract the spring tension. Those valves could be either in the lines, Proportioning valve or built into the Master Cylinder if it is the correct one for Drums.........in either case it sounds as if the shoes are hanging up / dragging on the drum ?

Which I would then ask the question how did the arch in the shoe's once installed fit the ID in the Brake Drum? Back in the day most drum brake shoes were arched via a machine that cut the shoe's to fit the ID of the drum...........look and see if just the corner leading edge of the Shoe is what is showing the wear or heat.........Might get you closer to the problem.

 

The combination valve has only two functions. Its only braking-action function is to hold off the rear brakes some under emergency (panic) braking. This prevents rear lockup under the severe front-wheel weight transfer you have in a panic stop. In normal braking, it does nothing.

It also houses the switch for the brake warning light.

One option would be to replace the combination valve with a plain distribution block such as http://www.ebay.com/itm/67-70-Mopar...Brass-Block-Proportioning-Valve-/190820429717 plus an adjustable proportioning valve for the rear circuit http://www.ebay.com/itm/67-70-Mopar...Brass-Block-Proportioning-Valve-/190820429717

The combination valve on that page should also work as a replacement.

You don't want the disk/drum valve type valve, which has another holdoff stage that is not used with 4-wheel drums.

Read the section in the TSM about these valves. http://oljeep.com/gw/74_tsm/9-BrakesWheels.pdf I'm not adding any more content than what is described in the manual, other than pointing out the parts you might use.

 

Any residual valve will be in the master cylinder. If the OP used the original cylinder, or a replacement, he has the residual valves that he needs.

My shop says nobody arcs shoes any more. Last drum brake job I did, I had the drums turned and simply installed the shoes. If anything, the corners of a new shoe will be too far from the drum surface, as long as the shoes are properly adjusted. My guess is that the brake shoe bends to match the arc of the drum, since the hydraulics push on the ends of the shoe and the center will always be highest. Considering the forces involved, it's not unreasonable to expect the shoe to conform to the drum under severe braking, as long as the drum is not wildly oversized.

Another thing you can try is a shoe adjustment caliper. This is what the pros use. http://www.nationaltoolwarehouse.co...-P15928.aspx?gclid=CPiP8qLq08gCFZYXHwodsMQDBQ Once you have the shoes initially adjusted, the properly assembled and functioning automatic adjusters should snug up the shoes properly, if any addition snugging up is needed. Do the backing-up procedure in the FSM to assure proper adjustment.

 

Another comment - proper assembly is key. If you put things together wrong, the wheel that is mis-assembled will immediately start to de-adjust and get worse and worse.

The left and right sides are mirror images of each other, and the adjusters are also specific to the left or right sides. Also, you need to put the parts on oroented right with the front and back. If you look at the picture in the TSM, the left-right and front-rear are clearly shown. These brakes CAN be assembled both backwards and reversed.

Maybe you put everything together perfectly, but improper assembly of drum brakes happens a lot when the mechanic is not practiced at putting them together.

 

maybe your brake push rod is adjusted too far in? Back it off. Give yourself at least 1/4" free movement of the push rod at the master with the brake pedal return spring off before it starts to push the master cylinder piston.

 

If you can feel it slowing you down, but have zero drag when you spin it by hand, something isn't adding up.

Jack it up to see if there is drag when it is hot, as soon as you stop. If there's drag then and not when cool, you have a kinked or clogged line, too much residual pressure that eventually bleeds down, etc...

Are you 100% sure it's your brakes? And not other friction from a toasted wheel bearing or something grinding somewhere?

 

All great input, and appreciated, all.

But often an extra set of eyes ears and brains(or better yet, several) can illicit the answer. So again ty all for the help.

I am going to disassemble the rears tomorrow morn. Too beat now after work.

Those links ya shared are both for a disk/drum setup, Tim. But It may well come to this.

Pretty sure I followed the threads against the star wheel properly, threading outwards or "tighter into drums", the "easy" way on the star wheel.
Disassembled adjusters, lubed with anti seize, and worked in and out several times when installing new shoes drums and hardware.

Also fairly certain there isn't any adjustment on my brake pedal rod.

Most of the hardware and springs are new. Some was missing when I took it apart the first time. No rear equalizer bars installed, as one was missing. But 100% only for e brake.

Three new cables, but loose enough that they are not pulling at all.

Have a copy of this pdf, and a haynes, and a chiltons. Consulted all for assembly after what I found, despite some newer hardware and springs.

Brakes worked great for a few weeks, few hundred miles.

Rear slaves just about the only parts I didn't replace ne,. but I think PO replaced them. If I can't find much else, I might replace them for the $20 it would cost.
Brake lines are all new stainless braided, routed carefully, but I will check that, too if I can't find anything else. Came with new rear junction block.

Actually thought about that check, but didn't feel like dragging the jack out tonight. My personal gut feeling. Makes the most sense, if I can see anything dumb inside of the drums. Seems unlikely, but anything is possible atm.

The Master "Could" be wrong, somehow, but highly doubt it after hundreds of miles. May have failed.
I did check both reservoirs and about where I filled them to, last.

We shall see. Thanks again everyone for the food for thought. If ya can think of anything else to mention, please do.

I'll let ya know what happens...

 

If the master cylinder reservoir is overfull the brake fluid will/can expand with underhood rise in temperatures and cause the brakes to apply. When brake fluid cools down the brakes will then release. I'd double check assembly of everything and the master cylinder pushrod clearance also. Make sure no brake lines are routed close to a heat source like exhaust.

 

Forgot to mention, @ 1" pedal travel before brakes lock, while jacked up.

Both drums slid right off. Again, if anything too loose.

Passenger rear drum is getting so hot, steel slightly browned!!

Star wheels, all hardware, springs correct, near picture perfect. Springs are on tight side if anything, I didn't mention. When assembled, had to brace against my knee to install. Yellow, and blue springs. No weird wear patterns on drum, other than slight glazing. Nice symmetrical wear pattern centered on shoes.

Levels in Master are 1/2" below top of reservoirs, where I filled them to.

Rear brake hose is still nicely routed, plenty relaxed, flex dispersed, with no observable damage.

Bearings wore, sure, but nothing scary felt to feel is cause or warrant immediate R/R.

Convinced a return problem. Why I am confused.

Everything works perfectly untill @ 2-3 miles. Has to be heat related. Lines and master are far away from any exhaust.

In this pic, we can see the brake lines closest to any exhaust, is an inch below the pipe, to the fronts, under a well heat insulated flex pipe, on a diesel.
Under hood temps are as cold as I have ever felt on any vehicle I have ever touched. And that is hundreds of cars, trucks, medium and heavy diesel equipment, semis, and aircraft.

Little bragging, if I might.
Astute will notice no adapter plate between engine and bellhousing. Only a factory 1/8" backing plate. And my crowning pride, if one Googles the Isuzu diesel
engine code, 4f b1(no space), my engine is the #1 result pic.


Slaves are most likely culprit. Perhaps after a few hundred cycles, they are swelling enough from absorbed heat from drums that they start seizing in their bores. And they compound the situation, getting worse and worse. As both are the same age, and last thing that isn't brand new, the fact that one more so than the other, but both, enforces that theory, to me.

At this point I am doing another inspection of entire rear circuit. Might pop pistons out of rear slaves and see if there is damage, crud or rust in them.

 

This might be a stretch, but how are your grounds? I've seen poor grounding cause the brake likes be forced to act as ground straps and heat up, super-heating the fluid.

 

This is an excellent suggestion!

So bizarre I wouldn't think of it, but possible! Diesel warming to go to parts store. I will check line temp when there. TY!

 

This kind of brakes are what we head in the past, before the disc era. It is easy to control, except that it is boring!

When you put a big distance between the shoe and the drum, it should not heat! It should not brake perfectly, but it normally works.

Maybe the shoes are too thick? When you turn the wheel, it must turn freely.

There is obviouly something wrong somewhere!

Maybe it come from the transmission axle? No good to drive like this.

I repaired my drum brakes so many times in the past, I don't see why it becomes hot.

Of course you could drive with electric thermometers in somes places and check what happens, but we are not in a LE MANs race.

In my opinion, the truth will surge at one moment, there is a problem somewhere, but do not drive like this please!

 

It would actually only make sense when your lights are on or when starting. Otherwise, there isn't enough of a current draw to cause a problem.

I hope you figure it out. This type of thing is maddening. It will drive you insane trying to figure it out.

 

how old are the rubberbradided lines? recent? ive had a few issues with the line having a loose flap of rubber that acts like a check valve just an idea.

 

I had this exact problem on my Chevy

 

I R/R both rear slaves, and brake system working exactly as should!

And I bet the ones I took off only need a cleaning and gentle hone with some 400 to become good spares.

Thank you everyone for your concern, interest, and sound advice. Why I come here. Awesome people on the same team helping each other out.

Just
Empty
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jeep toss

 

So you think the wheel cylinder pistons were hanging in the bore enough to keep brake applied? Glad you have your brakes working again..