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No Rear Drum Brakes - 91' YJ - Please Help

10K views 37 replies 9 participants last post by  DREDnot 
#1 ·
Currently when my jeep is on jacks the rear wheels will not stop when the pedal is pushed. The wheels slow down but never stop. I will outline everything below that was done and what is new which is just about everything and yet there is still no rear brakes. I am no interested in doing a disc conversion and would like to find someone who has pretty good answer and not just a guess (no offense to anyone).

The Jeep just got out of the shop today from being there for 3 weeks with them not finding a solution. Luckily then waived my entire bill since the failed to fix the issue.

HERE IS WHAT IS NEW:
Master cylinder.
Proportioning valve
Wheel cylinders
Drums
Shoes
Springs
Brake Fluid
Booster (previous owner installed).

HERE IS WHAT WAS CHECKED:
Brake pressure was checked at the MC, After the proportioning valve & at the wheel cylinder: Pressure was consistent at 800 PSI.
Brake lines have been flushed and blown out confirming that there is no blockage.
Shoes have been adjusted to the proper specs and the wheel can not be hand turned when in N and brake is pressed.
There is NO water or air in the lines. 100% pure fluid.
There are NO leaks.
Spring and shoe config is set to the 91' yj diagram.


Suspected Issue:
Since everything is either new or tested good from the brake pedal to the wheel cylinder I am suspecting that there is something wrong with the shoe/spring configuration. Is is possible that the springs are causing too much resistance to the braking action requiring more pressure that does not exist to stop the wheel. This sounds like a long shot but what else When Not Hooked Up Properly can cause brake failure in the drum assembly?
 
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#2 ·
That's a weird issue, especially since everything is new.:confused:

So, when the vehicle is on jack stands, you're starting it and putting it in gear, and the rear brakes don't have enough force to stop the rear wheels?

How does the brake pedal feel? Does it firm up or sort of "squish"? Are you getting a good vacuum connection to the brake booster?

How does it behave on the the road? Any issues? If you brake hard, does it nose dive?

I'd try some hard brake stabs at low speed. You're proportioning valve may just be stuck. Some hard brake stabs should unstick it.
 
#3 ·
Have you double checked the lower shoe adjustment? There is a star nut that separates the lower end of the shoes. Usually this is adjusted automatically during normal driving. When you back up and brake it will turn slightly and adjust the shoes as they wear. If your gap between the shoes is too close, the shoes won't expand out enough by the wheel cylinder action to make proper contact with the drum.
 
#5 ·
The proportioning valve is new (OEM) just like the MC. As stated in my previous email, everything is new and or tests okay from the brake pedal all the way down to the wheel cylinder. There is nothing wrong with the booster, mc prop valve or brake lines. It has been check 6 or 7 times.

Yes, the shoes are adjusted properly.

If it is on stands and in D the wheel will spin and there is never enough force to stop them.

I have found some posts about this across the internet for different types of vehicles but nobody has a solution for it.
 
#8 ·
Keep in mind that the part numbers from 88 for drums are different than the 89 drums. Verify your year and part numbers/dimensions as stated above.

My only other suggestion would be to see if the cylinders will actually expand the shoes. Place a ratchet strap loosely around the shoes (to keep the cylinders from popping out) and hit the brakes gently (without breaking the strap).

Slightly aside, how do the front brakes feel? It sounds like they work fine, and you can eliminate the booster and master cylinder. 800 psi sounds like plenty of pressure but I haven't found any specs on it.
 
#14 ·
Update and replies for all contributors.

I checked the drums, shoes and backing plate and everything measures for 9" brakes. The backing plate is 10" which is what 9" brakes should fit on so I am told. Hence, 10" brakes need a 11" backing plate.

I was messing with them last night and I pressed the brake pedal lightly with the drum off to see the action. The leading shoe moves but the trailing shoe does not. I have heard that this can be normal as when the leading hits the drum then more pressure is distributed to the trailing and then that will move....I tried pulling the trailing shoe away from the cylinder by hand as if the cylinder was pushing it. I know that I maybe only got 10lbs if that of force on it but it does not budge. If I do the same on the leading shoe there is play on it.....With that being said, I disconnected the parking brake cable to relieve some tension and applied the brakes. Both shoes know started moving in a way which I would say is normal.

After about 3 light pumps on the pedal i lost all brake pressure and it went to the floor. I popped the hood and saw that the shop left the MC cap unlocked with the steel bar and brake fluid was everywhere on the bottom and the valve. Since I drop it about 10 miles I assumed that it was all spillage and the MC sucked in air.....So now I need to re bleed everything again to get at lease my front brakes back to normal.

BUT that question that I keep asking my self is: If the wheel cylinder has 800PSI of force that has been tested with a gauge....Then Where is all of that force being distributed to if NOT the drum?
 
#10 ·
This is what I was saying, but put a ratchet strap around the shoes or else the wheel cylinders will pop.
 
#11 ·
Like Mud Magnet & ABT said, Drums for a 91 are 9". Make sure you don't have 10" drums. I have a 91 jeep with a 87 donor rear end. 87 is a 10" drum. Big difference between the two. A picture of your set up would help. Verify the wheel cylinder wheel cylinder links are in and in the right spot on the shoes. Also you have a primary and secondary shoe. THE LARGER SHOE SHOULD BE TO THE BACK OF THE REAR END (Secondary shoe is the one with the most pad). Make sure those are correct.

Follow Mud's advise with strap for testing wheel cylinder. Hope you find your solution.

KMD
 
#12 ·
I'll try to make it as short as possible BUT....
I had a similar problem when I converted to Disk/disk. After a lot searching testing parts replacing and head scratching and finally sending rig off to a mechanic who spent 4 days scratching his head too, finally figured out.....

The New Crown double diaphram booster had the WRONG master cylinder (disk/drum) a shipping error.

I needed a disk/disk MC - once replaced and all is well.

Seems disks take more pressure and less volume and drums take more volume-less pressure, it's a matter of bore diameter (who new) . If your pressure is measuring 800 psi at both ends you MAY have the wrong MC (disk/disk and need disk/drum).

Something to investigate, good luck.
 
#15 ·
Shoes Sticking?

A older gentlemen at Autozone made a comment about something that if it was occurring then it would explain everything that is happening.

What is the possibility of the shoes getting stuck on the back of the backing plate if they perhaps wore down an area to a groove?

I guess I wont know until I pull everything off again and check it but it would be something the check.

The wheel cylinder gets 800psi, so WHERE is that pressure going? Solving that is the answer.
 
#16 ·
It's hard to say for certain without seeing the brakes in front of me, but it's definitely possible. That's the reason you never reuse hardware on disk brakes, since the pads will wear grooves in the hardware and can get stuck. Wranglers don't have this "hardware," per-say, except the grooves on the caliper bracket. If the shoes wear grooves into the plates, they'll be riding in those grooves.

If the shoes wore a groove in the backing plate, that pressure could simply be pressing against the backing plate rather than onto the drums. I would look into it more, it seems worth it.

Parts counter employees can be hit or miss, I've gotten some of the best advice (packing bearings, soaking lifters in oil for longer than suggested, etc) from them, and some of the worst advice from even the same employees.

But what else could it be? Hydraulics are good up to the cylinders, shoes are within contact range of the drums. It goes back to your original thought of the springs being stuck. The thing that surprises me is nobody here has had this issue.

Hope you solve this... I'm curious.
 
#17 ·
Yeah at this point I am exploring every possibility that is considered "uncommon or slim to none".

We know that the PSI is there its just a matter of finding where it is going. I am going to try and tear the brakes down tomorrow and inspect that backing plate. When I inspected the rear side of the backing plate tonight I did notice a difference in space between the plate lip and the edge of the drum from the top to the bottom. (hope that makes sense.)

It could be that the backing plates are bent which is causing the pads to stick against it.

I really hate to get my hopes up and say THIS IS IT until I know for sure but I am going to honest and say that this is the only theory that I can say with confidence that makes sense from the cause and effect standpoint.

Once I figure this out I am going to do an entire writeup on my blog about it because I have had so much trouble finding anyone else with the same issue and nobody has published a cause of solution.
 
#25 ·
The wheel cylinder looks old in the picture, maybe binding or stuck from contamination within? Backing plate bosses smooth and light lubricant? Possible shoes and/or drums on both sides contaminated with oil or lube?
 
#27 ·
Major Discovery

Today I did a reverse search for all vehicles that had the Dana 35 Axle installed on the rear along with all vehicles that used 538 brake Shoes. I found that Jeep was the only make that used the D-35 in the Rear across their wranglers, Cherokees, Grand Cherokees and Comanches.

The 2001 Jeep Cherokee has 9" brakes with 768 or 670 brake shoes. The backing plate on this looks identical to my 91' YJ except my YJ has 4 bolts on the backing plate and the Cherokee has 4. The wheel cylinders are the same for both.

The Jeep TJ later models were the only other model that that used the 768 brake shoe with 9" brakes.

After 4 weeks of research I found out that my 91 Jeep Wrangler YJ had a d-35 axle from a 2001 Jeep Cherokee with 9" brakes along with a backing plate made for a Cherokee with shoes installed for a 91 Wrangler. The backing plate on my jeep was stamped with the part number 2102 which returned no results in a search.

After installing the 768 shoes I regained about 50% more braking power and the parking brake worked for the first time. I also found a loose fitting at the rear brake distribution block which was sucking air but not leaking fluid. When bleeding the drivers side rear the fluid was fizzing prior to tightening the fitting.

My brakes are still not working in the rear 100% and the pedal has to go all the way to the floor to stop the wheels, and I mean you have to put all your might into the pedal. My idle speed changes when in P or N and when I press the brake. I am now suspecting a vacuum leak somewhere that I have not found. My Jeep has a 97 Cherokee engine in it (I6 4.0) If anyone has a vacuum system diagram that would be awesome!
 
#28 ·
I think I have either a 1999 or 2000 XJ FSM in my signature. That may help, though my friends with the 99 and 00 Jeeps said that vacuum only affects heater controls and cruise control. The info about the brake booster should be in the manual.
 
#29 ·
How'd you figure out about the 01 XJ axle? Does it look like the perches and bump stops were cut off and rewelded/rotated?

What application did you use when you bought the new booster? the new master cylinder? the new proportioning valve?

If I were you, I would have replaced the rubber line to the rear axle. I have run into a case where the inner lining of the rubber hose was delaminating and blocking flow in one direction like a flapper valve.

Your hissing sounds like a bad booster and your pedal to the floor sounds like a bad/incorrect master cylinder.
 
#30 ·
My brake system has no rubber tubing as it has all been replaced with braided line.

I did a reverse shoe search for the 538 brake shoe which was used across several Jeep models with the D-35. The only models that did not use the 538 that had 9" brakes was the 2001 Cherokee & the later models of the TJ's as they used the 768 shoes.

The major difference in my backing plate from what is in my Haynes manual for post 90 wranglers is the number of bolts that secure the backing plate to the axle.

After I put the 768 shoes on I regained total stopping power on the passenger rear and the driver side will come to a stop but it then starts moving again with the foot on the pedal.

there is nothing wrong with my booster, MC or valve as it is all new and the correct parts. Although, The loud hissing sounds is coming from the idle air control valve slot. I have already replaced the IAC valve once before and I am not sure if it is normal but the hissing sound usually is worse when in R, better when in D and nonexistent when in N.

As far as the brake issue in the driver side rear, I really dont know where to start because if any major component PRE rear axle brake dist block was failing then why would the passenger rear stop just fine and the driver side not?

I am going to replace the braided line from the dist block to the driver side wheel cylinder just in case there is a blockage so I can at least factor that out.
 
#31 ·
Final Solution

The issue with my brakes was the jeep had a 2001 Cherokee axle on it and I had shoes for a 91' Wrangler. The backing plates on these are very similar and the way I found this out was doing a reverse part search on the 538 shoe to see all the models that did not use the 538. The 01 Cherokee and some later TJ models used the 769 shoes.

After the new shoes were on only one side of the Jeep was coming to a stop. After driving around for about 20 miles I took the Jeep to a dyno testing place and both wheels stopped on demand.

It looks like the problems has been solved.

So 3 weeks later I now have rear brakes.
 
#36 ·
The issue with my brakes was the jeep had a 2001 Cherokee axle on it .
Cherokee axle is spring over axle.
Your pics are spring under axle and look like they came that way. So it cant be a cherokee axle unless someone did a great job flipping the perches and bumpstops
 
#32 ·
Grats, I applaud your fortitude. I never would have figured THAT out and I have been monkeying around with brakes for 40 years.

Good Job!!!

To a moderator ---- this needs to be marked.
 
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