Working on Brakes (especially Rear Drums) - TJ

Hey...I am about to pull my brakes apart due to some persistent brake fade issues (dry or wet) I've been having with my rear brakes; I want to make sure everything is ok/fix whatever's wrong with them.

Anyway, I'm going to start scouring the 'Net tonight to look for info how to work on brakes, diagrams, instructions, etc., especially for the rear drums (the front discs are more straight-forward from what I understand, and I'm pretty sure I'll be able to figure out what's going on with them a little easier).

So, if anyone out there can provide me with any links to instructions they've found particularly useful in the past, that would be awesome. Pictures and diagrams are great, too. Bill, if you feel inclined to put up a link to the appropriate section from the FSM or something, that'd be awesome too. Also, any tips or suggestions what all I should do when servicing and checking my brakes (beyond the obvious inspection and replacement if necessary of the pads...) would be great!

Thanks everyone.

/Bob

Applicable specs:

1997 TJ Dana 44 Rear (drum brakes) Dana 30 Front (disc brakes) Stock brakes front and rear. Last brake service performed 15 months ago.
Reply to
Bob
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Drum brakes are not that much more complicated than disc brakes. The brake shoes expand to exert pressure on the inside of the drums, instead of pinching down on the rotors as what happens in a disc brake. The complexity is entirely related to positioning the springs and related hardware.

Reply to
CRWLR

Are you sure you aren't just seeing the effects of a properly working combination valve?

It acts like an anti lock brake for the rear wheels so they don't lock up easy if at all. Normally you don't want the rears locking, you can do 360's faster than you can blink if the rears lock up at speed.

The combination valve stops them from locking until you are almost stopped even if you really mash the pedal down.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Bob wrote:

Reply to
Mike Romain

Reply to
L.W.(ßill) Hughes III

Here is a good site and explanation with photos for servicing drum brakes:

formatting link
Tom

Reply to
mabar

is that like a proportioning valve? Give the 60/40 braking on the front/rear?

Reply to
SB

Exactly. A combination valve is also called a proportioning valve. It distributes the braking power heavily to the front brakes and much less so to the rears. On a TJ, the front brakes do the lion's share of the braking, probably 80 to 90%.

Tom

snip

Reply to
mabar

Yes.

It is a bit more complicated than just a 60/40 split. On pickups and Jeeps it really tries to never lock the rears while keeping braking. It plays with the pressures.

Mike

SB wrote:

Reply to
Mike Romain

Wow...do the front actually do that much?

Sure feels like it the way the front dives down.... actually shared an arse clenching experience with a dog today! Nosed down and skidded....but all's ok!

Reply to
SB

Oh, it's an "on the fly" type of doo-hickey! On the older muscle cars, wasn't it something that you set by a knob and left? Or was there a way to do a real time adjust on that too?!

instructions

Reply to
SB

Yep. On most cars, the front brakes do about 70% (+) of the braking. On the TJ, because of the extra short wheelbase, the fronts do MUCH more of the braking. The rears do very little of the actual braking.

Try this test. Raise the rear wheels off the ground with a floor jack or jack stands. With the engine at IDLE and with the transfer case in 2-wheel drive, put the transmission in drive or 1st gear, then try to stop the rear wheels from moving with only the foot brake. On my 6-cyl TJ with 3.73 rear axel ratio, it is almost impossible to stop the rears, even while mashing the foot brake with all my might. Applying the parking brake will stop the rears easily.

Tom

Reply to
mabar

I'm pretty sure it's not just that.

I've been getting a seat-of-the-pants feeling that my braking power has diminished of late; on the highway when traffic has stopped suddenly, I've found myself having to smash down on the brakes harder than before to get the jeep to stop in the same amount of time. While I can still lock the front up, it just doesn't seem to be as effective.

This last weekend on the trail was my final straw: I was on a slight incline, and tried to go up a couple of rocks (I was in 2wd), and spun tires. So, I put the clutch in and hit the brake simultaneously, in order to put it in 4-low to get through the little bit of rocks. As soon as the clutch was in, the vehicle proceeded to roll back about

10+ feet, with me standing on the brake pedal (in retrospect, perhaps I should have pumped it). Either way, it was a bit freaky. The others in my group said my front wheels were locked up, but my rears were rolling, as I just rolled backward. It was like my rear brakes were doing nothing, and just the locking-up and subsequent dragging of my front wheels was all that stopped me.

The braking improved a bit as the day progressed, but I decided maybe I'd better check and see if the brakes were (a) in good shape still and (b) not out of adjustment.

Reply to
Bob

Thanks, Bill.

Mabar, thanks for the link.

/Bob

Reply to
Bob

On really steep stuff, I have had to use my e-brake on many occasions to help in those kind of situations. Not just with Jeeps, pickups were way worse.

Others have posted about not being able to lock the rears at low speeds.

One Jeep out with us actually lost his rear brakes and wow what a difference. He literally could not stop the roll back on a ravine climb. He nailed a tree 3 times in sliding backward and we had to drive around to give him a pull from the front just to get him out of there.

It is worth inspecting though.

Mike

Bob wrote:

Reply to
Mike Romain

It works in both 4wd and 2wd. This technique works with open axles too, it's been in use since Model T days when most vehicles got stuck more due to there being more unpaved roads back then. :)

Jerry

Reply to
Jerry Bransford

but if it's so hard to add resistance to the rear wheels by braking....well, I don't know why I'm going on about this...it OBVIOUSLY work, else you would do it no more!

Reply to
SB

Both.

I can get my open rear spinning up both tires and sometimes the front as well, but the drum brakes seem to be better at slowly modifying the torque rather then the hit disks give.

The valve is dynamic, it sends so much pressure to the rears, then shunts the rest front, then brings it back to the rear for the final stop.

If the fronts stop really easy, no more pressure goes to the rears, if the fronts stop hard, you 'can' lock the rears as you come to a stop.

I think that's why the jack in the air thing works so well to totally confuse folks.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

SB wrote:

Reply to
Mike Romain

Jack in the air thing?

Reply to
SB

It sounds like you just need to adjust the brakes.

Reply to
CRWLR

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