Adjusting JB7 Duo-Servo shoes

[Pinger]

I've read the GM manual as to how to - but have a few questions.

1999 C2500 Suburban with JB7, 8 lug, and 14 bolt axle - will it have 'knock outs' to permit adjustment without having to remove the drums?

Does the adjuster move freely in both directions or, like other self-adjusters I've encountered, does the pawl have to be manipulated?

GM - method has mis-print I think. Does it mean tighten until wheel won't turn then back off 33 clicks? (It also says wheel should be free by 15 clicks wound off. How critical is that?

My normal method with drums is to adjust until contact is made than back off until light scuffing or just free. Am I aiming for the same here, doing it exactly as per GM manual (minus 33 clicks)?

Reading some of the threads on the subject and some adjust as per my usual method (ie, light scuffing or just free). Is this OK or does the Duo-Servo complicate things and/or require a different method?

TIA.

 

[termite]

I personally can't say you're right or wrong in your approach but it follows along with my views at least. I aim for backing off just enough the wheel spins free with little to no contact with the shoes and a firm pedal.

The whole backing off 33 teeth is rather challenging to judge when working through a small hole in the backing plate and laying in the rocks.

 

[Schurkey]

Perhaps I'm doing things "wrong". However, it has served me well.

MOST of the time (not always) I just ignore any "knock-outs"; I'd rather adjust the brakes with the drum on/off/on/off. Of course, that's entirely impractical when dealing with full-float drums on the wrong side of the hubs.

OTOH, if you've got drums married to the hubs, you're going to have the hubs 'n' drums off to clean/inspect/replace the shoes anyway. So the knockouts are going to be totally obvious at that point.

With non-full-float axles, if I can't slide the drum off, the adjustment is too damn tight. If it slides off too easily, tighten the adjuster some more.

I'm quite satisfied to adjust for moderate drag between shoes and drum on one side. I can't think of a time that I've "backed-off" the adjuster. On RWD axles, where the two sides are connected via the axle shafts and differential, remove that drum, install the other. Again adjust for moderate drag between shoes and drum. Install both drums, then apply and release the brakes at least once, preferably two--three times, holding the last "apply" for 60 seconds before releasing. This aligns the shoes, makes everything fit like it's supposed to. Also assures that you have a firm pedal that doesn't sink--a basic yet effective leak-test of the entire system.

Go back and check for brake drag, one side at a time, with the other drum removed. Generally, the drag is reduced because the shoes are aligned to the drums better than when they were adjusted previously. I may adjust them tighter, depending on the amount of drag I'm feeling.

I guess I allow more shoe-to-drum drag to start with. Install wheels, torque lug-nuts as appropriate. Then, of course, you go on a test-abuse test-drive that has some fairly heavy brake application--burnishing/breaking-in the shoes/pads and the iron they ride against. I keep the speed up so that the rotors, especially, have plenty of air flow through them. Don't overheat the brakes.

By the time you have finished the job, a fair amount of brake drag is magically "gone", because the shoes are perfectly aligned, and the shoes/pads have been burnished to perfection.



Backing-off the adjuster "33 clicks" just seems insane to me. As if there'd be problems if you only went 32, or the brakes wouldn't grab if you went 34.

 

[Pinger]

Thanks guys. I've got the measure of where to adjust it to - I think!

This bit though:

Does the adjuster move freely in both directions or, like other self-adjusters I've encountered, does the pawl have to be manipulated?

Does the adjuster move freely in either direction or does its pawl have to be moved away from it to move it in one direction (the slacken direction usually)?

 

[evilunclegrimace]

Thanks guys. I've got the measure of where to adjust it to - I think!

This bit though:


Does the adjuster move freely in either direction or does its pawl have to be moved away from it to move it in one direction (the slacken direction usually)?

You have to hold the adjusting pawl away from the toothed wheel to loosen the brakes.

 

[Pinger]

You have to hold the adjusting pawl away from the toothed wheel to loosen the brakes.

How is that done?
I'm trying to push it through the cut out hole (drum still on) where I think it must be but nothing is moving.

edit PS.
Ignore the above - I've sussed it.

 

[termite]

How is that done?
I'm trying to push it through the cut out hole (drum still on) where I think it must be but nothing is moving.

I use a small screwdriver or pick to push the pawl away (from backing plate knockout) while turning the adjuster with a second flat screwdriver. To tighten the brakes it should move freely with the pawl in contact with adjuster (i don't know off hand which direction to turn to tighten/loosen).

If you can't get it to turn or its difficult, may need to open the drum and clean/replace the adjuster while inspecting everything else.

 

[packer0440]

As long as you have the right adjuster on the correct side, you hold the arm up with a skinny screwdriver and pull down with the tool on both sides. When in doubt, just see which way it will tighten up the shoes (without having to move the arm) then just do the opposite. If you can't move it either way the threads on the adjuster are seized. It also helps to have the tool designed to adjust them in this manner.

 

[Pinger]

All done.
Adjusters were free (they'd been worked on not that long ago) and they came up a fair bit (especially driver's side). I could possibly have been more aggressive but the tendency toward tightening when the wheel is rotated in reverse direction (normal I presume) made me a bit wary. I can always go back to them. No driving today but I'll be out in it later in the week and I'll see what difference (if any!) there is.

More worrying, was finding a load of axial play at the passenger side wheel - but no rocking (eg in 12-6 O Clock or 3-9 O Clock directions. Presumably a wheel bearing on its way out? - but no rocking has me confused. Normal failure mode for an axle with half-shafts?

 

[Pinger]

All done.
Adjusters were free (they'd been worked on not that long ago) and they came up a fair bit (especially driver's side). I could possibly have been more aggressive but the tendency toward tightening when the wheel is rotated in reverse direction (normal I presume) made me a bit wary. I can always go back to them. No driving today but I'll be out in it later in the week and I'll see what difference (if any!) there is.

Drove it today and there's a definite improvement in reduced pedal travel so well worth the effort.

It's that I've read countless times (and it finally sunk in) on this forum that 'long pedal travel is almost always an adjustment at the drums issue' that prompted me to adjust them. Thanks to the forum for the prompt - and for the advice given on this thread. Much appreciated.