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Need to do rear brakes but confused by rear end

Early ABS was quite frankly experimental. :rof:

1992 4 wheel ABS on an Olds Bravada would scare you by just letting the brakes off. I bent the brake pedal on one with the ABS unit fighting me.

RWAL has been quite nice to stop rear wheel skids and keep you straight. I have always liked this from the start esp when unloaded.

1995+ Yukons and Suburbans IMO are more of a decent and useable system.

I was reminded the other day to pump the brakes when an old full size van started to go sideways on me - A skill you forget with modern ABS.

Here is the proportioning valve info for suburbans.
http://www.thetruckstop.us/forum/showthread.php?14050-Brake-proportioning-valve

Here is a valve failure like I had.
http://www.thetruckstop.us/forum/showthread.php?14105-combination-proportioning-valve
 
Thanks War, I'll tag the links. Well I'm pooped. This stuff is HEAVY! Backing plate offset is right at 1" and as Don said earlier the backing plate is against the U Bolts when the center hits the mounting flange. Gotta move it out 1 1/8" to get the shoes to line up with the drum. That's plus or minus start point.

Backing plate mount bolts are 1/2x20x1" but stuck thru the mounting flange by right at 1/4" so I got some grade 8's 1 3/4" long. Big box of 1/2" flat washers..First couple in each stack will need to be ground to sit against the flange, after that they are in free space.

Grade 8's snap before they bend but not being hit with a hammer. Since the torque is further out the bolt I wanted tough without custom ordering Grade 10 Cat head bolts.

I found that the rubber cap that comes on the bleeder will fit over the open end of the hydraulic tube so it's not peeing everywhere.

I also discovered that the HD 1 3/16" wheel cylinders for 3 1/2" brakes are listed under K3500 with 454 only. Shopped a bit and settled on Raybestos from AZ at $11 bucks each. Cost me less cuz long customer and old fart discounts.
 
Couple of tid bits, my hubs had been changed over to the woodruff key retainer nut style. What a breeze to do. Seal races are worn less than a thou, can barely feel where they run after cleanup, no shims. Axle splines show only slight polish, no grooving or edging. E brake cable goes thru clamp at pinion retainer bolt, will move to top cover bolt and will fit fine, keeps the factory turn in the cable. Tomorrow, after I get the backing plate installed I will get a pic. Then I will have to go to town, thought I got a box of 100 washers but only 50. Takes 12 in a stack so 48 per side.

War, I had a Dodge 3/4 ton with early ABS, going down grade on a dirt road in 4 hi at about 25, water truck coming up hill, blind corner, hit the brakes and the damn truck actually sped up. Needless to say I hit the semi head on with spedo showing 30. Shattered the semi's fiberglass front shell and pushed it's rad into the engine. We both had to be towed out from 11 miles up a logging road. Dodge was DOA. While I agree that they are way better now, they are still calibrated for hot dry asphault not dirt or snow and certainly not for off road.
 
Well guys, this won't work without lots of extra bucks.

Hub inner bearing ID is different, location within the hub is different. Outer is the same. End result, hub outer face is not in the same place so a different axle would be required, and a spacer ring behind the lock ring.

All in all, a bust, not worth the parts cost and machine work to get it to work.
 
So axle housing is different or axle shaft? Just wanting to be clear. A set of the right shafts would be doable but sounds like swapping the rearend is gonna be the easiest way.
 
Differences I found in housing, backing plate flange in different location on the housing, backing plate has different offset. Shaft collar extension rear bearing inside diameter different and inner bearing step in different location. Hub differences, drum flange in different location on hub, inner bearing location inside hub different. End result, different axle shaft length.

I do not know if the spring boss location is different.
 
There's something I got to wondering about during this project and haven't had the time to check out. Could the original hub be used and the 3 1/2" drum be put over the outside. The backing plate for the 3 1/2" shoes would need to be used so the brake cylinder would set correctly. I'm thinking a spacer between the backing plate and axle would be needed. Just curious and haven't had time to check it yet.

Don
 
Don, The 1 ton hub has two steps on the outside of the flange, one for the drum, (slightly larger diameter), and a second one for the wheel. The 3/4 ton hub has only one for the wheel, the centering step for the hub is on the inside.

I see two possibilities here, 1--weld up and cut the steps, or, 2--place the drum on the hub, center it and fill with JB, let the lug nuts center the wheel.

I have the backing plate mounted on spacers now but lined up for the other hub. Have the original hub on now and will be setting the wide drum on to see how much further out I need to go. Am using Grade 8 bolts and a stack of flat washers for extension and spacers. Fortunately, the sholder on the bolts is very snug so the backing plate is tight. The first few washers in the stack need to be cut to clear the tapered casting.

One thing I will look at is the splined lug bolts. Occurs to me that the splines in the hub might not go all the way thru. Now that the drum is not on the inside they will need to be driven deeper into the hub. I did notice that they did not reach the end of the nuts with the wheel on. Wondering if there is a difference in length.

Oh well, guess I will do some labor on labor day and look forward to beer thirty.
 
Here is the info on using the 3/4 ton hub with the wide drums on the outside: the proper backing plate needs 2 1/2" standoff from the flange.

IMHO: given the weight of the drum, the heat generated, etc. using JB aint in the cards, weld up and cut to put the step in is doable. However;

Consider a gvw on the high side, say 10,000 lbs, and a 60/40 brake bias, each rear brake is stopping 2000 lbs at perhaps 3 g's or 6000 lbs. The torque required multiplies toward the center from the tire diameter to the diameter of the bolts. Call it a 4" to 30" ratio, side load on the bolts, approximating, 8 x 6000= 48000 divide by 4 = 12000 lbs per bolt. A half inch diameter grade 8 shears somewhere around 75k. However, in this case the pressure is exerted at the head while the anchor is 2 1/2" away and leveraged by the washers/spacer. Plug the distances and angles in and 12000 goes above 100k.

I am sure somebody out there will have a slide rule to do the exact numbers, my 'guestimating' says to me no way.

So, unless someone has a brilliant solution, am gonna abandon this as a way to get better rear brakes.
 
Upon inspection and measurement, the wheel cylinder bore diameter was 1" even. I think it was supposed to be 1 1/16.

I have a new set of 1 3/16" and I measured the center to the backing plate and they are the same. So, at least that's not a waste of money, and, should improve the rears. 1.571 sq in for 1" up to 1.865 sq in with 1 3/16" per shoe. That's about 20% added pressure for the same PSI.
 
War, you posted that the adjuster wasn't working. If the spring at the botton of the shoes is installed wrong way around it will prevent the adjuster arm from cogging the wheel.
 
THEFERMANATOR said:
All of the 2500 BURBS with a diesel or 454 have the 3.5" rear shoes. The 350 2500's got the 9.5" 14 bolt semi floater and only had the 2.5" wide shoes. And make sure it is teh RAYBESTOS blue shoes, not the red.
Click to expand...

"Old proportioning valves can stick in the limiting position and the rear brakes don't work very well. My 1st 1993 had this issue. My second 1993 was day and night better brakes. Adding the $100 shoes also improved the brakes.

The auto-adjustors don't. You need to snug up the drums every other oil change. A screwdriver works for this. Block the front wheels, raise the rear wheels, and spin them while tightening the brake wheel. Stop when you hear the brakes start to drag. Apply the brakes a couple times to make sure you don't need more esp. on brakes that haven't been adjusted in a long time (miles). "

I think these are the best tidbits FOR ME in this thread. Thanks for the good read.

Is it possible to clean out or refurbish the proportioning valve?
 
The star wheel on these is fairly coarse so they do not adjust in small increments. While I had these apart and being re-assembled I worked the system--does fine. HOWEVER--only the rear shoe works the actuator. When you are going forward the front shoe binds up rotating both shoes keeping the rear top against the stop. That does not operate the adjuster lever. Backing up and hitting the brakes binds up the rear shoe and the reverse happens, that works the lever. To keep them adjusted you need to back up and hit the brakes fairly hard several times.
 
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