Nightmare 10” drum brakes

[ShadeTreeMechanic]

I have a 97K1500 with junk 10” drum brakes. I’ve been fighting clunk and popping ever since I can remember. I’ve been fighting e-brake disfunction as well. Here recently, the right cylinder front cup blew out. Replaced cylinder, shoes, and hardware. Bled and drove, and blew it out again. Noticed when all reset and shoes adjusted to slight drag, front cup nearly to end of travel. Moderate hard braking blows cup out of cylinder. Anyway, I’m done with these 10” drums as I have been doing a lot of research on them and consensus is they are junk. I was considering a disc brake conversion for ease of maintenance but have read mixed results. I’m not concerned about gaining stopping power. I want mechanical peace of mind. MY MAIN QUESTION, some have recommended swapping the entire axle with the 11 inch dual servo axle from a larger truck or burban. What do I need to consider a must when finding the salvage yard axle. Gear ratio? Tube length? Etc. Do I also need the master as the disc conversion kits do?

 

[Schurkey]

97K1500

junk 10” drum brakes.

Yup. Technically, 254mm, but "ten inch" is close enough.

I’ve been fighting clunk and popping ever since I can remember.

Good chance that's the driveshaft yoke binding/sliding on the transfer case splines. I'm thinking GM has a bulletin on that where you use some special grease on the splines.

I’ve been fighting e-brake disfunction as well.

Usually seized or partially-seized park brake cables.

Here recently, the right cylinder front cup blew out. Replaced cylinder, shoes, and hardware. Bled and drove, and blew it out again. Noticed when all reset and shoes adjusted to slight drag, front cup nearly to end of travel. Moderate hard braking blows cup out of cylinder.

Drums worn out-of-spec for diameter?

Anyway, I’m done with these 10” drums

Excellent idea.

some have recommended swapping the entire axle with the 11 inch dual servo axle from a larger truck or burban. What do I need to consider a must when finding the salvage yard axle. Gear ratio?

Gotta match the gear ratio to the front differential.

Tube length?

K2500 6-lug axle width is a match for the K1500 axle and wheels.

C2500 6-lug axle width is a match for the C1500, but the C1500 uses 5-lug wheels. Gotta install 5-lug axle shafts or use 6-lug wheels.

You need new U-bolts and nuts, the U-bolt plates that were under your K2500 axle, and a conversion U-joint, likely a Precision 447 or equivalent.

Do I also need the master as the disc conversion kits do?

If you have JB5 brakes now--and that almost guaranteed--the master cylinder is fine as-is provided it's in good condition.

You'll want to totally flush the brake fluid, and you'll need a scan tool to activate the solenoid valves in the ABS unit. See attachment.

 

[1998_K1500_Sub]

Gear ratio?

I believe the 3.73 is the most common 6-lug 9.5"

IIRC, @Schurkey once managed to find a 3.42"

Tube length?

Axle-flange to axle-flange distance needs to be the same, or close. @Schurkey gave you good guidance.

For my K1500 Suburban, the OE 8.5" mounts the wheels inboard by 0.5" compared to the 9.5". See here:

Semi float rear end

It came from a 4x4 I did check that. Iv called a few places about changing out the gears in it. One shop told me $400+ parts (they also did my transmission a year or two ago) one shop said they might have a ring and pinion new in the box that he would sell me for 1/2 price if it’s what I need...

www.gmt400.com

Also see here for U-bolt plates:

14 bolt 454 1991 differential ID question again

I recently picked up a 14 bolt rear end 5 lug . Outside is pretty rusty for sitting outside. My plan is to put it in my 88 c1500 2wd. I pulled the cover off and it is 373 with locker. Has backing plates with drum brakes . I will post pictures as soon as i can, My question is what...

www.gmt400.com

There are of course 8.5" rear ends with the 11" drums, often found on Suburbans (all C/K1500 Suburbans may have gotten the 11" drums) but found on other pickups too (likely the larger C/K1500 trucks).

If all you do is move light cargo / trailers, you might consider an 8.5"

Me? I spun carrier bearings in my 8.5" some years ago and it wasn't cheap to fix. I have an 9.5" on sawhorses now and it'll be under the Suburban as soon as I have the time.

https://www.gmt400.com/threads/what-are-you-working-on-what-did-you-fix-today.55459/post-1440959

 

[alignman88]

Ever think the primary and secondary shoes are in wrong position? Shorter friction material shoe in front is primary, longer material in back. I always had good brakes on my ‘88 went through them one time never a bit of trouble but hear lots of complaints.

 

[Schurkey]

Ever think the primary and secondary shoes are in wrong position? Shorter friction material shoe in front is primary, longer material in back.

Entirely true for Duo-Servo brakes. Not so true for the 1500 Leading/Trailing shoe brakes. With the L/T brakes, all four shoes are the same.

 

[ShadeTreeMechanic]

Yup. Technically, 254mm, but "ten inch" is close enough.


Good chance that's the driveshaft yoke binding/sliding on the transfer case splines. I'm thinking GM has a bulletin on that where you use some special grease on the splines.

I have a fluid leak at the output shaft. I replaced the tail shaft seal a while back but it didn't seem to slow the leak. Ive been told by a transmission tech that the tail shaft housing bushing is bad and I need to replace it to resolve the leak. I will check the splines when I do the housing.

Usually seized or partially-seized park brake cables.

I did notice the cables operate the shoes when the e-brake cable is depressed. However, the driver side cable is missing the retainer on the bracket where it loops through the frame and so the entire cable moves back and forth when the brake is applied and moves the shoe minimally. Will have to work on that.

Drums worn out-of-spec for diameter?

Drums were replaced with shoes and hardware. Forgot to mention that. They have never been turned so I dunno.

Excellent idea.


Gotta match the gear ratio to the front differential.

I will get to searching salvage yards immediately!

K2500 6-lug axle width is a match for the K1500 axle and wheels.

C2500 6-lug axle width is a match for the C1500, but the C1500 uses 5-lug wheels. Gotta install 5-lug axle shafts or use 6-lug wheels.

Ive got a six lug 10 bolt so I'm good from that aspect.

You need new U-bolts and nuts, the U-bolt plates that were under your K2500 axle, and a conversion U-joint, likely a Precision 441 or equivalent.

Conversion U-joint... so take the vin or application from which I got the rear axle and head to the parts store and get a u joint using that info? if I get a u-joint for that application, what is the probability it will fit in the salvage yard axle pinion flange but not my K1500 driveshaft? I guess the question is, will the "conversion" u-joint fit seamlessly in both ends?

If you have JB5 brakes now--and that almost guaranteed--the master cylinder is fine as-is provided it's in good condition.

If I decide to go with a ABS equipped rear axle, will that cause issues if I only have 2whl ABS on my K1500? Essentially, the diff sensor would just sit unplugged, no harm, no foul, correct? Or is it essential to find one with no ABS?

You'll want to totally flush the brake fluid, and you'll need a scan tool to activate the solenoid valves in the ABS unit. See attachment.

I don't have a tech 1 scan tool nor the money to invest in one. Would carrying the truck to a gravel parking lot and sliding to activate the ABS allow the air to be pushed out of the unit?

 

[ShadeTreeMechanic]

Ever think the primary and secondary shoes are in wrong position? Shorter friction material shoe in front is primary, longer material in back. I always had good brakes on my ‘88 went through them one time never a bit of trouble but hear lots of complaints.

I am going to check that out. I replaced components back to their original position according to the way they came off. Of course, this was a while back when I serviced them. But who knows if the last owner didn't install them correctly and I was just following his incorrect method. I always take pictures and video of drum bakes before removal because there's always that one spring man!

 

[1998_K1500_Sub]

But who knows if the last owner didn't install them correctly

You can’t screw this up on a 10”, the shoes are identical all around.


Regarding the U joint, Google
for this.

Precision U-Joint 447​

If I was you, I would wait until I got the donor rear end, then I would measure both my driveshaft U joint cap size and that of the donor rear end. Make sure you get a U joint that has the same cap sizes and the same retainment method (straps, snap ring…).

The donor will probably have a 1.18” diameter cap size and uses straps to retain the caps. My driveshaft was 1.125” and uses a snap ring to retain the caps.

Here’s what I wound up using from RockAuto:

 

[ShadeTreeMechanic]

@Schurkey I have purchased a 14 bolt semi floating rear axle from a salvage yard. It came with no drums, no shoes, no hardware, and no wheel cylinders. I am having trouble figuring out which drums and which shoes to get considering lack of info on the axle (11" or 13"). The yard could not find the vehicle it came out of nor the VIN. They CLAIMED it was out of a 95 C2500 with a 3.73 ratio (which is what I need). I would like to confirm that before I move forward. The only info I was able to find myself was what was written on the axle with a paint pen. According to the writing, it is out of a 95 C2500.
1. How do I determine ratio without knowing the VIN or option code?
2. How do I determine if I need 11" or 13" hardware?
3. 7200lb or 8600lb GVW wheel cylinders?

 

[Schurkey]

I have purchased a 14 bolt semi floating rear axle from a salvage yard. It came with no drums, no shoes, no hardware, and no wheel cylinders... ...They CLAIMED it was out of a 95 C2500 with a 3.73 ratio...
1. How do I determine ratio without knowing the VIN or option code?

Pop the cover off--you're going to have to do that anyway--and LOOK at the ring gear. (You'll want a fresh gasket, and correct gear lube. While you're in there, verify the condition of all the other gear teeth, look for rust/pitting, check the debris stuck to the magnet, and so forth. Pull the cross-shaft, then remove the C-clips and slide the axle shafts at least part-way out--If the seal surface isn't grooved or pitted, and the bearing surface isn't grooved or pitted, and there's no actual evidence of axle leaks...you probably can slide the axle shafts right back in without dicking with the axle seals or axle-shaft bearings. Be sure the cross-shaft itself isn't worn.)

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In this case, 41 / 11 = 3.73

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2. How do I determine if I need 11" or 13" hardware?

Do you have backing plates attached to the axle? Measure the backing plates, and hope they're about 12", to accommodate 11.x brakes suitable for a 6-lug truck. If you've got backing plates that are ~14", the thing has probably got 8-lug axle shafts, and you'd be better off with a different axle.

3. 7200lb or 8600lb GVW wheel cylinders?

It probably came with 7200 GVWR wheel cylinders. SOME guys are installing the 8600 GVWR cylinders (slightly larger than the 7200 cylinders) as an "upgrade". I have no opinion on this. I haven't done that mod.