rear wheel disk conversion

[Joe Guldan]

Does anyone have a template for the bracket to mount calipers when converting to rear disk brakes?
'88 GMC C1500

 

[Schurkey]

Your C1500 has the shiittiest rear brakes, and (likely) the shiittiest front brakes of the GMT400 lineup.

If you look on your glovebox decal, you'll probably find JN3 or JB3 or Jx3, which is the option code for the crappy brakes. JB5 has much better front brakes, master cylinder, and booster, but the same crappy rears.

I wouldn't say that rear discs is the best upgrade. MOST rear disc "upgrades" were "engineered" by idiots, placing the caliper mounting bolts in severe stress they weren't designed to take.

The better upgrade is to scrap the entire weak-*** 8.5" rear axle for the MUCH stronger 9.5" job; which includes bigger 11.x" Duo-Servo rear brakes that actually stay adjusted. The stock 10" leading-trailing shoe rear brakes are a disaster.

Downside of this is that the better rear axle with the better brakes...have six lug studs instead of five like your wheels.

 

[Erik the Awful]

I have an '89 C1500, and my brakes work great. I have no idea if I have JB3s or JB5s because my glovebox decal is unreadable, but I'm pretty sure they're JB3s.

You want good pads and shoes. I like Raybestos. Make sure all the calipers and wheel cylinders work like they're supposed to with no hanging up nor leaking.

De-scuzzify your rear drums and backing plates. Replace any broken hardware. Install the shorter shoes in front and the longer shoes in back. **VERY IMPORTANT** - adjust your star wheels so there's not a lot of take-up in your rear drums.

Bleed the crap out of your brakes until the fluid comes out nice and clear with no bubbles.

The ONLY advantage of discs over drums is that they don't need adjustment. If you use your parking brake and the star wheel works properly, you shouldn't have to adjust them often.

 

[Joe Guldan]

I've junked the crappy rear wheel abs system and replace the master cylinder with the GM 19209249 master cyl and installed an adjustable proportioning valve, this has improved my brakes 100%. I don't want to switch to 6 lug wheels but would like to have disk brakes on the rear

 

[Schurkey]

I have an '89 C1500, and my brakes work great. I have no idea if I have JB3s or JB5s because my glovebox decal is unreadable, but I'm pretty sure they're JB3s.

Look at the booster. If it's a "pancake", you've got the weaker JB or JN or whatever "3". If it's the much-bigger dual-diaphragm unit, you've got JB5.

JB5 on left, JB or JN or whatever "3" on right.

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Install the shorter shoes in front and the longer shoes in back.

The Leading/Trailing shoes on JB/JN3, and JB5 are identical. There is no primary / secondary shoe.

Your advice is correct for Duo-Servo drums.

**VERY IMPORTANT** - adjust your star wheels so there's not a lot of take-up in your rear drums.

Bleed the crap out of your brakes until the fluid comes out nice and clear with no bubbles.

The ONLY advantage of discs over drums is that they don't need adjustment. If you use your parking brake and the star wheel works properly, you shouldn't have to adjust them often.

Quoted for truth.

Early RWAL ABS had a bleeder screw on the ABS unit. I guess later ones didn't.

Bleeding 4-wheel ABS is a real pain. Official procedure requires a gallon of fluid

I've junked the crappy rear wheel abs system and replace the master cylinder with the GM 19209249 master cyl and installed an adjustable proportioning valve, this has improved my brakes 100%. I don't want to switch to 6 lug wheels but would like to have disk brakes on the rear

If you have JB/JN3, JB5 or JB6 brakes, that is a completely WRONG master cylinder. Your brake pedal is likely to be impossibly hard if the power booster fails. The master cylinder bore is too large for the caliper bores of JB5 or JB6, it'll be even worse with the JB/JN3 calipers.

 

[Greg Hansen]

Does anyone have a template for the bracket to mount calipers when converting to rear disk brakes?
'88 GMC C1500

I have had both the SSBC and Little Shop Mfg. rear disk brake conversion on 97 C1500. The little Shop calliper brackets are sold separately and these guys are awesome to deal with to help you out with what you need. As well there is another company if you Google it that has a rear disk brake conversion bracket that uses rotors and calipers that you can source yourself. A little digging and odd you go. Good luck. I know what your going through and there has been some good suggestions in this forum so weigh the responses and choose whatever fits you.

 

[Black98Burb1500]

My truck has the jb5 system I completely rebuilt the system when I got it and they work really well so maybe find a later year k1500 at a junk yard and just go to town tanking the whole brake, drivetrain and suspension parts they should all bolt on basically I like drum breaks for 1 reason if there done correctly and stay adjusted they last forever I've gone threw 2 or 3 sets of pads up front since I did the rebuild and the drums are still good to go just food for thought I always try and find cheap ways to improve my truck before throwing China made **** from the parts store at it nothing I've bought in store has compared to oem.