ABS delete

[DonYukon]

I unplugged mine about 10 years ago. I havent had issues. even the light went out eventually lol (burnt out)

 

[FrankieD61]

Will unplugging the ABS module have any I'll effects? Just for now at least.

 

[FrankieD61]

I guess I'm overdue to connect the Solus Pro to the '88, then.


Yeah, I did some research, and I'm thinking you're right that it does three things. But brake fluid LEVEL may not be one of them. Something is going to warn the driver when the front and rear pressure isn't equal.


Do the rear brakes get warm when used hard?

I'll have to check on this.

Have you tested resistance of the solenoid coils in the ABS unit?

I'd hope that using the scan tool ABS auto-bleed to chatter the valves might clear or unstick them. Worth a try--or ten.

Are you talking about the iso dump valve? And, are ABS modules still available.

 

[FrankieD61]

2. Do your calipers work properly? I've seen them get really crusty; they "work" but the piston doesn't move as freely as it should. Thus the front brakes don't apply like they should, leading to "weak" braking. Secondary issue--the earlier "regular cab" trucks got JN3 brakes, which have the smallest pistons in the calipers. I don't remember when they got rid of the JN/JB3 option. JN/JB5 calipers are a substantial upgrade.

If I upgrade the calipers to the ones you suggest, will I need to change the prop valve as well?

 

[Schurkey]

My '88 started out as a JN3 horse-shiit-brakes regular cab.

First, I changed rear axle to get away from the horrible 254mm leading/trailing shoe rear brakes. 11.x Duo-Servo rear brakes came with the 9.5" axle.

Later--and almost by accident--I slapped on the upgraded "JB5" calipers and rotors; the goal was to replace a damaged steering knuckle. By pure chance, my donor vehicle happened to have the more-powerful front brakes included with the Extended-cab trucks. I didn't know 'til I got home from the Treasure Yard. Had to go back and get the more-powerful booster and bigger-diameter master cylinder to match my more-powerful front calipers and wider rotors.

So from the weakest "power" brakes offered on a GMT400, (JN3) I now have the equivalent of JB6. Still with the original RWAL ABS, still with the original combination valve.

When I first bought the truck--late 1997--among the first things I did was to replace the ABS module. It was expensive even then. No promises on it still being available. With luck, you can get one from the Treasure Yard, and hope it works.

 

[FrankieD61]

My '88 started out as a JN3 horse-shiit-brakes regular cab.

First, I changed rear axle to get away from the horrible 254mm leading/trailing shoe rear brakes. 11.x Duo-Servo rear brakes came with the 9.5" axle.

Later--and almost by accident--I slapped on the upgraded "JB5" calipers and rotors; the goal was to replace a damaged steering knuckle. By pure chance, my donor vehicle happened to have the more-powerful front brakes included with the Extended-cab trucks. I didn't know 'til I got home from the Treasure Yard. Had to go back and get the more-powerful booster and bigger-diameter master cylinder to match my more-powerful front calipers and wider rotors.

So from the weakest "power" brakes offered on a GMT400, (JN3) I now have the equivalent of JB6. Still with the original RWAL ABS, still with the original combination valve.

When I first bought the truck--late 1997--among the first things I did was to replace the ABS module. It was expensive even then. No promises on it still being available. With luck, you can get one from the Treasure Yard, and hope it works.

Will the upgraded calipers bolt on to my stock steering knuckle?

 

[Supercharged111]

I had an 88 with the atrocious brakes that Schurkey speaks of, but what was even worse was the RWAL's performance one day on a muddy ass road. It was so bad I decided to delete it altogether. All I did was use a single adapter to move the rear brake line from the ABS unit to the prop valve itself. My 98's 3 channel setup was also fvcking garbage, so I retrofitted junkyard lines from an 89 to mimic what I'd done to my 88. There is such a thing as good ABS, it just never came on these trucks.

 

[stutaeng]

What is the history with those JN3 brakes anyways? Were they carryovers from the square body generation?

My Dad's 88 RCSB I'm sure has those. I drove the truck for a short while many years ago out of high school. I do remember the brakes were definitely not the best on the stopping distance department, LOL.

We had a 72 C20 Custom with a Buick 402 prior to the 88 GMT 400. I never drove that truck, but I never heard anyone complain about the brakes. Only complaint was it wasn't easy on gas. It used to belong to my oldest brother, then went to Dad and he sold it for some drywall work...

 

[Supercharged111]

What is the history with those JN3 brakes anyways? Were they carryovers from the square body generation?

My Dad's 88 RCSB I'm sure has those. I drove the truck for a short while many years ago out of high school. I do remember the brakes were definitely not the best on the stopping distance department, LOL.

We had a 72 C20 Custom with a Buick 402 prior to the 88 GMT 400. I never drove that truck, but I never heard anyone complain about the brakes. Only complaint was it wasn't easy on gas. It used to belong to my oldest brother, then went to Dad and he sold it for some drywall work...

I dunno, I thought every square body I ever drove had better brakes than that garbage.

 

[Schurkey]

Will the upgraded calipers bolt on to my stock steering knuckle?

Do you have JN3 brakes now?

The JN/JB5 calipers will bolt to the steering knuckle. I've been told that the hubs are different between the "3" brakes and the "5" or "6" brakes. I know that the rotors are different; (thicker) that's probably why the hubs are different.

When it was me, I just used the knuckle, hub, rotor, and caliper from each side of the donor vehicle. The booster and master cylinder also have to be updated to the JB5/JB6 style.

I had an 88 with the atrocious brakes that Schurkey speaks of, but what was even worse was the RWAL's performance one day on a muddy ass road. It was so bad I decided to delete it altogether. All I did was use a single adapter to move the rear brake line from the ABS unit to the prop valve itself. My 98's 3 channel setup was also fvcking garbage, so I retrofitted junkyard lines from an 89 to mimic what I'd done to my 88. There is such a thing as good ABS, it just never came on these trucks.

When they work properly, there's no problem with the ABS units. But most of the time, they're not working properly. Either they're outright defective; or (more often) they haven't been bled properly.

What is the history with those JN3 brakes anyways? Were they carryovers from the square body generation?

No. They were just cheap, bottom-feeder, small, cost-cut pieces intended for the smallest, lightest (most popular) C/K GMT400s.

We had a 72 C20 Custom with a Buick 402 prior to the 88 GMT 400.

Chevy had a 402. Buick had a 401 (Nailhead) which was labeled a 400 when installed in the Skylark. Last year of production for the Nailhead was '66. Starting in '67, Buick had a modern wedge-head 400, along with the 430. Both the wedge 400 and 430 were dropped at the end of the '69 model year in favor of the Buick 455.