1999 Sierra brake system question

[Jesseyourcalipers]

Hello friends of the amazing bitog community

I have a 1999 gmc Sierra regular cab 4x4
Swapped diff for calipers on back

Did the brakes last weekend and did not bleed the brakes. Had some stuff going on and did it in extreme rain and needed to get going. I stupidly Just opened the reservoir moved pistons in get them on and took off. Super happy with akebono pads. But today I had to hit my brakes kinda hard and truck locked up. I repeatedly pumped the pedal and tried to move out of the cars way and nothing. After a few minutes truck moved all back to normal. Probably calipers? Would flushing fluid maybe work? Could be abs problems since these trucks have soldering issues on the abs module from factory?

 

[kschachn]

Soldering on the abs module from factory?

 

[Jesseyourcalipers]

Soldering on the abs module from factory?

Yes it’s a thing lol YouTube has a lot of videos about it

 

[Jesseyourcalipers]

I meant to put issues in between soldering and on. No wonder you were like wth lol gm had soldering issues on the abs modules from factory

 

[Furious]

Soldering on the abs module from factory?

GM vehicles of this era are notoriously known to have solder joints fail in the ABS module. I actually have to either repair the solder joints or replace the module on my Chevy at some point, just havn't got to it.

 

[Bud_One]

An ABS module failure shouldn't affect the brakes to lock up. Most failures I've seen regarding the EBCM leave the brakes in a non-ABS mode.

 

[meep]

If you stomped the brakes and they stayed locked, there may be a sticking “proportioning valve” inline with the rear circuit. They are somehow designed to reduce the impulse to sudden brake surge to the rear, and/or delaying rear engagement. Sometimes they are built into a load sensing valve which reacts to rear axle position. I’d be curious about that….

 

[paulo57509]

When the ABS module has issues, both the ABS and Brake lights will illuminate.

 

[atikovi]

But today I had to hit my brakes kinda hard and truck locked up. I repeatedly pumped the pedal and tried to move out of the cars way and nothing. After a few minutes truck moved all back to normal. Probably calipers?

Brake hoses collapsed internally. Had that happen on my '92 C3500 rollback at the scrap yard after unloading. Front wheels locked up. Truck wouldn't move. Walked an hour to my shop to pick up a wrench to loosen the bleeder screws. Walked an hour back, and by that time the brakes were free and I could drive it again. Avoided hard braking until I got back. Replaced the hoses and problem solved.

 

[Dave9]

It's not an ABS issue and not because you didn't flush the fluid.

It's either the soft hose collapsed (weakened from manipulating it while doing the brake job), or caliper seized, or pad ears dragging on caliper.

If it has original soft hoses, I'd start by replacing them (both rears) as they are due for it anyway, and take the caliper off while you're at it, inspect it, and derust and lube the caliper slide rails for the pads if you didn't do that last time. Once you have the hose replaced, automatically needs that line flushed to bleed the air out.

This is assuming you can get the soft hoses off the hard lines without damage which may not be the case with something that age if very rusty. If you damage the hard lines then have to replace those or tow it somewhere that can and pay $$$.