Need help with brakes plz!

Stringer

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Hi, I couldnt find a brake section. I have a newly aquired 1996 C1500 i think it's called. 4.3l, 8 ft bed. I bought it for a teenage stepson and really need to figure out the brakes. The owner before me put in new brake hoses, new master cylinder, new rear drums, new rotors and pads up front. brake goes almost all the way to the floor, and pulls to one side only when the brakes are depressed. he seemed to think it was the abs module. Does that sound right, or is there anything else i should look at first? I have alot of experience wrenching on my gmt-800 but never had an issue like this. Thanks for any suggestions.
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Zerio29

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Spongy brakes are a VERY common problem on all of these trucks. There's dozens of threads here that have many people addressing the issue with various solutions.

The spongy brake pedal itself often points to air in the ABS module. Either remove it and replace it with a proportioning valve, or have it bled with a scan tool at a shop that has one.

the pulling to one side could be a part of the faulty ABS module (IIRC '96 has the chelsea hayes one) but points to a seized caliper on the opposite side that it's pulling to.


 

Zerio29

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Should mention that there are also a number of upgrades that can be done, as the factory set ups on these left a lot to be desired.

the vacuum booster can be replaced with a hydroboost. this writeup is excellent

The master cylinder can be replaced to improve pedal feel, although imo it does little to actually improve stopping power/performance

If you're going all in, there are options on disc swaps and entire rotor swaps to 2500/3500 setups, but hopefully one of the wonderfully more knowledgeable people on here would be willing to chime in with some advise on those.
 

SAATR

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It could very well be an issue with air in the ABS module, or anywhere downstream of it. If you can confirm that both calipers are compressing when the pedal is pushed, then you can try this: drive the truck at low speeds a wet driveway or parking lot (lots of room to avoid any possible accidents) and perform several emergency stops. This should make the wheels lock and engage the ABS system. Do this a few times, then bleed the brakes again and see if you can dislodge any additional air from the system. I have had it work as often as not, and it's free. I'm lucky enough to have access to a scan tool that can run the ABS bleed on these trucks, so I can also confirm that that will often help spongy brakes.
 

1998_K1500_Sub

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Nice looking truck BTW!

You might want to pull the wheels and make sure the prior owners did everything to the brakes that was said. Assuming so...

SAATR (above) gave some good advice. Others have used the same method and you can read about their results in other posts on GMT400. The key is to make sure EACH of the wheels locks-up at least once, so that each wheel's ABS fluid circuit is utilized.

Zerio29 (above) posted a link above to "How to: NBS master cylinder swap for firm brake pedal". I think that's notable and here's why.

I worked on my 1998 K1500 Suburban for a few years trying to make it brake well... i.e., bleeding the brakes using multiple methods in those years and once replacing the master cylinder with one of the same style. The Suburban would brake straight (which yours doesn't, but read on) but it would never brake well, typically leaving me anxious when braking in urgent situations and consistently leaving me unhappy in regular driving.

Then I tried replacing the MC with a 2001 MC from a K1500 and WHOA... what a difference. OMG, it braked with much more authority, much better response to pedal input. For me, this one change made the most significant difference and made me love the truck.

I made other changes on my Suburban patterned after those which you can read about here on GMT400:

- I replaced the front calipers with those from a K2500, which have a larger diameter piston. Reportedly the same brake pads (from the K1500 calipers) can be used.

- I replaced the rear brake cylinders with larger cylinders from a K3500. HOWEVER, your rear brakes are likely not the same as mine and this change may not apply. Yours are likely 10" drums; mine are the 11". The 10" drums are notorious for not being the best (better) drum setup... but my father's K1500 had them and they didn't seem to be a problem (that truck was simply a "driver" for him, he never pulled a trailer or carried a load). The 11" drums are an improvement over the 10" in general, and allow the K3500 cylinder "upgrade" as an option.

- I installed stainless steel lines. These gave me an improved pedal feel, but they aren't something I would advocate unless you just feel like installing them.

My $0.02.
 
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Schurkey

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Perhaps a moderator will move this from the ENGINE section to AXLES & BRAKES.

Installing the so-called "NBS" master cylinder on a vehicle with low-drag front calipers is CRAZY. Low-drag calipers need a 3-chamber/step-bore "Quick Take-Up" master cylinder, and the "NBS" unit is not. It is totally unfit for the job. IF (big IF) it works in normal situations, it'll be a crumpled-fender mess if the brake booster fails because the "NBS" master cylinder throws away hydraulic advantage on the wheel cylinders. Your kid better be a Football player--beefy with huge leg muscles.

The 254mm (10") rear drum brakes are a total disaster. GM should have been sued. They're invariably far out of adjustment 'cause no-one uses the park brake often enough.

Air in the ABS is ultra-common after brake work.
 

1998_K1500_Sub

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Installing the so-called "NBS" master cylinder on a vehicle with low-drag front calipers is CRAZY. Low-drag calipers need a 3-chamber/step-bore "Quick Take-Up" master cylinder, and the "NBS" unit is not. It is totally unfit for the job.

Are the K2500 calipers “regular calipers”…. not “low drag”?

My setup with the NBS MC and K2500 calipers (w/ SS lines and K3500 cyls on 11” drums) works exceedingly well. These ARE the best set of brakes in my stable of vehicles. I get wood at every stoplight using these brakes :)
 

Schurkey

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WHICH "K2500"?

Most 6-lug 2500s will have option code JN6, JB6, or JD6. Those are low-drag front brakes.

Most 8-lug 2500s will have option code JB7 or JD7. Those are not low-drag.

The big problem is that if the booster fails, pedal effort is very high. Even with a booster, the pedal effort is higher than GM intended due to the bigger master cylinder bore. Thus the advantage of the "3-chamber" master cylinder, where the third chamber moves a heap of fluid at low pressure, moving the pads into contact with the rotor, then the smaller bore develops the higher pressure to force the pads against the rotor with little pedal effort.
 

1998_K1500_Sub

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WHICH "K2500"?

Most 6-lug 2500s will have option code JN6, JB6, or JD6. Those are low-drag front brakes.

Most 8-lug 2500s will have option code JB7 or JD7. Those are not low-drag.

OK, I wasn't aware GM put the JB6 brakes on the K2500s, so I've been ignorant in my posts. I thought all K2500s got JB7 / JD7 brakes.

My K1500 Suburban came with the JB6 brakes, i.e., (as you know) 2-15/16″ bore low-drag front calipers, 11" rear drums and vacuum assist.

I now have the JB7 calipers/pads, which have a larger bore (3-5/32”) and are (based on your note) not low-drag.

This setup as I described earlier works *great*, although it was a work in progress over a span of years. At one time I had considered changing my system to hydroboost and I actually bought the booster new (which I still have, in box), but after completing all the changes I noted prior I'm completely happy with the vacuum boost.

The order in which I upgraded follows; these happened from 2013 to 2018:

- JB7/K2500 front calipers : ACDelco 18FR742, 18FR741

- SS brake hoses in front : Russell Performance

- NBS master cylinder (BIG improvement) : ACDelco 18M1159

- SS brake hose in rear and K3500 cylinders (noticeable improvement) : Russell Performance ACDelco 18E1362
 
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