Whats wrong with gmt400 brakes?

[User_name]

I just wanna ask what's wrong with these trucks brakes. What is it that people HATE about them? Why MUST hydroboost be the answer?
I replaced the front rotor/hubs and pads with delco parts and rebuilt the rears with carquest parts. (the one near me is still locally owned) the rears consisted of wheel cylinders, shoes, drums, and hardware.
These brakes feel better than my gmt 800s by a million miles lol. They feel (almost) as good as my camarys brakes. I still have the original master and lines, also the front calipers are original.
Maybe it mostly was an issue with the 1500s? I will be looking for an 88-94 1500 soon so it would be nice to know
(Current 400 is a 1995 c2500 8 lug sclb)

 

[HotWheelsBurban]

I just wanna ask what's wrong with these trucks brakes. What is it that people HATE about them? Why MUST hydroboost be the answer?
I replaced the front rotor/hubs and pads with delco parts and rebuilt the rears with carquest parts. (the one near me is still locally owned) the rears consisted of wheel cylinders, shoes, drums, and hardware.
These brakes feel better than my gmt 800s by a million miles lol. They feel (almost) as good as my camarys brakes. I still have the original master and lines, also the front calipers are original.
Maybe it mostly was an issue with the 1500s? I will be looking for an 88-94 1500 soon so it would be nice to know
(Current 400 is a 1995 c2500 8 lug sclb)

I think you're correct on the 1500 pickups. My 1500 Burb always stops well unless there's a problem in the system (bad master cylinder etc.). But Burbs got JB 6 brakes which gives them the 11 5/32" rear drums and bigger rotors up front.
And the 2500/3500s got 13" rear drums and big rotors. They do very well for stopping my 21' long CCLB! When my hydro boost unit was bad and locking them up/self applying the brakes, that big truck DID NOT WANNA move!
The 1500 pickups and some Tahoe's got the JB 3 or JB 5 brakes which have smaller rotors and 10" rear drums. No personal experience with them but most people on here say they work okay IF they're assembled correctly and properly adjusted. I didn't want to deal with that,so that's one reason I wanted a 2500 or 3500 pickup. Be careful what you wish for I guess....

 

[Caman96]

I have zero issues with brakes(JB5, 10 bolt). But I still want a 14 bolt SF!

 

[GrimsterGMC]

Mines a K1500 with the JB3 brakes and 33 inch tires. I replaced the master cylinder with the smaller bore to counter the larger diameter tires. You definitely have to keep the rear brakes adjusted as well as the parking brake as that has an affect on the main brake action. The biggest concern that I have is driving for a long time without needing to use the brake and the rotors etc get cold and then when some fool makes you jump on the brakes they take a couple of seconds to heat and bite. That feels like forever when the gap is closing fast. Once they have some heat they are fine. I have been reading on here about getting a higher friction rated pads but the suppliers don't specify what friction rating they have so it's a bit hit and miss since I can't just fly over there for the day to go brake shopping.

 

[Caman96]

Mines a K1500 with the JB3 brakes and 33 inch tires. I replaced the master cylinder with the smaller bore to counter the larger diameter tires. You definitely have to keep the rear brakes adjusted as well as the parking brake as that has an affect on the main brake action. The biggest concern that I have is driving for a long time without needing to use the brake and the rotors etc get cold and then when some fool makes you jump on the brakes they take a couple of seconds to heat and bite. That feels like forever when the gap is closing fast. Once they have some heat they are fine. I have been reading on here about getting a higher friction rated pads but the suppliers don't specify what friction rating they have so it's a bit hit and miss since I can't just fly over there for the day to go brake shopping.

What year K1500? Raysbestos Element3 for my 96 have HH rated pads, which I put on about 3 months ago.

 

[GrimsterGMC]

What year K1500? Raysbestos Element3 for my 96 have HH rated pads, which I put on about 3 months ago.

It's a 1988 so has the narrow 1 inch discs. I have been reading about those and will have to take a punt and order some and hope they are rated HH as well.

 

[454cid]

Have you ever driven an 8-lug GMT-800 or GMT-610? I've driven 2 of the 610s (Express van) and the brakes are much better than my 8-lug 400 ever was.

 

[Caman96]

It's a 1988 so has the narrow 1 inch discs. I have been reading about those and will have to take a punt and order some and hope they are rated HH as well.

Contact Raysbestos, they should be able to provide that answer.

 

[Schurkey]

I just wanna ask what's wrong with these trucks brakes. What is it that people HATE about them?

In approximate order of importance:
1. 254mm (10") Leading/Trailing shoe rear drum brakes on 1500s. More 1500s are sold by far compared to 2500/3500 that have decent rear drums (or discs on the C3500HD)
2. The first few years of regular-cab 1500 production got JN3-spec brakes--crappy power booster, crappy front calipers, and the crappy Leading/Trailing shoe rear brakes.
3. Failure to properly bleed ABS systems. First few years of GMT400 production, the RWAL had an iron body and a bleeder screw. After that...you need a scan tool to bleed the brakes.
4. Negligent owners/operators who don't maintain the brakes properly. Sticking calipers, degraded brake hoses, leaking wheel cylinders or leaking axle seals that contaminate brake linings, degraded brake fluid, etc. But this is not limited to GMT400 owners like the first three, it's pretty-much universal.

 

[1998_K1500_Sub]

I just wanna ask what's wrong with these trucks brakes. What is it that people HATE about them?

Other than what's already been said...

I wonder if some of these brake systems have wound up being serviced with incorrect parts, notably, a mix-up of low-drag calipers (or not) with quick-take-up master cylinder (or not).

AFAIK the JB5/JB6 brakes got low-drag calipers and a quick-take-up MC, which is relevant b/c these brakes were often OE on the C/K1500s... a popular version of the GMT400. At some point in their lives, these JB5/JB6 brakes may have been serviced with improper replacement calipers or MC. See the attached .pdf from Bendix, where they say:

"Most loaded caliper re-manufacturers do not differentiate between Low-Drag and conventional, listing just one model to cover many years of applications."

So unintentionally, a JB5/JB6 system might wind up with non-LD calipers, while retaining the original QTU MC.

If the caliper and MC components aren't matched (low-drag & quick-take-up), the brakes aren't likely to work well... and so the brakes on the GMT400s get a "bad name".

On the other hand, there were without a doubt certain brake / vehicle combinations in the GMT400 family that were simply duds.

The thread at this link (GMT400) goes into some discussion about the "low-drag / quick-take-up" mix-up: https://www.gmt400.com/threads/gm-low-drag-calipers-a-discussion-on-jalopyjournal-com.60055/