JB5 Rear to JB6 Drums 6 Lug - Help with Models to pick

[1998_K1500_Sub]

I have the NBS MC.

I have the NBS MC as well and I'm very pleased with the brakes. However, knowing what I know now, I would recommend the JB7+ MC instead, but I'm not about to replace my NBS MC and I don't suggest you replace yours either. The NBS MC has a notably larger bore (1.34" / 34mm) than the GMT400s (1.25" or 1.125", depending on vehicle and boost method), so arguably the NBS MC takes more pedal pressure to yield the same braking ability, all other things being equal. However, my use of oversized (for my vehicle) caliper pistons (3.15" vs. 3") and oversized brake drum cylinders (1.1875" vs. 1") helps re-establish more-or-less the master/slave cylinder ratio which the vehicle had originally.

That said, for the front then it sound like I should get the 80 or 83mm calipers off a 3500 chassis as noted above. Is it the same prodcedure then? Swap the correct hub/rotor/caliper from a 3500?

The larger-piston calipers come in two flavors, 86mm/3.385" piston calipers and 80mm/3.15". My OE were 76mm/3". I replaced them with the 80mm calipers. I wasn't aware at the time of the 86mm calipers. See...

Suburban axle swap

is he maintaining rabs functionality? Or... whatever a suburban has? That could get spicy 4 wheel ABS is standard in the 95+ and it wont be a problem. There are no ABS sensors on any GMT400 rear axle. As long as the gear ratio is the same, the ABS wont know the difference. My '00 Yukon...

www.gmt400.com

and

Upgrade Front Brake Calipers

How much of an upgrade is it using larger 12.50 caliper with the smaller 11.86 pads? Isn’t the pad to rotor surface the same? Is it just that much better a caliper? Not knocking any of this ^^^, just curious. Convince me, I may be interested.

www.gmt400.com

Regarding pads, some very modest tweaking is required. The JB7 pads are physically larger and (in most cases) rub against the 11" rotor's hat. See the posts in this thread:

Upgrade Front Brake Calipers

Hi I am new to the forum. I Looking to upgrade my brakes. I have a 88 GMC K2500 with 6 lug wheels..(7200lbs). I have front calipers with the 2.94 diameter piston. Has anyone upgraded to the 3.15 calipers from the 8 lug (8600lbs) calipers. Is this a direct bolt on caliper. The only difference...

www.gmt400.com

In the same thread also note the comments from others (such as @Supercharged111)
who have used the smaller JB5/JB6 pads in the larger calipers; they claim they'll fit with a little bit of tweaking.

Do take note: Somewhere in the GMT400 production run GM changed from SAE fittings to metric. I believe it was around 1997/1998 b/c one of my Suburban's front fittings was metric and the other was SAE (I was scratching my head about THAT one for a LONG time when I was trying to install replacement SS brake hoses). This shouldn't matter to you unless you're going to replace the hoses b/c, obviously, you'll want to get hoses that have fittings that mate with existing brake lines.

You may need to bleed your system, and with ABS that can involve other steps. @Schurkey may comment; I know he has posted on this topic. I have never bled the ABS on my 1998 and my pedal's as firm as any IMHO, perhaps I've just been lucky; I've bled the rest of the system, yes, but not the ABS using the service manual's procedure.

Here's another thread you might peruse over dinner:

Need help with brakes plz!

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...

www.gmt400.com

(edit) I've said here and in other posts that there are 86mm piston calipers for the GMT400, and occasionally I've included part numbers. I've not personally seen the 86mm calipers, I've simply quoted the specs. I do have a PICTURE, which I believe was posted on GMT400, of a caliper with a piston that's ~3.25" / 83mm diameter. So... be advised. I've attached the picture below. (edit) This observation is explained in a later post, read on...

 

[Redsled]

Excellent information! I have read it and your supporting thread links a few times and feel like I get it all now. I truly appreciate the time you put into writing a response. It has been truly helpful.

I will swap to the 2500 hub/rotor and run either the 80 or 86mm caliper (since i have the NBS MC). I can modify the 8600 pads no problem.

So the only thing I am wondering now is if I will run into a clearance issue running the 86mm caliper with my factory 16” wheel? If so, then hopefully the 80mm will work without that problem.

 

[1998_K1500_Sub]

I will swap to the 2500 hub/rotor and run either the 80 or 86mm caliper (since i have the NBS MC). I can modify the 8600 pads no problem.

So the only thing I am wondering now is if I will run into a clearance issue running the 86mm caliper with my factory 16” wheel? If so, then hopefully the 80mm will work without that problem.

With your K1500 you'll have to stick with the JB5/JB6 11" rotors. The heavier trucks could be had with 12" rotors but they're not an option here.

The 80mm calipers will work with the factory 16" wheels, I know that from my own truck. I suspect the 86mm will work as well but I do not have personal experience. If you look through the threads, I know somebody (@454cid?) posted about the 86mm calipers and may provide some insight. I think they were discussed in the context of the dual rear wheel trucks but I might be mistaken.

 

[Redsled]

With your K1500 you'll have to stick with the JB5/JB6 11" rotors. The heavier trucks could be had with 12" rotors but they're not an option here.

The 80mm calipers will work with the factory 16" wheels, I know that from my own truck. I suspect the 86mm will work as well but I do not have personal experience. If you look through the threads, I know somebody (@454cid?) posted about the 86mm calipers and may provide some insight. I think they were discussed in the context of the dual rear wheel trucks but I might be mistaken.

Yeah i just realized that about the rotors. I have building an excel spreadsheet all day with all this info. I should post here as a sticky for othets who go down this path, lol !!

Ill keep searching for an answer on the 16” wheel clearance question. But that is good know the 80mm will work. The parts store is just down the street from me. I thought about popping in, have them pull both calipers and see what the size difference is. That may give some insight….

 

[454cid]

With your K1500 you'll have to stick with the JB5/JB6 11" rotors. The heavier trucks could be had with 12" rotors but they're not an option here.

The 80mm calipers will work with the factory 16" wheels, I know that from my own truck. I suspect the 86mm will work as well but I do not have personal experience. If you look through the threads, I know somebody (@454cid?) posted about the 86mm calipers and may provide some insight. I think they were discussed in the context of the dual rear wheel trucks but I might be mistaken.

I have the largest calipers GM put on our trucks (no idea about piston diameter offhand), but that's 8-lug stuff. There are people that put "3/4-ton" calipers on their half tons, but I'm unsure of clearance issues, and I don't believe that's a combination that was ever factory. My setup was factory, just not on my truck.

 

[1998_K1500_Sub]

Take a look at this thread, it’s where I remember the 86mm calipers being discussed.

I’ll re-read it myself…

Link to post in thread 'Upgrade Front Brake Calipers'
https://www.gmt400.com/threads/upgrade-front-brake-calipers.58795/post-1266982

(Edit) In that thread @Schurkey illustrates how the 86mm piston will measure ~83mm b/c it’s necked-down at one end, put the piston is genuinely 86mm(!).

 

[Schurkey]

Wild Guess with no evidence: The 80mm and 86mm calipers are the same casting, with different machining for the piston bore.

If one fits...the other will, too.

 

[1998_K1500_Sub]

@Schurkey's post (above) got me thinking.

I copied these three pictures from RockAuto's site. They're ostensibly the 86mm, 80mm and 76mm calipers, pictured from the back.

The casting numbers seem different but that may be irrelevant.

The calipers pictured are a mix of "LEFT" and "RIGHT", so the bleeder appears on the opposite side; do not be confused by this.

Note:

- relative position of the bleeder to the adjacent caliper mounting boss; on the larger piston calipers, the bleeder is close to the mounting boss

- thickness and length of the web in the casting (illustrated with a red arrow in one picture, compare it to the others)

I'll have to study these a bit more. Others, please comment.

Large images are below; further down I've created a mosaic of smaller images which makes them easier to compare to each other

Centric FRC10183C 86mm (below)

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Centric FRC4413 80mm (below) - compare web size (red arrow) to those above and below

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ACDelco 18R746C 76mm (below)

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Mosaic - 86mm 80mm 76mm calipers (86mm top, 76mm bottom)

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[454cid]

Perusing that thread again, it's brought up about mixing and matching 6 and 8-lug parts and self clearancing. I haven't mixed 6 and 8 lug parts myself, and therefor won't recommend any of those combinations. I'm running all DRW parts up front (on my SRW K3500) except the spacers for the dually wheels. GM also did this on the later GMT-600 vans and according to Rockauto on the SRW extended cabs (but weirdly not the SRW crew cabs).

 

[Redsled]

Excellent comparison. Thank you for putting that together @1998_K1500_Sub . Interesting that the banjo bolt appears to be slightly different location on each. Based on these pictures I would guess I shouldn’t have any clearance issues with the 86mm, as @Schurkey indicated above.

Oh man I cant wait to do this upgrade! 86mm in lieu of my pathetic 63mm will be fantastic!! Now i need a beer!