Swapping 13"x2.5" to 13"x3.5" drum brakes

[1998_K1500_Sub]

Assuming my K2500 has 13"x2.5" drum brakes, and I am almost certain it does (5.7L, 8600 GVWR, JB7 code), would it be possible for replace the 2.5" components with 3.5" components (e.g., drums, wheel cylinders, hardware, etc.)? (Sorry, just have not had time to take a peek at the rear brake component yet.)

Here's a random question:

If one uses the same slave cylinder, and same diameter drum / shoe (13" in this discussion), does it matter if the drum / shoe is 2.5" or 3.5" wide?

Clearly it does, but why?

An answer probably ought to address, at least:

- The braking force (torque required to turn the drum, manifest as a force at the tire edge) depending on hydraulic pressure applied to the slave cylinder. Is the braking force the same or different? Why?

- The braking capacity, which could be interpreted as "How long can I have the brakes applied before they fade?" or "How much heat can I sink into the drums before braking degrades?" Is the brake's capacity the same or different? Why?

 

[xXxPARAGONxXx]

That is how I would understand it. Mine is a 98 k2500 350, NV4500, 10.5 ring gear with 13x2.5 (JB7) brakes. I think 3500 single wheel trucks and possibly 2500 suburbans came with 13x3.5 (JB8) brakes.

Wait, you have a K2500 with a 5.7L Vortec with a 10.5" full-float rear axle? I didn't know that was even possible.

 

[HotrodZ06]

Wait, you have a K2500 with a 5.7L Vortec with a 10.5" full-float rear axle? I didn't know that was even possible.

According to my vin it came from the factory that way. May have something to do with the NV4500 though.

 

[HotrodZ06]

Here's a random question:

If one uses the same slave cylinder, and same diameter drum / shoe (13" in this discussion), does it matter if the drum / shoe is 2.5" or 3.5" wide?

Clearly it does, but why?

An answer probably ought to address, at least:

- The braking force (torque required to turn the drum, manifest as a force at the tire edge) depending on hydraulic pressure applied to the slave cylinder. Is the braking force the same or different? Why?

- The braking capacity, which could be interpreted as "How long can I have the brakes applied before they fade?" or "How much heat can I sink into the drums before braking degrades?" Is the brake's capacity the same or different? Why?

In theory the added surface contact area would provide better braking and more material in the drum should help with heat dissipation some, the question is how much is the cost/benefit of upgrading.

 

[stutaeng]

In that case, I'd be tempted to just swap a GMT 800 2500HD+ 14 bolt 10.5 with discs. There are thousands of them across the country. And it's been done before, I just don't have the specifics.

I actually have one of them in my parts "stash" but I'm still not decided if I'm going to keep my GMT 400 K3500... otherwise I would swap it.

I know OP said not interested in a "conversion" but the GMT 800 10.5 is not a direct swap, but it would be an upgrade... debatable if it's worth it.

I'm pretty sure the 2500HDs got the higher brake code, as the GVWR was 9200#, same as the C/K3500 SRW.

What do you think OP?

 

[HotrodZ06]

I think the spring perches are further apart on the GMT800 but not sure. If you have one to measure would be good info, but even if it is nothing a welder couldn't fix.

 

[stutaeng]

I think the spring perches are further apart on the GMT800 but not sure. If you have one to measure would be good info, but even if it is nothing a welder couldn't fix.

Yes, 1" wider. The MWS is 1" wider overall IIRC.

I can sorta weld, so that's not really a concern for me.

Brakes scare me, just because I haven't really messed with them. The e brake is what I really don't know. Someone here said they used brake cable extensions? Again, not a brake expert by any means...

Just have done brake pads and rotors. I've never messed with drums or brake bleeding. Maybe a shame on my part.
.

 

[HotrodZ06]

Yeah , not sure about the e-brake either. I will just stick with my 13x2.5 brakes if I can't find the backing plates and put the dually front rotors on I already have.

 

[Dropped88]

Wait, you have a K2500 with a 5.7L Vortec with a 10.5" full-float rear axle? I didn't know that was even possible.

Mine was a c3500 5.7L 4l80 with 10.5 full float so yes they did some odd combinations.

Why a 350 in a 1 ton.

 

[Schurkey]

The C/K2500 BBC/Diesels also got the 10.5", but I don't know what brake RPO code they got?

My '97 K2500 7.4L (8600 GVW) has JD7 brakes.

I'll have those rear brakes apart as soon as I get the intake gaskets installed on the K1500. Again.

In '97, at least, there's JB8 single-rear-wheel, and JB8 dual-rear-wheel. The difference is in the front rotors--same diameter, but about 1/4" thicker on the DRW. That may mean that the calipers are also wider to accommodate the thicker rotors.