10 Bolt to 14 Bolt Full Floater Swap

[Schurkey]

How interchangeable are the axles from GMT800 to GMT400? Widths, spring spacing, shock mounts, park brake cables?

Rear discs don't interest me all that much. Mostly, rear-disc conversions are a lot of effort and expense for no real benefit. Front discs are another story. I've converted a few cars from front drum to front disc, one of them started with a single-circuit master cylinder which also got upgraded.

HOWEVER, in that I still haven't managed to tear apart my rear drums on the K2500 10.5" rear for inspection of the shoes, I guess the easier servicing of rear discs could be an advantage on those (full float, drums "riveted" to the hubs using the lug studs) axles.

 

[b454rat]

The later axles will work but as mentioned need to move perches. Not sure on cables, might swap over. My crew cab has regular brakes, tho haven't really driven it much, the pedal is right there. Just as much pedal movement as my 08 Tundra has, with huge discs all around. They both stop on a dime. Discs are also a heck of alot easier to change than drums!!!! Can swap pads on my tundra in about half n hour. Takes longer to jack it up n take tires off than to do the actual brakes.

 

[Crankshaft Brad]

I should have been a little more clear in my first post. The number one reason I am using a former sprint car engine (ish) is because at work we have a customer who phases out parts after so long, and I can get the parts at a good price. When this engine goes together; it will have less compression (to run on premium pump gas), will have a smaller camshaft to not beat the snot out of the valve springs and be easier on valve-train overall, and will not see north of 8,000 RPM hopefully ever. I am using the former race parts for two reasons; availability and absolutely overbuilt for what I need. If I make 500-600 HP, that is all I want for now. My theory is over-build the engine and it will not be under a strain.

This truck weighs in at 3,280 LBS with a 1/4 tank of gas and me out of it. I wouldn't say that I plan on racing this truck, but more of a fun weekend toy. I have had this truck since high school, and before that it was my grandfathers. I want to keep the rims as well because I revived those rims with my grandfather over christmas break my sophomore year of high school. They are American Racing outlaw rims, that i had stripped of clear using aircraft remover, and then a LOT of sanding from 80 grit to 1500 grit.

The reason I was thinking the 14ff was purely because it seemed to be the strongest, after some quick searching. I had no idea that a 14 bolt was that heavy, never would have guessed... I know there are plenty in the junkyard near me, and seemed to make sense (so I thought...) After reading i should go with an 8.8 or a 12 bolt?

This truck will never have enough tire or traction to seriously bust rear end parts. But with my luck I could really break some stuff. This truck will do burnouts a few times a year, and be driven throughout the year, but much less in the winter. I dont have any brand loyalty one way or the other. I was thinking GM rear ends because in theory more parts will line up, and save me the headache making everything work together. The disc brakes in the rears would be a plus, but not a must by any means.

 

[454cid]

How interchangeable are the axles from GMT800 to GMT400? Widths, spring spacing, shock mounts, park brake cables?

They don't interchange without moving mounts....no idea on brake cables.

Rear discs don't interest me all that much. Mostly, rear-disc conversions are a lot of effort and expense for no real benefit.

Don't confuse a real factory rear disc setup with steel plates and old Cadillac calipers. GMT-800 brakes are much better than ours, that date back to at least 1973 for the 14BFF.

HOWEVER, in that I still haven't managed to tear apart my rear drums on the K2500 10.5" rear for inspection of the shoes, I guess the easier servicing of rear discs could be an advantage on those (full float, drums "riveted" to the hubs using the lug studs) axles.

So is your RPO is JB7, then?

 

[Erik the Awful]

This truck weighs in at 3,280 LBS with a 1/4 tank of gas and me out of it. I wouldn't say that I plan on racing this truck, but more of a fun weekend toy. I have had this truck since high school, and before that it was my grandfathers. I want to keep the rims as well because I revived those rims with my grandfather over christmas break my sophomore year of high school. They are American Racing outlaw rims, that i had stripped of clear using aircraft remover, and then a LOT of sanding from 80 grit to 1500 grit.

A 5-lug 14-bolt is hard to find, but alternatively, 6-lug 14 bolts can be re-axled,. The advantage of a 14 bolt is that it would bolt in and go. I think we need to get a 14-bolt on a scale, but I don't have one handy. If it's close to an 8.8", re-axling the 14-bolt would be a prime choice.

A 12-bolt would be even harder to find as they were only produced between 1965 and 1972. If you don't mind spending money, motortrend.com says Moser is making new 12-bolt housings.

The main advantage of the 8.8" is they hit the trifecta of strong, light, and cheap. The hurdles would be mounting and figuring out if your brake system needs mods to play well with the discs. If I get a chance today, I'll put my 8.8" on a scale.

 

[b454rat]

12 bolts went up to 76-77, after that was the 10 bolt. 14sf are prolly 30lbs-ish. I never had one or messed with one in a long time. I know the 14ff's are heavy mo fo's, drop a nut trying to move one of them around. As for brakes on the 14sf, i think it was in here somewhere, but 6 lug stuff, that can use brake set up off burbs and Tahoes/Yukons. They have the bigger brakes, and want to say can unbolt the backing plate, and all swaps over to the 14sf. But, never looked into it. Im going right to the 14ff over the 10 bolt in my Yukon.

 

[Schurkey]

Don't confuse a real factory rear disc setup with steel plates and old Cadillac calipers. GMT-800 brakes are much better than ours, that date back to at least 1973 for the 14BFF.

I'm no fan of the crappy disc conversions as you mention.

Haven't driven a GMT800, but the JB6-equivalent brakes on my K1500 are making me smile, RWAL and all.

So is your RPO is JB7, then?

On the K2500, yes. A mess to service. They work well enough, but the design is dumb. Who puts the sacrificial rotors and drums on the INSIDE of the hub, held in place with the friggin' lug studs???

 

[stutaeng]

I think the WMS is a bit wider on the newer axles, maybe an 0.5" or 1". I compared them, but I can't remember at the moment. Yes, spring perch relocation. I don't know on the parking cables, but I've seen threads of it being done. As mentioned the discs/pads are easier to change. I've never owned a vehicle with drums until the K3500. I think the discs is a bit lighter brake system vs drums, not that it really matters. Don't know how braking power would compare?

I honestly don't understand why this not a common swap on the GMT400 line. There's A LOT of GMT-800/disc axles (10 bolt, 14 bolt 9.5" and 10") on wrecking yards and they are really cheap. I can't imagine myself installing parts from 70s Eldorado or whatever to gain discs on a drum setup if I was going to.

I think I can sell my 14b/4.10/G80/drum that's in the truck right now to some Jeep enthusiast, and recoup my cost. But the swap for me is very low on the priority list, LOL.

 

[smdk2500]

but the design is dumb. Who puts the sacrificial rotors and drums on the INSIDE of the hub, held in place with the friggin' lug studs???

More time for doing repair work means more money in dealer/shop/techs pocket less in customers pocket. I agree it is a very stupid idea to do it that way. The 1500 stuff wasn't like that why make the 2500/3500 stuff that way. Some one was smoking some good stuff when they thought of it.

 

[Erik the Awful]

My Explorer 31-spline 8.8" with 3.73s and LSD weighs 186 lbs with parking brake cables and rotors, but without calipers.