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Stupid 14 Bolt FF Drum Question

kf4zht

Red Skull Member
Joined
May 20, 2020
Member Number
561
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1,074
Trying to do the rear brakes on my 96 K2500 Suburban (8 lug full float). Issues with the drums I got

Old brakes - 13x2.5 Shoes
3-1/8" Drum braking surface
Drum is about 5" tall. Studs were pressed in from the back, thru the drum and into the hub

New Drums (Autozone PN 8945C - Desc Says for 13x2.57 brakes)
3-1/4" braking surface
Longer outer lip
Drum is about 6-5/8" tall

I pressed the studs into the drums as before and thats when I noticed that when installed on the spindle there are only a couple threads showing on the spindle nut. Are these the wrong drums? Meant to go over the hubs maybe?

Help greatly appreciated. About over this project...

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you were given either

Drw drums, im not 100% on that because theyre traditionaly 3.5" surface

Or slip on drums. Which you axle should be if its a 96.

Slip on drums pinned to the back is most likely situation.
 
My guess is slip on drums. Maybe the listing for your application sucks because most 2500 Burbs have a semi float 14 and not a FF.
 
Truck is a 96 so it would be 7.4 or 5.7

Was that vintage ever offered as a BB 2500 4x4 with a FF?
 
Yeah, it's a 7.4 with a full float. With hydro boost

Looks like there are 2 versions of the 13x2.5 drums, I've ordered the other option to see if it will work. These did not work as slip overs, they were about 3/4-1" too short


What seems odd is most of the bb ff setups used the 3.5 wide drums my cousin has the same truck in a 93 with that setup.

I'm wondering since the hardware kits are identical if swapping to the 3.5 wide would be as simple as different shoes and the slip over drums. But I'm tried of screwing with this and just want it done. I'm sure the failed spindle seal dumping oil all over the brakes was a good part of my terrible braking performance
 
'96 Burb 2500 FF had slip on drums. Those new ones look like slip on drums.

The fact that you have back-mounted means it's a 2500 pickup axle. I'm 98% sure its been swapped. Why GM did it both ways the later GMT400's I don't know. The hubs are different between backmount and slip-on.

Edit: more trivia, the 3500 SRW used the slip-on-drum axle too.
 
u2slow said:
'96 Burb 2500 FF had slip on drums. Those new ones look like slip on drums.

The fact that you have back-mounted means it's a 2500 pickup axle. I'm 98% sure its been swapped. Why GM did it both ways the later GMT400's I don't know. The hubs are different between backmount and slip-on.

Edit: more trivia, the 3500 SRW used the slip-on-drum axle too.
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Yeah we would need to see some shit on that axle. Pinned on seemed odd to me too.
 
Sounds like it's been sorted out. But your new drums def look like to be for a semi float axle.

From the pic you have , if you had your hub mounted back on your old drum....it looks like the wheel mounting surface on you FF hub is close to the same distance as the wheel mounting surface of that new drum where the lug studs would poke out on a SF axle. Not saying the overall wms is the same between the 2 axles but I'm sure it's close.

Long winded but sounds like you just got the wrong drums, bc from the info I gather in this thread they did offer your burb with a factory option FF rear??

Edit: I bet if you put that that hub back on your old drum and put a straight edge from that wms to that new drum wms they prolly very close to each other. Not sure wms difference between SF to FF..gotta b close :smokin::smokin::smokin:
 
Snoop dogg said:
Sounds like it's been sorted out. But your new drums def look like to be for a semi float axle.

From the pic you have , if you had your hub mounted back on your old drum....it looks like the wheel mounting surface on you FF hub is close to the same distance as the wheel mounting surface of that new drum where the lug studs would poke out on a SF axle. Not saying the overall wms is the same between the 2 axles but I'm sure it's close.

Long winded but sounds like you just got the wrong drums, bc from the info I gather in this thread they did offer your burb with a factory option FF rear??

Edit: I bet if you put that that hub back on your old drum and put a straight edge from that wms to that new drum wms they prolly very close to each other. Not sure wms difference between SF to FF..gotta b close :smokin::smokin::smokin:
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If the new drums had slipped on and covered the shoes I would have ran it that way. Its already got spacers in the rear and duramax wheels so a small change wouldnt matter. I really think slip on 13x3.5 drums would fit, but I'm done putzing with this. Autozone's fit documents were trash and after going to all 3 parts stores to find one pair of shoes I'm tired of these. Got other stuff to do on this project.

total newb said:
Yeah we would need to see some shit on that axle. Pinned on seemed odd to me too.
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I'll snap some pictures. It it was swapped it wouldnt surprise me - no obvious wreck damage but this thing has led a hard life
 
kf4zht said:
If the new drums had slipped on and covered the shoes I would have ran it that way. Its already got spacers in the rear and duramax wheels so a small change wouldnt matter. I really think slip on 13x3.5 drums would fit, but I'm done putzing with this. Autozone's fit documents were trash and after going to all 3 parts stores to find one pair of shoes I'm tired of these. Got other stuff to do on this project.


I'll snap some pictures. It it was swapped it wouldnt surprise me - no obvious wreck damage but this thing has led a hard life
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I hear ya on that. I had a few beers last night and just thought I'd trow my .02 in.

Your front brakes work? No need for rears!:flipoff2:
 
Snoop dogg said:
I hear ya on that. I had a few beers last night and just thought I'd trow my .02 in.

Your front brakes work? No need for rears!:flipoff2:
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These were the fronts when I bought it
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I've done rotors and pads and they are better but not great, need to bleed/flush them now.
 
The FF with slide off drums showed up on the 2500 Burbs with BBC or 6.5td. Nearly always 3.73.

350ci got a semi-float; dunno if the FF was could be optioned. The C6P rpo is a heavy duty package, but the semi float still shows up with the lesser engines.
 
u2slow said:
The FF with slide off drums showed up on the 2500 Burbs with BBC or 6.5td. Nearly always 3.73.

350ci got a semi-float; dunno if the FF was could be optioned. The C6P rpo is a heavy duty package, but the semi float still shows up with the lesser engines.
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This one is a 3.73 ratio

Here are the RPO codes (per my glove box sticker)
C6PGVWR, 8600 lbs. (3901 kg)
GVW RATING 8, 600 LBS/3, 900 KG
GT4Rear axle, 3.73 ratio
AXLE,REAR,3.73 RATIO
G80Differential, heavy-duty locking rear
Differential, automatic locking rear
Differential, limited slip
Auto-locking rear differential
AXLE,REAR,POSITRACTION,LIMITED SLIP
JD7BRAKE HYD POWER, DISC/DRUM, 8,400 LBS

and pictures

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Looks like a 2500 pickup diff to me. The proper Burb version hub has more 'stickout', and the backside is not machined to accept a backmount drum

I'm not aware of an rpo code that indicates FF vs SF. It's seems to be other rpo's that trigger the upgrade (454/6.5td).

The caveat of the slide-off drum is the hub bearings don't get looked at routinely.... Probably run to oblivion and whole axle got replaced.

Edit: Burbs usually had a rear sway bar, and unique brackets on the axle housing. Half tons for sure. Cant recall on the 2500.
 
u2slow said:
Looks like a 2500 pickup diff to me. The proper Burb version hub has more 'stickout', and the backside is not machined to accept a backmount drum

I'm not aware of an rpo code that indicates FF vs SF. It's seems to be other rpo's that trigger the upgrade (454/6.5td).

The caveat of the slide-off drum is the hub bearings don't get looked at routinely.... Probably run to oblivion and whole axle got replaced.

Edit: Burbs usually had a rear sway bar, and unique brackets on the axle housing. Half tons for sure. Cant recall on the 2500.
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Very well could be swapped. Its got 290k on it, but based on mechanical I'd say the engine has been either swapped or rebuilt at least once.
 
Ok so I can be dense....very dense. But I'm struggling to see why this can't be sorted out?

You got the drum off......why not take it in to the parts store and run through some part #s till you match up the right drum on the counter top at the store?

Also....have you used rockauto? Probably a dumb question but go there to your 96 k2500 Burban and it brings up all the options for SF and FF drums.

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Click on the part and usually gives you multiple views. Use that pn# at napa/AutoZone...whatever.

Next thing. I was a little drunk last night. But is it not obvious that with your old hub on that new drum that is taller....isn't it obvious that setup would make your FF axle shaft too short? Look how much higher up the axle shaft bolts to hub compared to your old setup. I know you mentioned you didn't have enough threads for spindle nut which totally makes sense but I also don't you would have any engagement with the shaft splines at the carrier.
 
Rock auto shows some with a 4.6 and 4.8 hub hole....didn't check to see the depth for each one. But looks like plenty of options at the 5~5.25" drum depth.

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Like I said I'm naive and shit goes over my head way to easy...just trying to help and maybe I'm missing something obvious. Reading comprehension owns me:homer:
 
Ask for drums for a K2500 pickup with 454 or 6.5TD.

Edit: 4.6" is Chevy wheel pilot, so 4.8" is likely the backmount drum.
 
Last edited:
The wheel flange is moved on the hub body
For different things like srw/drw/slip on.

Axle shafts stay primarily the same with generations but the newer you get the more there are.

Srw and c&c use the same shafy despite the 4" wms difference.
Vans are wider housings with srw hubs, longer shafts
Drw full width have longer shafts, wider housing, and drw hubs.

After the 90 shit gets wierd with housing widths, slip on drums, discs, lots of variances.


U2slow keeps saying pickup axle, idk. I dont know the diff between the 2 but that is 100% a gmt400 axle.
 
total newb said:
Fucking why?
Thats how theyre supposed to be
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Not exactly. When you take them off and even put them on, you spread them out a little bit. It’s good practice to crimp them (mostly the yellow one) down a tad to ensure they won’t come off.
 
total newb said:
The wheel flange is moved on the hub body
For different things like srw/drw/slip on.

Axle shafts stay primarily the same with generations but the newer you get the more there are.

Srw and c&c use the same shafy despite the 4" wms difference.
Vans are wider housings with srw hubs, longer shafts
Drw full width have longer shafts, wider housing, and drw hubs.

After the 90 shit gets wierd with housing widths, slip on drums, discs, lots of variances.


U2slow keeps saying pickup axle, idk. I dont know the diff between the 2 but that is 100% a gmt400 axle.
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Good to know.
Well there's a whole list of part #s and measurements on rock auto. I figured it was common practice on older shit that you might have to do some digging to find the right pn#.

But I wouldnt have even spent the time to mount the hub to that new drum seeing the difference in depth between the old drum and new drum.

I guess that's where I'm confused....they are blatantly different. So why even try to mount the hub on that new drum? Was this supposed to be some upgrade?:confused:. It's not like these drums are hard to find....took me a few minutes on rock auto. Sorry maybe I'm dumb:homer:
 
Snoop dogg said:
Good to know.
Well there's a whole list of part #s and measurements on rock auto. I figured it was common practice on older shit that you might have to do some digging to find the right pn#.

But I wouldnt have even spent the time to mount the hub to that new drum seeing the difference in depth between the old drum and new drum.

I guess that's where I'm confused....they are blatantly different. So why even try to mount the hub on that new drum? Was this supposed to be some upgrade?:confused:. It's not like these drums are hard to find....took me a few minutes on rock auto. Sorry maybe I'm dumb:homer:
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Because they finally showed up after I'd had too many beers ok, some of us have solutions that get in the way sometimes. And I'd already pulled the drums off the hubs days before, they were on the floor under a stack of crap.

And none of the local places had any option in stock. But fawk autozone. In the list of compatible items they have shoes that are too wide and the springs off the smaller setup. Had to search by PN to even find the right one.
 
total newb said:
U2slow keeps saying pickup axle, idk. I dont know the diff between the 2 but that is 100% a gmt400 axle.
Click to expand...

25 years ago I worked at wrecking yard for 4 years that did GM products, and GMT400's were the mainstay. I dunno why I soaked up so much info :laughing:. Wish I'd programmed my head with something more useful :homer:
 
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