GMT400 - a love/hate relationship

[vargsmetal]

The only common denominator I can find on the 8600lb 2500 trucks is the engine size. It seems to be broken down by small block (5.7, 5.3, 6.0) have had the SF and the big blocks (7.4, 8.1) have the FF. Again this is only from what I REMEMBER seeing I havent found any documentation either way. Dreis gmt900 2500 burb has the 6.0 and FF but it was a LE order vehicle so that may be the exception or maybe all gmt900 2500 burbs are FF.



Thats because the reg cab gmt 400 2500s were all 7200lb gvw or less so they would have the SF whether they were 6 or 8 lug. As for the gmt400s Im pretty sure only 2500 ccsb (cclb were 3500) and burbs were 8600lb gvw.

You could get any combination of options. There are tons of 8 lug (SF and FF) 8600lb 2500 regular cabs out there going back to the squarebody. Engine size didn't matter, although I agree that if it had a big block or a diesel it usually had the FF. The six lug 7200lb 2500 was pretty much always a regular cab, but I have seen some ext cabs. This became the 1500hd/2500 non hd but they're less common in the GMT800. The 1500hd is usually a crew cab, the 2500 non hd is usually a reg cab. I think they were all 6.0L but I seem to remember seeing the 5.3L being an option for the 2500 non hd.

I've seen lots of GMT800 2500hd's with a 6.0 and the AAM 10.5in FF. Regular cab or crew cab or suburban doesn't matter, it was just another box to check. Also, because these trucks are getting older and it's such an easy swap it's always possible somebody upgraded to the FF (or downgraded to the SF to get a dead truck back on the road).

8.1 and duramax trucks got the AAM11.5, I don't know if that was an option for the suburban/avalanche. I assume not, just like they didn't get the allison.

Point is you have to look to see what the truck has. When I bought my 1990 1500 I just assumed it had a 10 bolt because I didn't know any better. Found out it had the 14 bolt SF (RPO F44) from the factory when I went to service the brakes.

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[lilkia]

I was just going off the average lot truck. It would make sense you could order what ever combo you wanted. As for the 10.5 or 11.5 im not really sure how to visually tell the difference. Im guessing my burb has the 10.5. I do have a 3500 allison back on the farm I would guess is a 11.5 but Im no where near to compare the two.

 

[zelseman]

We enjoy our 2000 Cab and Chassis (school bus) It is DRW and has the FF 14B as stated.
I am weary of it as the 6.5L gets a bad rep, but my granddad had a 97 3500 SRW go FOREVER as a farm truck and hauling the boat to the lake. Good enough for me!

 

[Flazer]

I was just going off the average lot truck. It would make sense you could order what ever combo you wanted. As for the 10.5 or 11.5 im not really sure how to visually tell the difference. Im guessing my burb has the 10.5. I do have a 3500 allison back on the farm I would guess is a 11.5 but Im no where near to compare the two.

You should be able to tell by looking at the drive shaft input into the diff. I think the 10.5 will have some sort of collar for the pinion? Been a while since I looked into it.

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[vargsmetal]

I was just going off the average lot truck. It would make sense you could order what ever combo you wanted. As for the 10.5 or 11.5 im not really sure how to visually tell the difference. Im guessing my burb has the 10.5. I do have a 3500 allison back on the farm I would guess is a 11.5 but Im no where near to compare the two.

If I remember right the the AAM10.5 has a ribbed differential casing, the 11.5 is smooth like the older Corp 14 bolts.

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[usanumber1]

We enjoy our 2000 Cab and Chassis (school bus) It is DRW and has the FF 14B as stated.
I am weary of it as the 6.5L gets a bad rep, but my granddad had a 97 3500 SRW go FOREVER as a farm truck and hauling the boat to the lake. Good enough for me!

The 6.5 is solid for some and notsomuch for others. I was one of the unfortunate ones. Keep it cool and have spare PMDs on hand.

 

[jonathon]

Got the intake done. I think the trace of coolant in the oil was likely from the heater quick connect leaking and getting in through the distributor hole. There wasn’t gasket on the distributor. Also rebuilt the throttle body.

The only hiccup was I installed the distributor a tooth off so my marks didn’t line up. Rotated it one tooth and bumped the engine over so the distributor dropped right on the oil pump.

 

[Watt maker]

These are good trucks and makes me want to get another one. I had a 92 Z71 with the 5.7 and 5-speed manual. It was a great truck and took us all over the US. At one point, it had a screaming ProCharged 383 in it but I swapped back to a NA 350 after the 383 let go one night. The weakest link was the 10-bolt rear, which I eventually upgraded to a 14-bolt SF after the 3rd 10-bolt let go. I love the style on these trucks and found them super easy to work on. I always wanted to swap in a 6.0 LS with the NV5400 but sold it before that happened. Mine had over 200k miles on it when I sold it but ran great down the road. Unfortunately, the kid I sold it to wrapped it around a tree pretty hard about a year after I sold it to him.

 

[jonathon]

Still just driving it. Intake gasket is not leaking and now that it’s getting colder it’s nice having hot heat instead of just barely warm.

I’ve had a rattle in my exhaust for a while and noticed a high knock counts when driving with the laptop hooked up to it. Turns out at some point the rear most exhaust hanger broker causing all the weight of the tail pipe to be on the muffler which in turn cracked. I suspect I backed it into something

Being a cheap bastard I broke the sawzall out and zipped the tail pipe off at the muffler. I wanted to see if I could stand it dumped under the bed. Not annoying at all and no exhaust in the cab. Long bed helps a lot! Installed a new Summit two chamber muffler, a cheap turn down, and a couple u bolt clamps. Works great and cost me all of $60 since my catalytic converter and mid pipe were still good. Added benefit is the exhaust isn’t in a position to get destroyed now.

I also got to drive in our first snow. Have to say for cheap tires the Black Lion Voracio holds it’s own. LT version is severe weather rated with 16/32 tread when new. They took very little weight to balance too.

I’ve really learned to appreciate how well this long wheel base works. Looking forward to more winter trips.

 

[TwinDuro]

Any updates on your K2500 @jonathon? Good looking truck!

 

[jonathon]

I bought a new truck for family hauling. I still have the K2500 and am still driving it around the forest. The old 350 is chugging along nicely. It always had a cold start clatter until this last oil change. I did an oil change before winter and used some 8 year old Mobil1 5w30 I had from another truck and it is now quiet on cold start. Not sure what the next fill will be since I think Mobil1 has changed since I bought this.

My next project is to SAS it. If I can I am going to try and use a high pinion Dana 44 out of a 78-79 F250. Goal is to keep it as low as possible and run 33’s or at most 35’s.

I’m also watching sale pages locally for a TH400/NP241 combo as a backup for when the 700R4 inevitably dies from one too many loads of firewood.

 

[TwinDuro]

Sounds good! I’ll look forward to seeing the SAS swap here in the future. It’s a ways down the pipe, and I don’t currently need the capability at the moment, but I have thought about the exact same thing for my ‘92 Standard Cab Short Bed K1500: SAS with a ‘78-‘79 8 lug F-250 Dana 44, converting the rear 9.5 SF to 8 lug (easy) and doing a low lift on 315/70R17s.

Sounds like a plan on the TH400... that’ll do it!

 

[vargsmetal]

Considering how much cheaper the 73-87 Chevy Dana 44 or 10 bolt is, I'd lean that way if you didn't want/need a dana 60. However, by the time you add in the cost to get crossover steering on any of the dana 44's or 10 bolts, a kingpin 60 starts looking like a good deal - especially the 86-91 ford 60s which are available anywhere for around ~$400

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[Explorerinil]

Following. I have a 2000 K2500HD I picked up as a government surplus vehicle. Been looking into mods and maintenance for it. 120k miles and going strong.

Only thing weird is it's an 8 lug semi-float 14 bolt. Usually they're 6 lug when they have the semi-float.

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Nice dead ass reliable truck. If memory service me correct, they made a light duty 2500 or a heavy duty 1500. I rember a gm 1500 diesel truck in the 90’s along with a diesel full size blazer that had a semi floating 14 bolt.

 

[jonathon]

Considering how much cheaper the 73-87 Chevy Dana 44 or 10 bolt is, I'd lean that way if you didn't want/need a dana 60. However, by the time you add in the cost to get crossover steering on any of the dana 44's or 10 bolts, a kingpin 60 starts looking like a good deal - especially the 86-91 ford 60s which are available anywhere for around ~$400

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All very valid points. The main reason the 44 is attractive is I could keep it 6 lug and keep the 9.5” 14 bolt in the rear and keep my wheels. Going 10b is not a bad option either since they are basically free. I would need a passenger drop NP241 and those are a little less common but maybe cheaper and easier to find than an HP Dana 44.

I’ve been surprised at how cheap a Dana 60 can be had now.