Optional rear springs

[Dieselwrencher]

I've never personally seen a 2wd GMC with coil springs. I've heard they existed but it's rare enough to see a GMC around here anyway.

[Mike C]

I currently have a ‘71 GMC 1500 127” wheelbase v-eight truck that is a factory big block and coil spring truck. My buddy has a ‘71 GMC as well with factory coils and is a small block truck.

2500 series GMC trucks from 69-70 is where most of my experience lies and I have had 4 of those. A ‘69 127” 350 small block truck that is leafs and a 7000# gvwr, a ‘70 127” wb 6 cylinder 3 speed truck with leafs and a 6600# gvwr, a ‘70 Longhorn small block 4 speed truck with 6600# gvwr which is obviously leafs, and a ‘70 big block turbo 400 truck that had a 7500# gvwr with the HD leafs. One of the things I find interesting is just how much variance there was within the 2500 platform for GVWR. The “3/4 ton trucks” capacity could vary by more than half a ton!

Special K is correct in his analysis, in my opinion, that GMC spec’d leafs on trucks unless coils were specific ordered. And since the trucks were made on the same assembly lines, they used the same nomenclature for the Chevy and GMC trucks for consistency which explained the paper trail.

And you are correct in stating, “At least for 1971” with your paperwork!

[davischevy]

I personally have never seen a half ton GMC with a standard coil spring option on the SPID.

This 72 GMC belongs to my friend. It has coils in the rear, and no mention at all of springs in the SPID.

[Steeveedee]

Originally Posted by sloGMC

So, I recently acquired a pile of GMC dealer general letters and service letters and ran across this gem. I understand that the vast majority of surviving GMCs have rear leaf suspension, but this is straight from the horse's mouth. Hopefully it clears up this great debate, at least for 1971!
As for Tow hooks on chrome bumper equipped trucks, I saw a dealer letter that, while referring to series 4500 and up, said that dealers can have the factory install Accessories (i.e., non-RPO equipment) using the Special Equipment process. Light duty trucks were covered under the COPO system, so I would speculate that some keen dealers may have used the COPO system to have the factory install tow hooks, which happen to be both an RPO and an Accessory. Seems to be no different than how Camaros were being outfitted with RPO engines not available as an RPO on that model.

I'd like to know where the mechanic achieved the 600 to 800 Ft-Lbs of torque on the pinion nut, on note 5 at the bottom right of the sheet you posted. We didn't get that kind of torque on the fasteners on steam lines in the engine room, and we used slugging wrenches.

[sloGMC]

Originally Posted by davischevy

I personally have never seen a half ton GMC with a standard coil spring option on the SPID.

And I think that's the what Service News Letter is confirming:

C1500 Series
Standard rear springs are coil rated at 1250.
C2500 Series
(includes 2590 and 2600 models)
The 2590 model has coil rear springs rated at 2000lbs. each as standard
The 2600 model has leaf rear springs rated at 2750 lbs. each.

This is also why on Longhorns, you don't see G70 for HD leafs. It is standard equipment.

As for the torque thing, I agree its a crazy big number but I can't speak to whether or not that's a typo or just how medium duty rear ends are.

[Killer Bee]

I've been using these 600lb wrenches in every shop I've worked in the last 30 years.. add torque multipliers for big jobs..



my guys are lazy nowadays, this hytorc gun runs 25 - 700 ft-lbs one handed

[57taskforce]

Originally Posted by Killer Bee

I've been using these 600lb wrenches in every shop I've worked in the last 30 years.. add torque multipliers for big jobs..



my guys are lazy nowadays, this hytorc gun runs 25 - 700 ft-lbs one handed

Yep we use 650 ftlb 3/4 drive Proto torque wrenches and multipliers on our big Ajax compressors, and some of the bigger Waukesha’s at work. Takes a big ole boy to run the 3/4’s. At 5-9 and 170lbs I don’t have enough lead in my ass to do it most days.

[Killer Bee]

Originally Posted by 57taskforce

Yep we use 650 ftlb 3/4 drive Proto torque wrenches and multipliers on our big Ajax compressors, and some of the bigger Waukesha’s at work. Takes a big ole boy to run the 3/4’s. At 5-9 and 170lbs I don’t have enough lead in my ass to do it most days.

yah but you fit everywhere us husky guys get stuck

I've got plenty of ballast but thankfully I don't have to yank on those anymore..

pinions, u-bolts, torque arms, load body mounts, cylinders, outriggers, aerial turrets, torque hubs, final drives, mains, head bolts, etc. all workouts I don't miss, especially the ones over head..

for the most part I just need these in my garage nowadays 1/4" dr - 1/2" dr

[sloGMC]

Originally Posted by Mike C

One of the things I find interesting is just how much variance there was within the 2500 platform for GVWR. The “3/4 ton trucks” capacity could vary by more than half a ton!

Yeah. So in '71 the GVWR goes from 6200-7500, but what's really funny is that the front/rear "Maximum Weight" can increase depending on the tire type ordered, but unless you got the bigger springs the GVWR won't, and vice versa. So there are trucks out there with the heavy spring option(s) but because they have base tires, they get the lowest GVWR rating. Seems like dealerships didn't really understand how it all worked, or didn't care. My truck happened to come with the base springs but heavier tires.

[sloGMC]

Found the "reference" letter from February, 1971. Look at the Note:

"These models have coil rear springs as the standard rear suspension. If a customer does not want coil springs, he can order RPO-G70, which is a two-stage rear leaf spring with the same rated capacity as the standard coil spring."

I see no logical reason why by year 4 of the model run, GMC would be spreading erroneous information to their dealers on multiple occasions. Coils must have been standard, but dealers felt like populating their lots with G70 equipped trucks.

[Richard]

My dear old dad long departed from us. Had told me GMC trucks were marketed as work trucks, heavy duty. Where as Chevrolet's were more marketed as a common every day truck. Dealers ordering GMC's to sell with higher rated load capacities does not seem like a bad idea.

[Dieselwrencher]

Originally Posted by davischevy

I personally have never seen a half ton GMC with a standard coil spring option on the SPID.

This 72 GMC belongs to my friend. It has coils in the rear, and no mention at all of springs in the SPID.

Larry, can you share pics of this truck in another thread? IDK if I've seen another Highlander GMC, and a GMC that had the wheel base on the spid. For what ever reason they always have a blank in the WB spot. Maybe this is plant specific as well? I have noticed ST.Louis built GMC's had a WB listed but none of the other ones do.

[Dieselwrencher]

Originally Posted by sloGMC

And I think that's the what Service News Letter is confirming:

C1500 Series
Standard rear springs are coil rated at 1250.
C2500 Series
(includes 2590 and 2600 models)
The 2590 model has coil rear springs rated at 2000lbs. each as standard
The 2600 model has leaf rear springs rated at 2750 lbs. each.

This is also why on Longhorns, you don't see G70 for HD leafs. It is standard equipment.

As for the torque thing, I agree its a crazy big number but I can't speak to whether or not that's a typo or just how medium duty rear ends are.

That may be but I haven't had many Longhorns that didn't have some sort of rear spring option code on the spid.

And, yes, that's just how big medium duty and heavy duty stuff is. Re torquing u bolts sucks. These new electric impacts are mint.

[Dieselwrencher]

Originally Posted by Richard

My dear old dad long departed from us. Had told me GMC trucks were marketed as work trucks, heavy duty. Where as Chevrolet's were more marketed as a common every day truck. Dealers ordering GMC's to sell with higher rated load capacities does not seem like a bad idea.

I have heard this more and more but who knows for certain? Here are a couple of GMC spids and they both have G70 as an option so maybe the GMC's weren't standard with leaves?

[sloGMC]

Originally Posted by Dieselwrencher

That may be but I haven't had many Longhorns that didn't have some sort of rear spring option code on the spid

Yup, and it still all makes sense. Those longhorns have optional leaf springs (G60, which includes G50), rather than the base leaf springs (2000# 2-stage leafs-- not G70), which would never be shown on an SPID (again, for Longhorn).

The truth is that between the 3 truck models (15/25/35) and the two sub-models (127"/133"), it is complicated, which is why GMC sent out the Service Letter in April-May, 1971 in post 25 , to "further clarify Data Book specifications concerning the optional rear suspensions available", and help dealers select the appropriate suspension package (post 35)