Leaf or coil standard rear spring on GMC?

[71CHEVYSHORTBED402]

Originally Posted by Mike C

I think one that that I don’t remember being referenced is that over time GMC became much less it’s own thing and much more just like the Chevy’s. So a ‘72 GMC is most likely equipped almost exactly as the Chevrolets while a ‘69 is more likely to be more of its own thing. Whatever that is.

I have owned 4 C2500 GMC, and they all have different GVWR and they all had leaf springs. They also all had Dana 60 rears. A 69 small block TH400, a 70 Longhorn small block SM/465, a 70 250 3 speed, and a 70 Sierra Grande 402/TH400. None of them had Leaf Spring on the SPID.

And then I have the 71 C1500 which is on coils. It’s a 402/TH400 truck and spring type is not listed on the SPID, but that jives for a Chevy of that same vintage.

My ‘69 short step C10 is a leaf spring truck with 307/TH350 and it is on the SPID. A parts 69 short step I have is a 250/3 speed truck on coils and they are not on the SPID.

So earlier GMC seem to follow the leaf thing and the later ones seem more likely to be coil in my small sample informal analysis.

And the Canadian trucks? Who the heck knows what’s going on there.

Makes some sense of it.

I can only speak for two trucks personally, both after 1970.....99% sure the 71 SWB was special ordered with rear leafs by the dealer, for a specific customer.

I think the random plate matching both engine badges is called irony..Destiny?

[Mike C]

I see SPIDs that have an order number on the lower right and I have always assumed that was a vehicle with a specific option list requested by a customer while the SPID that did not have that was just bought off the lot. Not sure if that is true or not, but the short bed SPID you show does not have an order number at the bottom right. The longbed truck we can’t see that.

My 72 Jimmy does NOT have an order number at the lower right, but the 72 Jimmy we restored for my kid DOES have an order number at the lower right.

[sloGMC]

Originally Posted by 71CHEVYSHORTBED402

I know an old thread, miss some of these guys, including SStim, who hasn't showed his head 5-6 years now.

Looks like this has been beat with a dead horse over the years, perhaps adding confusion however...... I learned nothing reading through this thread and 1-2 like it, beyond it's confusing though maybe there's a dose of clarity into these murky waters.

I think the gist is for C10's built in the USA is:

A. Perhaps conflicting with GM's "clarification" document below, C10s were generally built with rear leaf springs, just cuz, and show a leaf spring RPO on the SPID.

B. Rear coil springs were standard in C10, which is RPO G50.

Not sure on years though, a change seems to have occurred in 1971. Perhaps that change was coil springs became standard in C10 Chevy, but not in C10 GMC, just cuz.

The service news letter from 1971 is part of a series of communications beginning with the 1969 model year about available suspensions, sagging, and overloading the trucks. There remains no documented evidence that GMC was any different than Chevrolet regarding base equipment -- coils were standard, and leafs were optional. Some literature indicates that both were optional and neither were base. Reality 50 years later makes it appear that most GMCs were made with leaf suspension, but there's at least two explanations at play here:

1) GMC as a brand decided that they wanted more leaf suspensions on dealer lots, so that's what they built and provided to the dealers; the optional leaf suspension

2) Survivorship bias; they fact that more leaf-equipped GMCs exist today does not prove that more existed when they were built or that it was base equipment, merely that more leaf-equipped trucks are still on the road.

Consider the following scenario:

For some reason, 50 years into the future the current K2XX truck platform is super popular. If you were going to infer base equipment on the volume of said option or model, decades after production, you might talk yourself into thinking that the Crew Cab, Short bed, SLT or Denali trim were base equipment, because all the single-cab work truck models have long been scrapped. Obviously that would be an incorrect assessment.

The same argument applies here -- no documentation has ever specified that that leaf springs were base equipment on GMCs, but why it appears that more GMCs were built with the optional leaf suspension, take your guess.

[71CHEVYSHORTBED402]

Originally Posted by Mike C

I see SPIDs that have an order number on the lower right and I have always assumed that was a vehicle with a specific option list requested by a customer while the SPID that did not have that was just bought off the lot. Not sure if that is true or not, but the short bed SPID you show does not have an order number at the bottom right. The longbed truck we can’t see that.

My 72 Jimmy does NOT have an order number at the lower right, but the 72 Jimmy we restored for my kid DOES have an order number at the lower right.

Interesting. Well, I find it a little peculiar this garage would simply stock a SWB 402 2WD with rear leaf springs, camper mirrors, and step bumper too. That's assuming the (*)^ saddle tanks were installed post factory, it had those too - I'd think factory would show on a SPID.

Doesn't strike me as a winning combination when a LWB is much better choice for the cause, so I figure number or not, 90/10 "special" ordered by the garage if not the customer, small town stuff perhaps. Gardnerville Nv. sure was, and still has a small town flavor, nice place. The original owner installed a boat launching hitch too, cut the front bumper to do it. There was a BA camper on it, and brackets welded onto the frame to destroy the bed floor for a fifth wheel too. Assaulted the cab's top rear for a CB too....dude liked recreation.

Pic. of a recreation of the garage, done many moons ago. It was on the wall of my buddy's shop.

[71CHEVYSHORTBED402]

Originally Posted by sloGMC

The service news letter from 1971 is part of a series of communications beginning with the 1969 model year about available suspensions, sagging, and overloading the trucks. There remains no documented evidence that GMC was any different than Chevrolet regarding base equipment -- coils were standard, and leafs were optional. Some literature indicates that both were optional and neither were base. Reality 50 years later makes it appear that most GMCs were made with leaf suspension, but there's at least two explanations at play here:

1) GMC as a brand decided that they wanted more leaf suspensions on dealer lots, so that's what they built and provided to the dealers; the optional leaf suspension

2) Survivorship bias; they fact that more leaf-equipped GMCs exist today does not prove that more existed when they were built or that it was base equipment, merely that more leaf-equipped trucks are still on the road.

Consider the following scenario:

For some reason, 50 years into the future the current K2XX truck platform is super popular. If you were going to infer base equipment on the volume of said option or model, decades after production, you might talk yourself into thinking that the Crew Cab, Short bed, SLT or Denali trim were base equipment, because all the single-cab work truck models have long been scrapped. Obviously that would be an incorrect assessment.

The same argument applies here -- no documentation has ever specified that that leaf springs were base equipment on GMCs, but why it appears that more GMCs were built with the optional leaf suspension, take your guess.

Was 1969 a cutoff point for something? Were all 67-68 GM trucks leaf spring or?

[sloGMC]

Originally Posted by 71CHEVYSHORTBED402

Was 1969 a cutoff point for something? Were all 67-68 GM trucks leaf spring or?

69 is the change of bedside trim. There's a service news letter that discusses "sagging suspensions" and GMC points to two possible culprits:

1) old bedside trim sits higher, so it might make newer trucks appear lower

2) customers and dealers don't understand the suspension options and are overloading service bodies. for example, RPO G70 "hd rear leaf suspension", isn't actually heavy-duty -- it's just the 2000# rear leafs. the upgraded suspension is G50 and G60.

Looks like I'm remembering an earlier communciation from '71, not '69. If I haven't already posted it, here it is. I also just noticed the line in the middle that explicitly says "these models have coil springs as the standard rear suspension".

[71CHEVYSHORTBED402]

Originally Posted by sloGMC

69 is the change of bedside trim. There's a service news letter that discusses "sagging suspensions" and GMC points to two possible culprits:

1) old bedside trim sits higher, so it might make newer trucks appear lower

2) customers and dealers don't understand the suspension options and are overloading service bodies. for example, RPO G70 "hd rear leaf suspension", isn't actually heavy-duty -- it's just the 2000# rear leafs. the upgraded suspension is G50 and G60.

Looks like I'm remembering an earlier communciation from '71, not '69. If I haven't already posted it, here it is. I also just noticed the line in the middle that explicitly says "these models have coil springs as the standard rear suspension".

Cool....That was released 2-3 months before my truck C10 was built.

[Mike C]

Originally Posted by 71CHEVYSHORTBED402

Interesting. Well, I find it a little peculiar this garage would simply stock a SWB 402 2WD with rear leaf springs, camper mirrors, and step bumper too. That's assuming the (*)^ saddle tanks were installed post factory, it had those too - I'd think factory would show on a SPID.

Doesn't strike me as a winning combination when a LWB is much better choice for the cause, so I figure number or not, 90/10 "special" ordered by the garage if not the customer, small town stuff perhaps. Gardnerville Nv. sure was, and still has a small town flavor, nice place. The original owner installed a boat launching hitch too, cut the front bumper to do it. There was a BA camper on it, and brackets welded onto the frame to destroy the bed floor for a fifth wheel too. Assaulted the cab's top rear for a CB too....dude liked recreation.

Pic. of a recreation of the garage, done many moons ago. It was on the wall of my buddy's shop.

My dad bought the Jimmy off a used car lot here in Austin in 1977. It was bought by a rural realtor who had already put 113k miles on it. Truck is a Custom with AC, positraction, power steering, gauges, 4 speed and other things you would expect to see on a well optioned truck, INCLUDING cruise control and AM/FM radio. But neither the cruise nor the AM/FM were on the SPID my assumption being the truck was one that was on the lot and the customer wanted those additional options so they were added by the dealer. Other than the in dash AC, 4 wheel drive or rear suspension type, almost everything else could be easily swapped or added by a dealer at the time so who know what you might find on the lot. But I will probably never know how it actually played out.

[factorystock]

Originally Posted by factorystock

This is were we need to be year specific and assembly plant specific, many a times, we start throwing out info, without knowing any history of the vehicle. The Canadian built pickups always throw a monkey wrench into the discussion. First post says nothing about year, and a Canadian sales sheet to boot. Almost like Dana or corporate axles in a GMC?

My advice then, and now, the same. Reminds me of the GMC trim thread. Wait till an owner GMC 1/2 chimes in and doesn't mention it's a '67.