IRS in a gmt400

Wont an IRS from a car have too low a roll centre for a truck?

Whoa, I had no idea about that truck. Pretty cool! I wonder if Eddie still has his, or well now, his son Wolfgang. Which truck was left outside to rot? -Probably Eddies. I imagine the dude who in Lansing who won the other one has cherished it.

Pinger said:

Wont an IRS from a car have too low a roll centre for a truck?

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Maybe for a stock height truck, but I really doubt OP is putting this one something with 33's

Pinger said:

Wont an IRS from a car have too low a roll centre for a truck?

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Shouldn’t be a problem, I’m aiming for about a 6-7” rear drop

Why? The only reason I can see to do this would be to make a "show truck" where the "Wow" factor of what you've done matters more than how well it actually works.

For a truck that does truck things, the rear suspension GM put in these trucks is the most efficient way of gettin' it done.

If I were building a race truck, I'd put a 4-link and coilovers on the solid axle before I'd swap an IRS from another vehicle in. If the IRS isn't designed for the vehicle, you're likely to make the handling worse. Also, that IRS with the subframe is heavier than a solid axle, so you're facing diminishing returns on the work required.

0xDEADBEEF said:

Might be easier to weld in the back half of a new suburban frame. No idea. Assuming you can find one.

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That might be close enough in design to work well, but it's a lot of effort when you could probably get better value tackling a real deficiency.

...but...

If it's your dream, go for it. I think the TIXX Suburban IRS would be the best option, provided you have room to get the wheelbase near the same.

EDIT: I highly suggest reading this book before attempting an IRS swap. www.amazon.com/Chassis-Engineering-Building-Performance-Handling/dp/1557880557/

Erik the Awful said:

Why? The only reason I can see to do this would be to make a "show truck" where the "Wow" factor of what you've done matters more than how well it actually works.

For a truck that does truck things, the rear suspension GM put in these trucks is the most efficient way of gettin' it done.

If I were building a race truck, I'd put a 4-link and coilovers on the solid axle before I'd swap an IRS from another vehicle in. If the IRS isn't designed for the vehicle, you're likely to make the handling worse. Also, that IRS with the subframe is heavier than a solid axle, so you're facing diminishing returns on the work required.


That might be close enough in design to work well, but it's a lot of effort when you could probably get better value tackling a real deficiency.

...but...

If it's your dream, go for it. I think the TIXX Suburban IRS would be the best option, provided you have room to get the wheelbase near the same.

EDIT: I highly suggest reading this book before attempting an IRS swap. www.amazon.com/Chassis-Engineering-Building-Performance-Handling/dp/1557880557/

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I have a few reasons I’m debating doing the IRS. I’ve seen it done on c10s and the results seem to be great as far as handling and ride quality. Yes it would be heavier than just doing a 4 link but it is significantly less unsprung weight. It’s far cheaper than doing a 4 link and building the axle, disk brakes etc… as I can get a complete subframe with all suspension components, 14” Brembo brakes and drivetrain for under $2000.

Also I looked into the suburban IRS and it’s to wide, the wheels would stick out about 1.5” past the fender on each side

DerekTheGreat said:

Whoa, I had no idea about that truck. Pretty cool! I wonder if Eddie still has his, or well now, his son Wolfgang. Which truck was left outside to rot? -Probably Eddies. I imagine the dude who in Lansing who won the other one has cherished it.

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EVH's truck sat beside his home studio/converted garage for years. Tires flat, paint cracked & faded, covered in leaves from the trees it was parked under. It was in pretty sad shape.
Just after Boyd's passing, it was restored by the same crew that built it. Boyd's kid's wheel co. made up a new set of larger wheels in the same design as the originals.
Shortly after, it went across the block at Barrett/Jackson & sold for less than the cost of the second resto. EVH was still alive at that time. Like his guitars, with his passing, it's probably worth considerably more now.
The give-away truck used to be spotted fairly often in the mid-west, but it hasn't been seen for a few years now. 10 years? Maybe more. The last pix I saw of that truck, it looked like it had been used as a truck, daily, since it was built.
Apparently, it's changed hands a couple of times since it was given away.

There was a member here a few years ago that slid a C4 IRS under his 4/6 dropped ExCabSB. Took him a couple of weekends. According to him, it wasn't all that hard to do (obviously, he had skills) & with the experience of the first swap, claimed that it could be done over a weekend. In Friday afternoon, done by Sunday night.
Yea, the C4 IRS is heavier. But as these trucks are weight-biased towards the front anyways, the additional in the rear actually made that bias more favorable when it came to corner-carving.

That newer style looks considerably heavier than the C4.

Erik the Awful said:

Why? The only reason I can see to do this would be to make a "show truck" where the "Wow" factor of what you've done matters more than how well it actually works.

For a truck that does truck things, the rear suspension GM put in these trucks is the most efficient way of gettin' it done.

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How many "truck things" do you expect a truck with a 6" drop like OP mentioned to do? A lot of folks on this site seem to really struggle with the concept of a truck not being used for cargo.

Keep reading that post. I went into race trucks right after that. I did not go into "highway cruisers", and maybe that's the point I'm missing.

351FUN said:

How many "truck things" do you expect a truck with a 6" drop like OP mentioned to do?

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If the drop is done correctly, a 6" dropped truck can do all the truck things it was intended to do from the factory.

351FUN said:

A lot of folks on this site seem to really struggle with the concept of a truck not being used for cargo.

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Yeah, and also with the idea that manufacturers have specific goals when they engineer things, if a person's goals differ from those of the manufacturer, modifications are better than stock. The Mercedes folks are the worst. "Why do you think you know better than a Mercedes engineering team? Leave it stock." Uh, no.