Independent Rear Suspension (IRS) Possible?

Maverick6587

Well-Known Member
It was a thought I had the other day so, I figured I would mention in this group and see if it's a possibility for the GMT360's.

I assume that no light-duty or heavy-duty trucks have IRS. Does anyone know if any SUV's have had an IRS that might fit the GMT360 frame? I know the Buick Rendezvous has IRS but, that seems too small to fit the GMT360, maybe not.

Just trying to figure out if there is any axle out there that might fit the GMT360, with minor tweaking.
 

HARDTRAILZ

Moderator
I do not know of anything as heavy or sized as ours with IRS, but I am curious why you would want to weaken the rearend setup?

I mean you may be able to adapt a corvette diff setup, but it would need some strengthening to handle weight. The diff would likely be enough and width not too far off, but I am sure double the weigh carrying even sans towing or loading the hatch area would require significant strengthening.
 
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Maverick6587

Well-Known Member
I do not know of anything as heavy or sized as ours with IRS, but I am curious why you would want to weaken the rearend setup?

I mean you may be able to adapt a corvette diff setup, but it would need some strengthening to handle weight. The diff would likely be enough and width not too far off, but I am sure double the weigh carrying even sans towing or loading the hatch area would require significant strengthening.
I understand that I would lose some of the durability in not having a solid rear axle. I don't plan on racing it or going off-roading at all. The ride is just not very good at all. My GF's old 2003 Rendezvous and her newer 2008 Ford Escape, both rode A LOT better than my 97x.

I do have to still change my struts and probably convert the rear shocks back to Bilsteins, but it's not even close to the ride of most vehicles I ride in. Both of her vehicles had/have IRS. That's mainly my interest in the possible conversion.

I was actually thinking of using a corvette IRS. I've seen them put on older 50's I think Ford trucks. I think the Corvette IRS even fits the Ford Lightning series trucks.
 

C-ya

Well-Known Member
Does your vehicle have air rear suspension or spring? That is where you get the cushy ride. The shock absorber just dampens the oscillations. I have an '05 TB EXT that rides pretty darn nice. It has springs and Bilsteins at all four corners. If you have a bags, you could ensure the sensors are working correctly to control the pressure and that the check valves and bleeders are functional. Too much air = too stiff.

I think you could get by with a spring swap - either softer springs or spring replacements for the bags - for much less effort and money.

ETA after reading @HARDTRAILZ 's comment below - you can get a "softer" shock that responds more slowly and less harshly. The Bilstein was a bit stiff when new but settled in nicely for my tastes.
 
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HARDTRAILZ

Moderator
There are several spring options if you want a smoother ride. Combine that with some good shocks and your desire may not like the bilstein since they tend to be stiffer than others.
 

TollKeeper

Well-Known Member
I have a Pontiac Aztek (Buick Rendezvous clone in Pontiac clothing), and the IRS on it is actually quite substantial and weak, and I can guarantee you would never get it to mount in the GMT platform without sectioning the frame, and rerouting the frame.. Its mounting bolts are probably 30-36 inches apart front to rear and side to side, square. It sits on a aluminum cradle. The differential is also a huge HUGE pile o sh** (I just replaced mine Saturday), and its a passive diff (electromagnetically activated) with a torque tube that runs half the length of the FWD platform. On our RWD platform, the torque tube would probably go all the way to the transmission.

Have to remember that the Aztek/Rendezvous was based on the U-Van chassis, The Chevy FWD Uplander/Venture. And the AWD system it has was borrowed from the same chassis, just shortened to fit in the Az/Vous chassis.

The later years Ford Explorer also had IRS, and actually rode fairly decent, as did the Expedition. So I would say that the conversion is possible, if you dont mind using Ford parts.... :lipsrsealed:🤮

Having riden in a a Escape, a Rendezvous, and a Aztek, that have apsolutely horrible ride, I could not even imagine have that harsh of a ride on a GMT. I like my Cadillac ride.
 

Sparky

Moderator
Huh, I always thought my Trailblazer had a much better ride than the tin can my brother's 01 Escape was (as far as I know the 08 is mostly a refreah and suspension remained basically the same).

IRS will handle uneven roads a little better than SRA, but a bigger player wl be shocks. What shocks do you have right now?
 

northcreek

Well-Known Member
My Jeep GC has IRS and is a similar sized vehicle and can handle gobs of power but, you would be adapting from a unibody to a frame vehicle which might take some doing.
 
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Maverick6587

Well-Known Member
Does your vehicle have air rear suspension or spring? That is where you get the cushy ride. The shock absorber just dampens the oscillations. I have an '05 TB EXT that rides pretty darn nice. It has springs and Bilsteins at all four corners. If you have a bags, you could ensure the sensors are working correctly to control the pressure and that the check valves and bleeders are functional. Too much air = too stiff.

I think you could get by with a spring swap - either softer springs or spring replacements for the bags - for much less effort and money.
C-ya - I initially had bags and swapped them for cheap bags when they started leaking (horrible mistake) I swapped the cheap bags out with springs from a trailblazer. I could tell the difference. I agree bags are a much soft ride in the rear. The front is pretty bad as well though. Still running original Billsteins there. I'll buy new Billsteins probably in the next few weeks. Currently at about 170,000 miles, so those struts are probably close to shot, they're not leaking but, internally are probably junk.
 
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Maverick6587

Well-Known Member
I have a Pontiac Aztek (Buick Rendezvous clone in Pontiac clothing), and the IRS on it is actually quite substantial and weak, and I can guarantee you would never get it to mount in the GMT platform without sectioning the frame, and rerouting the frame.. Its mounting bolts are probably 30-36 inches apart front to rear and side to side, square. It sits on a aluminum cradle. The differential is also a huge HUGE pile o sh** (I just replaced mine Saturday), and its a passive diff (electromagnetically activated) with a torque tube that runs half the length of the FWD platform. On our RWD platform, the torque tube would probably go all the way to the transmission.

Have to remember that the Aztek/Rendezvous was based on the U-Van chassis, The Chevy FWD Uplander/Venture. And the AWD system it has was borrowed from the same chassis, just shortened to fit in the Az/Vous chassis.

The later years Ford Explorer also had IRS, and actually rode fairly decent, as did the Expedition. So I would say that the conversion is possible, if you dont mind using Ford parts.... :lipsrsealed:🤮

Having riden in a a Escape, a Rendezvous, and a Aztek, that have apsolutely horrible ride, I could not even imagine have that harsh of a ride on a GMT. I like my Cadillac ride.
Thanks for the information on the suspension for the rendezvous and escape! Glad to hear with the right new parts mine will ride better than those two! Worst case scenario, if the new parts do not feel much better than the current ride... Are you familiar with the corvette IRS sizes? I know there are a few kits out there to get them to fit a few truck models. If all else fails I'll see what I can find for that, without having to lower the ride much that is.
 
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Maverick6587

Well-Known Member
Huh, I always thought my Trailblazer had a much better ride than the tin can my brother's 01 Escape was (as far as I know the 08 is mostly a refreah and suspension remained basically the same).

IRS will handle uneven roads a little better than SRA, but a bigger player wl be shocks. What shocks do you have right now?
Nice secondary comment that the gmt360 can ride better. Thanks Sparky!

My Jeep GC has IRS and is a similar sized vehicle and can handle gobs of power but, you would be adapting from a unibody to a frame vehicle which might take some doing.
The Jeep axle was in my thoughts as some of their bodies are a similar size and weight to the trailblazers and everything else.

I appreciate all of the remarks. I guess I'll work on replacing current suspension components and then evaluate from there. I just wanted to make sure it would be worth it in the end and it sounds like it will be. I'd much rather swap parts than having to design/rig steel plates for fitment. Safety was a concern in that idea.
 

C-ya

Well-Known Member
I swapped the cheap bags out with springs from a trailblazer. I could tell the difference.
I wonder if you grabbed springs from a Rainier or Bravada if it would ride better - if springs were even an option for those. A TB may have stiffer suspension since it was the more "utilitarian" model. There are many spring weights in this platform, so maybe look for a softer one. If the current springs still have their ID sticker, you could try to use that to move toward the softer end of the range. If the springs came from a 370, they may be stiffer than ones from a 360. Maybe try to find a pair from a 360.
 
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Maverick6587

Well-Known Member
I wonder if you grabbed springs from a Rainier or Bravada if it would ride better - if springs were even an option for those. A TB may have stiffer suspension since it was the more "utilitarian" model. There are many spring weights in this platform, so maybe look for a softer one. If the current springs still have their ID sticker, you could try to use that to move toward the softer end of the range.
Yeah, I have no idea which year I grabbed them from but, I remember that it was a standard trailblazer and not an EXT or anything. I'm almost 100% sure the rainier has bags on all/most years. I'm not sure about the bravadas though. I'll look around for softer springs though.

In the end, I'd like to go back to bags but, I would want a new air compressor for that system first, at least as a backup. I'll start with the struts though. Paying like $400-$600 for a new compressor, plus the $200-$300 for bags, is not in my current budget, lol. The rear is going to have to continue to take a beating for a little bit longer.
 

Sparky

Moderator
If you have 170k on original shocks then I'm not surprised if they ride like crap.
 

Mektek

Well-Known Member
The idea of converting to IRS is a lot like converting a 2wd to 4wd. With enough time and money you could probably do it, but it's not an efficient solution.
The stock "computer selected suspension" is normally pretty good when everything is working right. The problem I found was when fully loaded (1300 lbs+) the suspension is nearly bottoming out and the headlights shine up to the sky. But I rarely need that capability so it's a minor annoyance.
 

DocBrown

Well-Known Member
I'm surprised no one asked about tires. What tires do you have? Are they OEM spec or are they an AT or LT tire?

I ran AT tires on my Sierra for 3 years. They replaced some very old nearly bald tires that were on the truck when I bought it. They seemed like a big improvement. As time went on the ride got stiff and, well rather truck like. I just simply thought the shocks and struts were wearing. I just put on OEM speced Bridgestone Dueler H/Ls. Wow, a dramatic difference. Very quiet, very smooth. And the ride isn't nearly as harsh.

Coupled with the suspension upgrades new tires might just give you what you are looking for. Just a thought.
 

littleblazer

Gold Supporter
I'm surprised no one asked about tires. What tires do you have? Are they OEM spec or are they an AT or LT tire?

I ran AT tires on my Sierra for 3 years. They replaced some very old nearly bald tires that were on the truck when I bought it. They seemed like a big improvement. As time went on the ride got stiff and, well rather truck like. I just simply thought the shocks and struts were wearing. I just put on OEM speced Bridgestone Dueler H/Ls. Wow, a dramatic difference. Very quiet, very smooth. And the ride isn't nearly as harsh.

Coupled with the suspension upgrades new tires might just give you what you are looking for. Just a thought.
On top of this, if they're 10 ply for whatever reason that'll make a difference as well. :tiphat: You beat me to my post damn it. :laugh:
 
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Maverick6587

Well-Known Member
On top of this, if they're 10 ply for whatever reason that'll make a difference as well. :tiphat: You beat me to my post damn it. :laugh:
Yes, tires are also probably a problem. I think they are getting hard, as I can feel every little crack in the road. So, that is probably adding to the rough ride of the other suspension issues.

I have Michelin Lattitude Tour HP 109Vs on it for now. I think those have around 5/32 left on them. I think I'm going to switch to the Michelin Premier LTX's either this year or next.
 

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