2004 Suburban Reality Check

Peak torque for the 8.1 is at 3200 rpm, see below comparing to the LB7 Duramax

I tow a 29' trailer that is less than 8,000 lbs, but with a tongue weight of 1200-1300 lbs per my Sherline scale. Mine is a 2003 Suburban with 4.10's and the 8.1L. It tows great. I use a Reese Dual Cam system and it works great. I did replace my hitch with a Class V Reese with the 2.5" square tube opening. I liked it because it mounted further up along the frame than the stock hitch and the other options. I don't think they make it anymore however. Regardless, I'd replace it with something better than the factory one, it was pretty weak regardless of the ratings they put on it.

Mine started life in a Fire Dept. in Georgia from what I can tell, then an owner in Florida. A previous owner had removed the auto ride shocks and put on Rancho 5000's that were worn out when I got it. I put on Bilstein 4600, they work very well. I also added Hellwig sway bars front and rear on my Suburan. It significantly reduced body roll and I believe provides better control when towing also. I've towed to most of the states in the lower 48 with this combination and it tows great, even with 20-30 mph cross winds. We traveled 5000+ miles out west this summer and it did great.

I've relaced a LOT of parts as it is an old vehicle. All coolers, lines, radiator, etc. Fuel pump, water pump, etc. I've also replaced the accelerator pedal assembly and more recently the throttle assembly as the electronic controls and sensors go bad eventually and it leaves you in low power mode. Low power mode will not move a loaded travel trailer and hardly move an empty vehicle. We nearly got stranded due to the throttle issue this summer on our last day. It eventually started working and we made it, only because I could re-set the Service Engine Soon light on the fly.

Good luck with yours, it pulls fine over the mountain passes if you keep your speed up and keep the RPM at the power peak (4200 RPM). I think we did 60+ over Vail pass as we were unhindered by traffic. If you slow down you'll never get your speed back up, we ended up in 1st gear approaching the Eisenhower tunnel due to traffic.

mkirsch wrote:

anw7405 wrote:

mkirsch wrote:
Too bad GM didn't offer the Suburban with the 8.1 / Allison combination. Having that 5th gear is real nice, though I rarely ever drop below 4th as that puts the engine at maximum torque output at 65MPH.

I don't know if it's true or not but I read somewhere that it takes more torque and hp to turn the Allison than the 4l80. So an Allison would in theory have less hp and torque to the wheels.

It probably does, as it is a much larger transmission with more rotating mass. Simple physics.

The difference won't be enough that you'd feel it in the seat of your pants, and the extra gear more than makes up for it.

The lower gear in first, 3.1 vs 2.48 ally vs 4l80e is a good thing, 3rd is taller than 2nd, so not as many rpm loss when one can not hold direct.

Hp is double needed with the ally vs 3l80e, about 60 vs 30. Enough that one could very well notice it! But as noted, with better, slightly closer gear splits etc, the ally is the better trans option vs 4l80e.

The issue with the older burb bodies, is the frame will not allow the overall size of the ally vs the 4l80. You can install one, but need to do IIRC a minimum body lift of around 2". ALong with moving the crossbeam support for the transmission. Latter is easier than body lift aftermarket.

Marty

Couple points to clarify....

Good idea to replace brake lines, and if you do, I would replace the fuel lines too as they get just as rusty. Especially considering that you have to drop the main fuel tank to get to the rear brake lines. Bear in mind that you have TWO fuel tanks, each with its own fuel pump and sending unit.

Also good idea to replace the hitch receiver, the OEM does attach to the frame as well as the bumper, but the receiver design is flimsy. I broke mine, and many have reported getting a lot of flex in theirs. When the receiver flexes it's taking that torque that's being applied by the WD hitch and not sending the weight forward to the front wheels to level the truck. Get a good aftermarket hitch with a 12k rating like this one from e-trailer.

AutoRide....probably the most confusing thing that GM did. Both the 1500 and 2500 Suburbans have AutoRide but it is NOT the same system...on the 1500's, AutoRide means automatic load leveling with an on-board compressor and air shocks in the rear. On the 2500's, there is NO auto-leveling or compressor, instead AutoRide uses shocks that have magnetic fluid. There is a ride height sensor at every corner, and a separate ride control computer that uses data from a variety of systems including speed, steering angle, etc, to vary the stiffness of the shocks 1000 times/sec. This is called Real Time Damping (RTD) and is similar to the system GM uses on the Caddys. Replacement shocks are extremely expensive, but there is a way to bypass AutoRide and use regular shocks (I did that).

The springs need no help whatsoever, the leaf springs in the rear are very stout and have an overload leaf. The torsion bars up front are also very tough despite what the haters say about GM IFS...

The 8.1 does use some oil, it's normal. There is a level sensor in the pan that will send a "low oil level" message when you are two quarts low.

I just replaced my stereo with a double-DIN Kenwood touch screen with navigation, I'll post some pics and a how2 if you're interested.

Happy to help if you have any other questions or issues.

anw7405 wrote:

kevden wrote:
I suggest upgrading the rear suspension with air bags, timbrens, or sumosprings. The suburban will certainly tow without them, but they will make it much more enjoyable.

just a question. Does this just help with absorbing bumps a little better? I don't think the springs need any help on the burb. My tongue weight is probably around 900-1000lbs loaded and the springs seem to be fine.

It helps bumps on mine, but more importantly it is much more stable and controlled overall. I installed air bags on our previous tow vehicle to control porpoising that bilstien shocks could not. The airbags not only cured that, but greatly improved overall handling both towing and empty. I liked the improvements so much that I wanted helpers for the Yukon, but decided on timbrens for simplicity and zero maintenance. Last winter I replaced the autoride shocks with Monroe reflex(front) and Monroe load adjusting(rear). Big improvement there as well.

anw7405 wrote:

mkirsch wrote:
Too bad GM didn't offer the Suburban with the 8.1 / Allison combination. Having that 5th gear is real nice, though I rarely ever drop below 4th as that puts the engine at maximum torque output at 65MPH.

I don't know if it's true or not but I read somewhere that it takes more torque and hp to turn the Allison than the 4l80. So an Allison would in theory have less hp and torque to the wheels.

It probably does, as it is a much larger transmission with more rotating mass. Simple physics.

The difference won't be enough that you'd feel it in the seat of your pants, and the extra gear more than makes up for it.

anw7405 wrote:

intheburbs wrote:

anw7405 wrote:

kevden wrote:
I suggest upgrading the rear suspension with air bags, timbrens, or sumosprings. The suburban will certainly tow without them, but they will make it much more enjoyable.

just a question. Does this just help with absorbing bumps a little better? I don't think the springs need any help on the burb. My tongue weight is probably around 900-1000lbs loaded and the springs seem to be fine.

The springs on a 2500 Burb need no help. No need to replace them with any of those products. A half-ton? Maybe. But not a 3/4 ton. See how flat and level mine is sitting? Stock suspension, 1100-lb tongue, no WD hitch. Perhaps the previous poster needed it because his quadrasteer Burb has more unsprung weight on the rear.

Now, on the other hand, the right shock absorbers will make a big difference. I installed Bilstein 4600s on all 4 corners on my Burb and the difference was like night and day. Wonderful, controlled ride, no porpoising at all.

Did you see a big difference loaded or unloaded with the 4600s? I think all the 8.1's had the autoride right? IMO my autoride sucks.

Biggest difference in ride was when towing heavy. I bought the truck used, and have no idea about how old those shocks were. Lots of bouncing/porpoising when towing. The 4600 shocks just about eliminated it.

anw7405 wrote:

mkirsch wrote:
Too bad GM didn't offer the Suburban with the 8.1 / Allison combination. Having that 5th gear is real nice, though I rarely ever drop below 4th as that puts the engine at maximum torque output at 65MPH.

I don't know if it's true or not but I read somewhere that it takes more torque and hp to turn the Allison than the 4l80. So an Allison would in theory have less hp and torque to the wheels.

The HD pickups got the Allison with the 8.1, but not the Suburbans. Reason was simple - the pickups were lifted and the body could clear the Allison bell housing. The non-lifted Suburbans didn't have the clearance, so the 4L80 was used instead.

mkirsch wrote:
Too bad GM didn't offer the Suburban with the 8.1 / Allison combination. Having that 5th gear is real nice, though I rarely ever drop below 4th as that puts the engine at maximum torque output at 65MPH.

I don't know if it's true or not but I read somewhere that it takes more torque and hp to turn the Allison than the 4l80. So an Allison would in theory have less hp and torque to the wheels.

Too bad GM didn't offer the Suburban with the 8.1 / Allison combination. Having that 5th gear is real nice, though I rarely ever drop below 4th as that puts the engine at maximum torque output at 65MPH.

intheburbs wrote:

anw7405 wrote:

kevden wrote:
I suggest upgrading the rear suspension with air bags, timbrens, or sumosprings. The suburban will certainly tow without them, but they will make it much more enjoyable.

just a question. Does this just help with absorbing bumps a little better? I don't think the springs need any help on the burb. My tongue weight is probably around 900-1000lbs loaded and the springs seem to be fine.

The springs on a 2500 Burb need no help. No need to replace them with any of those products. A half-ton? Maybe. But not a 3/4 ton. See how flat and level mine is sitting? Stock suspension, 1100-lb tongue, no WD hitch. Perhaps the previous poster needed it because his quadrasteer Burb has more unsprung weight on the rear.

Now, on the other hand, the right shock absorbers will make a big difference. I installed Bilstein 4600s on all 4 corners on my Burb and the difference was like night and day. Wonderful, controlled ride, no porpoising at all.

Did you see a big difference loaded or unloaded with the 4600s? I think all the 8.1's had the autoride right? IMO my autoride sucks.