GMT800 Suburban Towing issues: Gearing or power?

ExplorerTom

Explorer
Your Explorer has stick axles. They are much cheaper to re-gear than the Chevy Front IFS contraptions the GMT800 has.
You mean similar to the IFS that my Explorer had (when it was stock) that he regeared? Or the 10th gen and up F-150s that he's also regeared? You just need to pull the front axles out, disconnect the driveshaft, unbolt the front axle center section and carry that over to the bench. Watched him do it on my Explorer. Had the front axle completely out in about 20 minutes. I doubt Chevy did anything revolutionary in that regard.
 

Buliwyf

Viking with a Hammer
I'm looking at $1000 for 4.88's and parts, $650 Yukon locker, and at least $1000 in labor. Almost $3000 for 4.88's and a front locker. I suppose you could knock $500 off of that if we reuse bearings and such. The truck is brand new after all.

If he does Jeeps for $880, give him a good tip. That's an excellent price.
 

ClovisMan

Observer
You mean similar to the IFS that my Explorer had (when it was stock) that he regeared? Or the 10th gen and up F-150s that he's also regeared? You just need to pull the front axles out, disconnect the driveshaft, unbolt the front axle center section and carry that over to the bench. Watched him do it on my Explorer. Had the front axle completely out in about 20 minutes. I doubt Chevy did anything revolutionary in that regard.
I went to Randy's Ring and Pinion and added their "cheap" parts brand to the cart and you can see for yourself. If your dude is doing all the labor for $120.00 bucks then he is stupid...
 

Buliwyf

Viking with a Hammer
Even sourcing used gears, and skipping the bearings, it's hard to get down that low. I charge $400 labor just for Super Duty brakes.

If he can do a Super Duty for $50/hr, I expect biz to pick up for him. That's one heck of a good resource.
 

BritKLR

Explorer
[QUOTE="rayra, post:
Lastly, you know the hard shift and screaming RPMs are coming, so just hit the hazard lights and ease off and make the gear change manually when more appropriate. Exert some manual control on what's going to happen anyway. Don't kill your motor or trans trying to maintain a higher speed. Pull over and let backed-up traffic pass you when you reach your state's limit

This!

I'm over that pass on a regular basis. I'm either in the Tiger or my K2500 loaded, pulling a trailer or unloaded. Neither of these vehicles have any automated towing feature. Once I start climbing from Georgetown I'm already out of overdrive and in third. Once it starts getting steep I'm in second and keeping my rpms around 3500 and in slow lane. I don't care about my speed as long as I'm keeping my revs in the power band. Just the nature of mountain travel with a trailer. Good luck!
 

ExplorerTom

Explorer
I went to Randy's Ring and Pinion and added their "cheap" parts brand to the cart and you can see for yourself. If your dude is doing all the labor for $120.00 bucks then he is stupid...
You’re assuming he pays retail.

I don’t know what he’s clearing, but he seems to be doing just fine. Business is steady for him and really picks up in the spring when people get their taxes back.
 

Martinjmpr

Wiffleball Batter
Does your vehicle have the towing option package, do you have the Tow/Haul mode and if so do you use it?
What octane of fuel do you use, have you tried higher octane on these uphill trips?
Problem is keeping your vehicle in the power band of the motor. More engine HP, or taller gearing.
More importantly, IIRC, you bought your vehicle somewhere south and flat (IIRC), have you ever had the battery disconnected / engine comp disconnected, had the vehicle 're-learn' your higher-altitude driving routine? It will make some (limited) accommodation for your higher altitude driving routine.
I believe there is a programming option to change and soften your shiftpoints. And If I'm not mistaken computer hardware available to swap that firmware on the fly, as needed.
Lastly, you know the hard shift and screaming RPMs are coming, so just hit the hazard lights and ease off and make the gear change manually when more appropriate. Exert some manual control on what's going to happen anyway. Don't kill your motor or trans trying to maintain a higher speed. Pull over and let backed-up traffic pass you when you reach your state's limit (in CA I think it is 5 vehicles stacked behind you)

IMAO it's these high load high RPM steep grade climbs that kill the 4L60. Trans temp is the key concern. Amend or improve that if you haven't already. I'm getting crazy low trans temps with my cooler install (verified with a laser thermometer, I have got the right data selected for my Torque app trans temp gauge). But I'm rarely topping 4-5k', not your 11k. 11k's rough on any vehicle not tuned for it, even computer-controlled and fuel injected. Even without towing a load.
So to answer your questions in order:

1. Yes, factory tow package with cooler and 145a alternator (alternator replaced in 2017.)
2. Octane: Yes, I'm a cheap SOB and typically run 85 (identical to 87 in the lower parts of the country) so I've never tried higher octane. I'm getting close to the bottom of the tank so I may give that a try, if for no other reason than to eliminate it as a possible cause!
3. Vehicle's "home" was originally Wisconsin but has been in Colorado since at least 2012, and battery has been replaced more than once so the ECM has certainly had time to "learn" the altitude.
4. I've gotten into the practice when climbing steep hills to go ahead and downshift manually to 2nd. Really, if it would stay in 2nd I'd be fine with it, the problem is that even in 2nd it sometimes bogs down slow enough to drop down to 1st for a few seconds and then jumps back up to 2nd. That's what I'm trying to avoid. Gears 3 and 4 aren't even a dream when climbing.

WRT trans temp, I'm running a SGII and I also have a trans temp gauge on the dash (had the dash rebuilt by Circuit Board Medics and had them add the trans temp gauge from the 6.0 V8 models - apparently all GMT800 trucks are actually wired for the trans temp gauge, but GM only put them on the trucks that have the 6.0 and larger motors.) On the SG I am seeing normal trans temps (on flat or intermittent up/down hills) in the 160 - 180 range. When climbing a steep hill, the trans normally goes up to about 210-215 but has gotten as high as 219. When I start going downhill again, the trans temps quickly drop below 200.
 

rkj__

Adventurer
I'm no expert, but I think a good custom tune might be all it takes to avoid that short, and annoying shift into first. Depending on how short you are on power, tuning for a midgrade fuel might be beneficial.

I've been towing my T@b with a GMC Canyon (242HP, 3.73 gears, 5,500 lb tow rating, 32" tires), and I live in a pretty flat part of the world (Southern Ontario, Canada), but when I got into the hills of PA, 4,200 RPM is how I maintained speed up a steep grade. I never encountered the length of hills you see out west though, so those high RPMs were not held for very long. The truck was pretty good at picking a gear, and holding it.

Random side note, I just bought a GMC Sierra 1500 (355HP, 3.42 gears, 9,200 lb tow rating, 32" tires), and I'm really looking forward to hooking up the T@b and heading north. The truck should be able to deliver a quiet and smooth tow.
 

DailyExpedition

Active member
Does your vehicle have the towing option package, do you have the Tow/Haul mode and if so do you use it?
What octane of fuel do you use, have you tried higher octane on these uphill trips?
Problem is keeping your vehicle in the power band of the motor. More engine HP, or taller gearing.
More importantly, IIRC, you bought your vehicle somewhere south and flat (IIRC), have you ever had the battery disconnected / engine comp disconnected, had the vehicle 're-learn' your higher-altitude driving routine? It will make some (limited) accommodation for your higher altitude driving routine.
I believe there is a programming option to change and soften your shiftpoints. And If I'm not mistaken computer hardware available to swap that firmware on the fly, as needed.
Lastly, you know the hard shift and screaming RPMs are coming, so just hit the hazard lights and ease off and make the gear change manually when more appropriate. Exert some manual control on what's going to happen anyway. Don't kill your motor or trans trying to maintain a higher speed. Pull over and let backed-up traffic pass you when you reach your state's limit (in CA I think it is 5 vehicles stacked behind you)

IMAO it's these high load high RPM steep grade climbs that kill the 4L60. Trans temp is the key concern. Amend or improve that if you haven't already. I'm getting crazy low trans temps with my cooler install (verified with a laser thermometer, I have got the right data selected for my Torque app trans temp gauge). But I'm rarely topping 4-5k', not your 11k. 11k's rough on any vehicle not tuned for it, even computer-controlled and fuel injected. Even without towing a load.
So to answer your questions in order:

1. Yes, factory tow package with cooler and 145a alternator (alternator replaced in 2017.)
2. Octane: Yes, I'm a cheap SOB and typically run 85 (identical to 87 in the lower parts of the country) so I've never tried higher octane. I'm getting close to the bottom of the tank so I may give that a try, if for no other reason than to eliminate it as a possible cause!
3. Vehicle's "home" was originally Wisconsin but has been in Colorado since at least 2012, and battery has been replaced more than once so the ECM has certainly had time to "learn" the altitude.
4. I've gotten into the practice when climbing steep hills to go ahead and downshift manually to 2nd. Really, if it would stay in 2nd I'd be fine with it, the problem is that even in 2nd it sometimes bogs down slow enough to drop down to 1st for a few seconds and then jumps back up to 2nd. That's what I'm trying to avoid. Gears 3 and 4 aren't even a dream when climbing.

WRT trans temp, I'm running a SGII and I also have a trans temp gauge on the dash (had the dash rebuilt by Circuit Board Medics and had them add the trans temp gauge from the 6.0 V8 models - apparently all GMT800 trucks are actually wired for the trans temp gauge, but GM only put them on the trucks that have the 6.0 and larger motors.) On the SG I am seeing normal trans temps (on flat or intermittent up/down hills) in the 160 - 180 range. When climbing a steep hill, the trans normally goes up to about 210-215 but has gotten as high as 219. When I start going downhill again, the trans temps quickly drop below 200.
On your choice of gas I found (just this past week when I was up there) that 85 octane sucks, I got better performance from using the mid grade which up there is typically 86-87 octane, the octane does matter, I’m a cheapass too so using the higher octane sucked my wallet dry but my truck ran better and had noticeably more power. I noticed it especially on the way from Durango up through Silverton and like wise headed from Vail into Denver. That being said, your cheapest route is going to be a tune, especially if your tires are larger than stock. My stock tire size is 30.5 inches tall versus the 33in y’all tires I have now. I’m going to do a tune first to help with that and shift points since I will be taking yearly trips into your neck of the woods, after that I’ll know if I need to do something more. Just my two cents


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rayra

Expedition Leader
martin I'd really suggest an aftermarket trans cooler to replace the tiny factory unit included with the towing package. Those temps are elevated but they don't leave much margin. Those factory gauges are redzoned at 275F IIRC. And there's plenty of anecdotal evidence that's the death knell for the 4L60, the high heat and differential heating between trans casing and pump causing seal failures etc.
I'm really getting some remarkably lower trans temps with my aftermarket cooler, even leaving the in-radiator plumbing as is. I just today cut the ends off my factory external cooler lines and fit some nicer compression fittings and reduced the huge extra loops of hose I did during the initial install. Just posted in my built topic about it with a bunch of pics. And the original install was about 10mos ago in that topic.
It's an easy project and I think it would be a potential transmission saver for you.

eta was actually 13mos ago in that topic, this was a size comparison pic of the tiny factory external trans cooler (which mostly sits behind the chevy logo on the grill, it's really a poor mounting position)



and this morning as I got started re-working the plumbing.

 

Buddha.

Lurker
Closing in on 3 years now of using the 2004 Suburban (1500, LT, 5.3, 4x4, 4L60, 3.73 gears) as our primary tow vehicle. Previously we had a 2,000lb T@B trailer but in January we upgraded to a ~ 3500lb R-Pod 179.

The "issue" I'm having is when climbing steep, high passes (here in CO you can't get from the Front Range cities to the mountains without crossing at least an 11,000' pass.)

As I slow down, of course the 4 speed 4L60 drops into a lower gear. 2nd gear is actually pretty good for climbing and I can typically keep up with traffic at around 50 mph even in 2nd. But as the hill gets higher, the weight bogs the rig down and speed drops. When it drops below about 35, the truck wants to kick the transmission down a 1st gear - which of course makes the engine spin around 4500 rpm (screaming.) That typically only lasts a few seconds before it shifts up to 2nd but then it bogs down again and drops back down to 1st. This sometimes happens 5 - 10 times while ascending a steep pass (think Eisenhower Tunnel or Berthoud Pass, for those familiar with them.)

When we had the T@B this never happened, we could stay in 2nd gear the whole time. But our trailer weight has nearly doubled and I can really feel it when climbing those steep passes.

Not only is it a bit of a shock to feel the truck dropping down into 1st gear, I'm worried about what those hard shifts and high RPMs will do to my transmission and engine (transmission was rebuilt 2 years ago @ 150,000 miles and has worked fine since then.)

So my question for the GMT800 Hive Mind is this: If my goal is to be able to ascend passes more easily, should I be looking at doing something to boost power/torque or should I be looking at lower gearing?

I'm not looking to spend a ton of money and I don't want to put too much stress on an already middle-aged drivetrain (170k) so I don't think turbo/supercharging would be a good idea for me. Are there less "radical" power mods that would boost the power of the engine?

EDITED TO ADD: I'm not a huge fan of things like Cold Air Intakes or air box removal - I'm just skeptical that they really improve power. Ditto for "reprogramming" the computer, as I think that assumes that the "tuners" know more about the engine than, you know, the people who BUILT it. Adding power and sacrificing reliability or utility would pretty much defeat the purpose of what I'm trying to do here.

Or would it be a better idea to simply change the gearing to, say, 4.11? And if I was to do this, what would I be looking at, cost-wise, to replace the front and rear gear sets (and ideally retaining the G80 locker in the rear?)

Anyone else had this issue with a 1500 'Burb towing? (If I'd known we were going to be getting a heavy trailer like this I might have held out for a 2500 but that's 20/20 hindsight at this point.)

Thanks in advance!
Sounds about how my 6.0 6l90e 4.10 combo does pulling 10k over those same passes. Rating is 13k pounds bumper pull. Cruise control wants to downshift to 2nd gear (I think) at 5,000 rpm to maintain 50mph. I'd rather it be in 3rd at 4,000 rpm which will slow down to about 35mph. I don't know how long the truck is designed to rev at 5,000 rpm with such a load but the 10+ minutes it would take to climb those passes seems too much.
Truck is locked out of six gear while towing, and only shifts into fifth of I've got a tail wind or downhill. I wish I had 4.56 or even 4.88 gears with stock 32.5" tires.

This is my first truck with a decent transmission cooler, temps never go over 190f.

Anyway I think a Dyno tune would help us both.
 

NMC_EXP

Explorer
Octane rating is a measure of how much compression the air/fuel mix can handle without detonating. It is not a measure of the energy content of the fuel.

Engine compression determines what octane ought to be used.

Ethanol has a higher octane than pure gasoline and is used to increase the octane of gasoline. Ethanol contains less energy than gasoline so more ethanol means less energy.

https://en.wikipedia.org/wiki/Octane_rating
 

DailyExpedition

Active member
Octane rating is a measure of how much compression the air/fuel mix can handle without detonating. It is not a measure of the energy content of the fuel.

Engine compression determines what octane ought to be used.

Ethanol has a higher octane than pure gasoline and is used to increase the octane of gasoline. Ethanol contains less energy than gasoline so more ethanol means less energy.

https://en.wikipedia.org/wiki/Octane_rating
That’s fine and all, I wouldn’t trust wiki to tell me if white is white or black is black though, also newer engines were made to work well on a certain amount of octane such as bmw Cadillac Porsche Ferrari etc all of which have to have premium in order to not knock, same principle applies here. While it may not contain power, the right amount of octane can make the vehicle run better, which in turn produces power. Going from 87 octane to 85 then back to 87 I felt the difference without even thinking about it. If you believe in wiki then Read the last sentence of the wiki page pretty much says it all



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Buliwyf

Viking with a Hammer
Newer flex fuel trucks will adjust timing with higher octane fuels. I can feel the difference between 87 and 91 octane with 10 000# behind me. I run higher octane for towing in hot conditions.
 

NMC_EXP

Explorer
If an engine experiences knock due to low octane fuel there will be a loss in power. My 2F powered FJ60 has the timing advanced past factory spec far enough that it has significant knock on 85 octane.

Due to ever higher CAFE requirements engines are getting smaller and manufacturers are doing things such as higher turbo boost, supercharging and higher compression to maintain horsepower. The manufacturers are therfore lobbying for higher octane gas. Bad news for us with carbuerated engines operating at high altitude. Ethanol has a lower boiling point than gas so vapor lock becomes a problem.

What octane is specified for Martin's Suburban? I suspect 87.
 
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