GMT-800 owners, info, strong points and weak points?

[Twin_Cam_Turbo]

Parents are looking to buy a 18FT pontoon boat with trailer ASAP (3500-4000lbs), and we are going to need a tow vehicle for it as well. I am planning to purchase the vehicle as I have always wanted a truck, and plan to buy another ATV down the road as well as would like the practicality for going skiing and such. Coming down to it my budget is under $10000 for sure, and I want a crew cab so we can all pile in and go skiing this winter. Not interested in a 2WD either. Working for GM I don't really want to mess around with a Ford or Dodge. I don't see a lot of the GMT-800s coming in anymore as they are quite old so I am not as well versed on the high an low points of them. Looking for some opinions on what to look out for, what to stay away from, and what to pay specific attention to.

[corsvette]

Well the engines are basically indestructible. The 6.0L can crack exhaust manifolds, other than that they are super dependable. The transfer case are a bit of a weak point in these models, they have a problem called "pump rub" this is when the t-case pump actually rubs a hole in the case causing an oil leak. most dont even notice the leak as it only leaks while driving. Look for any loud bang or excessive t-case noise, and if you get a chance to get under the truck look for cheap JB weld t-case fixes (google GM pump rub to see the location)

The fronts and rear diffs tend to be noisy as the miles pile up. Not much to worry about in the rear diff as they tend to make some noise no matter what. Noisy front diff usually means a bad bearing and also indicates lots of constant 4wd use. Either way very cheap to rebuild front diffs. I did my Denali once myself and was a cheap easy job. Rear disk brakes are fussy at times if there is no shield to keep rocks and dirt out. GM put little rubber flaps to protect the rear brakes in later models. Brake parts are very cheap for these rigs.

Trannys are the 4l60E/4l65E and 4l80E, strongly recommend the 4l80 for towing, it's a pretty stout unit. The 4l60's can live a very long time if you DONT tow heavy! Stock the smaller trannys are not good towing units. This being said I would look for a 1500HD model, they came only in crew cab short box and have the 6.0L and 4L80 tranny along with the big rear diffs or a later model with the Vortec MAX. Other than that you need to go 3/4 ton/2500 to get the bigger tranny. If you end up with a 1/2 ton figure spending about $3000 for a GOOD rebuild on the factory tranny if you plan to tow alot trough the mountains, mind you the 3-4000lbs pontoon should not bother even a 1/2 ton one bit, an auxillary tranny cooler will go a long way.

Inside, look out for faulty instrement clusters on 2003+ models. Needles will be sticky and inaccurate, also backlighting is a weak point as well. You can get the entire clusters rebuilt for around $200 on Fleabay. Heated seat elements tend to burn out with age as well. Other than that they are pretty durable inside, but very dated and cheap looking dashes imo.

I think overall these are about the most reliable used trucks you can get. I've seen the original drivetrains go 500,000+ kms. They also are well built and not rattle boxes. They still look good too imo, there should be a good selection of very nice, well kept trucks out there under 10K.

[Twin_Cam_Turbo]

Originally posted by corsvette
Well the engines are basically indestructible. The 6.0L can crack exhaust manifolds, other than that they are super dependable. The transfer case are a bit of a weak point in these models, they have a problem called "pump rub" this is when the t-case pump actually rubs a hole in the case causing an oil leak. most dont even notice the leak as it only leaks while driving. Look for any loud bang or excessive t-case noise, and if you get a chance to get under the truck look for cheap JB weld t-case fixes (google GM pump rub to see the location)

The fronts and rear diffs tend to be noisy as the miles pile up. Not much to worry about in the rear diff as they tend to make some noise no matter what. Noisy front diff usually means a bad bearing and also indicates lots of constant 4wd use. Either way very cheap to rebuild front diffs. I did my Denali once myself and was a cheap easy job. Rear disk brakes are fussy at times if there is no shield to keep rocks and dirt out. GM put little rubber flaps to protect the rear brakes in later models. Brake parts are very cheap for these rigs.

Trannys are the 4l60E/4l65E and 4l80E, strongly recommend the 4l80 for towing, it's a pretty stout unit. The 4l60's can live a very long time if you DONT tow heavy! Stock the smaller trannys are not good towing units. This being said I would look for a 1500HD model, they came only in crew cab short box and have the 6.0L and 4L80 tranny along with the big rear diffs or a later model with the Vortec MAX. Other than that you need to go 3/4 ton/2500 to get the bigger tranny. If you end up with a 1/2 ton figure spending about $3000 for a GOOD rebuild on the factory tranny if you plan to tow alot trough the mountains, mind you the 3-4000lbs pontoon should not bother even a 1/2 ton one bit, an auxillary tranny cooler will go a long way.

Inside, look out for faulty instrement clusters on 2003+ models. Needles will be sticky and inaccurate, also backlighting is a weak point as well. You can get the entire clusters rebuilt for around $200 on Fleabay. Heated seat elements tend to burn out with age as well. Other than that they are pretty durable inside, but very dated and cheap looking dashes imo.

I think overall these are about the most reliable used trucks you can get. I've seen the original drivetrains go 500,000+ kms. They also are well built and not rattle boxes. They still look good too imo, there should be a good selection of very nice, well kept trucks out there under 10K.

Yeah I am 100% certain I want to go with a 1500HD. I have seen the pump rub before, as I recall its a pretty expensive fix too, the case half is like half the cost of a new T/Case from GM Diffs I did not know about, ill pay attention to those. I know GMs are bad for corrosion build up on the rotor surfaces and then eating pads. Ill probably plan to spend the money and put an aux trans cooler unit on no matter what, they seem to work great on the customer ones we have done. Have seen lots of clusters, those I can get remanufactured through work pretty easily. Heating elements and connectors melting on heated seats seem common as well come to think of it.

[Anomaly]

Corsvette pretty much nailed it. My GMT-800 had just shy of 300k when I sold it, It had the typical issues; Gauge stepper motors went, power window motor, front diff seals leaked, transfer case whined...and I blew the 10 bolt diff goofing off in it. . That said, they're great trucks with tons of aftermarket available. I towed a car hauler, and horse and trailer probably a couple times a month (4-5000lbs) and it did it really well. (Better than my newer Ford....)
Definitely try to find a 1500HD, as they have the 14bolt rear diff. Also check the glove box RPO codes for rear gear ratio:

GT4 -- AXLE REAR, 3.73 RATIO
GT5 -- AXLE REAR, 4.10 RATIO
GU4 -- AXLE REAR, 3.08 RATIO
GU5 -- AXLE REAR, 3.23 RATIO
GU6 -- AXLE REAR, 3.42 RATIO
G80 -- AXLE REAR, LIMITED SLIP

[corsvette]

In those axle codes the G80 ltd slip is the real whiner, noisy noisy noisy bugger but they never seem to grenade.

[Twin_Cam_Turbo]

I'd like to find a G80 equipped one even if they are noisy.

[Twin_Cam_Turbo]

Trying to tell myself I don't need a Duramax, as much as I want one