97 k2500 suburban front and rear diff. gear issues

[monsterburb]

Hi Guys, new to the thread. Jus picked up a sweet 97 burb out of Arizona. Took it out in the snow last week to work the 4 wd, and it bound up terrible pretty much immediately. It appears this truck was a 373 geared truck when built. My mechanic told me someone swapped out the 373 gears in the rear end for 410s, presumably while in Arizona for towing purposes.

Trouble is, it seems they left the 373s in the front diff, and this was unknow to me when I purchased. QUESTION: Are the Diff housings interchangable for these two gear set ups? Can my mechanic just swap out the gears and associated parts, or will I need to replace the housing and other stuff? Also, I drove the vehicle in 4 wd in fairly heavy snow at low speed for about 400 yards before I realized something was very wrong.

Did I completely Eff up my front diff. in doing so?

Any help would be appreciated.

LC

 

[1998_K1500_Sub]

It appears this truck was a 373 geared truck when built. My mechanic told me someone swapped out the 373 gears in the rear end for 410s, presumably while in Arizona for towing purposes.

Ok, so decide which ratio you want to keep (3.73 or 4.10) and swap the other. Think about how your decision might impact the speedometer reading and whether your want to correct any resulting readout errors (which requires reprogramming the ECU).

You can swap only the gears, or swap the entire gearbox (front gearbox assy / rear axle) whichever is better for your time / wallet. In my particular case, to change my entire drive from 3.42 to 3.73, I swapped rear gears (ring and pinion) but swapped the entire front gearbox with one from a donor truck with 3.73s.

Is the drivetrain making any unusual noises now? Since you were in heavy snow you might have done no harm.

 

[Supercharged111]

Was the 4.10 a guess or did the mechanic count gear teeth or gear turns to come to that conclusion? Could also be a 3:42 if the gears don't match.

 

[stutaeng]

Yep, time to jack the rear and count the # of driveshaft vs # of wheel turns.

If they swapped to 4.10s in the rear from 3.73, your odometer is already off, assuming they didn't correct the new gear on the tune.

I've watched a few videos on regearing the GM 9.25" axle and it looks pretty challenging, even more so than a solid axle. I'm sure it can be done by the DIY/typical mechanic, but probably easier to swap axle with 4.10s if that's what ratio you want to go with.

4.10s are awesome btw...

 

[1998_K1500_Sub]

If they swapped to 4.10s in the rear from 3.73, ...

OP, take a look at the rear diff (8.5”, 9.5”,…) and rear drums (10”, 11”,…) and see if they are correct for your K2500 (check RPO list in glovebox). If the rear axle has been swapped you may have an odd combination… one which you may wish to remedy.

 

[Supercharged111]

OP, take a look at the rear diff (8.5”, 9.5”,…) and rear drums (10”, 11”,…) and see if they are correct for your K2500 (check RPO list in glovebox). If the rear axle has been swapped you may have an odd combination… one which you may wish to remedy.

His is a 2500, I don't think they did 6 lug 2500 Subs? So he's between a 9.5" and a 10.5" more than likely. Any other differences in 2500 stuff for truck vs SUV?

 

[Gibson]

I suppose you have the 454 engine?
For a '97 K2500 their were only 2 ratios from the factory.
The 350s were ONLY shipped with 4:10 ratios.
The 454s came standard with 3:73 with 4:10 an option.
Unless you're doing a lot of highway speed cruising the 4:10s give better all-around performance/response.

 

[1998_K1500_Sub]

His is a 2500, I don't think they did 6 lug 2500 Subs? So he's between a 9.5" and a 10.5" more than likely. Any other differences in 2500 stuff for truck vs SUV?

Good point... if someone did swap the entire rear (which was my suspicion), it would have to be 8-bolt for 8-bolt... so he certainly didn't get stuck with an 8.5" R&P or 10" drums on the rear end.

I'm not aware of any other differences in the "rear end" or "IFS front end" for the K2500 trucks vs. Suburbans... that doesn't mean there aren't any, it just means "I think not".

@monsterburb, did you check the RPO codes to see what gear ratio it got from the factory? Here's a partial list from the 1998 service manual:

GT4: Rear Axle: 3.73 Ratio
GT5: Rear Axle: 4.10 Ratio
GU4: Rear Axle: 3.08 Ratio
GU6: Rear Axle: 3.42 Ratio
G80: Rear Axle: Positraction

Here is the brake RPO list too, if you're interested...

JB5: Brake System: Power, Front Disc, Rear Drum,
6400 Lbs.
JB6: Brake System: Power, Front Disc, Rear Drum, 7200 Lbs.
JB7: Brake System: Power, Front Disc, Rear Drum, 8400 Lbs.
JB8: Brake System: Power, Front Disc, Rear Drum, 10000 Lbs.
JD5: Brake System: Dual Power, Front Disc, Rear Drum, 6400 Lbs.
JD6: Brake System: Hydraulic Power, Front Disc, Rear Drum, 7200 Lbs.
JD7: Brake System: Hydraulic Power, Front Disc, Rear Drum, 8400 Lbs.
JF9: Brake System: Hydraulic Power, Four Wheel Disc

A partial explanation of the RPOs and the equipment associated with each was given by @Schurkey in this post:

https://www.gmt400.com/threads/need-help-with-brakes-plz.56196/post-1212113


I attached the entire list of RPOs for 1998 if you want to learn more about your new truck.

 

[stutaeng]

His is a 2500, I don't think they did 6 lug 2500 Subs? So he's between a 9.5" and a 10.5" more than likely. Any other differences in 2500 stuff for truck vs SUV?

Yeah, I was thinking they re-geared his axle, not axle swap. But who knows... Maybe they did swapped his 14 bolt 8 lug for another with different ratio.

@RichLo has a beast snow plow rig. Instead of regearing his swapped 14 bolt, he swapped some tractor wheels to get the overall ratios to match. Not saying this is what OP should do, but it does work, in case of a "bind!"

 

[1998_K1500_Sub]

he swapped some tractor wheels to get the overall ratios to match. Not saying this is what OP should do, but it does work, in case of a "bind!"

Yup... OP can put 10% larger tires on the back than the front, so that the overall drive ratio (driveshaft turns per foot driven) is the same front and back. Easy peasy.