97 vs 99 IFS Differentials, Different??

[nomad]

Does anyone know if the 97 and the 99 differentials are interchangable (with the same gearing)

I have upgraded from 3.42 to 3.73 in the rear and have a chance to get a 3.73 front diff from a 99. Some listings show they are not interchangable but I think that is because the early model 97 uses thermal axle activation which was changed to electric late in 97. Mine is electric so I am hoping it will fit.

Anybody know or done this?

Thanks

 

[steamroller]

I don't see why it wouldnt work as long as they have the same actuator and are from the same body style truck

 

[07Burb]

Yes, I believe 97 and 99 have the same IFS setup.

 

[SunlitComet]

Have to check but perhaps a difference between the auto and non-auto systems maybe? Which do you have? Can backtrack part numbers.

 

[96ProCompTahoe]

other than possibly the auto trac (as sunlit said) there shouldn't be a difference in them

 

[nomad]

As I understand it the 99 has a 246 transfer case with is part time/full time selectable. The 97 has a 243 part time. Both the 97 and 99 differentials look identical and both have the electric actuator. About the only difference I have noticed is the half shafts, the 97 are a solid circle where the 99 have scollops cut between the bolts making it look a little like a star pattern. It appears this may have been done to cut down on the weight of the half shafts. No differences in the axle shaft coming out of the diff.

 

[steamroller]

I really don't think the Autotrac diffs are any different than the ones with the 243 and electric actuator. When in Auto 4wd the front actuator is engaged and the TCCM and encoder motor/shift fork in the transfer case apply the clutches depending on how much the front tires are slipping....there's no partial engagement at the front diff, it's either locked in or not.....at least that's how I understand it works

The electric actuator I robbed from an Autotrac Suburban looks the same as the ''upgrade'' they sell for the thermal units. I had to make my own spacer since the thermal one extended around an 1" more but other than that it works fine.

 

[nomad]

I really don't think the Autotrac diffs are any different than the ones with the 243 and electric actuator. When in Auto 4wd the front actuator is engaged and the TCCM and encoder motor/shift fork in the transfer case apply the clutches depending on how much the front tires are slipping....there's no partial engagement at the front diff, it's either locked in or not.....at least that's how I understand it works

The electric actuator I robbed from an Autotrac Suburban looks the same as the ''upgrade'' they sell for the thermal units. I had to make my own spacer since the thermal one extended around an 1" more but other than that it works fine.

I went ahead and picked up the 99 IFS unit. I have pulled it apart and replacing the axle bearing and seals. One thing that is interesting is that the axle seals are MUCH better than the one's used on the 97. The total seal area is about 2 times the surface space on the 97. Once I pull the old unit I plan on doing some comparisons. For those with leaky seals on pre 99 Tahoe's, Yukons, burbans this would be an excellent upgrade. I should have everything needed to wrap this up next week and post my findings.

 

[nomad]

Final on the subject

The front IFS differential is the same between a 97 and 99 1/2 ton 2dr or 4dr Tahoe, Yukon and Suburban. There were some improvement that can be retrofitted to the older years, they are:

Axle actuator, older 97 and earlier used a thermal actuator. They can be removed and replaced with an electric unit. A wiring harness is available that make it a snap.

Axle seals, the 99 and later use a MUCH better axle seal instead of the flange seal used in the 97 and older front diffs. The newer seals do not have a flange but will install into the same place and offer 2 times the seal area. They also support the axle half shafts much better.

Hopefully this will help someone looking to swap IFS units...

Dan