I am looking in to buying a 1988 GMC Subyrban High Sierra. Its got a 350 with newer center bolt valve covers, automatic transmission, its a 4x4 1500 with leaf spring. Everything seems to be really nice for its age, is there anything special I should be on the look out for ?

There seems to be a small leak in the transfer case in the bearing seals for the yokes, its a NP 208 case, is this common ?


The underside is super clean, I know this bodystyle is prone to rust but this one seems to have escaped fairly clean. Are there any hidden areas of rust I should check for ?


Does anyone know which transmission it might have, Its probably a 700R4 since it has overdrive but I'm not sure.


Is there any problems with the fulltime front axle ? I'm used to Fords with the option to open the front hubs so the axle isn't spinning away underneath. And did any of these come with a front locking differential ? With the transfer case engaged I made a tight turn and the front wheels slid and skipped like a locker would.

Any info will be greatly appreciated, I will make the deal sometime this week, thanks.  

The seals are likely to leak at that age, the rear bushing in the NP208 may be worn also needing replacing.

The transmission is the TH700R4.

The front axle is not full time, it just has auto locking hubs so you don't have to get out to lock and unlock them; you just need to back up for short distance to unlock the hubs after switching the transfer case back into 2Hi.  The front never had a locker or limited slip from factory.  The front wheel slid/skip is because of the U-joints.

Good luck with your purchase.  

I have a 89 4x4 1500 GMC burb that I bought new. It has been a good vehicle. It has 185K on it now and no leaks yet. First thing to do it to change all the fluids (axles, Tcase and tranny and filter as well as engine) to start out fresh. Next I would pull and inspect auto locking hubs to make sure they are clean and rust free(you do not want much grease in them) and also check bearing that end of stub shaft rides on in hub. (I had one dry out and go bad once years ago). Look in glove box at option codes and look for things like VO5 (HD cooling) KC4 (aux engine oil cooling) Z82 (HD trailering) and axle ratio code. It can be GU6 for 3.42 or GT4 for 3.73 (you want GT4) Also if there is a G80 in there is has posi. One more tip, that engine LOVES higher octane fuel and if you run timing around 6 to 8 BTDC and use 89 in winter and 93 in summer it will run a lot better and MPG will pick up enough to more than offset extra fuel cost. If you stay with 87 it will perform well below its true potential. I can get 18 MPG with mine on a long trip using A/C if I stay under 70. (it has stock type load range C tires running near max pressure and GT4/3.73 gears and all options mentioned above except G80 which I have never missed on it)  

Thanks for replying, I posted this on 4 forums and these are the only responses.

How hard is it to change the tailshaft bearings ? It is probably a good idea to change the u-joints while I've got everything apart isn't it.  

Never changed one. It is a bushing not a bearing.Mine is still original.