4WD Problem, Please Help

[Megatruck]

I have an 87 Suburban V10 with an NP208 C transfer case. My problem is that when shifted to 4wd it doesn't seem to be engaging. What are some troubleshooting ideas that are most common with this vehicle. Here are some of the stats that may help with ideas:

Transmission-TH400
Transfer Case-NP208 C
Front End-Dana 44
Manual Hubs- Warn
Wheels- trXus MT 37/12.50 15

Any help is greatly appreciated. Thank you.

 

[1987 GMC Jimmy]

So it's shifting fine but not engaging? The front driveshaft is there, correct? Is it making any grinding/whining/clunking noises, or is it okay on that front? It sounds like it's not locking and probably not an issue with the t-case. I hope someone else will chime in because there are plenty who know this stuff better than me.

 

[HotRodPC]

My first guess will be locking hubs also. BUT... could be a broken front axle also, or even broken ring and/or pinion. If it's an open differential up front, all it'll take is 1 broke axle and the spiders will rotate the broken axle since it will have the least resistance and not feel the weight of the vehicle.

 

[Megatruck]

Update to 4wd issue

After further research and looking at the front axle, I noticed a large hole in the top of my differential. What would cause a hole like this? it seems to be broken outward.

 

[CSFJ]

Catastrophic failure due to abuse.

 

[Megatruck]

that's just it, It hasn't been abuse, It has occurred within the last month and hasn't hardly been driven in 4 WD.

 

[HotRodPC]

So part of the mystery is solved. At least now you know why it's not engaging.

Damage could be from age and wear too. Bearings may have gone first then that's the first domino that falls.

To bad you're not closer. I've got a spare 10 bolt front axle I'd probably let go of for $100.

 

[HotRodPC]

Catastrophic failure due to abuse.

Yes, we're talking 10 bolt here buddy. It don't always take abuse. A little wear on some parts, ring gear get cocked a little, or pinion bearing wears and the pinion gear gets cocked, then there you go. Ring and Pinion bind up and something has to let loose. In this case it looks like it threw some gears through the case. Now it's all junk. Need a new case, ring and pinion, and probably a carrier too. At this point gonna be cheaper to start with a good used 10 bolt front case.

Do you by any chance know what your gear ratio is?

 

[Megatruck]

Thanks, I figured I'd try to find a whole new (used) front axle assembly. Gonna take the front cover off tonight and see how bad it is. I appreciate everyones help.

 

[Honky Kong jr]

Thanks, I figured I'd try to find a whole new (used) front axle assembly. Gonna take the front cover off tonight and see how bad it is. I appreciate everyones help.

If you do look for a 90-91 Blazer or Burban. 30 spline axles. 89 was the first year for 30 spline axles but were hit or miss another thing front and rear 10 bolt guts are the same as in posi up front. That way if you break an axle you will still have 1 front pulling. You can run a gov. Lock up front too. Some will say they suck but in a front rear not aggressively driven work awesome in normal 4x4 applications.

 

[HotRodPC]

If you do look for a 90-91 Blazer or Burban. 30 spline axles. 89 was the first year for 30 spline axles but were hit or miss another thing front and rear 10 bolt guts are the same as in posi up front. That way if you break an axle you will still have 1 front pulling. You can run a gov. Lock up front too. Some will say they suck but in a front rear not aggressively driven work awesome in normal 4x4 applications.

I'm not sure if that applies to the front axles. I think they are all 27 splines.

 

[Honky Kong jr]

I'm not sure if that applies to the front axles. I think they are all 27 splines.

Nope my front is 30 spline 90 burban. The Eaton posi carrier is from a 90 1/2 ton truck back rear which were 30 spline from 88 on. Older 10 bolt fronts were 28.

 

[HotRodPC]

Yes, I meant 28. I thinking Th350 and 700r4 output shaft.

 

[HotRodPC]

That is good to know for sure on the front's though about the 30 spline. I wasn't sure if it was rears only or not. I just sold my Detroit Locker 10 bolt 28 spline that I was saving for a front but I'm going to use the ARB air locker instead and 14b FF in the rear.

 

[Honky Kong jr]

Yes, I meant 28. I thinking Th350 and 700r4 output shaft.

I figured as much. When I was rear shopping to replace my rotted front rear I looked 89-91 and 60%of the 89s were 28 spline then I found the 90 burban rears for 110 for the pair 5 hr round trip but worth it I ended up scrapping the rear housing and kept the axles put the Eaton in the front now it's apart again for the regear. But now I have enough to make a 30 spline rear 10bolt set up as a spare that my disc swap will fit on.