Front Differential

[blueridgegmc]

Hey guys, my 1990 GMC Sierra 1500's four wheel drive went out. I peaked under the truck and looked at my front drive shaft, it spins when the truck moves forwards and backwards. And so do the front axles. I've replaced the acuater. My front diff. fluid was extremely low as in I put my finger in it and couldn't feel any liquid. When I took out the bottom plug only about a cup of diff. fluid came out. It was greyish shinny kinda color and I can't tell if it's me being paranoid or if there is metal dust in it. Am I looking at a blow front diff.?? Also on a side note, when I was in four wheel drive and it worked, there was a loud thumping whenever you made a right or left turn......and yes, I was not on pavement. Also, whenever I try to push the four wheel drive selector to four wheel low it's really hard....almost impossiable. Than when you finally do push it in, it grinds horriably until it kicks in. Does this all equal blown front diff.....

 

PS.

 

What are some vital things to replace on the front of the truck after 200,000 miles??? Gotta couple hundred bucks to work with.

 

Thanks!!

[citydriver]

only about a cup of diff. fluid came out. It was greyish shinny kinda color

 

DUDE THIS IS NOT GOOD!

 

Sounds like the diff.carrier bearings r wiped...low fluid not a good sign,probably due to a leaky seal,but the silver/grey color of the fluid that was in it is usually a sign of severe damage..gonna need to tear it down and take a look see...

 

If it is wiped,you may be better off searching 4 a donor vehicle at your local salvage yard...just make sure you get the right gear ratio if you decide to do this.

[99-2door]

I agree, that doesn't sound good at all. Probably cheaper to replace the entire front diff from a salvage yard.

[blueridgegmc]

How can I tell what gear ratio will work.....and what fits my year truck....??

 

1990 GMC Sierra K1500

 

 

Thanks

[asilverblazer]

While on the topic of front diffs I was wondering how hard it is to replace the seals on the diff. where the half shfts go out and the seal where the driveshaft goes in (all 3 big ones) on a 1999 NBS Z-71 with 3.73 gears?

[blueridgegmc]

Anyone?

[citydriver]

How can I tell what gear ratio will work.....and what fits my year truck....??

 

The easiest way to tell is check your RPO codes to see what gear ratio was installed @ the factory...the sticker may be in the glovebox...or take your VIN# to your local dealer and they should be able to tell you what gears it was built w/.....

last but not least...you can get the ratio when you pull the old diff/carrier out..

 

RPO CODES

[citydriver]

While on the topic of front diffs I was wondering how hard it is to replace the seals on the diff. where the half shfts go out and the seal where the driveshaft goes in (all 3 big ones) on a 1999 NBS Z-71 with 3.73 gears?

 

I'm not gona lie to ya'...I havent done any myself,but from what I've read in the manual,it seems fairly straight forward...best to refer to a repair manual and read up b4 you attempt it to make sure its within your abilities.....

[PeterbiltChrome]

I've known some guys that had the 3.42 in a K1500 stepside reg cab but they had 1994's and could be just certain cases.... most 4x4 half tons are probably 3.73 by '99 i suppose......

[99-2door]

I've known some guys that had the 3.42 in a K1500 stepside reg cab but they had 1994's and could be just certain cases.... most 4x4 half tons are probably 3.73 by '99 i suppose......

You would be suprised how many trucks have 3.42s.