Help identifying differential/locker

[Bullet4x4]

Hi Everyone,

I'm the proud owner of a new to me 88' K5. The gentleman I purchased the truck from had the 700R4 transmission rebuilt several months ago. During the transmission rebuild, he also had a "positraction" unit installed in the rear differential (10 bolt). While turning sharply (almost any 90* turn), I notice a bit of a grumbling sound coming from the rear end. While driving straight, or slight curves in the road, it doesn't make any noise. It also feels like there is some internal resistance while this occurs, causing me to throttle up more when parking/backing up while turning.

Is this a common characteristic of a limited slip differential? Is it possible that it is a locker such as a detroit? The gentleman who I purchased the truck didn't seem too sure of what was installed. Next week, I am going to contact his mechanic's shop to find out what was installed. In the meantime, please let me know your thoughts, I want to make sure that everything is working as it should.

Thanks Guys, I look forward to spending alot of time on this board!

 

[4X4HIGH]

The old saying, a picture is worth a 1000 words. Post a pic and we can help you. There are way to many different types of "positraction" devices to even begin to guess what yours has.

 

[trucknace]

I now for a fact that the gov lock makes that noise. this is the most likely installed posi, no its not great but they have to be better than a open diff

 

[Bullet4x4]

Hey guys, thanks for the tip. It took me a couple days to get around to taking some photos. It appears that I need to increase my post count before I can link any photos. I'll get there soon enough!

 

[Russell]

You can PM the links to me and I'll post them for you

 

[Russell]

Its a 10 bolt corporate diff, I can tell you that much, but here we go:

 

[dremu]

Gonna need a pic of the insides, so now's a good time to replace the diff fluid...

-- A

 

[onetonbb74]

well, no bulges in the diff cover. That is good.

 

[trucknace]

Regardless of the diff/locker it looks to be a clean truck

 

[Bullet4x4]

I just spoke to the shop that did the transmission rebuild and differential install for the previous owner. He said that they installed an Eaton Limited Slip Positraction unit. He claimed that these were fairly aggressive, and some resistance in turns is normal. He did add that they need the new gear oil, and a friction modifier added every 15,000 miles.

So, anyone have experience with these Posi units?

 

[dyeager535]

Eaton posi's are good units. Been used by GM in various forms for at least 40 years, if not longer.

Not real good for wheeling, they don't physically lock the axleshafts together, which is why their road manners are pretty good, but they are certainly a benefit even on a truck, better than open.

Make sure it's got the right gear oil, or else you'll get chatter as you corner. Some come with the friction modifier already included, 15,000 miles sounds awfully low, I bet with newer fluid it's a lot higher interval than that.

 

[Bullet4x4]

He told me that they filled the Diff with Amsoil Synthetic gearoil and friction modifier when they did the install, about 7,000 miles ago. In the past, I've heard some people have problems with synthetic fluids causing problems in their trannies/differentials. What would you guys recommend in a quality gear oil?

I definately hear some grumbling noises from the rear. Mostly when doing right hand turns and turning in/out of parking spaces. The problem occurs more often when power is applied during a turn. Is the "chatter" you describe any different?

 

[dyeager535]

Probably the same thing. Never experienced it myself, probably depends on the springs installed in the diff when put in as to how "tight" the differential is.

Amsoil is good stuff, we've got some dealers here, they can probably answer if you need to do anything additional. It's certainly not going to hurt anything as long as it's appropriate for that application.