Sorry for this potentially foolish question, but it's important. I've read the recent postings about ID'ing a posi rear-end and calculating rear axle ratios. I've paid close attention. However, a potentially "stupid" question is nagging at me.
Should the tranny (4sp in my case) be in neutral or not? (hold your laughter) The reason I ask is because of the instructions to ID a posi rear. Wheels spin the same=posi; wheels spin opposite=non-posi, right?
Well, if I spin my left rear wheel while in neutral, the other spins same direction, but intermittently and slower. If I put the 4sp in gear, the other wheel spins in the opposite direction. What do I have? (ok you may laugh now... :)

Hmmm, I don't know a hole lot about rear ends but it doesn't sound like it's a posi to me. With both wheels off the ground both wheels should constantly be spinning at the same speed and when in gear I can't see any difference except that it would be harder to spin the tires http://www.chevelles.com/forum/smile.gif. Could be that you have an open rear end that is malfunctioning and that is why both tires spin the same way, by my understanding you should do the test in neutral. Wait till you hear from somebody else before you decide it is an open rear end.

Gandalf

I have posi but when I spin one wheel the other doesn't move.The reason being is that there is no torque to lock the rear.This is so when you go around a turn the outer wheel can spin at a different speed then the inner wheel.Otherwise your tires would chirp around turns just like having a spool(locked)

Jeez,TK you have spent more time typing these posts than it takes to pull the cover and be sure of what you have. I don't mean to be mean I just don't know any other way to put it. Nobody here can tell ya what you have. The car is 30 years old "anything" can happen in that amount of time. Please excuse my bluntness but I was a machine shop foreman for 20 years and we didn't have much for fool'in around with guess work. Anything short of pulling that cover is guess'in.
Harley

Sorry Harley. I simply haven't had the time to pull the cover (graduations, kids' softball, work, you know the drill). And if I did pull it, I don't know what I'd be looking at/for anyway. I haven't much experience with rear differentials and I thought there was a simple way to tell.

If the bottom-line answer is that you cannot reliably identify a posi rear via the wheel-spin test, then in my opinion, this discussion was worthwhile and I'm glad I asked. I guess I will bring it to a shop and have them check it out. TK

[This message has been edited by TK-70 (edited 06-21-99).]

My .02

I spun our diff with it out of the car and both wheels went the same direction. You can't get the trans in a more neutral position than that! (Course it also had the axle code for posi as well as the indicator tag screwed on the housing.

Tell you what though, even though the cover was off I can't immediately tell the difference between non-posi and posi either. What do they look like? Is it that set of springs (look like little valve springs) in the carrier that tells you what it is?

A stock posi rear will have a spring pack in the center of the carrier, consisting of two plates & 4 springs.

and a non-posi will just have a carrier housing with two spyder gears.....mgg

There are 4 spiders. One on the end of each axle where the c-clips are, and two on the cross shaft, these are for cornering. Posi rear ends have 4 spiders also (as does just about any stock rear I've ever seen) The springs in the center preload the clutch paks, and I believe you can get springs with different constants for more or less preload. I'm not an expert, but I am learning!

- Put your transmission in park (auto) or any gear (manual)
- raise both rear wheels by jacking under the center of the housing.
- attempt to turn either rear wheel
- turns easily, not a posi
- difficult to turn, a posi but possibly worn out
- can't turn, a posi or a spool

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Fred Aldrich
Web Site: www.GeoCities.com/~69_chevelle (http://www.GeoCities.com/~69_chevelle)

TK,
FIRST and foremost, there is no foolish question. If you don't know, ASK! All of the above is good info, but Harley has the ONLY true answer. Even if the housing has a posi code, it could have been changed out for any number of reasons in the past. You never know. It won't hurt to pull the cover and change the oil anyway and put on a new gasket. What are we looking at, $12 bucks for oil and a gasket?

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Thanks for the prodding. I scraped away the axle housing code and pulled the diff cover last night. Here's what I saw:

Axle housing stamp = CCF
# teeth on big gear = 43
# teeth on small gear = 13
4 springs and the 2 plates are in the center core

Keep in mind that if I spin one wheel, the other does not always spin in sync. What do I have?


[This message has been edited by TK-70 (edited 06-22-99).]

43 ring gear teeth divided by 13 pinion gear teeth works out to 3.31, and CCF does decode to a 3.31 Posi rear. At least thats the info from the following URL.

Here is the url

chevelles.com/years/70/70rearcodes.html (http://chevelles.com/years/70/70rearcodes.html)

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DG
Springfield, Ohio
70 Chevelle Malibu

www.wright.edu/~s001dga/chevy.htm (http://www.wright.edu/~s001dga/chevy.htm)

TEAM Chevelle Member #0086



[This message has been edited by DG (edited 06-22-99).]

Now we know "exactly" what you have.While it's up on stands ( I hope it's up on stands)
go out to the wheels and lift Up, we are looking for slop from an eat up axle/axles.
Note: When I was first looking at my 71SS Camaro the seller swore it was a posi and it passed all the afore mentioned tests. However when I got it home, pulled the cover,
what did I find; WELDED spyder gears, Go figure.
Harley

One easy way to test to see if you have posi is to floor it from a stop with an auto or rev and pop clutch (std) and see what the patch looks like. If you have 2 tire marks then you have posi.

Mark

Everything points to the fact that I have a 3.31 posi. Thanks everyone for getting me this far.
Now back to my original question - If I spin one wheel, the other only spins intermittently (same direction). What can I look for? Everything in the differential looks good. Could it simply be that the previous owner did not add "posi lube" to the differential? What does that stuff do anyway?

Mark-
You beat me to it! I was just thinking of posting that as I read through all of the replys! http://www.chevelles.com/forum/wink.gif

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Steve
64SS-327-4spd-sold to Original owner!
In process of finding a 65
Team Chevelle Member #71

TK,
If both wheels are off the ground and you turn one wheel and the other DOES NOT turn at the same rate, then the clutches INSIDE the posi unit are worn and sliping. Possibly you will have some traction from both tires but not as much as you would have with a good tight posi unit (and, for a fact you do have a 3.31 posi based on your info, and I assume it is a 12bolt). There is a gear oil formulated for posi (limited slip) rears which should be used. Also you should buy and add the posi additive sold at Chev parts. It keeps the clutches from chattering.
Now, for the good part. And this all depends on how bad you want good, equal traction from your posi (if the clutches are worn and not allowing both rear wheels to get full traction, it's OK, it will NOT hurt anything in the rear end). Removing and changing the posi clutches is not all that difficult. It is a rather straight forward mechanical procedure. If you feel totally uncomfortable about doing any of it, take it to a good mechanic. If you just want to pull the posi unit out but don't want to change the clutches, BE SURE YOU PUT THE SAME BEARING RACES AND SHIMS FROM EACH SIDE BACK EXACTLY WHERE THEY WERE! Use a hammer and punch to mark the bearing caps and housing so they go back in the same place. Then take the removed posi unit to a mechanic that you have confidence in, and have him change the clutches. And stand there and watch him do it so you will know how it is done. (then when he is done, you will say "I could have done that") The best way to learn how to do your own repairs is to watch someone who knows what they are doing or just do it yourself and use the trial and error technique. Don't be afraid to tackle anything. (using a shop manual of course)

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[This message has been edited by DZAUTO (edited 06-22-99).]

Mark, Steve, I considered the burnout test too, but didn't want to chance it with an unknown rear. And although it is the most enjoyable way to determine posi or not, we've proven that the test is not 100%. My slipping posi would have fooled us.
DZAUTO, thanks very much for the insights and info. I will likely get a new gasket and reassemble for now.
Everyone else, thanks for your input. I learned alot. I accomplished my mission and determined what I have. I have some legal issues about what I was told versus what I was sold (see other postings if interested), which I have to deal with now.
Has anyone mentioned what a great site this is and how wonderful the members are? I know they have... I just had to say it again. Thanks...TK