In the 50 years I have been running limited slip G.M., Chrysler, and Ford rear ends I have never done any "figure eights" after changing the rear end lube because I knew normal driving would accomplish the same thing. Since the clutch plates were already sloppy wet with the old lube I felt figure eights would be a waste of time.

What are your thoughts regarding figure eights? Beneficial or a waste of time?

 

Ive always heard it was to evenly/properly distribute the oil and to prevent groaning.

And even it it doesn't do anything, its not like it takes hours to do, find an open lot and drive your Vette, sounds like a great way to "waste time"

 

Wives tale....I have changed the rear diff fluid at least 4 times in 30+ years on my 78 with mobil 1 75W-90 synthetic and never done figure eights...posi operates perfectly.

Also have done the posi on my 94 Mustang GT a few times with no special breakin procedure..perfect.

 

I can understand an advantage if the rear end was rebuilt and put together dry but as I always dip the frictions in oil as I go they are already coated with oil.

 

It depends on which clutches you have. 65-70 uses solid clutches. 71-79 uses slotted clutches. Slotted clutches allow the lube to soak into the slots so figure 8's aren't needed but do speed up the process. Solid clutches will take forever to soak up lube on their own so figure 8's should be done.
Mike

 

The man has spoken, end thread.

 

/thread

 

........

 

But as the clutches are already sloppy wet with oil what gain is there? Sloppy wet is sloppy wet.

 

The sloppy wet gear lube is the problem. There is no friction modifier in it. The modifier (additive) prevents the clutch plates from sticking to each other. With stock, slotted discs the modifier will penetrate and then coat the discs almost immediately when you start turning. Since there are two 9 disc clutch packs only the inside (of a turn) clutches will slip, the outer won't. So you do figure 8's. But first the 4 oz. of additive need be mixed into the 50+ oz. of gear lube.
On 65-70 and new solid clutches there are no slots on the 4 discs (per side that engage the side gear) for the lube/additive mix to penetrate into. Eventually just sitting there it will seep in but only 1/3 of the clutch packs sit in lube. The other 2/3's is above the oil level. So you do figure 8's to help speed it along.
Jeff, jb78L-82, makes an interesting point. Why hasn't he ever had a problem? Jeff answered his own statement. Mobil 1 Synthetic is designed for use with limited slip and already contains friction modifiers. But Eaton does not want synthetic lube used with their clutches. For a person like me that has to warranty rebuilds I can't recommend synthetic lube.
Also he has changed his lube over the years and has put a quality lube in. I doubt his cars have ever been to $19.95 lube shop and had the diff topped off with $10/barrel universal gear lube. Which just happens to be the way I learned this on my own vette almost 40 years ago. Yes, I did it to myself.
For the average mechanic/rebuilder that doesn't know about, or how to, pre-seat the clutches, shim the clutchpacks to set spider gear backlash, or just reuses the same shims since that's "how the factory set it up", this usually isn't a problem. By the time the discs seat-in, the lube/additive has worked its way in. Once they do get seated the stub axles now have .010 - .015 more end play and the spider gear backlash is more than the .005 maximum.
Hope this helps clear things up
Mike

P.S. Jeff, we met several years ago at Carlisle. Enjoyed talking with you and looking at your car.

 

This post reminds me I need to change the rear end gear oil.

Brian

 

What do you mean when you say the old oil doesn't have any friction modifier in it? When you drain out the old oil with the friction modifier in it and add new oil with friction modifier in it what has changed other than the oil and friction modifier are new? Just a single right or left hand turn in town could turn the clutch plates maybe a dozen times. If a guy wants to turn figure eights its okay with me as long as I'm not sitting in the car with him.

 

If you drain gear lube with modifier out and install new fluid with modifier why would you even need to work it in? I don't quite understand your question. If the clutches aren't popping from lack of modifier in the old lube, you don't need to work in the new lube. Because there ain't no problem.
If the clutches are popping with the old lube it's because of lack of friction modifier on the clutches. That's why they are popping. They are sticking to each other. The lube with friction modifier needs to be worked into the clutches. Hence figure 8's.
Really? On a 90 degree turn in town the outer wheel is going to rotate a dozen times more than the inner wheel. How big are the streets in your town?

 

Hey, if you feel figure eights are needed go for it. Best to do it in the wee hours of the morning when nobody is looking...................

 

Gary Vossberg at Vtech Corvette rebuilt my differential and recommended doing the figure eights. I did them. Differential works great. Traccdogg2 recommends doing figure eights. Both of these people know more about differentials than I ever will. If I wasted 15 minutes of my life doing figure eights - so be it.

 

Most everyone on here that is changing their fluid is because of a problem. Hence add new stuff, do the tight radius turns to work it in.

I have the feeling there were paint chips in someones cereal growing up.

 

Mike has never steered me wrong on anything in over 6 years. His knowledge and advice has always worked for me.

 

'tracdogg2'

I am actually GLAD that I read this post. I was doing some 'looking' to see if I could learn something or add information to help...and OBVIOUSLY you covered it.

I FEEL your PAIN. Explaining the dynamics of a system or component to a degree that a person would have to be an imbecile and not understand it...and still the information gets challenged.

Years of doing work on Corvettes and having screwed up so badly to find what it takes to repair 'something' WITHOUT a problem would make most people quit and do something else.

I NEVER claim to know it ALL...because I KNOW I don't. BUT...what people who do something with passion for years and years DO HAVE is experience and KNOW ...what to do and what NOT to do.

AND.....when these people who perform work and repairs with a diploma from the 'school of hard knocks' express their experiences to try to HELP people...some people will still insist to try to re-invent the wheel and find their own path. And to 'those' people...I give a and wish them the best. Because they will often times head down the path that will make them ( spin in circles) and until they feel like they are and what they created is going to turn into a major . BOY-oh BOY...have I done that...and sometimes I realize that the 'wheel' is just fine and needs no improvement....because ...I feel it is insane to try to make something 'more round' that is already round.


basically...keep up the good work....there are people who do appreciate it.

DUB

 

Thanks Dub,
I have a feeling you and I have a lot in common, more than just age.
Mike