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Gear oil question

beanhead

beanhead

May I Land My Kinky Machine
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Just pondering something here...the shop that rebuilt my 742(clutch sure-grip) pumpkin told me to run 85/140(+additive) which I am. Since the weather turned coldish, every now and again I get some clunking or snapping noise coming from back there... Only during very low speed turning, like in and out of a parking stall etc, and sometimes it doesn't do it at all.. I noticed in many other threads on here, nobody seems to run an oil that heavy... is it a possibility that in the cooler weather it's not lubricating enough causing the inconsistent noise? I did the recommended break in process and I've got about a thousand miles on it at this point, the noises started a few months back...Thanks!
 
I usually use the Redline 75W90 gear oil in street cars. It already has limited-slip additive in the oil.

https://www.redlineoil.com/75w90-gl-5-gear-oil

In my 1-ton truck, I run the heavier weight Redline 75W140 oil.
In the race car, the Redline Shock-Proof light weight "Film thickness greater than 75W140" according to their web site.
The manual trans uses the redline MTL (Manual transmission lube.)
 
I was advised by a drive line shop (that also specializes in old mopars), to use 80-90 +additive. I’m using Brad Penn 80-90 in rear and trans., no problems.
 
I run the thicker gear lube without an issue, but your idea sounds reasonable. Maybe buy a bottle of additive & have Jiffy Lube suck out the thick stuff & replace it with thin. Worth a shot to answer your question. I think they change gear lube for about $90.
 
Why such a thick oil for street use
I run Lucas synthetic 80 90
Has additives in it
 
What do you consider coldish? As I recall and based on my limited experience, the lighter would work OK and it seems that some friction modifiers work better with the clutch type units than others.
 
I do not think you have enough friction modifier sounds like clutches are hanging up use the ford stuff I do not think the weight is the issue just suck a little out and add the bottle
 
Thanks guys...I was told today also to at least use the additive from the chrysler dealership, as opposed to whatever kind from the parts store (which is what I did..!) so I'm going to change things up and see how it works.. gtxno1 thanks I see others are running the ford stuff too with good results..
 
If I recall correctly, back when the "clutch type" limited slips (early 8 3/4 & Dana 60) were common there was a big difference between the Chrysler "skunk oil" or the Ford version and the friction modifier for GM "posi's". Both my 8 3/4 & Dana worked fine with the Chrysler stuff, don't know if it's the same modifier today though.

Just to clarify, the Chrysler & Ford stuff seemed about the same (at the time) & the GM stuff didn't seem to work with the clutch types.
 
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We used to call the ford stuff butt juice that stuff stinks I worked for Lincoln Mercury as a tech for 26 years Also if you check with Dr Diff he only uses ford additive
 
I had the same thing with my Roush 9" posi unit. I had changed the diff fluid with Lucas 80/90 syn with additive already in it. Afterwards it chattered on tight turns at low speed. Added 4oz more of the Motorcraft posi additive and it took care of the problem.
 
I use the 75-140 full synthetic for towing
If you read the bulletins even Chevy and FORD recommend a xx-140 for HD use even if he glovebox manuals do not say so
none of the OEM oils from the 60s and 70's are available today- that especially includes motor oil and trans fluid
IDK about snake oil but Redline is top notch- they used to supply our trans-am car
 
The mechanic who set up my rear recommended the heavier wt. lube and additive. However I'm running those noisy Richmond gear and I think he was hoping it would quiet them some. I really notice it on the rare mornings when I push and roll it out of the garage to get it out from under my lift - instead of starting it up.
 
MW 413 said:
I had the same thing with my Roush 9" posi unit. I had changed the diff fluid with Lucas 80/90 syn with additive already in it. Afterwards it chattered on tight turns at low speed. Added 4oz more of the Motorcraft posi additive and it took care of the problem.
Click to expand...
Sometimes the clutches will stick after sitting for long periods also. Used to always make a couple 360’s in both directions to make the clutches work harder& get more oil in between them; slow speed worked fine.
 
Seems to me I read on the forum here year or so ago that someone suggested the GM posi additive over the mopar sure grip additive. I'm going to be changing the oil as it has around 500 miles now since rebuilding and a buddy had some GM additive he gave me I have sitting on my garage shelf still wondering if I might use it for the change. I initially put in the mopar additive and the rear emits the same friggin noise it did before unless it's coming from elsewhere.
 
Don't think it affects noise, just the smoothness of the limited slip action, especially with the 8 3/4 or Dana clutch type.
 
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