The Stovebolt Site Forums The Parking Lot Tons 'o Fun tinny noise coming from Eaton Rear

Well after finally accomplishing my wheel dilemma on my 70 C30, I took it for its maiden voyage.... Had to run an errand at Lowes....While in the lot, I made a hard left with basically the left rear wheels pivoting and the right rear wheels making the swing...I heard a very unusual tinny clanking noise I never heard before. I drove home with no incident.....The truck has a Posi 4:56 rear.....I double checked the lugs & they were tight...???

That's normal for a limited slip carrier in a tight turn. What kind of lubricant are you using? GM and Ford used to have a 6-ounce additive that had to be used with the ones with cone clutches. If you've got the Detroit Locker carrier, the two pieces that lock together ratchet over each other and make a clicking noise if a tight turn is made with power off the engine. If moderate to heavy throttle is applied, both axles lock together and the vehicle tries to go whatever direction the rear axle is pointed.
Jerry

Embarrassed to say, I never changed the fluid in the rear, or transmission...Thanks for bringing it to my attention...while on the subject...what fluid would you recommend?...I guess hard surfaces (blacktop/concrete) and lets say soft surfaces (dirt road) would have a different effect whether the noise is heard or not??.....When I changed the gear oil in my sons 2000 Ram a few years back I obtained an additive from the dealer, so I'm guessing this is what your making reference to......So this noise is nothing to be concerned about? I haven't heard it since.....As usual your expertise is always appreciated......

The normal 90 weight "multi-purpose" gear lube would be fine for that rear end. It's got the hypoid additive needed for proper lubrication of the ring and pinion that the "mineral oil" lube for transmissions doesn't have. The cone clutch limited slip rear ends have a bad shudder when the additive isn't used. If yours is just making a rapid click, it will do the same thing with the additive, also. The difference is that the Detroit Locker actually mechanically joins the axles together- - - -it doesn't use clutches. Another place the locker was used was in the GT-350 Hertz Mustangs, and it really spooked some of the people who rented those cars.
Jerry

So the transmission uses 'mineral oil'? - not the same 90 weight as the rear? - yeah GT 350 Hertz Mustangs....sure was/is a winner.......

"Mineral oil" refers to the base stock from which the lubricant was derived, as opposed to "synthetic". Not the clear stuff at the pharmacy!

The extreme pressure lubricants intended for use in Hypoid-gear rear axles can interfere with the operation of the synchronizer rings in some transmissions with heavy gears that require a lot of braking to prevent grinding while shifting- - -like the SM-420, for instance. Back when I was doing a good amount of repair on Fuller Roadranger transmissions I could tell which ones had used multi-purpose lube- - - -the synchronizers would be blackened by carbon deposits caused by slippage and overheating of the brass synchronizer rings.
Jerry

OK - Just to be clear...What brand, or number specifications should I be looking for on the transmission...I have 2 trucks that I will need to service.....

Royal Purple 75W90

90Weight Mineral oil from NAPA

Ditto on the NAPA mineral oil for use in transmissions. Regular 90 weight "multi-purpose" gear lube or synthetics like 75W-90 or 85W-120 work well in rear ends, NOT older transmissions.
Jerry

The Detroit Locker actually replaces the differential carrier and gears. Since your truck is a C30, it probably has a locker rather than a positrac. The clicking sound is normal.