Shaking out all the little things on my "55 GMC. One thing is that it feels real rough when making turns. I have a Ford Nine inch posi for the rear end. Had someone look at the truck while I made turns in my driveway and you can hear the roughness (lack of a better word) in the turns coming from the rear end. I will check gear fluid level etc. Any ideas?
I believe a Ford tractionlok needs a friction modifier(oil additive) in the oil . If the oil is old, change it, if its fresh, try adding the additive(parts store or ford). Goodluck.
Thanks. It's a fresh set up. New ring and pinion with the orig. posi unit. I had it all put together and had a guy install it. No smarts needed to fill it with gear oil. He could have left out the additive. No drain plug on the rear, so I may have to suck out some gear oil to make room for the additive. Thanks for the reply. Stay tuned...............
There is a break-in proceedure for new gears. You might want to be sure that is done correctly also. Something like drive a few miles and check for overheating. Do this three times. Then a 200-250 miles trip and change the oil.
As said before, definitely sounds like it needs a friction modifier (additive). ALL clutch style limited slips use a friction modifier. Don't worry about removing any oil from the rear, the additive comes in a little 3.8oz bottle. Just squeeze it in there. Definitely use the Ford Racing kind. Trust me here, I've built thousands of diffs and the Ford stuff just seems to work best. Oh yeah, do yourself a favor and don't run synthetic oil either if you drive the car a lot. Just good ol' fashioned EP 80-90. In my experience, synthetics break down to far and cause premature wear and destruction in diffs.
Reminds me of a similar problem I had with a 65 El Camino 327, 300 HP, 4 Speed years ago. Kept replacing clutch discs and pressure plates cause It wouldn't come of the line without chattering. A friend of my Dads who was an auto mechanic had me drive it in a circle in a parking lot. You could feel the rear end waddle. Added GM friction modifier and all was well. Expensive lesson.
Update. Put in the friction additive and about 12oz. of 80-90 gear oil. ( a little low) Did circles in a parking lot going left then right. Seems to be loosening up. I'm thinking this is not an instant fix maybe have to get a few miles on it? Thanks. Kent
Ford 9" posi is defintely loosening up. I like it. Real different from the Tru-trac posi in my '37. don't even know it's there till it bites. However, in my '55 GMC the original type posi really goes with that truck. A little rough, you know it's there kinda thing. Thanks for all the input. Friction modifier is killer stuff. Kent
Put in the friction modifiers and your just defeating the positraction effect. The clutches grab each other (friction) and cause the axles to turn the same. With the modifers the clutches slip defeating the action created by the posi unit. Won't affect a new unit very much but a worn unit will almost useless if the clutches are allowed to slip. Frank
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