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Technical Ford 9 Inch - Sticking Differential

Discussion in 'The Hokey Ass Message Board' started by DirtEmpire, Sep 9, 2021.

  1. DirtEmpire
    Joined: Sep 9, 2021
    Posts: 12


    I recently bought a 1971 Mercury Colony Park that's a bit of a time capsule. I think it sat in the garage for about 20 years. Before that it had a period of going to shows. It had a leaking pinion and wheel seal. It's 2.70 Traction Lok axle. The first 3-5 miles I drove it, the diff seemed normal but at this point, it's like driving with a detroit locker that won't disengage properly. I pulled the thing apart expecting to find a smoking gun but, everything rotates freely. The gear oil was especially sticky with a horrible rancid smell (and I like the smell of gear oil)

    I've been around plenty of old LSDs that didn't do much of anything. I've never seen one act like this. As far as I can tell, tires haven't broken loose while turning but the action is violent, it feels a lot like the worst moments with a detroit locker. There's no chance of getting differential action while spinning tires by hand.

    Has anyone had the same experience? I suppose at this point I'm inclined to clean it up, reseal (and probably re-gear), and put it back together with clean oil. I could change clutches but... they look pretty good (and I imagine I would then have to re-shim).

    Attached Files:

  2. MeanGene427
    Joined: Dec 15, 2010
    Posts: 1,946

    from Napa

    Be sure you get the Ford Friction Modifier and add it to the new gear oil, or the clutches will go south quick. Then take it to a big empty parking lot and turn it as tight as it will go, do about 10 circles, then go the other direction, to get the oil into the plates- that's probably all it needed
  3. saltflats
    Joined: Aug 14, 2007
    Posts: 10,934

    from Missouri

    Clean and lube the clutches with fresh proper gear oil and go do some figure 8s.
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  4. Budget36
    Joined: Nov 29, 2014
    Posts: 7,262


    When I’ve done similar posi’s I dip the discs in the rear end lube before putting them together.
    Maybe just old lube and sitting a long time is the issue.
    And yes, use the additive, allows the discs to slip.

  5. Mr48chev
    Joined: Dec 28, 2007
    Posts: 30,056


    The sticky and stinky part makes me thing that in a past life of that rear end someone stuck some snake oil additive (s) in it for some reason or other. Possibly because of noise including the clutches making their "we don't have the right gear oil stuff and we are going to fuss" noises or some concoction to slow down a seal leak .

    If everything looks good it is a 25/30 dollar gamble to put proper gear oil, the additive and a new gasket in place and run it as Mean Green 427 suggested and that I a gamble I'd take.
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  6. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,474

    from phoenix

    Had a narrowed 9.3" Olds in a Chevy II when I was a kid and replaced the original warped/cracked housing with a clean properly welded one. Unaware of the required limited slip additives and put straight 90wt in, chattered in tight turns. Was right again after adding some.
    Deuces, 427 sleeper and Budget36 like this.
  7. greybeard360
    Joined: Feb 28, 2008
    Posts: 1,813


    The old Ford limited slip additive stunk to high heaven. The new stuff doesn't. If that car sat that long it probably still has the original stuff in it.
    We were glad when they changed it.... We had a mechanic that liked lubing his air tools with it. You could smell him heading to the parts room from 100 feet... Lol
  8. mrspeedyt
    Joined: Sep 26, 2009
    Posts: 711


    maybe 15 years ago (or perhaps 20) somebody stole my two Ford 9 inch rear axles from the 5 acre property where I lived in Winona Arizona… (A few miles east of Flagstaff…) they knew EXACTLY what to look for. there was also a 62 cad rear end sttting there that was very similar to the two ford 9 inchers… they didn’t take the cad rear end.
    Last edited: Sep 9, 2021
  9. DirtEmpire
    Joined: Sep 9, 2021
    Posts: 12


    I suppose it's possible it had been refilled without the additive. I tried just working it till it was free but yeah, it just got worse.

    "someone stuck some snake oil additive (s) in it for some reason or other."

    I was thinking the same thing since it has two seals that are leaking pretty bad.

    I don't really have any experience with an LSD without the friction modifier. I never would have guessed it would result in holding power like this. When it lets go, you can feel the whole front of the car move over.

    One way or the other, between the 2.70 gears and inability to hold oil, it needed to come apart. Now it's just a question of how many parts I throw at it.

    "The old Ford limited slip additive stunk to high heaven."
    Most everything I was playing with even 20 years ago that would have been the right vintage had open diffs so yeah; I didn't have anything that would have even come to me filled with it. It's amazing how much this smells just like rancid gasoline mixed with gear oil though.
    Boneyard51 likes this.
  10. oldiron 440
    Joined: Dec 12, 2018
    Posts: 2,425

    oldiron 440

    I picked up an 8 3/4 LS differential back in the eightys from my local yard at the time, it had been sitting out of the axle for some time. If never would work smoothly no matter what oil or additive used. It was tight enough that you could put the RT wheel in the grass the Lt on pavement punch it and the Lt side would leave one helluva black mark.
    It was in my shop truck for twenty years, it never got better.
    Put a kit in the diff.
    Boneyard51 likes this.
  11. AldeanFan
    Joined: Dec 12, 2014
    Posts: 749


    I had that same problem when a dealer took it upon themselves to change gear lube and not used the limited slip additive. I added a bottle of friction modifier and the problem went away almost immediately.
    Boneyard51, VANDENPLAS and Deuces like this.
  12. indyjps
    Joined: Feb 21, 2007
    Posts: 4,406


    Wondering with a 2.70 diff, (Big boat, wide low speed turns, and highway gear) did the rear wheels actually disengage the LSD during a turn ? It could have locked itself up over time.
  13. MeanGene427
    Joined: Dec 15, 2010
    Posts: 1,946

    from Napa

    Did you ever smell the old Texaco Havoline engine oil? The Ripe Stuff
    Deuces likes this.
  14. big john d
    Joined: Nov 24, 2011
    Posts: 255

    big john d
    from ma

    did you ever smell the chrysler / jeep rear axle limited slip addative it would clear the shop
    Deuces likes this.
  15. DirtEmpire
    Joined: Sep 9, 2021
    Posts: 12


    I expect sitting and drying out for 15 or 20 years had a lot to do with it. You can see the highwater mark in that picture of the carrier; Red glyptol below, and deposited evil above.

    It's strange to me that it ran perfectly smooth at first and then got super grabby. I think the current plan is to clean it up, soak the clutches in friction modifier, and reassemble with new seals and wheel bearings.

    The small bearing 9" appears to be pretty marginal for endgame plans for the car. There's a Disc-brake coil sprung 9" for sale locally. ...I know the wheel bolt pattern wont match but I am curious if the housing and axle flang-to-flange distance would be the same. Seller claims it's out of a Mark.
  16. MeanGene427
    Joined: Dec 15, 2010
    Posts: 1,946

    from Napa

    I wouldn't soak the clutches in pure friction modifier, just get it from Ford and use the recommended ratio of modifier to oil- too much might be as bad as not enough. I always used to just put in the recommended amount, drive it a few miles to let it mix, and then did the turn tight trick. Pretty sure there's a procedure in the Shop Manual or your Motor Manual to get it right. If you ever have it sticky again, the tight turn trick should fix it right up
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  17. I don't know what your plans are for this other rear but, not knowing exactly what car it came out of, it could be 9 3/8" not 9" and, it has been my experience, the larger cars came with 31 splines so, if you are hoping to use the 'pig', it may not work for you. BTW, a 9 3/8 housing accepts 9" 'pig' if I recall correctly.

    Just wanted to mention incase you are thinking of just tossing the "Mark" pig into your existing housing/axle combo.
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  18. Dan Timberlake
    Joined: Apr 28, 2010
    Posts: 1,331

    Dan Timberlake

    I think some parts galled and welded themselves together around mile 5.
    I guess some folks have had spider gears etc gall to shafts.
    I don't recall hearing of the posi clutches doing that.
    Deuces likes this.
  19. RJP
    Joined: Oct 5, 2005
    Posts: 2,012

    from PNW

    Always used the GM rear end stuff. One big jug, and two little bottles. Worked in Ford, GM, Mopar. Posi or open. Drain, fill, then a few figure 8's in the parking lot and it was good to go.
  20. MeanGene427
    Joined: Dec 15, 2010
    Posts: 1,946

    from Napa

    Why would you want to use GM lube in a Ford rear? The only thing I've ever heard recommended for the clutches in the Ford diff is the Ford friction modifier- just makes sense
  21. You know the clutches in a limited slip don’t know what brand they are in or the brand of oil right?
  22. Truckedup
    Joined: Jul 25, 2006
    Posts: 4,214


    OP, you said you pulled it apart, did you remove the clutch pack and separate the drive and driven plates? Bike clutches are similar and sometimes the plated will stick together like they are glued... Need to actually pry them apart....
  23. MeanGene427
    Joined: Dec 15, 2010
    Posts: 1,946

    from Napa

    Do you know the composition of the clutches in the different brands, what materials are used? Why take a chance?
  24. At auto parts stores, they used to (and maybe still do) sell one type of auto trans fluid for GM and a different one for Ford. Would it be OK to put the Ford fluid in a GM trans based on the "it doesn't know one fluid from another" thought process? I don't know, just asking ...
  25. GM has what I suspect is similar posi-trac additive (#88900330). But I've always been under the impression that it was more of a detergent additive. Most hypoid rated gear lube seems to work fine in GM's posi differentials without the additional additive. But with age and use, if the clutch plates became varnished or glazed that was when the shuddering and clunking noises started up.

    More often than not (as mentioned by several before me), adding a bottle of the detergent additive, getting the gear lube warmed up, and cutting some big figure 8's in a parking lot would clean the varnish or glaze off the clutches and the noises would go away. GM even suggested using this additive with an oil change to help free up sticky lifters and valves.
  26. DDDenny
    Joined: Feb 6, 2015
    Posts: 15,376

    from oregon

    Many years ago a fellow truck club member put an Auburn positraction (cone style) unit in his 66 Chevy pickup, said it made quite a ruckus so I said give the GM friction modifier a try, he said it worked like a champ.
  27. jaracer
    Joined: Oct 4, 2008
    Posts: 1,225


    Has anyone had the same experience? I suppose at this point I'm inclined to clean it up, reseal (and probably re-gear), and put it back together with clean oil. I could change clutches but... they look pretty good (and I imagine I would then have to re-shim).[/QUOTE]

    I've got a 9 inch with Ford TracLok differential in my Model A. I've only got about 400 miles on it, but the clutches in the rear shudder badly on low speed semi-tight corners. It is worse on right turns than it is on left turns. I haven't put any additive in yet, but I intend to see if I can get some of the Ford stuff. I did rebuild this differential and put new clutches in it probably 8 years ago. I did soak them in gear lube before installation and used the special tool to determine clutch pack clearance. I remember having a TracLok in a 70 Mk III and it never did shudder.

  28. It was pretty common years ago to use Type-F (Ford) A/T fluid in both GM and Chrysler automatic transmissions. Type F fluid had a slightly higher coefficient of friction which made for a little quicker, crisper upshifts in the GM and MoPar transmissions.

    But you likely wouldn't have wanted to use the Type-A fluid in your Ford transmission.
    SS327 and 427 sleeper like this.

  29. Have you seen GM or Ford limited slip additives in parts stores? Some understanding of how things operate goes along ways in this stuff as opposed to statements implying only an idiot would put anything other than Ford oil in a Ford etc. ( not you )
  30. Do you suppose Ford or GM or Chrysler actually make the clutches? Do you only buy engine oil from the manufacturer that assembled the engine? It’s a valid question. A little knowledge about this stuff helps minimize the “risk” in choosing things. Amazing any of us build Hot Rods that function.

    Maybe I’m just a hoodlum because I take a chance on differential lubricants.
    Desoto291Hemi and 427 sleeper like this.

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