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Technical Differential experts, rust on gears

Discussion in 'The Hokey Ass Message Board' started by bobj49f2, Apr 25, 2021.

  1. bobj49f2
    Joined: Jun 1, 2008
    Posts: 1,848

    bobj49f2
    Member

    I have a '37 Buick Special. The trick to getting a one of these low geared cars more highway speed friendly is to swap in a ring and pinion gear from a Century into the differential. The Century gears are getting fairly hard to find. I was contacted by a person who has a set he bought many years ago for his Special and decided not to use them and stored them in his garage for some years. He offered them to me but said they have surface rust on them. Any differential knowledgeable members out there that care offer their opinions on these? Are they still good? I've been told by one person any rust at all makes them useless because it penetrates the thin hardened surface and the gears will hum and eventually fail.

    Img_0305 _cropped.jpg
     
    Last edited: Apr 25, 2021
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 50,964

    squirrel
    Member

    We can only guess at how rusty they are....you have to get the rust off, and see how much metal is left. Glass bead blasting will tell you pretty quickly how bad they are.

    If the pitting leaves less than half the original surface intact, then they're probably not going to last too long. But any rust at all will have an effect on life, and possibly noise.
     
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  3. bobj49f2
    Joined: Jun 1, 2008
    Posts: 1,848

    bobj49f2
    Member

    The seller said only surface rust from setting on the shelf, or wherever he had them. It's hard to tell from the picture how bad the "surface" rust is. These gears in good shape can bring a decent buck, he hasn't got back to me with a price but if he's willing to let them go for $25-50 it might be worth it to get them and see what they are in person. It wouldn't be the first time I've blown money on a part and it turned out useless. Just want to get some input from people who know a hell of lot more than I do.
     
  4. Mike VV
    Joined: Sep 28, 2010
    Posts: 2,585

    Mike VV
    Member
    from SoCal

    I'd bet that that's more than "surface" rust..!
    Maybe not the entire hard surface, but, I'd bet you'll end up with some ugly pitting.

    I don't think I'd sand blast the surface, I'd use one on the many chemical rust cleaners and actually "remove" the corrosion, rather than to push some of it, deeper into the metal. Even to the point of going to a chrome shop and have them chemically clean it (if they would).

    Mike
     

  5. harpo1313
    Joined: Jan 4, 2008
    Posts: 2,404

    harpo1313
    Member
    from wareham,ma

    The shelf was outside, 25 for a look isnt bad. but if you like to roll on the hyway, I would pass.
     
  6. Just use plain, cheap white vinegar to remove the rust, rinse them clean, and you will have an idea what you have.
     
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  7. squirrel
    Joined: Sep 23, 2004
    Posts: 50,964

    squirrel
    Member

    yeah, but you need the surface of the gear teeth....having it rusted away isn't good.
     
  8. Bird man
    Joined: Dec 28, 2009
    Posts: 742

    Bird man
    Member
    from Milwaukee

    Couple of '40s Buicks out at Jack's Auto Ranch, I think at least one is a Hydra car? That Carrier/R&P is junk.
    Good Luck!
     
  9. Pontmerc
    Joined: Jul 13, 2013
    Posts: 152

    Pontmerc
    Member
    from Finland

    I have a 12b gm truck that has been full of water frozen solid and completely rusted.
    Cause i have nothing to loose, i just cleaned it and put new oil.yes, its a bit noisy, not bad at all.
    Been cruised it several thousand miles and its not getting any louder.
    Not hi perf usage, more like cruising.
    What im saying is, it might work just fine.
     
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  10. pitman
    Joined: May 14, 2006
    Posts: 5,151

    pitman

    I'm recalling some 'lapping-compounds' like the hand seated Valve grits.
    Might be worth trying to clean up the worst appearing teeth, and see what you have. In gear design, 'overlap' delivers the torque, thru 1.5 to 2-3 tooth faces. Always more than one engaged pair. So even if you lighten the load transfer a couple tenths, on one ring tooth, the neighbors take on a bit more. Esp. when you have the 'correct' weight lube, I might worry If, there are 3 loose fits in a row. Otherwise I might try it. Aim for a clearance that is just snug, on tight fits & acceptable on a loose 'pair', if you can. (Machine design exp., not road vehicle R&P background on this subject, all gears have a precision rating value, affecting 'fit' w/their mates.)
     
    Last edited: Apr 25, 2021
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  11. Marty Vanin
    Joined: Feb 22, 2017
    Posts: 74

    Marty Vanin
    Member

    Those gears are pretty bad. After you get the rust off they will be a lot of surface imperfections that will make them pretty noisy.Not worth the trouble.
     
  12. bobj49f2
    Joined: Jun 1, 2008
    Posts: 1,848

    bobj49f2
    Member

    Only '37 & '38 will work. I've been told '38s will fit both cases, '37 will fit a '38 but would need some machining to make the ring gear fit in what I assume a slightly smaller case. No other years will work. I'll give them a call this week to see if they have any '37-38 Centurys, if they do I'm sure they'll be stripped but you never know.

    I bought this '38 "Century" a few weeks ago.

    172150123_10220454817540524_2430003187130781273_n.jpg

    Before paying for the car I pulled the diff pan off, when I pulled the two bottom bolts water streamed out. I thought for sure the gears were junk but were nice and oily and smooth, no rust what so ever. Bad part was when I got it home and started looking it over I realized it had the smaller Special engine and it turned out it was a Special someone had dumped a rusty Century body on. I went off the information on the ID tag on the fire wall.
     
  13. theHIGHLANDER
    Joined: Jun 3, 2005
    Posts: 8,590

    theHIGHLANDER
    Member

    Soak the whole gig in molasses/water solution for a cpl weeks. Rinse, oil, see where you're at. 2 things here about gear heat treat, and I spent some time at Chevy Gear and Axle in Hamtramk, MI so it's not wives tales and urban legend. Back in the day heat treat was serious shit. They worked harder at it and the process was wasn't to be mullered with, ever. It was even more important in the prewar days, and it took a while for the industry to "catch up" to what they could get away with, use, longevity, etc. Bottom line is the rear differential is likely the most "digestive" part in the whole car and takes a shit ton of abuse. How bad is it? Well now you can by a "Pro Gear" for your drag racer that's not heat treated nearly as much, the gears flex a bit (for lack of wanting to bang out a lotta words) but they also have a limited life span, but they don't break teeth off when launching a racer with 5000lbft of TQ at the slicks. Do what you will, but a soak to check for excess pitting and I'd bet those old gears are treated deeper than anything you get today. The molasses won't hurt em but will slowly remove anything oxidated by mother nature. Good luck, and let us know too. BTW, you want about 10+% solution of cheap feed grade molasses to hot water to make it. It doesn't have to stay hot, but it mixes nice and fast in hot water. I used 5 gal to about 40 gal of water 4 years ago in a plastic drum. Stuff comes out new lookin.
     
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  14. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 2,498

    ekimneirbo
    Member
    from Brooks Ky

    I agree with Highlander ^^^^^^^ The only difference is I would buy some powdered citric acid from Amazon. I would take a small toothbrush like wire brush and knock the heavier rust off. Remove the gasket. Then put it in a five gallon plastic bucket and mix the citric acid with some water. The stronger the solution the better as it won't hurt the metal but will remove the rust. Leave it for at least a week or hopefully more. I don't believe you will have any problem unless after removal from the acid you can see definite pitting in the gears.....and I doubt you will. Many old 9" Ford rear ends have set for years. The oil drains off the gears and they get exposed to some rust inside the housing. People clean them up and use them all the time. Often rust buildup looks worse than it really is. Here are some pics of a Cad engine I soaked in citric acid for a couple weeks because the coolant passages were in terrible shape. There was some flash rust when I pulled it from the tank because of the rusty water. Also, I'd offer the guy $50 for the gears and take a chance on them. If everything looks good after the soaking, pressure wash it and set it in a bucket of clean oil and rotate it. Might need new bearings. 472 Rust 5x.JPG
    DSCN2854.JPG
    DSCN2855.JPG
     
    Last edited: Apr 25, 2021
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  15. It looks more then light surface rust.

    I would sand blast them with a light abrasive like crushed glass or baking soda ( I use this at work for cleaning gears etc.

    once it’s cleaned you can see if there is any putting on the gears. If there is putting , they are probably still fine to use in a car that’s just cruising around but you may end up with noise. The life of the gears maybe reduced , but again on a car that’s not getting pounded on or driven everyday this might be just fine.

    no real way to know until it’s clean. They might clean up and be cherry. Like you said for under $100 bucks I’d be in for the challenge.
     
  16. 1934coupe
    Joined: Feb 22, 2007
    Posts: 4,750

    1934coupe
    Member

    For $25 bucks I would buy it in an instant especially if they are that hard to find. Soak in Molasses, white vinegar, diesel fuel or whatever snake oil you have for a month. Rinse well and install. It will probably last longer than $25 bucks worth of beer.

    Pat
     
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  17. AVater
    Joined: Dec 9, 2008
    Posts: 2,775

    AVater
    ALLIANCE MEMBER
    1. Connecticut HAMB'ers

    Good advice & experiences shard above.

    I’m willing to bet if you go through with these gears and get them cleaned up and installed, quickly thereafter you will find a better set.

    Just a thought based on my luck and history. “ Your results may vary”.
     
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  18. Budget36
    Joined: Nov 29, 2014
    Posts: 8,434

    Budget36
    ALLIANCE MEMBER

    I pulled a Dana 44 from an early 60’s GMC pickup, when I got it home and drained the oil, lotsa water came out as well. The bottom of the ring gear must have been sitting in the water for quite some time. About 6 or 8 teeth had rust, after wire wheeling it off, there was clearly pitting on those teeth.
    Maybe I didn’t know any better, but new bearings, clutch pack and seals, I set the pattern up and ran it for three years as my DD in my 59 PU. No noise, but never pulled the cover after putting it together, so don’t know if there was more wear in that area or not.
     
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  19. big bird
    Joined: Feb 16, 2014
    Posts: 111

    big bird
    Member

    Is this going in a drag car? I's be worried. For a cruiser, not so much. Has the longevity been affected? Maybe. Are they junk? Get a better look.
    NO to sand blasting, glassbeading, etc. Those will "Pick" at any pits and make them worse.
    Brush off the loose rust, brass brush would be best. Soak in vinegar or molasses and clean well with brush and scotchbrite pads. Oil them up and wipe down. inspect. if they look passable, install and enjoy.
     
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  20. bobj49f2
    Joined: Jun 1, 2008
    Posts: 1,848

    bobj49f2
    Member

    Never fails, best way to find a lost tool or part is to buy a new one. On your way into your shop you'll stumble over whatever you were looking for.

    No drag racer for sure, just a seasonal cruiser. From what I have read and have been told as long as I'm using the gears from a '37 Century in my '37 Special I use the same axles and bearings. If the Century's gears are from a '38 and want to install them into a '37 I need to also use the '38 axles. Most be something with the diameter of the axles.

    Guys, really do appreciate the advice. Really helps. Just found out from a friend there is a guy in the area that is really good at setting up rear axle gears. I'm going to try to get a hold of him and see what he thinks. I know he'll probably give me the same advise most of you are giving me, can't really tell the condition from a picture, I totally agree.
     
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  21. big bird
    Joined: Feb 16, 2014
    Posts: 111

    big bird
    Member

    I was under the impression you were only using the ring/pinion off that. I wouldn't stick that whole third member in without a very thorough overhaul (disassemble/clean/rebuild). No way I would trust those bearings, especially with all the rust to be cleaned around them.
     
  22. bobj49f2
    Joined: Jun 1, 2008
    Posts: 1,848

    bobj49f2
    Member

    Since this is said to be from a 37 Century I would use the good axles, housing and bearings from my Special. I was told if I use a gear set from a '38 Century I would have to use the axles from a '38.

    I would only use the pinion and ring gear from the picture.
     
  23. Blues4U
    Joined: Oct 1, 2015
    Posts: 6,468

    Blues4U
    Member
    from So Cal

    I've seen worse gear sets used in wheel loaders or other tractors, and they weren't cleaned up with molasses either, just a wire brush and some solvent or maybe some WD-40, maybe a roll-lock Scotchbrite disc or two. And those wheel loaders are more heavily loaded than any Buick Special. If those are available for ~50 bucks or less, I'd get them and give them the molasses treatment and see what you got.
     
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  24. bobj49f2
    Joined: Jun 1, 2008
    Posts: 1,848

    bobj49f2
    Member

    This Buick has been a long running project and like the other projects I've built I start out with junk and piece them together using parts from 4.5.6 vehicles. The Special project started out when a '37 Buick Special followed me home about 7 years ago that I paid $550 for. After I got it in my shop I found out it was a total pile of rusty crap from front bumper to rear bumper. The only thing I saved was the front fenders which have the pockets for the side mounted spare tires, the grill surround, hood and radio. I basically bought a parts car. The parts I salvaged were worth the $550.

    One of the major solid chunks of rust were the engine and differential. You can see the water line of high the water was in the case.

    picture069.jpg
     
  25. 1971BB427
    Joined: Mar 6, 2010
    Posts: 7,273

    1971BB427
    Member
    from Oregon

    Rust is usually harder than the metal was before rusting. But I don't think hardness is the concern on these gears. The concern I'd have would be smoothness, and it doesn't take much rust to ruin gear sets. They will indeed howl, and then eat themselves up. Unless the rust is very minor, and you can clean a spot off easily before buying the gears, I'd pass on them. Waste of time and money.
     
  26. Fortunateson
    Joined: Apr 30, 2012
    Posts: 4,546

    Fortunateson
    Member

    Buy it and then use reverse electrolysis which will clean it up overnight. Only removes rust. And don't forget to post pics...
     
  27. bobj49f2
    Joined: Jun 1, 2008
    Posts: 1,848

    bobj49f2
    Member

    I offered the guy $50 if he cuts off the torque to make it easier to ship. He seemed OK with that. He said he's having health problems and it'll take some time for him to go to the shop that works on his car. I'll see what I get. Like I said, it wouldn't be the first time I spent money on a part that turned out to be useless.
     
  28. tubman
    Joined: May 16, 2007
    Posts: 6,052

    tubman
    ALLIANCE MEMBER

    Do yourself a favor : No blasting, No acid. Soak them in Evaporust and see what you have before going further.

    The aforementioned processes are degenerative.
     
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  29. squirrel
    Joined: Sep 23, 2004
    Posts: 50,964

    squirrel
    Member

    The minute amount of solid metal that blasting or the liquid process will remove, won't make a bit of difference in whether or not the gears will work, or how long they'll last.

    This is an 83 year old rear gear set, don't think about it too much...just see how much metal is left, and decide if it's worth the trouble to swap them into the car, and see how they work.

    Also check the tooth count before you put too much effort into it :)
     
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  30. deathrowdave
    Joined: May 27, 2014
    Posts: 2,830

    deathrowdave
    ALLIANCE MEMBER
    from NKy

    I’d clean it up as suggested , and take the chance . My bet is every bearing in it is BAD , and will need to be tossed and replaced . My old Power Wagon , OT has lock out hubs . You would be amazed at the amount of surface rust collects on the part of the ring gear that is above the oil level . I try to engage the hubs a few miles a month just to lube the junk up .
     
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