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  1. #1
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    Default Planetary gears for a forklift diff - can I realistically make some??

    So the old forklift I bought to use at home turned out to have a busted diff. Broken cross shaft and chewed up side and planetary gears.
    While I'm waiting to find out if I can even get replacement parts, and if so how many kidneys I'd need to sell - I thought it would be an interesting discussion as to whether I could practically make some myself.
    I've only ever cut spur gears using an involute cutter, and I know that there's a bit more to making bevel gears.

    So - the items of discussion.
    Two side gears: has ground stub shaft and back face, internal splines for the driveshaft, and some bevel gear teeth.
    Two planetary gears: has a bore that runs on a cross shaft, spherical back face that runs in the diff carrier and some bevel gear teeth to match the side gears.














    First thing I need to point out for those that aren't familiar with diffs, is that these gears aren't turning at any appreciable speed (unless you spin an individual wheel). They are there to allow the wheels to move at different speeds as you turn - ie the outside wheel moves faster than the inside wheel in a turn. reasonably high load on the teeth but slow speed of rotation.

    I've got a mill with vertical and horizontal spindles, index head, shaper, and potentially the T&C grinder if I really needed to do some grinding.

    Is it do-able, and if so what are the challenges?

    Steve

  2. #2
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    I've had good past success with brazing up damaged gear teeth in vintage spur gear gearboxes and re -cutting them. Can't remember which rods I used as it was a number of years ago now. After viewing your pics the main tooth profiles are still there so I reckon you would have a fair chance of success given the jobs and work I've seen you produce. The beauty of the brajing is that the teeth lap in and I was told that they eventually work harden. Given the limited use of your fork it is a process worth considering if you cant find replacement parts.

  3. #3
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    Just throwing about ideas as I am no expert, as said above, or is it possible to adapt a car or truck diff eg F100?

  4. #4
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    Its stretching the old brain box a bit, someone like elanjacobs may be better placed to answer, but I believe the cross section of the bevel tooth is not the same a the minor end and the major end due to needing to maintain tooth contact. I think you would have to fully remake all the gears and I think toy would have to do passes on different angles along the tooth to get an approximation of a real bevel.

    I wouldnt take it on unless I had no other projects, and can any of us claim that?

    Might have to wait for another cheap forklift or weld the whole diff up drift style

    Sent from my SM-G973F using Tapatalk

  5. #5
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    Quote Originally Posted by caskwarrior View Post
    I believe the cross section of the bevel tooth is not the same a the minor end and the major end due to needing to maintain tooth contact. I think you would have to fully remake all the gears and I think toy would have to do passes on different angles along the tooth to get an approximation of a real bevel
    That is correct. Keith Rucker has a video on DIY bevels here https://www.youtube.com/watch?v=RBco7PVuPDI&t=1633s

    You'll never get it 100% on a mill, but you can get a pretty good approximation which should be fine at low speeds, if a bit noisier than a properly generated bevel. It is a fair bit of effort, but definitely doable if you have the patience.

    Those gears you have appear to be sintered powder metal, not sure if that will affect how a braze filler would hold

  6. #6
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    Is it possible it may be off the shelf parts from an automotive diff?

    If I count correctly it’s 17 spline, old GM 8.2 diff was 17 spline.
    https://www.ebay.com/itm/1955-1964-G...-/231533097405

  7. #7
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    Thanks guys.

    I've thought about possibly adapting another diff. Happen to have a couple of spare Landrover Salisbury diffs here (basically a metricated Dana60). I'd have to crack one open to refresh my memory but pretty sure the gears would be similar size.
    Good thing about the forklift ring gear is its just a simple helical, not your typical hypoid diff type. Would be easy to adapt to the outside of a donor carrier.

    Good thought on building up the gears by brazing. Might be a good application for TIG brazing.

    Cask - I seriously thought (briefly) about a "CIG locker" , but given the rear steering almost allows the machine to turn on the inside drive wheel decided it wasn't going to be a good idea. With a decent load its likely that the fully locked drive axle with lots of weight and traction would prevent it steering effectively.

    Elan - I was actually watching that video of Keith Rucker's earlier tonight. Gave a good insight, basically saying its not difficult, but also not simple and that you definitely need to understand how it works before attempting it.
    I also picked up Ivan Law's book on gears again to start refreshing a few concepts.

    I doubt the gears will ever move fast enough to make any noise. As long as the teeth don't break off, don't bind or have a huge amount of backlash that will cause large shock loads they should be fine in this application.

    Don't think they are sintered material though. Looking at the surface finish on the non-machined areas I'd guess cast steel, and then case hardened. You can see the case hardening layer flaking off the outer end of some of the teeth, and the main damage is typical spalling which from memory is fatigue and poor lubrication related, and starts from deformation of the softer core under the case.

    Steve

  8. #8
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    Don't get me wrong, I absolutely love my ancient forklift. It's the best. But there is a firm 0% chance i would ever remake diff gears for it. Simply because as soon as I do something else will fail.

    Unless you can get parts, or sub some in id send it to the smelter and keep looking.

    Sent from my SM-G973F using Tapatalk

  9. #9
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    Hello from Brisbane.
    Do a Google search on cutting bevel gears with a shaper. I have seen a few examples with good results. One was a large gear for a 1/2 size traction engine. I think in NZ.
    Regards
    BC

  10. #10
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    Somewhere I have a copy of Building the Shay by Kozo Hiraoka which details his build of a live steam ride-on size version of a Shay steam locomotive. The Shay was a US narrow gauge engine of unconventional design (it was popular in the logging industry, good on steep and twisty tracks) that used a lot of bevel gears in the drive. I recall there were extensive details on making the bevel gears including work holding and cutting tool design.

    I like steamloco1954's post, we know that making involute spur gears on the shaper used to be commonplace. Perhaps there was also a recognised method of making bevel gears on the shaper.

  11. #11
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    Quote Originally Posted by caskwarrior View Post
    Don't get me wrong, I absolutely love my ancient forklift. It's the best. But there is a firm 0% chance i would ever remake diff gears for it. Simply because as soon as I do something else will fail.

    Unless you can get parts, or sub some in id send it to the smelter and keep looking.

    Sent from my SM-G973F using Tapatalk
    I'm hearing you

    By all accounts these units were really solid and never gave much trouble, but I'm familiar with the moving point of failure scenario on old gear.
    Practically I doubt I will re-make the gears from scratch, but its an interesting exercise to at least know whether its achievable and how I'd go about it.
    There's also an element of "why did you buy a broken one" being directed on the home front. Perfectly validly, but as they say - now its personal......
    It WILL move under its own power. Worst case I'll weld one side gear into the case and make it one wheel drive!!

    Edit: Thinking deeper - I'd actually weld BOTH side gears in, only install one axle. and make up a blanking plate for the other axle flange.
    If that breaks, swap to the other axle!

    I think I can do better than that though, and currently leaning towards building the teeth up with silicon-bronze using the TIG then reshaping them - either by hand or form cutter in the shaper.

    Steve

  12. #12
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    Steve i think that if you do a googs for forklift wreckers you might find the parts, failing that one of those blokes might give you a hint of what diff was used then you might get the parts from a car wreckers.
    Or a diff rebuilder....

  13. #13
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    I forgot to mention that when I did the brazed gear teeth I machined the bulk of the filler out and because the braze is soft it was easy to file finish the profile of the tooth then trial assemble and touch up any binding teeth. I used the oxy so the heat was concentrated on the tooth and prefluxed rods. In fact I found out this morning that a replacement bevel & crown wheel for my 4wd tractor is $2500, so quite soon I will be repairing the chipped bevel gear tooth. I'll try to remember to take pics and post the process when I do it.

  14. #14
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    Quote Originally Posted by shedhappens View Post
    Steve i think that if you do a googs for forklift wreckers you might find the parts, failing that one of those blokes might give you a hint of what diff was used then you might get the parts from a car wreckers.
    Or a diff rebuilder....
    I've spoken with a few places, and have a couple sourcing parts at the moment. Sounds like they are likely available, but whether they are affordable is another question.
    Also spoke to a bloke yesterday who has been in the forklift repair/refurb game forever, but semi-retired within the last 6 months.
    He said that historically industrial equipment had longer lifecyles than eg passenger vehicles, but there was a general change in the industry about 10 years ago and people just stopped wanting older machines.
    He used to regularly get diff gears made if they couldn't get parts, but very few places around now that can do it and in most cases its not economic. The end result is that the older machines typically go straight to the scrappy.

    I hate it, but I get the economics of it.

    As I explained to my wife, the reason I went down this road rather than drop ~$5K on a fully functional used machine is that:
    a. Unless you buy from a dealer (in which case throw in another couple of grand) then there is zero warranty anyway. Works today. Dead tomorrow and no comeback.
    b. Its still likely to be old and pretty flogged and will need a few more dollars for maintenance up front.
    c. if it does crap itself big time the whole "uneconomic to repair" has a lot bigger dollars attached.

    That's aside from the fact that I can't justify the $5K for a start!!

    Anyway - back to making/repairing, any clues on how to identify the basic tooth form if I was going to use an involute cutter and use the multi-pass "Keith Rucker style" method on the mill to cut the teeth?

    Steve

  15. #15
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    Hi Steve, id be happy to send out a gear tooth vernier if that would help (if you have any good teeth) with that, a protractor and a copy of machinery handbook you should be good.

    Being automotive i would put about 50/50 odds on them being non standard in some way, like using a normal DP but with an odd pressure angle or strange center distances.

    Sent from my SM-G973F using Tapatalk

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