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Forklift tranny slip

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JohnS View Drop Down
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    Posted: 04 Oct 2017 at 8:57pm
I have an Allis chalmers forklift ft-20-24 it has an automatic transmission. I just got it running, as soon as it warms up the transmission slips, then eventually stops moving. Any ideas would be greatly appreciated

Thank you
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Coke-in-MN View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Coke-in-MN Quote  Post ReplyReply Direct Link To This Post Posted: 12 Oct 2017 at 8:40am
Seems it should have torque converter - so would say low oil or such - unless it's a fwd reverse clutch pack - then could be pump pressure or worn friction plates in clutch pack - check your oil levels first before digging into unit 
Faith isn't a jump in the dark. It is a walk in the light. Faith is not guessing; it is knowing something.
"Challenges are what make life interesting; overcoming them is what makes life meaningful."
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JohnS Quote  Post ReplyReply Direct Link To This Post Posted: 12 Oct 2017 at 8:52am
Thank you for replying. When I first checked oil level it was low on tranny fluid. I added some, now it won't move in forward or reverse. I think I'm going to change out the transmission fluid, maybe a clog ? The guy I bought this from said it's sat for the past 32 years, engine is running fine now, it just won't move. I appreciate your reply
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Coke-in-MN Quote  Post ReplyReply Direct Link To This Post Posted: 12 Oct 2017 at 9:30am
Might pay to find a service manual for it , could be filter or ? On many of these there is a hot and cold mark on dipstick - also some require checking with engine running . 
Faith isn't a jump in the dark. It is a walk in the light. Faith is not guessing; it is knowing something.
"Challenges are what make life interesting; overcoming them is what makes life meaningful."
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JohnS Quote  Post ReplyReply Direct Link To This Post Posted: 12 Oct 2017 at 9:49am
I'll do that, thank you
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rustydollar Quote  Post ReplyReply Direct Link To This Post Posted: 12 Oct 2017 at 10:03am
After 32 years of sitting the seals on the clutch packs have hardened up, oil is by passing the seals.

I'm not an advocate of seal conditioners, some mechanics are and have had success with adding a conditioner to the oil to soften up the seals.

If it were mine, the transmission would be coming out for an overhaul. At his point with the bad seals your not having to replace a whole lot of hard parts. Just a sea;l and gasket kit.

Do you know who made the transmission.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JohnS Quote  Post ReplyReply Direct Link To This Post Posted: 12 Oct 2017 at 1:59pm
The transmission is allis chalmers as7-t12. Powershift. Do you think it's a good idea to change out the fluid?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rustydollar Quote  Post ReplyReply Direct Link To This Post Posted: 12 Oct 2017 at 4:24pm
Originally posted by JohnS JohnS wrote:

The transmission is allis chalmers as7-t12. Powershift. Do you think it's a good idea to change out the fluid?


IMHO there is no quick fix for hard seals.

The seals I speak of are large seals that are installed onto hydraulic pistons, the valve body directs oil to which ever gear has been selected.

High pressure oil closes the piston against a pressure plate that compresses the clutch pack. A clutch pack consists of the pressure plate. friction / steel plate / friction plate . steel plate / friction plate until the full pack is made up.

With hardened seals the oil when heated becomes thinned out and will pass by the seals and will not close the clutch pack.

The clutch pack will be splined to a drive hub, there will be planetary gears etc. to the final output shaft going into the differential.

Changing the oil will not fix hardened seals.

You might want to drop the oil pan on that transmission, give the oil the sniff test to see if it smells burnt. What your looking for in the oil pan and hopefully you do not fins is metal particles, brass and iron.

A thin film of black residue on the bottom of the pan is normal clutch wear.

You got lucky, the trans number you gave says that the transmission is made by Borg Warner so parts should be relatively easy to obtain.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote JohnS Quote  Post ReplyReply Direct Link To This Post Posted: 12 Oct 2017 at 4:29pm
Thank you very much for replying. You are right! The transmission has a tag with Borg Warner on it, sounds like I got my work cut out for me. I think it will be worth it, it's a real nice forklift, runs great other than the fact it doesn't move lol. Thanks again
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rustydollar Quote  Post ReplyReply Direct Link To This Post Posted: 12 Oct 2017 at 4:53pm
Originally posted by JohnS JohnS wrote:

Thank you very much for replying. You are right! The transmission has a tag with Borg Warner on it, sounds like I got my work cut out for me. I think it will be worth it, it's a real nice forklift, runs great other than the fact it doesn't move lol. Thanks again


Your welcome, if your not able to find a shop manual for that Borg Warner take plenty of pictures.

Lay your parts out in sequence as your disassembling the transmission.

You do not want to mix up springs and spools from the valve body, this was my first lesson on the bench.

At my age plenty of pictures helps a failing memory.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote DonBC Quote  Post ReplyReply Direct Link To This Post Posted: 12 Oct 2017 at 6:42pm
In my opinion you could try the oil conditioner to soften the seals. It wont do any harm and if it doesn't work you have only spent a couple of bucks to try. Years ago I had a Jimmy 4x4 with the 350 automatic transmission that started to leak about a quart a month at 70,000 miles. I decided that I would try two cans of conditioner because I had little to lose. Within a week it stopped leaking and never leaked again in the next 60,000 miles that I owned it. Even did a transmission oil change in that time and added a can of conditioner to the new oil. I also tried oil conditioner on a leaking power steering component seal and it did not help.
Jack of all trades, master of none
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JohnS Quote  Post ReplyReply Direct Link To This Post Posted: 12 Oct 2017 at 9:06pm
Thank you, I'll give it a try, do you have any suggestions as to which one?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JohnS Quote  Post ReplyReply Direct Link To This Post Posted: 12 Oct 2017 at 9:14pm
This afternoon I had a bottle of Lucas transmission slip, I figured what the heck put it in and ran the engine for a while. When I would first start it, it would move and slip for a few minutes then stop moving completely. After I added the anti slip I waited a few hours for it to cool and started it back up. This time it wouldn't move at all . Tomorrow I plan to drain the fluid and clean the control valve
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rustydollar Quote  Post ReplyReply Direct Link To This Post Posted: 12 Oct 2017 at 10:26pm
Originally posted by JohnS JohnS wrote:

This afternoon I had a bottle of Lucas transmission slip, I figured what the heck put it in and ran the engine for a while. When I would first start it, it would move and slip for a few minutes then stop moving completely. After I added the anti slip I waited a few hours for it to cool and started it back up. This time it wouldn't move at all . Tomorrow I plan to drain the fluid and clean the control valve


All your going to do with insufficient oil pressure applied to the clutch frictions is burn them out with all that slipping.

Keep it up then you'll be looking to replace some hard parts as well, hard parts defined. Frictions, steel plates, thrust washers, pressure plates, planetary gears, sprag clutch.

A seal kit is cheap by comparison. 

If a new filter didn't change things cleaning the valve body won't either. Your troubles are further in.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote JohnS Quote  Post ReplyReply Direct Link To This Post Posted: 12 Oct 2017 at 11:29pm
I should just go ahead and have it rebuilt?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JohnS Quote  Post ReplyReply Direct Link To This Post Posted: 12 Oct 2017 at 11:30pm
Seal kit I mean
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rustydollar Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 2017 at 12:48am
Originally posted by JohnS JohnS wrote:

Seal kit I mean


Seal and gasket kit should do it.

Years ago I apprenticed with a Mr. Transmission shop, our manager who had worked in various shops under different shingles would tell us of some of the scams that some of the shops would pull on a customer.

Customer gets lured in with that cheap advertised filter and oil change and don't know one oil pan from another. While sitting in the receiving area drinking free coffee the service technician brings out an old pan full of broken bits to show the customer.

Customer chokes on coffee, in shock agrees to signing an open work order, vehicle is held hostage until the bill is paid in full.

That dirty oil pan full of broken parts had been shown to many unsuspecting customers, if your not planning on doing the work yourself at least do BBB on the shop of your choice or at least get several referrals.

Oh and always ask for the broken and worn parts that have been replaced in your transmission this helps to keep em honest.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JohnS Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 2017 at 9:28am
Thank you, i will probably look for someone to do the work. I really appreciate you taking the time to provide me with some much needed guidance!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WDman1949 Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 2017 at 9:42am
John I sent you a couple of Private messages of stuff to check before you remove the trans if you haven't checked these you may be making a mistake BUT what do I know as Ive only worked on lifts for 30 some odd years
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JohnS Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 2017 at 10:27am
Hey thank you very much, appreciate your help!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rustydollar Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 2017 at 10:50am
Originally posted by WDman1949 WDman1949 wrote:

John I sent you a couple of Private messages of stuff to check before you remove the trans if you haven't checked these you may be making a mistake BUT what do I know as Ive only worked on lifts for 30 some odd years


Your just the fellow were looking for, where are the gauge ports located on this Borg Warner AS7-T12 transmission and what pressures are we expecting to find under test.

A pressure test at the ports will reveal faulty seals or a bad pump. I just purchased the hydraulic test gauge set from eBay that comes with three gauges and a bunch of adapters for $60.00

The pressure chart below is for the Borg Warner Velvet Drive used as an example, what we need is the pressure chart for the AS7-T12 transmission.








Edited by rustydollar - 13 Oct 2017 at 11:12am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JohnS Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 2017 at 11:28am
I've located the pipe plug, thank you!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rustydollar Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 2017 at 11:34am
Originally posted by JohnS JohnS wrote:

I've located the pipe plug, thank you!


If your forklift uses a shuttle transmission chances are it's similar to the Velvet Drive used in marine applications.
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