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Washington WheelHorse
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Discussion Starter #1
Hello!

I have two early 1970's Sundstrand 90 series hydro transmissions. Models 1136 and 1137, used on my WheelHorse C120 (1974). Both are terribly weak to dead in forward. The units are very clean. The condition becomes total stop once they are warm. However, in reverse I can climb a tree. So, any ideas? Are the units shot? Anyone have a good one to sell potentially? I bought the 1137 to replace the original but it played out in 20 hours. Thanks!

Paul - Monroe WA
 

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Hi Paul and welcome. I'm assuming you have changed the filter and oil in the transmission correct? I believe you should use 10w30 in that Sundstrand. Does it have the hydraulic lift too? If so, does that work correctly? Let's get those questions answered first...
 

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Have you checked the linkages to be sure that they are throwing the control lever all way into forward position? May just be out of whack with linkage adjustment or something bent.
 

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Washington WheelHorse
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Discussion Starter #4 (Edited)
Hi Paul and welcome. I'm assuming you have changed the filter and oil in the transmission correct? I believe you should use 10w30 in that Sundstrand. Does it have the hydraulic lift too? If so, does that work correctly? Let's get those questions answered first...
Yes, totally new oil, filter, etc. Funny thing however, the 1136 called for 30W oil. When I purchased the 1137 (off a 1974 C160) it had standard trans fluid in it, so I used basic hydraulic fluid in that unit. Worked by not great. I am wondering if I should drain and go back to 30W? Once hot, I can stand in front of the tractor in full forward and keep it from moving. Drive belt is new. No hydro lift. Wish it did. Pulling the deck up by hand takes some brute. Does this help? Thanks!!! Paul
 

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Washington WheelHorse
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Discussion Starter #5 (Edited)
Have you checked the linkages to be sure that they are throwing the control lever all way into forward position? May just be out of whack with linkage adjustment or something bent.
Checked linkage. Actual movement is pretty short and moving parts few. I will check again. I hope it is something simple but man, I am way frustrated. If the unit is bypassing the pistons, rebuild looks like 1K ! Thank you!!! Paul
 

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I believe it should use 10w30. Try draining it and add the dino oil back in and see what happens.
 

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Machinery enthusiast
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As been posted, I'd start with troubleshooting the linkages 1st.
On my 66 876 w/a Sundstrand HST, pushing the speed control forward produces 2 to 3 times more movement than when pushed to the rear.

On the 876 which may be the same as your C120, the movement of the speed control actually rotates an eccentric of a cam in a plastic slot on the front of the HST. This movement rotates a shaft that goes into the HST which controls the angle of the swash plate. The linkages could be misadjusted, the cam worn, the plastic guide worn or a combination of them all. I'm not sure on your model but on the 876 I can remove the instruction plate under the dash and easily see and access the linkages and controls.

I also found this reference re. type of oil to run in the earlier model Sundstrand HST's.
 

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Washington WheelHorse
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Discussion Starter #8
Thanks! Tranny seems to work fine if not on a grade.... But the original would pull to front tires off the ground. I checked the plastic slot linkage quite close and it works well. I compared the travel to the pulled transmission I have vs the one installed and it looks identical. The transmission I have on the C120 now is from a 1975 C160. When I got it on ebay, it had traces of red trans fluid in it. Should I replace with motor oil??
 

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Washington WheelHorse
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Discussion Starter #9
Worth a shot... history is the original unit I had to replace was motor oil based. It went south, so I found a newer unit on eBay (1975 C160 trans). One year difference.

What threw me is the C160 trans had traces of Dexron in it instead of 10-30. I pulled the valves today and they look very nice. Oil clean as new snow.

Nuts!

Thank you!!!!!!!!!!

Paul
 

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I have a C-120 (75 model) that i picked up a year or so ago--from the original owner.

He had the original manuals--and the local dealer in this small town in N.C. had always serviced it yearly...seems like somewher back in the 80's--the manual specified 10w30 motor oil in the hydro, but the dealer had 'crossed it out'-written in Dexron II, recommended by manufacturer"...
Now why--or how come--I don't know , but when I serviced it with a change and new filter--I used NAPA Universal Dexron Tranny fluid, as just Dexron II cannot be found....

I like Volfandt's analogy about the travel cam and bushing under the seat--They are a wear item----and doesn't take a lot of travel; to get out of whack.
There is alkso a place in Michigan thatsells parts and does complerte rebuilds on these things last I heard--I can go back and find the info, if needed...

We got to get that 'Horse up and running--they are built to work!!
 

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I'm going to make a few guesses on your problem...

Since you said reverse has been unaffected, I'd assume that the pump and motor are still performing OK otherwise motion would be dead in both directions.

When you replaced the transmissions, did you replace the entire rear end (transaxle) too, or just the hydro portions? I'm betting on just the hydro components. And, did you swap out the entire hydro assembly (coupled pump and motor) or did you just replace one or the other?

This is completely speculating, but I'm betting you replaced only the pump portion (IF you indeed replaced everything my next sentance will be moot). There are two "acceleration valves" in the lower end of your tranmission. They allow the tractor to start/stop with minimal jerking and help prevent pressure spikes. The one that controls the FWD loop on yours is defective, dirty, or plugged.

If these internal valves remain open, the fluid will just circulate thru them and will not make it to the motor circuit.

Again, just a guess. If you replaced the whole works I'll have to back peddle a little and try to come up with something other than "strange coincidence".

Get the sundstrand manual and locate both valves. Remove, clean, and inspect. I'm betting your problem is down there. I know this has been discussed on this board before, so you might have luck with a search here as well.

As for the oil...

I prefer 10W30 to ATF in these for my personal use since I always have oil on hand and feel it works perfectly fine for this application. If you want to swap one for the other you should make an honest effort to purge the entire system so you have mostly one fluid in there. They will mix fine and I don't think it will cause you any problems to have a little cross contamination. Since these are not 'true" automatic transmissions with friction bands and all that other stuff in them you really just need a fluid to carry the energy from one place to another. Could probably use water, tomato juice, or olive oil if you wanted to....j/k.

ATF tends to have a lower viscosity so might be better for winter use. 10W30 is a little thicker and may help compensate for wear and internal leakages. Not sure which is better for the gears in the transaxle, but probably not that critical as long as you KEEP IT CLEAN and use the Toro/WH filter and not some "will fit".

Best of luck with this thing!

Steve
 

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Steve is dead on, its either the accel valves or the spings therein. If this happens in both directions then either the pump or motor is worn.
I have changed my hyrogear from autotrans over to motor oil with no problems, just make sure you let it drain well and turn the pump over by hand a few times and refill, and of course make sure you use a hydraulic filter. I always get OE, might cost a little more but its worth it.
 

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Washington WheelHorse
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Discussion Starter #14
Steve is dead on, its either the accel valves or the spings therein. If this happens in both directions then either the pump or motor is worn.
I have changed my hyrogear from autotrans over to motor oil with no problems, just make sure you let it drain well and turn the pump over by hand a few times and refill, and of course make sure you use a hydraulic filter. I always get OE, might cost a little more but its worth it.
Thanks for all the help. I get so frustrated with this problem. When I replaced the older unit, I replaced both pump and motor assembly. I have a full set of differential gears, but they were fine so I passed on swapping those out. The old tranny did the same thing, except before it went out, it pulled so hard in forward the front tires would lift! Boy do I miss that much power. The new one worked but briefly. On the pump, I removed the two large recessed plugs and inspected cap, spring and ball bearing. On the acceleration valves, how can I tell if they are bad? They are clean as a surgical room. I will pull them again. Gotta drain the unit anyway!
 

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Washington WheelHorse
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Discussion Starter #15
Hi Steve,

I pulled the valves. They look very clean, very small amounts of residue. The springs however I cannot tell if they are bad, so I guess I need to find replacements. The trans will work in forward but when it gets hot, no dice. I have been doing the hills in reverse. It is good to know the pump and motor are probably fine... I will post a report once I find some springs and swap out those and the oil again to 10-40W. Thanks!

I guess I could reverse the valves maybe to test it.
 

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Try LJ Fluid Power out of Delton, MI.
TEl# 269-623-4150.
 

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Washington WheelHorse
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Discussion Starter #17
Me again. Pulled the acceleration valves, cleaned what I could find in them, replaced springs. Same problem. No power on a grade. Still did not swap out the oil for dino yet but am skeptical to spend the $$ when it is clean as a whistle. I contacted a person that rebuilds these and he claims the pump is passing oil and must be rebuilt. Deal is it will take over $1200 for the rebuild, if he can get parts.... I probably still will swap out the oil, but if it does not work I may part it out. I need a working tractor. The rest of the rig is really nice, balanced engine runs like a Rolex... excellent deck, snow blade... Bums me out. Any other ideas all? Thanks for all the posts and God Bless.



Paul
 

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Looks like to nice of a unit to 'part out'--see if you can find something else to swap out with-----Still--try the LJ power that Volfandt posted--that was the addey I was going to list also--wouldn't hurt to call them--I think it's just a small operation....
 

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Shoot. I was really banking on the accel valves...

I haven't checked in here for a while so i apologize for the delay.

Having power in reverse but none in fwd has me stumped. Seems like unless there was a problem with the loop the accel valves were in you'd either be able to run both directions or neither.

have you done a pressure test? The procedure is outlined in the manual. It should show if you have excessive internal leakage that is keeping the unit from developing pressure. You will need a short length of hydraulic hose, a guage, and the appropriate fittings. I think these are low pressure systems and you should see around 700 psi if everything was OK.

Since you completely swapped in another unit and are having the same problem I think you may either have an incredible coincidence or it might be worth another look at your linkages. Double check that your brake pedal is coming back all the way when in neutral. And check belt tightness/parking brake linkage was well. I know you checked already, but I just can't imagine why you'd be having this one way problem.

i wish I could be of more help but I am drawing a blank.

I don't have any manuals here at the office, but I wonder if there is a pressure relief valve in there somewhere that is popping off. Seems like it would do it in both directions, but perhaps it is only protecting one loop.

I'm stumped.

even if you have the money to spend I'd think twice before sinking $1400 into this old tractor. Give me another day or two and I will hunt around here and see what I can find in my manuals and parts to see if I can come up with anything to help.

Stay tuned...

Good luck,
Steve
 
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