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Sunstrand 15 tranny rebuild


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#1 jacreech OFFLINE  

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Posted December 13, 2011 - 05:09 PM

Warm greetings to all!

I'm a new member here and appreciate the community wisdom and experience. I own a 1975 (approx.) Bolens QS16, still running strong. Twice I've had the Sunstrand model 15 hydro rebuilt (LJ Fluid Power in MI), but this time am tackling it myself.

Anyone on the forum worked on one of these? Mine was very little worn, so I think my malfunction must have simply been a clog somewhere. I cleaned and examined all parts, reinstalled with new fluid and filter, and it is so far running like a champ.

But one worrisome question: The Sunstrand service manual shows a spring within or holding the cylinder block assembly. Mine has no springs there at all. Very strange. My original Bolens parts diagram also shows the springs. If they are necessary, why does mine run without them (and it ran for years with no problems)?

I can't tell from the diagrams if the springs serve a crucial function or simply hold the cylinder block together while reassembling the entire unit. Looks to me like the valve plates that ride on the end of the blocks hold the blocks in position, once assembled.

Anyone worked on one of these or otherwise know the purpose of those springs, and where I could find them 0r specs to add them to my unit. Bolens did not give a part number for the springs, requiring purchase of the entire cylinder block assembly - which I don't need to do. Mine look very good.

Many thanks, and Merry Christmas!

By the way, I am happy to offer amateur help to anyone who needs to tackle this same project. The Sunstrand manual posted on this site is very helpful.
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#2 Texas Deere and Horse OFFLINE  

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Posted December 13, 2011 - 05:15 PM

jacreech, WELCOME to GTtalk, Glad you joined us. There are several members here who can help you. I'm sure they will jump in here shortly. Again Welcome...

#3 olcowhand ONLINE  

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Posted December 13, 2011 - 05:17 PM

The springs stay intact inside the cylinders. I have a Sundstrand 15 apart right now off a Massey. I'll go snap some pics. Twice rebuilt is strange. Usually they last years & years.

DSC00632.jpg

Edited by olcowhand, December 13, 2011 - 05:23 PM.

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#4 mjodrey OFFLINE  

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Posted December 13, 2011 - 05:46 PM

jacreech,welcome to the forum.Glad to have you with us.

#5 jacreech OFFLINE  

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Posted December 13, 2011 - 05:47 PM

I'm feeling pretty stupid at this point - but that's always a good humbling experience to learn something!

I took some pix of mine before I reinstalled them, but unfortunately I have four all from the other side that won't show the spring. It's quite possible they're in there, I just don't remember seeing them. If they don't come out without disassembly, they must be, since I did not remove the pistons from the ring. And my tranny is presently working, back in my tractor. This was one of those "after the fact Oh No I left something out" panics. I'm going to assume my springs are intact and I simply did not look for them and thus didn't see them.

I agree two rebuilds is odd. That's why I decided to tackle it myself this time. I don't know what was done the times earlier - if parts were replaced, etc. I found nothing very worn at all on mine this time, so think I merely had a clog. We'll see how it runs when warmer weather comes.

Thanks much for the good pictures and advice.

#6 jacreech OFFLINE  

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Posted December 13, 2011 - 05:58 PM

What is the function of the springs? Do they give some pressure to keep the pistons or their holding collar in place against the thrust plate until they are moved as the control arm is rotated? When I removed my cylinder blocks the pistons slipped up and down very easily - nothing held them then except the collar, which kept them together, more or less.

Thanks again.

#7 olcowhand ONLINE  

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Posted December 13, 2011 - 06:08 PM

What is the function of the springs? Do they give some pressure to keep the pistons or their holding collar in place against the thrust plate until they are moved as the control arm is rotated? When I removed my cylinder blocks the pistons slipped up and down very easily - nothing held them then except the collar, which kept them together, more or less.

Thanks again.


When you put the shafts in place, there is a raised area on the shaft that catches onto the springs inside the cylinders, placing constant pressure on the thrust plates. Without this spring loading, the hydro cannot work as it will just bleed all the pressure from inbetween the cylinders & the thrust plates.

#8 KennyP ONLINE  

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Posted December 13, 2011 - 06:10 PM

Welcome to the forum. I see olcowhand stepped in and is helping. Never been inside any of these, so will follow along for the info. Good luck!

#9 olcowhand ONLINE  

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Posted December 13, 2011 - 06:13 PM

Look closely at the thrust plates. If they have visual wear, then they will need machining. I turned some badly worn ones on my lathe to renew the surface. These had deep grooves, plus the cylinders in the above pics were worn where they contact the thrust plates. I machined their faces as well.

DSC00633.jpg

These plates still show a trace of the old groove, but I was mostly just practicing on these as it's been a while since doing any. The hydro I will use is still not taken apart, and I'm hoping it's internals are in great shape. It was still working when the engine on the Massey died.

#10 caseguy OFFLINE  

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Posted December 13, 2011 - 06:42 PM

:wave: jacreech Welcome to GTTalk! We're happy to have you with us! I am very glad to know that we were able to help with some literature that was useful to you. I'm also glad to know that you plan to stick around and share your knowledge with us! You've got some excellent help with olcowhand's expertise too. Thanks for signing up and we look forward to hearing more from you!

#11 jacreech OFFLINE  

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Posted December 13, 2011 - 06:48 PM

Since my hydro is working - at least for the 20 minutes I've had time to drive it around my yard - I'll assume I must have the springs inside my cylinder blocks. I was surprised to find all my internal parts in very good condition with little wear. Some very light scratches on the end faces of the pistons, but a good 1 mm of surface on them above the indentation where the small hole is, in the center, no bevel worn on the edges. Thrust and pressure plates looked good, as did the various valves.

Biggest job I had was removing my deck lift cylinder. It's hoses are very hard to get at. I wanted to flush out the cylinder and its lines to make sure I didn't reintroduce any filings or crud back into the hydro after cleaning it and putting in new fluid.

Are you using a manual for guidance? The one posted as a download on this site is very good. I have another one from Sundstrand I can upload or email you if you want. It is not quite as detailed as the other, but still helpful.

I didn't remove my drive shafts, as they looked good and turned smoothly and quietly in their bearings. None of my seals were leaking.

I expect you use your tractor much more than I use mine, only about 100-125 hrs. per season - nothing in the winter, because I don't have a snow plow. I ought to try to retrofit something to save my back. Had one 30" snowfall last year.

Let's compare notes on the tranny project, as time allows.

#12 olcowhand ONLINE  

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Posted December 14, 2011 - 03:49 PM

When I get into my hydro, I hope to have time to take many pics as I go & make it an article for others as a guide. I only look at the manuals for pressures & clearances, as I tend to forget. I've had enough of these apart that the rest sticks in my head.
This Simplicity/Allis Sundstrand manual I just uploaded is pretty good also. Basically the same unit as in Massey's & others using the model 15. Just the tail-shaft area is different. Simplicity Sundstrand model 15 SERVICE - Manuals - Garden Tractor Talk - Forums
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#13 JDBrian OFFLINE  

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Posted December 14, 2011 - 04:30 PM

Welcome jacreech. Thank You to olcowhand and jacreech for sharing their experiences on rebuilding the model 15. It is one of the areas of these tractors that most people won't touch so it will be nice to have an article on how to evaluate and rebuild one.

#14 jacreech OFFLINE  

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Posted December 15, 2011 - 07:53 AM

Thanks, olcowhand - that Simplicity manual has a little info beyond what I found in the QS/QT service manual. I'll look forward to reading your rebuild article, and if I think of anything from my experience that might add in some small way, I'll post it. I do think this will help others who have model 15 Sunstrands (which are apparently common). I didn't find the rebuild project terribly complicated, having the manual. But it is really helpful to have someone who has hands on experience doing this (you're the man).

One question: Have you found a good source of replacement parts, when you need them? LJ Fluid Power in Michigan sold me a gasket kit, but I'm not sure how many parts they have or can still get, and are willing to sell to a do-it-yourself-er.

#15 olcowhand ONLINE  

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Posted December 15, 2011 - 09:45 AM

I've always had spare used parts in good shape when needed. The 2 reasons I'm getting into this hydro are 1: the output shaft where the bevel gear is held with a C-clip....someone has welded the end of the shaft, as apparently the clip let go due to a wallowed clip groov(?) 2: just to be sure the rest of it is in good working order before putting this on a MF 1855 rear end, then putting it all under my (now diesel) Bush Hog JBI tractor.
Gaskets I just cut myself from roll stock gasket paper.




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