loudtractor 46 #1 Posted May 2 (edited) Hi all, maybe you can help me out. I'm working on my latest acquisition, a 74 C120 Automatic. I'm pretty sure it's the 1136 trans. Got it cheap at auction, and it's coming together pretty well, but I have run into a problem with the hydro. It jerks hard going into either forward or reverse. even if I feather the handle, it makes no difference. The linkage is all good, fluid and filter new, etc. I understand that the acceleration valve springs beak or wear, and he tiny orifice can plug up. I need to know: Is it necessary to drain the oil from the trans before pulling the valves out? Does the forward valve (In the back of the assembly) ,when removing, fit between the trans and the rear axle housing? It looks really close, but not knowing the size of the valve, it has me worried. Anyone done this repair? I'm good on engines and just about anything else, but have 0 experience on hydros. Thanks for any help! I'll put a picture in a minute. Edited May 2 by loudtractor Added pics Share this post Link to post Share on other sites
moe1965 738 #2 Posted May 2 By chance did you make sure your wheel hubs were not wiped out. Or a sheared key way in the hub 1 Share this post Link to post Share on other sites
gwest_ca-(File Mod) 11,045 #3 Posted May 2 Noticed some of the springs are still available from Toro https://www.partstree.com/models/1-0485-c-120-toro-lawn-tractor-1974/hydrostatic-transmission-piston-piston-type-plate-4-5-17/ Share this post Link to post Share on other sites
daveoman1966 3,752 #4 Posted May 2 Acceleration valves. YES-- you can remove them without tearing down the whole thing. Remove the wheel though for access. NOTE---Be certain to NOT mix them up. One of the valves has wider FLATS than the other. Use the HEX plug to drain the trans. good idea to change the fluid AND filter when you do this. 2 Share this post Link to post Share on other sites
ol550 830 #5 Posted May 2 Check the frame where it attaches to the transaxle. 1 Share this post Link to post Share on other sites
stevasaurus 22,741 #6 Posted May 2 I'm just curious, could the lack of a belt guard cause the issue?? Share this post Link to post Share on other sites
loudtractor 46 #7 Posted May 2 (edited) Thanks for all the replies! I only just removed the belt guard, so that's not an issue. I did install the original belt without tensioning the belt. OOPS. It needed a belt anyhow. Won't make that mistake again. The frame is fine, I checked that out. Also, the metal tab is good, the one that holds the control tensioner, so that's all good. The axle keys WERE sheared, I think that's why they junked the tractor, thinking the trans was shot. The jerking probably didn't heplp the keys any. Tomorrows plan is drain trans, remove Acc valves and , hopefully find a broken spring or clogged orifice. I'm glad to know I don't have to tear down the whole thing to get that rear valve out. The oil is real clean, but Ill use new and put in a new filter, theyre not that pricey anyhow. Fingers crossed! I was surprised how well the engine runs, I fully expected to be rebuilding it. I did see the spring on Toro. Ebay has it too, and a little cheaper. That's a salty spring! Thanks again for the help! Edited May 2 by loudtractor 2 Share this post Link to post Share on other sites
daveoman1966 3,752 #8 Posted May 3 Your '74 C-120 wants OEM belt #7478 for it to work as designed...AND--- the belt guard MUST be in place for the same reason. I'd urge you to use the OEM belt and not an aftermarket 'look-a-like'. Wheelhorse had proprietary pulleys back then and a-market belts just don't precisely match the geometry of those pulleys. It further occurs to me that, if you had an a-market belt on, that alone MAY be the root cause of the jerky jerky you get. Anyway---I've rebuilt a dozen or more of this very Sundstrand hydro unit and have a FREE download detailed .pdf manual on rebuild it. Inasmuch as yours hits its 50th Birthday this year, maybe consider the rebuild. Not difficult by any means. 1 Share this post Link to post Share on other sites
squonk 41,118 #9 Posted May 3 You don't need an OEM belt. Napa/ Gates belts work fine. I'm very been using them for over 20 years. Hydro's and 8 speeds. Wouldn't be surprised if Gates actually made the belts for Toro Share this post Link to post Share on other sites
loudtractor 46 #10 Posted May 3 (edited) Since it moves right along once it gets past that initial jerk, I'm optimistic, (So far) that the acc valve is at fault. I have it out and the spring looks fine. Is it necessary to take the valves apart? So far they look OK. I do not see the tiny orifice mentioned in the manual. Is inside the valve itself? BTW, I don't have much luck with aftermarket belts either. I did try a blue kevlar belt once, can't remember the brand, and it worked, but it did rattle against the belt guard a bit. After that, I just pop the extra $$ for OEM. I might try a napa/gates if I run into this again. The one I got for this project did say Wheelhorse on it, I was pleasantly surprised. If I do need to rebuild, I'll refer to your instructions. Update: I checked the manual again, and took the valve apart. (The pictures are small and blurry, so hard to see detail) I do see the tiny orifice. I'll blow it out after a solvent soak. Hard to tell if it's pluggrd up just by looking. Updates will follow... Edited May 3 by loudtractor Pic Share this post Link to post Share on other sites
