1862 Hydro Linkage – Possessed by Demons!

[ColoradoGuy]

Hi –

I’m having a little problem with the hydro linkage on my 1990 model 1862.

The symptom: at a cold start, depressing the brake pedal forces the speed control lever perfectly to the neutral position. After starting the engine and releasing the brake, the tractor is indeed idling in neutral – no motion at all.

After driving the tractor for a short time (including some changes in both forward and reverse speed without applying the brake), the speed control lever no longer accurately returns to the neutral position. If I manually move it to neutral, the tractor is moving slowly in forward or reverse. If the brake pedal is applied, the lever returns to the neutral position (as it should), but the hydro is engaged and straining to move the tractor.

HERE’S THE MYSTERY: if I stop the engine and let the machine sit for 10 minutes (or more), the linkage is again working exactly as it should!

I should note that this symptom is intermittent. Often, it works correctly for weeks at a time.

If I drive it with the tunnel cover off and the connecting-rod jam nuts loosened, I can manually (and carefully) twist the connecting rod to attain a correct neutral position of the transmission – the tractor is not moving. But of course, the speed control lever is no longer at the neutral position.

I removed the seat, fenders, fuel tank, and the fuel tank support frame, so I have a very good top-down view of the hydro linkage. All of the following have been performed from the top of the tractor.

I have removed, cleaned, and inspected all parts of the speed-control linkage. There is no rust or paint anywhere on the linkage parts.

A visual inspection of the triunion bracket reveals no signs of wear in the most obvious place; i.e., there are no “notches” worn into the bracket at the point where the compression springs’ end caps contact the bracket.

Likewise, the damper plate shows no obvious wear at the point where the springs and end caps are inserted. There is very slight wear to the pin, but it appears inconsequential. There is also apparently some wear to the bore, which allowed the damper plate to wiggle very slightly on the hydro shaft. I’ve corrected this by shimming it with an extra washer.

Also, neither the cam pivot bracket nor the control cam show any significant visible signs of wear.

Compression springs: the service manual specifies that the “maximum unloaded spring length is 1-1/16 inch”. On mine, the large spring measures just a bit shy of one inch. Consequently, there is a small amount of movement or “play” of the large spring between the end caps. Can this small amount of sloppiness account for the symptom I’m having? I’ve ordered new springs, but they haven’t arrived yet.

I found some sloppiness in the side-to-side movement of the linkage connections. I’ve added some washers of the appropriate thickness as shims, and all of the connections are now (almost) tight – just enough tolerance to permit free movement.

The connecting-rod ball joints are tight – no sloppiness.

I’ve also adjusted the cross shaft friction. I don’t have a pull scale, so I’ve adjusted the nut to yield a “reasonable” amount of effort to move the speed control lever.

After reinstalling the fuel tank, I’ve jacked up the tractor’s rear end, set the rear axles on jack stands, and performed the “Neutral Adjust” procedure (a.k.a. cam pivot bracket adjustment) as described on this site and in the service manual (Service Bulletin #CC-188). Here’s the interesting part: with the engine running at about ¼ throttle, and the speed control lever at neutral, I can adjust the cam pivot bracket so that the right rear wheel stops moving (the left rear wheel does not turn at all). Fully depressing the brake pedal leaves the wheel motionless. Everything seems perfect. Then, after turning off the engine, tightening the hex cap bolts to secure the cam pivot bracket, and restarting the engine, the right rear wheel is slowly turning again! While I can adjust the connecting rod to bring the wheel to a stop, the speed control lever is no longer at the neutral position. It’s like playing whack-a-mole!

Note that I have NOT done the recommended brake adjustment. The brakes seem to function well, and the brake pedal (when depressed) pulls the cam pivot bracket fully into the neutral ‘slot’ (except for the last 1/8” of travel). Could this be relevant?

Although not likely related to the symptom, I changed the Hytran fluid, filter, and gasket while the rear end was exposed. Except for one small metal shaving, there were no signs of wear. With the rear cover off, there was no hint of the famous “pink clumps” of sludge.

All the symptoms point to a linkage problem. However, I’ve cleaned, shimmed, and adjusted almost everything I can find.

Also, I’ve read many other posts on this site (and others) relating to hydro linkage problems; however, once the posters perform the recommended adjustments, their problem is solved and stays solved. Mine keeps recurring intermittently.

What am I overlooking?

Any real solution that I haven’t already tried would be deeply appreciated.

Thanks,

Jon

[ColoradoGuy]

Ideas, anyone? Please?

[ajgross]

Sounds like it could be the springs. If there is slack then it doesn't have anything to hold it place. I would recommend replacing the springs and adding a washer to stiffen them up a bit more.

[ColoradoGuy]

AJ -

Thanks for your reply!

The new springs have arrived, but I haven't installed them yet. Exactly where would you suggest I add a washer?

Thanks,

Jon

[ajgross]

You put in between the big spring and the end keeper. You want to try to find a washer that is the same diameter as the keeper.

AJ

[ColoradoGuy]

Thanks, AJ...

I'll give that a try! It might be a while, but I'll post back.

Your help is deeply appreciated.

Jon