Unconfuguliating a 782 SN 714899

[jchamberlin]

Post 2 of 2
Emergency Trunnion Repair: The next installment of "Unconfuguliating my 782 SN 714899.”

Figure 9: TrunnionCutFWide 49/64"

Figure 10: ETrunnionCutFLength 1-7/32"

After a little elbow grease it was “close enough for government work.” The urgency now was to get the work done and get some supper.

I don’t know why I didn’t grab my digital calipers, but I don’t usually associate “hacksaw” and calipers in the same sentence. I will say that a 64th of an inch is barely more than a “whisker.” I couldn’t read the increments on the ruler nearly as well in real life as I can in the photographs.

Figure 11: ETrunnionCutFTrial

With the cut-out below the original you can see how the spring “wallowed” in the slot.

Figure 12: EtrunnionIns

Doesn’t look too bad (if your standards are low). Let’s see how it works:

Figure 13: ETrunnionInsTestPull

Figure 14: ETrunnionInsTestPush

During the tests I was exerting “firm” pressure. The springs compressed until the larger damping spring began to compress, by pushing really hard, the rear of the Spring Damper Plate touched the Emergency Trunnion Slot; I could not force it hard enough to touch the front. I don’t know how much pressure the trunnion arm actually experiences in actual use, but the clearance seems adequate to “damp” the action of the linkage. (Note: All testing was done with new springs, the use of weak, old springs would likely require trimming the ends.) The two-metal-thickness of the repair did not seem to affect the operation of the linkage.

Because it seemed to work, and because I had cut the tab-slots so deeply (not to mention that supper was almost ready) I didn’t feel comfortable trimming the ends of the Emergency Trunnion Slot. But if care is taken when slotting the tab (that allows conformance to the Trunnion Arm’s curvature), then trimming the ends to the same dimensions as the original trunnion slot becomes a possibility.

If you check out the time stamps, the repair took about 4 hours. It certainly isn’t a job that someone would contemplate with having an urgent need to do so. Welding a new slot in seems like the best solution to me. But I had a lot of fun doing it, and I proved that the trunnion arm can be repaired and restored to reliable operation without welding. Some might say that this repair failed to “unconfuguliate” the 782, but only “confuguliated” it some more. Oh well, what can I say? It works for me, the operation of the transmission is improved as a result of installing new trunnion springs in the
"Emergency Trunnion Slot."

 

[jchamberlin]

The following shot was supposed to have appeared in the first post as the "Trunnion Slot." Just above the words, "This is where we started." I guess I'm going to have to number the pictures so I don't mix them up.

 

[dtanner]

Jeremiah Chamberlin

I like to add a washer between the springs and the ends of the caps , I find the springs last much longer and I get a better feel from the hydro.The washers seem to tighten the springs up in the trunion slot. My .02

 

[jchamberlin]

Thanks, Don. I'll have to try that. I'll add them next time I'm in there.

 

[kmcconaughey]

Jeremiah, I like your fix. Perhaps you could license (or give him the OK to make them) your part idea to Aaron at Xtreme Motorworks, he could make laser cut versions. Then all one would have to do is drill a hole in the trunion arm for the screw. Hmmm... Then even I could fix the trunions on my Cubs and I wouldn't have to bug Art to fire up his welder for me.

 

[jbaker]

Jeremiah, Very cool fix can you make more or as Kraig said get together with Aaron. I have 3 hydros that could use that.

This would be good for me since I dont weld and my metal fab skills have ALOT to be desired.

 

[jchamberlin]

Jeff, Craig: Thanks for the affirmation.

It's nice to know that others appreciate the inspiration and effort that often goes into what my family calls a "Jerry-rig."
(My childhood name was Jerry.)

The part is definitely a candidate for the laser cutter, although I hadn't considered marketing it. I just wanted to be able to drive it across the yard so I wouldn't have to push it.

I'll get up with Aaron next week.

 

[jchamberlin]

Well the "Emergency" has passed, and I've removed my temporary fix. I took the tractor to work and got one of the fellows in the shop to TIG up Charlie's Trunnion Repair plate.

There was a problem welding the unit inside the shop, insurance regulations prohibit welding on equipment with gas tanks . . .. So we had to remove to an outbuilding (still probably breaking the rules). Which leads me to conclude that the Welded Trunnion Repair is best done with the transmission removed from the tractor. Then it is not a problem to literally "carry it to a welder." Until or unless the tractor is broken down, my "Emergency Trunnion Repair" (which I am re-labeling my "Temporary Trunnion Repair") should be able to handle the spring for at least several months.

By-the-way, for interested parties, Aaron Schmidt at Extreme Motorworks has been contacted by me and I have given him permission to make the part to my dimensions, or to any dimensions he chooses. Meanwhile, I may have a few made myself.

 

[jchamberlin]

I think I've discovered why the slot in the trunnion arm wears as it does. If you examine closely the wear pattern of spring against the hole I cut out for the temporary repair, you will notice that the spring wears away from the transmission, so that the rear kicks out and the spring gets "cocked" at an angle to the transmission: the spring does not wear the outside of the slot evenly. You can also see where the "cap" has cut the outside of the slot; meanwhile, the front "cap" betrays a corresponding wear pattern. Both caps have worn notches in the trunnion slot, which of course, causes the transmission to "jump" into gear, after first getting hung up. Moving into and out of neutral becomes a chancey affair.

The reason I think the slot wears this way is because of the action of the plate that holds the trunnion spring, which some term the Hydro Damper Plate.

Trunnion at Rest (above)
(Sorry, the picture of the trunnion at rest keeps dropping out when I "post" the message, I'll repost the pair above. Oops, now its back. I'll leave it alone.)

Trunnion Actuated (Below)

It isn't easy to see in the pictures (you must imagine the frame aligned between the two pictures above), but when the Hydro Damper Plate is actuated, especially by the shift lever, the plate moves from the inside (from transmission side) to the outside, toward the frame. When this fact is added to the fact that shift lever is used primarily to actuate the forward gear (since the brake generally "backs it off" and reverse is not used as much), the wear pattern is accounted for. That is, when shifted forward, the damper plate pushes at the back of the spring, and because it is also shifting slightly from the inside to the outside, it "kicks" the rear of the spring out and puts more force at the outside of the front "cap," exactly as the wear pattern indicates. (Aside to D. Tanner, I'm saving the washer trick for later when the inside spring gets a bit compressed.)

The shearing action of the linkage is easy to verify by observing it in action.

The other actuator of the linkage, the brake pedal, doesn't transmit as much shearing force due to the "open" configuration of the link and because its action is more in-line with the Hydro Damper Plate.

The situation is not helped by the fact that the "peg" on the Hydro Damper Plate can get worn by the Speed Control Cam Assembly so that the Hydro Damper Plate gravitates toward the spot of most wear, exacerbating the situation further.

What is worse, I can't see that shimming the plates helps alleviate the plate wobble. It would seem to me that the plates themselves need to be bushed to eliminate the slop. Even replacing the the Speed Control Cam Assembly's plastic bushing doesn't seem to alleviate the wobble all that much.

I guess, from the fact that the bushing is plastic, the engineers anticipated the wobble of the Speed Control Cam Assembly, but I'm not sure they intended for the trunnion arm to wear as it does. I think if I were going to do anything to optimize the linkage, I would try to bush the Damper Plate as tightly as I could, perhaps even going so far as to press in a roller bearing, while letting the Speed Control Cam Assembly wobble on its own.

I don't think the clip I found on the Damper Plate "peg" is a good idea, it seems to promote the wear pictured above. I don't see that wear pattern on my older Model 149 that lacks the clip. (Actually, even though the 149 tractor looks worse cosmetically than the 782, I'm not finding as much wear on it mechanically. The 149 seems to have been maintained better than the 782.) Maybe it would be a good idea to put a plastic or bronze bushing on the peg and hold it on with the clip.

Anyway, the thoughts above are my theories as to why the Trunnion Spring wears the slot as it does.

 

[mgonitzke]

Shimming the plate WILL make the wobble much better. Myself and many others have done it and it works. Also, that would not be a good place for a roller bearing because the part doesn't make full revolutions. Rolling-element bearings don't last very long in applications where they make small back and forth angular displacements instead of full revolutions.

 

[jchamberlin]

Matt, I'll accept your verdict on the roller bearings, but I'm not sure about the shims. If the wobble is due to wear on either the male or female parts, the shims don't seem to affect it much. My insight is that while the shims may keep the hole from moving back and forth on the shaft they can't do much about keeping the piece from "tipping" on the shaft. If the wear is limited to the hole and not the shaft, then yes, replacement of the plate AND shimming it would seem to prevent premature wear on the hole.

At least those are my thoughts based upon my experience and observations. If you can get the wobble out of a worn hole/shaft with shims you must be packing a lot of them in there. I got all the shims in that I could and still get the clip on.

 

[mgonitzke]

I shimmed it until there was less than a 0.005" gap between the outermost shim and the snap ring. If there is that little axial play, it can't tip very far. You could anneal that bushing on the plate, bore it, and install a bronze bushing, but I have yet to find a need for this because the washers improve it greatly.

I have done this on 6 or 7 tractors with great success...you must not have put enough shims on yours.

 

[glippert]

I fully endorse Matt G's method. I've used his method on three of my tractors with great results.

It still amazes me how much knowledge and information folks on this site are willing to share. Thanks to all of you, and to Charlie for keeping it going!

 

[jchamberlin]

Well Matt, since you're a mechanical engineer, I have to bow to your authority.

However, my head is kind of hard.

The point I was trying to make with my post is that the wiggle on the damper plate promotes the wear in the trunnion slot. Perhaps I'm wrong that eliminating the wiggle will eliminate the wear. No matter what is done to tighten it up, unless the forces acting on the Speed Cam Control plate are somehow magically aligned, the wiggle will inevitably return. Whether the plate is bushed or shimmed, all one can do short of a redesign is slow the wearing process down.

Since engineering is a matter of trade-offs, the question becomes a matter of how much can be done and what is it worth to do it? To me, it would be worth bushing the damper plate just to see if the wobble could be effectively eliminated for a time. I might also look at modifying the attachment of the shift control to the Speed Cam Assembly Plate. The attachment point at the handle pivot seems to be in-line with the plate, it is shifted because of the use of the ball joint. I'm wondering if a clevis pin arrangement, like the "neutral-finding" rod to the brake, could be fitted at the Speed Cam Assembly end of the shift lever linkage so that the action of the shift lever is as linear as the "neutral-finding" brake rod.

I'm a tinkerer, not an engineer, so I'm more intrigued by the possibilities than worried about the practicalities of any situation. I like to push the limits of my knowledge and ability. Sometimes I have been known to "fix it until its broke." But I sure enjoy doing it.

 

[jchamberlin]

One last thought: Some empirical data on the wobble might help resolve the debate on how effective the shimming is. I'm basing my conclusions on modifying one tractor which had been left outside in the elements for several years, not maintained well, and had a good deal of rust on the trunnion shaft to which the damper plate attaches. My 149 is open right now, I'll get out my dial indicator and take some measurements.

 

[jbaker]

Jeremiah will you post a picture and measuerments to your tempeoary fix plate. I want to try to make one.

 

[jchamberlin]

Jeff: I tried to post all the info needed to make the part below. I'll review and do up a drawing. I've already transferred my original to my 149. Its working like a champ, and MUCH easier the second time around. All I had to do was mark and drill a hole! Pretty cool, if I do say so myself.

 

[jchamberlin]

Well Everyone, I got out my Dial Indicator and Feeler Gauge to gather empirical data last night, and to my surprise I managed to prove both Matt and Jeremiah correct.

1. Matt is correct that the PROPER INSTALLATION of shims will virtually eliminate wobble of the Trunnion Plate on the Trunnion Shaft.

2. Jeremiah is correct that when the shims are improperly installed they have virtually no effect on the wobble of the Trunnion Plate on the Trunnion Shaft.

A word of explanation: The shims need to be installed on the outside of the plate where the C-Clip is installed; the indent on the inside of the plate will "swallow" any shim installed there. An observant person might have noticed this fact, Jeremiah overlooked it.

I feel pretty foolish. (I assume the offset is there to keep grease on the shaft.)

I took pictures of the dial indicator and the feeler gauge, but they're pretty pointless now, so I'm not posting them.

Another point to consider: Since the fenders were off of the Model 149, I was taking the measurements on it: I discovered that the entire Trunnion Shaft on the 149 moved in-and-out much more than the Trunnion Plate on the 782 wobbled back-and-forth. Eliminating the wobble of the Trunnion Plate on the shaft does nothing about wear on the Trunnion Shaft itself. It looks like I'll have more work to do on the 149's transmission when I tear it down to restore it.

The opening for the spring on the 149's Trunnion Plate was also worn in a way the 782's opening was not. Note: the previous owner of the 149 didn't think that tractors with Hydrostatic Transmissions needed brakes, at least he didn't use them. See picture below:

Jeff: I've got the dims on the Temporary Trunnion Plate, I hope to get a drawing out today, my first full day of work this week since Monday.

 

[jchamberlin]

Jeff (and any other interested parties):

Putting together a drawing with instructions has proven more difficult than I imagined. I've had the part in my hand twice now, and even though I've taken numerous pictures and measurements, I seem to have overlooked a few that are critical to replicating the original piece. I realize now that manufacturing a part was not the reason I posted in the first place. I just wanted to share my idea and how I managed to implement it. To that end, I'm posting the sketch from which I worked when I made the "Temporary Trunnion Repair" last month. It functioned as MY guide to its construction.

The piece has now been installed on two different tractors. It is currently installed on my Model 149, and now that I've got the fenders back on and the tractor is up-and-running, I don't want to pull them back off just to complete this post. Although, I will say that when I last had it out, I noticed that the width of the slot that "grasps" the upright from the swash plate was very tightly toleranced, I actually had to "wiggle" it onto the upright. The tightness of the fit probably helps the piece remain stable in use, the screw's only function is to hold the piece tightly against the upright, the screw doesn't see much load.

Again, the reference for the design was the transmission side of the trunnion slot itself, all the cuts I made reference this line.

Also, the only reason the outside edge of the "Temporary" piece extends beyond the existing swash plate upright is because when I trimmed it originally I forgot to "hold an inch." But since it didn't look like a lot of metal would remain if I trimmed it to the 0.220" dimension of the upright, and because it wasn't symmetrical with the other edges, I let it overhang a bit.

The dimensions of the slot itself are given below, and can also be found on the FAQ "My transmission is changing speed by itself, how can I fix it?" link above. The raw material I used was a three foot long piece of 2" wide steel strip 1/8" thick from Lowes, for which I paid $7.00. The piece is tapped to receive a 10-32 machine screw.

Finally, it looks like I'll be splitting a tractor soon, when I get it apart, I'll go through the exercise of making a second "Temporary Trunnion Repair Piece." I'll keep track of all the dimensions and I think I'll try out a few new tool ideas. (Four hours is too long to be cutting with a hacksaw and a Dremel, especially in a vise lying on the driveway.) When I get through, I'll market the drawing and the piece itself. It really does work and it is easy to use.

Original working sketch below:

 

[jbaker]

Jeremiah did you ever get a chance to trace out and measure that emergency trunion repair part you made?