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Transmission locked in 2 gears at once

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Here is what I believe is causing the condition.

 

The shift rails are supported by blind bores in the transmission case and machined to a fairly close tolerance. Add gear oil to the mix and it gets even closer.

 

The top rail in the illustration is for 2nd and 3rd gears and the rear rail in the transmission. Both shift rails are in the neutral position.

 

The 2nd and 3rd rail when shifted into 3rd gear is slid farther into the case bore.

 

When you shift back to neutral from 3rd gear vacuum is created behind the rod. If you go through the neutral gate the shifter lets go of the 2nd and 3rd rail and enters the 1st and 2nd shift rail. The second the shifter leaves the 2nd and 3rd rail the vacuum behind the rail (rod) sucks it back into the blind bore and engages 3rd gear again. BUT the shifter has already selected 1st or R gear.

 

If you are is 2nd gear and shift to 1st or R the same thing happens but this time it is pressure in the blind bore that returns the rear rail to 2nd gear without the shifter in the rail.

 

To vent the blind bore my plan is to grind a shallow spiral groove in the rod so that the vacuum and pressure is relieved faster. Location of the ground groove is critical at the detent ball notches in the rod so it does not interfere with them. A spiral groove would minimize future wear in the casting.

 

I discovered this many years ago and have lived with it by pausing at neutral before shifting to the other rail. The pause gives time for the pressure or vacuum to dissipate and it works. I have since acquired a short angle drill and wonder if a vent hole could be drilled into the bottom of each shift rail bore. That would be even better but don't know if there is room to get the drill in to do it.

 

Garry

 

Adding

Wheel Horse addressed this problem in late 1964

As a result all the transmission model numbers used in 1964 got new model numbers in 1965. I suspect this was a result of the change.

 

It would be interesting to see what tractor models or transmission models still experience this problem today.

post-120-0-73331600-1412165757.jpg

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That makes sense Garry. Due to a broken shift fork  I purchased a replacement on Ebay which included rails and they were the upgraded style. I wondered what the deeper neutral detent was for and this is likely why. Interesting. The service bulletin states that the redesigned rails will eliminate the possibility of locking in two gears but doesn't state why it was happening. Here's a picture of the rails, the new and the old.

post-8408-0-95313200-1412168852_thumb.jp

Edited by Racinbob
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To add one more thing, dealing with a 5003-5010 transmission I would think this wouldn't be a problem because the holes for the shift rails are open ended. Not so with the two piece case. I used the redesigned rails in mine and now I kinda wish I wouldn't have. Not that it matters but it was a fix for a problem that a three piece case wouldn't have. Something tells me that there are folks out there that would like to have the revised rails. :)

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Garry and Bob:  We just had this happen to a 1054 transmission (an original -not updated one)  with original shifting forks that have the narrow moon cuts.   We just traded out the transmission for a rebuilt one.   But several years ago we changed a 1054 transmission with the same issue Garry mentions and the key thing to remember is that the 5614  stop pin (that rests between the 1/4 inch shifting balls ) is to use the new pin with the new -deeper moon forks.   I have heard folks cut the older forks deeper but never hear (until Garry mentioned above) the idea of drilling a vent hole or shallow groove to relieve pressure from the shifting.     The going to neutral first process is also a good point worth remembering too!

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Good point Lane. The service bulletin addresses the stop pins. The older style pin can be used with the newer rails but not vice-versa. I'm assuming the newer stop pin is a bit longer and offers a firmer grip in the neutral detent of the newer rails but in my case with the 5010 transmission it should be irrelevant. I like the idea of drilling the holes. Maybe it could be done with a smaller angle head drill.

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Something just hit me about a comment I made. Assuming the newer stop pin is longer it still has to let the balls clear the rail. Isn't the purpose of that pin to just be a guide for the spring? I would think the spring determines how firm the balls hold in the detent. A different spring isn't mentioned in the service bulletin. Is a different spring used along with the newer pin?

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Ols springs are ok to use -the new  #5614 pin is just a tad longer.  We took apart one and when placing the newer forks and pin with the detent balls had a problem getting them to stay in as we placed the forks in.    Our mother suggested we use a chop stick!   Which we tried the next day and it worked great.  The small bit of bamboo or ash wood chopped off when placing the forks in was not going to bother a thing!

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The two balls and pin are an interlock mechanism to prevent both shifting forks from leaving the neutral position at the same time.  Besides acting as a spring guide the pin maintains a minimum distance between the balls.  The only way either fork can leave neutral is for its ball to pop out of the detent.  If the opposite ball is in the shallower detents of its fork then the pin cannot move far enough to allow the first ball to move for shift fork to leave neutral.  A longer pin would be necessary if the modified neutral detents are deeper than the original detents.

 

 

All that said, if you have a problem with two gears locking in at once you either have a missing or damaged pin or balls.

Edited by jrc0528
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That makes sense jrc. So, for the sake of discussion and learning let me add this. The distance between the 'flats' of the rails hasn't changed. The old pin would have been sized to keep the overall length of the rod and balls to something more than the distance between the rails. The old pin still would have worked. Even though the ball in the deeper detent increased the distance it still wouldn't allow both to be out of the neutral position at the same time. Make sense? :) Now damaged or missing parts is another matter.

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I have noted the difference in interlock pin lengths in several transmissions.  

 

My scribbled (and oil soaked notes) state that the short interlock pin is .695" long, the longer pin is .740" long.

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The length of the pin and balls as a unit must be less than the distance from the bottom of a neutral groove to the solid rail of the opposite fork (so the second fork can move when the first is in neutral) and longer than the distance from the bottom of the shallower gear detent groove to the opposite rail (so that the opposite fork CANNOT move while the first is in gear).

 

 In reality having a pin long enough that it is longer than the distance between the solid parts of the rails should be enough as this prevents both forks from leaving neutral simultaneously.  Once a fork is into gear the spring will be a bit tighter in the opposite detent and suction alone shouldn't be sufficient to jar it from its place.  

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The way I see it is there are 2 shifters at play here. 

 

One is the vacuum or pressure making a shift because the stop pin/ball is relaxed in neutral waiting to be shifted. Once that has happened the stop pin/ball is relaxed again waiting for another shift.

 

The second is the shifter it's self now positioned in the other rail. The stop pin/ball is relaxed so the operator can make another shift.

 

It's no different than removing the shifter and using a screw driver to place each rail in a gear. It is easily done.

 

No doubt the deeper notch helps to retain the neutral position. My thought was to remove the pressure/vacuum shifter totally by venting the rail bore in the case. I tried to pull a rail out of it's bore and the vacuum ripped it out of my grasp and slammed it to the bottom with some serious authority.

 

If the transmission is in 2nd or 3rd and you shift to neutral the shifter is heavy enough to stay in that rail. Let go of the shifter and it will partially return to the gear it just left on it's own. Maybe that is a test one could do to see it a particular transmission is a possible candidate for the problem.

 

Garry

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Wow, I've never had a shift rail with that much vacuum behind it fortunately!!   I'd think the pin and balls would prevent you from engaging another gear if the first fork sucked back into gear, but that still leaves you needing to pop out the shifter lever to return the transmission to neutral!   I may just re-open my case on the rebuilt 8-speed from the C101 since I haven't swapped it into service yet.  Does anyone here know if mine would need this venting procedure or is it already a thru-bore?

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I should add the 7th time I took it out I initially did not wash it up and I immediately tried to remove the rails.in frustration. Once I had washed the parts to get rid of the stinking gear lube the rails would stay where they were put. The gear oil was sealing the bore restricting the passage of air.

 

The service bulletin is confusing to me. The first paragraph says to use the old pin with the new rails and the note at the bottom says you must use the new pin with new rails. Wonder if it should have read use the old pin with one new rail?

 

Garry

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It is a bit confusing Garry. :confusion-scratchheadblue: The way I'm reading it you can use the old pin with one new rail and one old or both new (any combination). But the new pin can't be used unless both rails are the new style. They recommend that, if one rail needs replacing, to just replace both and use a new pin.

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Likely the way they are looking at it is this...   

 

If the pin is too long, the forks will not be able to shift.  ->  Transmission is inoperable

 

If the pin is too long, the forks will shift fine, but won't be protected from jamming into two gears at once!   -> transmission incorrect but servicable.

 

 

Here's a quick way to calculate a good pin length....

 

Max:

pin length < (NeutralDetentDepth + DistanceBetweenRails) - 2 x BallDiameter

      measure both Neutral detents and use the SHALLOWEST here

 

Min:

pin length > (InGearDetentDepth + DistanceBetweenRails) - 2 x BallDiameter

      measure all 4 gear detents and use the DEEPEST for this calculation

 

Use a pair of calipers and measure the distance between rails against the solid portions while they are in the transmission bores.

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I thought I'd revive this as I've been playing with a couple of transmissions. They should both be 5053 trannys according to the tractors they came off of but I don't think one was. In post #2 you can see the updated rails per service bulletin #60 issued in 1965.The switch was made between the 5046 and 5048 trannys. They went a step further with the stop groves sometime later. Here's the shift rails out of the two trannys I'm playing with.

 

565dd12f9f349_ShiftRailsandPins.thumb.JP

 

You can see why I don't think they are both 5053 but then again, you know Wheel Horse and their usage of left over parts. The stop springs and balls are the same. The older stop pin is .697" and the newer is .743". Using 11/16" and 3/4" as in the picture is what you'll measure with a tape measure. I kinda wondered why the grooves went all the way around since the rails only move side to side.

 

An interesting change they made is shown in the picture above and here as well.565dd3292cab7_ShiftRailFlat.thumb.JPG.3d

 

 Garry was ahead of the times :). They milled a flat lengthwise to alleviate the suction issue. The grooves going all the way around probably wasn't necessary but, I think, a good idea because it ties the stop spring and balls into the relief flat. I suppose one could say that it also allows oil to get in there better but I really doubt that had any factor in them doing this. I don't see that as an issue.

Edited by Racinbob
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Bob, I'm working on a few unidrives this winter...a 5086 ,  5053 ,  and two 5025's off of two very early lawn rangers.  I had no idea that there were two different sized stop pins in these.

Do you know....is there any problem with using the other or wrong sized pin?  I would think not, but then I've been wrong more than once on replacing parts.   any comments appreciated .

 

Never mind,  I reread the above and I think I get it now...:)

 

Edited by Terry M

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Terry, the rails are interchangeable. The shorter pin can be used in any combination of rails. The longer pin can be used only if you have both later style rails installed. I thought my 5053's would have the rail on the left in post #2 and I was surprised at what I found. The idea was to make sure one of the detent balls was always in one of the neutral detents. That way it couldn't try to engage two gears and lock up. :)

Edited by Racinbob

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Wait a minute...are you saying you can have one of the grooved all around shafts and one of the just notched shafts and use the shorter pin and you will be OK.  I realize it is only a difference of 1/16" length, but is that what you found??  :)

Are you saying that you can use the shorter pin with both grooved around shafts??  :)

 

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You bet Steve. You won't have the benefit of what the later style and their ability to prevent gear lock up but it will work fine. Remember, when the tractor is in any gear that pin is doing nothing but floating in the spring. It's soul purpose is to limit how far the balls can be pushed together. They found that the first style wasn't reliable in doing that so they made the neutral detent deeper and used a slightly longer pin. Actually, you can say the longer pin is what stops the gear lock up and the rails had to be modified to accommodate the longer pin.

Make sense? :)

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if you are getting stuck between two gears you have wear or bent or broken problem nothing to do with the shiftier shaft grooves or vacuum from said holes

 

Brian

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Sorry Brian but Wheel Horse had service bulletins addressing the issue of the tranny locking up due to this. Sure, it may be that something is bent or broken but not necessarily. It was engineering as you go in the 60's

 

To make the pin length simple (works best for me) the distance between the bottom of the neutral detent and the other rail (not detent) minus 1/2" (the two 1/4" balls) will be the length not figuring any tolerances. That way it's not possible for the shift rails to move unless one of the balls in a neutral detent.

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On 10/1/2014, 11:15:49, Lane Ranger said:

Ols springs are ok to use -the new  #5614 pin is just a tad longer.  We took apart one and when placing the newer forks and pin with the detent balls had a problem getting them to stay in as we placed the forks in.    Our mother suggested we use a chop stick!   Which we tried the next day and it worked great.  The small bit of bamboo or ash wood chopped off when placing the forks in was not going to bother a thing!

use a 5/32 T handled Allen wrench

 

Brian

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5 hours ago, Racinbob said:

Sorry Brian but Wheel Horse had service bulletins addressing the issue of the tranny locking up due to this. Sure, it may be that something is bent or broken but not necessarily. It was engineering as you go in the 60's

 

To make the pin length simple (works best for me) the distance between the bottom of the neutral detent and the other rail (not detent) minus 1/2" (the two 1/4" balls) will be the length not figuring any tolerances. That way it's not possible for the shift rails to move unless one of the balls in a neutral detent.

your missing the big picture here the service bulletins were a quick fix for poorly made parts with too much tolerance/or not enough these problems usually showed up  within a short time after the tractor was put in

service not 40 + years later if you feel vacuum is hurting it's a simple fix to grind a small flat length wise on the opposed side of the scalps in the shift shafts the most likely cause on a old transmission is the ball on the end of the shift lever or a bent fork and I have seen a badly ground up gear hang one up also you say it right in your post above if all parts are the correct tolerance you can not move one shift shaft with out the other

in neutral detente position so if this was a perfect world and all parts were perfect there should be no way to get the transmission stuck between gears if the detente was working correctly

the new style shift shafts with the groove all around the shaft was probably for ease of manufacturing as the shaft could be made in a lathe instead of a mill

 

Brian

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