Random Transmission Failures

Hello Steve,
For all of the community it will be great if you can make video on how to do the preload shim properly.
I found some write up but a video complement will be great.
...If one day you have time.

Thanks

Yves, _Some day_ I'll have the time and will make a whole video series on rebuilding these units. To do it properly would probably be a dozen or more videos of 30~60 minutes each. That's a lot of work that I simply don't have time for now.

As for shimming the differential, the service manual documents the procedure and that's what I recommend doing. I should note that that's not how I do it now. Instead of setting the preload with the clearance, I only use the clearance to get it in the ball park. With the preload close I then check the rolling torque that gives a much better indication of the installed preload.
 
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Yves, _Some day_ I'll have the time and will make a whole video series on rebuilding these units. To do it properly would probably be a dozen or more videos of 30~60 minutes each. That's a lot of work that I simply don't have time for now.

As for shimming the differential, the service manual documents the procedure and that's what I recommend doing. I should note that that's now how I do it now. Instead of setting the preload with the clearance, I only use the clearance to get it in the ball park. With the preload close I then check the rolling torque that gives a much better indication of the installed preload.
What is your “new venture” launched last April?
 
Yves, _Some day_ I'll have the time and will make a whole video series on rebuilding these units. To do it properly would probably be a dozen or more videos of 30~60 minutes each. That's a lot of work that I simply don't have time for now.

As for shimming the differential, the service manual documents the procedure and that's what I recommend doing. I should note that that's now how I do it now. Instead of setting the preload with the clearance, I only use the clearance to get it in the ball park. With the preload close I then check the rolling torque that gives a much better indication of the installed preload.
Thank you Steve for taking the time to answer, yes it's absolutely true the time to make a video.
I cross my fingers and hope you will find time.

My best
Yves
 
The dog bone bushes are Nolathane 46007A, duro 75, for an Aussie Ford Falcon, but there are others around. I had to machine it to the right size, od 46.5mm, id 18mm, length 40mm.
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Below is a pic of the torque rod on the bench
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Yes, a nut welded on the back of the 1st plate welded at the rear of the engine support. The engine mount I used was one that the 19mm shaft had broken off the back plate, so I made a 25mm dia collar to be a press fit on the 19mm stub, welded to back plate, and also welded from behind.
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Also had to cut about 20mm off the transmission lug for clearance.
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Working on an alternate method for torque suppressor without engine mount modifications.

acquired the Eurosport UK exhaust mount which is a precision laser cut steel piece that mimics a ‘74 lower engine mount by bolting a flange to readily available later style mounts. Will use a short M8 end link to bolt the exhaust mount extension to the crossmember.

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Got a reminded of this part today so I thought I would add it to this thread.

I pulled a core to build recently and in the tear down process I found this failure. Its not a common failure but one that can really cause trouble. The core was one I got last year and I didn't know anything about it. In teardown I found most of the replacement parts were fairly new. It had all replacement sychronizers throughout. Yet all three sliders and shift forks showed excessive wear. Given the aftermarket gaskets and synchros it had clearly been rebuilt previously but was in terrible shape. At first I figured somebody just beat the heck out of the gearbox until I pulled the main shift rail out. The main shift rail is the rod that connects to the external shift linkage and carries the main shift rail translator linkage.

This is the main shift rail translator link that interfaces to the translator itself. The translator then engages the individual shift rails. This link had a huge crack where it fit to the rail's bore. The linkage was clearly bent and probably moved slightly with each shift. The feel and performance of the shift lever must have been terrible.

This was likely missed during the previous rebuild and caused a lot of damage.

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Got a reminded of this part today so I thought I would add it to this thread.

I pulled a core to build recently and in the tear down process I found this failure. Its not a common failure but one that can really cause trouble. I The core was one I got last year and I didn't know anything about it. In teardown I found most of the replacement parts were fairly new. It had all replacement sychronizers throughout. Yet all three sliders and shift forks showed excessive wear. Given the aftermarket gaskets and synchros it had clearly been rebuilt previously but was in terrible shape. At first I figured somebody just beat the heck out of the gearbox until I pulled the main shift rail out. The main shift rail is the rod that connects to the external shift linkage and carries the main shift rail translator linkage.

This is the main shift rail translator link that interfaces to the translator itself. The translator then engages the individual shift rails. This link had a huge crack where it fit to the rail's bore. The linkage was clearly bent and probably moved slightly with each shift. The feel and performance of the shift lever must have been terrible.

This was likely missed during the previous rebuild and caused a lot of damage.

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Steve, that's not the first one of those failures, and certainly not the worst. Recall the one I posted a year or so ago that looked like this when I opened the box (the fork was sitting separately detached on the bottom):

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Previous owner reported it would not go into any gears.
I'm curious what other damage was caused by that cracked fork in your case?
 
Jeff, I had seen you post this photo before. Having the entire fork break off is indeed rare. As I noted, its rare but not unknown. This was the first one I had thought to photograph and given the history thought it interesting.

To understand the damage its important to note the linkage's action. When the fork rotates long the axis of the main shift rail its from moving the shift lever left and right. This is the motion that selects which of the three gates to engage for the desired shift rail (1-2, 3-4 or 5-Rev). Moving the lever forward and backward moves the fork along the rotation axis. There is far more load on this fork moving it along its axis to select a specific gate's gear than in rotation to select the specific gate. This is because the rotation motion is only checked by the centering spring on the translator linkage. Selecting a gear on a specific gate must compress the synchronizer springs and apply pressure on the synchro's friction surface.

Given the above, the torque applied to the fork its usually moving the lever forward/backward to select a specific gate's gear that puts the most load on the fork and causes it to bend and then eventually crack. Once cracked it is much more likely to bend on either or both axis as much of its structure has been compromised.

Once the fork can bend under load it will be harder to select a gate and require more motion and effort to fully engage a gear within a gate. The result is damage to the engagement teeth and accelerated synchronizer wear. It can also likely jump out of gear easily due to shallow engagement. It will also compound the reverse issues as reverse puts the most load on the linkage during engagement.

The most common cause of the fork cracking or breaking is holding the lever in reverse to prevent it popping out. The load is applied directly to this part of the linkage. Same thing for popping out of any other gear. 5th is a common cause. In fact, wear on the 5th gear fork usually makes 5th hard to engage and thus the driver applied more pressure to the lever (and thus the linkage).

In your case, once the fork breaks there is no connection to the translator linkage internally so the shifter is no longer connected to the mechanism. The translator linkage itself can also break/fail and is actually the more common failure mode.

In this case I am assuming the rebuilder was repairing a failed reverse or 5th (or both) and didn't know, or bother, to check the linkage. Once back together the linkage was compromised and caused the shifting issues with beat up the forks, sliders, synchros and engagement teeth.
 
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The result is damage to the engagement teeth and accelerated synchronizer wear.
Thanks Steve. Makes sense that the collateral damage from a bad fork like these examples can be accelerated wear and tear on those other items, for the reason you described. I wasn't sure if earlier you were referring to some direct damage due to the bent/broken fort hitting other adjacent components or such. But now I see what you meant. ;)
 
I have a little time going into the holidays this winter so I thought I would catch up on a couple of transmission build requests (hint: if you are wanting one anytime soon, please let me know asap).

I purged a lot of deadwood before we moved last year but I kept as much of my core inventory as was practical. So I pulled the newest core from my inventory to build (one I got not long before moving last year) to use for this build. Step 1 is teardown and by the fact that you are reading this you can guess it wasn't a normal teardown.

I seem to be on a theme here but this was such an extreme example I figured I would post it. I'll just post the photos and you guys can probably figure this out.

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If there is any doubt. That is old GL1 that has varnished and been extensively contaminated with moisture, all mixed with rust residue. While this is a common issue with many cores I get, this is the worst I have ever seen by at least an order of magnitude. Virtually all of the gear teeth, bearings, races, and any other bear metal surface, is pitted with rust and therefore unuseable.

So I stored and moved what was basically a case and 50 lbs of scrap metal. :(
 
Mid Ohio...This one broke on me just before the end of the back straight (turn 5 at the time - sometimes turn 7 - just before Madness).
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Anyway I was dumb enough to man handle inserting the axles into the trans (I was in a hurry) and obviously damaged a tri-pole joint. When the little needle from that damaged bearing got stuck between the gear teeth the trans exploded. I was doing about 100mph when it happened and was extremely lucky that the trans didn't lock up on me! :eek:
Lesson learned - be very careful installing the axles on a 4 spd, those little needles are HARD!
 
Yeah, that's a lot of water. It probably got run with it enough to turn to milkshake status before it got pulled.

Brayden, I have seen that exact failure many times, including in my own car. That's a 3rd gear synchro explosion. Its what happens when you let the clutch out before the 3rd gear slider is fully engaged. The torque is transmitted through the 3rd gear synchro. You're lucky it didn't get ingested in the gear set or it could have done exactly what Mike's did.

Mike, I have seen that too. Interesting that it broke the shaft in half. I asume that was a webster conversion with the gear welded to the input shaft. I could see why it failed there. Usually, something getting ingested in the gearset will bend the shaft and break the case. And yes, needle bearings are very hard.
 
3rd gear tends to live a hard life in these transaxles.. Nee 110whp digested 4th gear at LeMons about a decade ago. Parts endure a LOT more stress during endurance races then they would ever see in club racing, track days to similar...

"The X ran without incident until mid-afternoon when I got a call that the transaxle lost 4th gear. During the driver change and re-fuel, I had a look see at the transaxle linkage and all appeared well. The X still ran, so we sent the X back out on the track with the transaxle basically stuck in 3rd gear. The X ran on track for about 3 hours stuck in 3rd gear until the end of day one. Adding insult to injury, the engine developed a mis-fire at high RPM…

That was when the decision was made to try and find a spare transaxle locally with no success. So, I decided to drive back home and put together a spare transaxle and another transaxle of unknown condition (for parts if required) and bring it back for installation later that night. The drive home took about an hour and a half. Once we got home, I dug out the spare, opened it up and made it right. When this was done, we looked and looked for the box of spare ignition parts.. an hour passed and that box of parts were not where to be found. I did find a spare dizzy and only a few other bits required which had to do for now.

We loaded everything in the SAAB, drove up to Sears Point and arrived just before 10:00 PM. The newly put together transaxle was unloaded from the SAAB where the rest of the crew began the installation process. "

~Putting together a transaxle in about 2 hours from random parts at about 11pm at night was... interesting.~

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Note overall position before 3rd gear died..


Bernice
 
"That's a 3rd gear synchro explosion. Its what happens when you let the clutch out before the 3rd gear slider is fully engaged. The torque is transmitted through the 3rd gear synchro."

So does that mean that we should be patient when shifting up or down into 3rd?
 
~Putting together a transaxle in about 2 hours from random parts at about 11pm at night was... interesting.~

Bernice
That probably explain why I had a 3 speed transmission when I went to the Canadian AutoSlalom Championship in... 2000. I had to rebuild the transmission (my first) at the last minute without new parts. So I had 1-3-5 only. In another thread I probably explained what happened when I made a downshift from 5th on the highway but missed the 3rd... and end-up in 1st at 60 mph... :mad:
 
In another thread I probably explained what happened when I made a downshift from 5th on the highway but missed the 3rd... and end-up in 1st at 60 mph.
Going a little off topic here, but you just made me think of a event way back in high school during our drivers education training. The local VW dealer had donated Bugs for the actual driving training so we learned with a manual trans. It was the instructor and three students in each car and the students rotated to practice driving around town. In our car one student had a lot of difficulty with the concept of shifting and at one point she managed to force the trans from third into REVERSE while doing about 45 MPH! A huge grinding, followed by a big crunch, then she let the clutch out and the car suddenly stopped going forward (until the instructor grabbed the stick and popped it back into neutral). Surprisingly the trans still worked fine....just another example of excellent German engineering and quality. :)
 
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