A G52 Journey
09-21-2014, 08:48 PM
#1
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A G52 Journey
As seen through the eyes of a guy who has just rebuilt his first standard transmission, here are some things I learned:
1: I never really understood how the gears worked or transmitted power until I took one apart. It was only after disassembling one that the Youtube videos made sense to me.
The gears on the output shaft are DRIVEN gears. The gears on the counter shaft do the driving. The only exception is when the input shaft gear, 4th on my G52, is set up so that when it is engaged it bypasses the counter shaft and transmits power directly to the output shaft.
Power is transmitted from the input shaft and it's gear directly into the counter shaft. The gears on the output shaft ride on needle bearings that lie between those gears and the shaft. They simply slip as the counter shaft gears rotate against them. Although the output shaft gears are all driven all the time by the solidly affixed and constantly driving counter shaft gears, they slip as the output shaft rotates underneath them. They only transmit power to the output shaft when they are "grabbed" and held by a device that is attached to the output shaft. That device is the slider. It is splined to a "hub" which is affixed to the output shaft. Because the hub is affixed to the shaft, the hub rotates with the output shaft whenever the output shaft rotates. On the outer surface of the hub is a set of splines. The slider is splined onto these, and rotates with the hub, but the spline fit here is loose so the slider can slide forward or backward on the hub.
While the output shaft gears can transmit power, they only do so when they are engaged, and the fact that they are meshing and spinning with the counter shaft gears means nothing in terms of them delivering power to the output shaft. Remember, the output shaft gears are slipping on needle bearings as the output shaft rotates underneath them, so to whatever extent the output shaft gears are meshed with and spun by the counter shaft gears, they still aren't transmitting any power to the output shaft until they are "engaged".
This is where the slider comes in. On one side of each output gear is a different set of teeth. They are short compared to the helical cut teeth, and they face the slider. They are shaped and sized to slip into the same splines the slider engages the hub with. When a gear is "engaged", the slider, which is mechanically tied to the output shaft via the hub, slides on to, and meshes with those small teeth, with the help of the synchro to get the two gears moving at the same speed. The slider slides over and "grabs" and holds those small teeth while remaining locked into the hub splines. It is wide enough to slide over the output gear engagement teeth and still be engaged with the hub. The engagement teeth are small, but they are plenty strong enough to carry the rotating force of the carrier shaft gear and it's output shaft gear and transmit that power into the slider, so that it can in turn carry that rotating force into the hub and into the output shaft.
The slider works on a kind of over-center principle where it is either fully engaged or fully disengaged. Once the slider has grabbed, or engaged those teeth, that gear becomes mechanically locked to the slider and thus to the output shaft through the hub, and is now not only driven by it's counter shaft gear, but begins delivering power to the output shaft through the slider and hub.
You can see this action at work when you have the tranny apart. With no gear engaged (neutral) you can hold either the input or output shaft and turn the other end by hand. Engage any gear by pushing a fork or slider (careful, pushing by hand it is possible to push the slider too far and end up popping the "dogs" out) and instantly both input and output shafts will be locked together through the slider and hub of whichever gear you have engaged.
Any time no gear has been selected to deliver power to the output shaft the transmission is in neutral. In neutral, power is being delivered to the counter shaft but none is being delivered through any slider and hub to the output shaft. Understanding the engagement teeth on the side of the output shaft gears, and how the slider and hub and synchro works to engage those teeth on that gear, and deliver that gear's power to the output shaft, and how the slider disengages from the gear as neutral or another gear is chosen, is the key to understanding how a manual transmission works, and what you are seeing when you disassemble one.
2: Gears are set in "clusters" on the output shaft. Each cluster consists of a hub attached to the shaft, a slider which rides on splines on the surface of the hub, two gears, typically in numerical order (one and two, or three and four) and a fork which rides in a groove or spline on the slider and pushes or pulls it into position via a shift shaft. Each gear section needs it's own shoulders to locate that section on the shaft, and to rotate within. Because there can only be one permanent shoulder built into the shaft, because there would be no way to install the gears, bearings and hubs between two permanent shoulders, there has to be a way to create removable shoulders to separate the groups. These are the shoulders that intersect with a check ball on the shaft. The shoulder can be removed after the check ball comes out, the gears and hub removed or installed on that section of shaft, and then the shoulder slid down the shaft to divide two clusters. The check ball is to keep the shoulder from spinning on the shaft. The gears spin and ride within the shoulders and the ball keeps the shoulders stationary on the shaft.
3: The first gear fork and slider take a beating. They need to be thoroughly checked during any examination of the transmission. Because we typically push the shifter toward the first gear position as we approach any stop or near stop situation, the first gear fork spends more time rubbing against it's slider than any other gear, by far. For this reason the first gear slider and fork should be carefully examined for wear.
When I began this rebuild I was still pretty lost about how it all worked. I knew what my symptom was, and kinda sorta how the tranny worked. A little. Not really.
My symptom was first gear popping out or failing to engage. When I got my cases off I could clearly see a big chunk of the first gear slider engagement teeth missing. OK I thought, there's the problem. When one side of the fork is lined up with those missing teeth (and fork ring) the fork flexes and the slider doesn't move far enough to engage. All my clearances were on the tight side. Thank you Sta-Lube. I took a look at the forks, but in my ignorance, and getting little help from the FM as to what to look for, I failed to understand that the first gear fork wasn't merely worn out, it was wiped out.
So, after installing a new 1-2 slider, I put it all back together and reinstalled the tranny, which worked fine, except that it still kicked out/failed to engage first gear. Man that was disheartening.
I'm a master electrician specializing is service work, so I do a lot of diagnose and repair. Sometimes when troubleshooting you discover that something at a certain point in the circuit is doing thus-and-so, except it can't be because you already verified the condition of that circuit upstream of the anomaly. When that happens you have to accept that something in the circuit has changed, and back up to a point where you believe the circuit is OK, and begin carefully diagnosing forward again. That's the pattern I followed here.
I asked myself if the problem could have been external all along. In keeping with that thought I replaced all the shifter parts with Marlin Crawler parts. Well, that definitely tightened up the shifter, but had zero impact on the first gear issue. So now I had to accept that I had missed something in there, something right in front of my face. Applying logic, the most likely suspect was the 1-2 fork I didn't replace. I ordered a new fork, and when it arrived it was obvious it had meat in places my old fork didn't have places. I pulled the tranny back out, pulled off the cases, and pulled all the shift shafts and check pins/balls out and replaced the fork. It was obvious the old fork was utterly wiped out. How that transmission continued to function right up until the end still amazes me. A year ago that transmission brought me back to east county San Diego from Oregon, down 395, over multiple mountain ranges above seven thousand feet, pulling an extremely heavy trailer, and never missed a beat. Thank you Toyota.
I reinstalled all the shift shafts and pins/balls and put everything back together, then put the transmission back in the truck. Reinstalled the Sta-Lube GL4. (Get it from Amazon) The rear wheels were off the ground so I started the engine and gingerly ran up through the gears. Tight and smooth and none of the shifter handle movement it had before when it wasn't forced in. I took it off the jack stands, loaded up the dogs, and took it for a drive. It was as good as I could have hoped for. Tight and smooth, every gear snicking in and holding perfectly. I am having to learn to drive it with a first gear that remains engaged again.
What an amazing learning experience. When I began I didn't know a slider from a fork. Now I can converse intelligently about standard transmissions, and I could probably do the entire job without the manual. Like so many things it just isn't that difficult once you understand the concept. The details seem to become obvious. For me it was the time between when when I discovered I still had my problem and when I disassembled it again everything seemed to click. By the time I was in there again I was working from the standpoint of getting it instead of just hoping I got it back together correctly.
I hope my experience and observations here are of some use to anyone who is contemplating rebuilding a G-52. Check your clearances and carefully inspect your parts, then put it back together. I used a kit that had new brass synchros and the same brand bearings that came out of it.
Special tools: Don't even think of doing this without a hydraulic press. I bought a bearing splitter from Amazon made by OTC. It was invaluable. Mine is like 1/2" to 3 1/2" or so. Very much worth the investment. You will need a pencil type magnet to remove/install check balls, pins and springs. Use the barrel of a Sharpie to place forward and upward force on pins and balls while you manipulate the shift shaft until the ball/pin jumps into place. It is the perfect size and shape for this tricky job. TAKE LOTS OF PICTURES AT EVERY STEP, FROM EVERY ANGLE.
1: I never really understood how the gears worked or transmitted power until I took one apart. It was only after disassembling one that the Youtube videos made sense to me.
The gears on the output shaft are DRIVEN gears. The gears on the counter shaft do the driving. The only exception is when the input shaft gear, 4th on my G52, is set up so that when it is engaged it bypasses the counter shaft and transmits power directly to the output shaft.
Power is transmitted from the input shaft and it's gear directly into the counter shaft. The gears on the output shaft ride on needle bearings that lie between those gears and the shaft. They simply slip as the counter shaft gears rotate against them. Although the output shaft gears are all driven all the time by the solidly affixed and constantly driving counter shaft gears, they slip as the output shaft rotates underneath them. They only transmit power to the output shaft when they are "grabbed" and held by a device that is attached to the output shaft. That device is the slider. It is splined to a "hub" which is affixed to the output shaft. Because the hub is affixed to the shaft, the hub rotates with the output shaft whenever the output shaft rotates. On the outer surface of the hub is a set of splines. The slider is splined onto these, and rotates with the hub, but the spline fit here is loose so the slider can slide forward or backward on the hub.
While the output shaft gears can transmit power, they only do so when they are engaged, and the fact that they are meshing and spinning with the counter shaft gears means nothing in terms of them delivering power to the output shaft. Remember, the output shaft gears are slipping on needle bearings as the output shaft rotates underneath them, so to whatever extent the output shaft gears are meshed with and spun by the counter shaft gears, they still aren't transmitting any power to the output shaft until they are "engaged".
This is where the slider comes in. On one side of each output gear is a different set of teeth. They are short compared to the helical cut teeth, and they face the slider. They are shaped and sized to slip into the same splines the slider engages the hub with. When a gear is "engaged", the slider, which is mechanically tied to the output shaft via the hub, slides on to, and meshes with those small teeth, with the help of the synchro to get the two gears moving at the same speed. The slider slides over and "grabs" and holds those small teeth while remaining locked into the hub splines. It is wide enough to slide over the output gear engagement teeth and still be engaged with the hub. The engagement teeth are small, but they are plenty strong enough to carry the rotating force of the carrier shaft gear and it's output shaft gear and transmit that power into the slider, so that it can in turn carry that rotating force into the hub and into the output shaft.
The slider works on a kind of over-center principle where it is either fully engaged or fully disengaged. Once the slider has grabbed, or engaged those teeth, that gear becomes mechanically locked to the slider and thus to the output shaft through the hub, and is now not only driven by it's counter shaft gear, but begins delivering power to the output shaft through the slider and hub.
You can see this action at work when you have the tranny apart. With no gear engaged (neutral) you can hold either the input or output shaft and turn the other end by hand. Engage any gear by pushing a fork or slider (careful, pushing by hand it is possible to push the slider too far and end up popping the "dogs" out) and instantly both input and output shafts will be locked together through the slider and hub of whichever gear you have engaged.
Any time no gear has been selected to deliver power to the output shaft the transmission is in neutral. In neutral, power is being delivered to the counter shaft but none is being delivered through any slider and hub to the output shaft. Understanding the engagement teeth on the side of the output shaft gears, and how the slider and hub and synchro works to engage those teeth on that gear, and deliver that gear's power to the output shaft, and how the slider disengages from the gear as neutral or another gear is chosen, is the key to understanding how a manual transmission works, and what you are seeing when you disassemble one.
2: Gears are set in "clusters" on the output shaft. Each cluster consists of a hub attached to the shaft, a slider which rides on splines on the surface of the hub, two gears, typically in numerical order (one and two, or three and four) and a fork which rides in a groove or spline on the slider and pushes or pulls it into position via a shift shaft. Each gear section needs it's own shoulders to locate that section on the shaft, and to rotate within. Because there can only be one permanent shoulder built into the shaft, because there would be no way to install the gears, bearings and hubs between two permanent shoulders, there has to be a way to create removable shoulders to separate the groups. These are the shoulders that intersect with a check ball on the shaft. The shoulder can be removed after the check ball comes out, the gears and hub removed or installed on that section of shaft, and then the shoulder slid down the shaft to divide two clusters. The check ball is to keep the shoulder from spinning on the shaft. The gears spin and ride within the shoulders and the ball keeps the shoulders stationary on the shaft.
3: The first gear fork and slider take a beating. They need to be thoroughly checked during any examination of the transmission. Because we typically push the shifter toward the first gear position as we approach any stop or near stop situation, the first gear fork spends more time rubbing against it's slider than any other gear, by far. For this reason the first gear slider and fork should be carefully examined for wear.
When I began this rebuild I was still pretty lost about how it all worked. I knew what my symptom was, and kinda sorta how the tranny worked. A little. Not really.
My symptom was first gear popping out or failing to engage. When I got my cases off I could clearly see a big chunk of the first gear slider engagement teeth missing. OK I thought, there's the problem. When one side of the fork is lined up with those missing teeth (and fork ring) the fork flexes and the slider doesn't move far enough to engage. All my clearances were on the tight side. Thank you Sta-Lube. I took a look at the forks, but in my ignorance, and getting little help from the FM as to what to look for, I failed to understand that the first gear fork wasn't merely worn out, it was wiped out.
So, after installing a new 1-2 slider, I put it all back together and reinstalled the tranny, which worked fine, except that it still kicked out/failed to engage first gear. Man that was disheartening.
I'm a master electrician specializing is service work, so I do a lot of diagnose and repair. Sometimes when troubleshooting you discover that something at a certain point in the circuit is doing thus-and-so, except it can't be because you already verified the condition of that circuit upstream of the anomaly. When that happens you have to accept that something in the circuit has changed, and back up to a point where you believe the circuit is OK, and begin carefully diagnosing forward again. That's the pattern I followed here.
I asked myself if the problem could have been external all along. In keeping with that thought I replaced all the shifter parts with Marlin Crawler parts. Well, that definitely tightened up the shifter, but had zero impact on the first gear issue. So now I had to accept that I had missed something in there, something right in front of my face. Applying logic, the most likely suspect was the 1-2 fork I didn't replace. I ordered a new fork, and when it arrived it was obvious it had meat in places my old fork didn't have places. I pulled the tranny back out, pulled off the cases, and pulled all the shift shafts and check pins/balls out and replaced the fork. It was obvious the old fork was utterly wiped out. How that transmission continued to function right up until the end still amazes me. A year ago that transmission brought me back to east county San Diego from Oregon, down 395, over multiple mountain ranges above seven thousand feet, pulling an extremely heavy trailer, and never missed a beat. Thank you Toyota.
I reinstalled all the shift shafts and pins/balls and put everything back together, then put the transmission back in the truck. Reinstalled the Sta-Lube GL4. (Get it from Amazon) The rear wheels were off the ground so I started the engine and gingerly ran up through the gears. Tight and smooth and none of the shifter handle movement it had before when it wasn't forced in. I took it off the jack stands, loaded up the dogs, and took it for a drive. It was as good as I could have hoped for. Tight and smooth, every gear snicking in and holding perfectly. I am having to learn to drive it with a first gear that remains engaged again.
What an amazing learning experience. When I began I didn't know a slider from a fork. Now I can converse intelligently about standard transmissions, and I could probably do the entire job without the manual. Like so many things it just isn't that difficult once you understand the concept. The details seem to become obvious. For me it was the time between when when I discovered I still had my problem and when I disassembled it again everything seemed to click. By the time I was in there again I was working from the standpoint of getting it instead of just hoping I got it back together correctly.
I hope my experience and observations here are of some use to anyone who is contemplating rebuilding a G-52. Check your clearances and carefully inspect your parts, then put it back together. I used a kit that had new brass synchros and the same brand bearings that came out of it.
Special tools: Don't even think of doing this without a hydraulic press. I bought a bearing splitter from Amazon made by OTC. It was invaluable. Mine is like 1/2" to 3 1/2" or so. Very much worth the investment. You will need a pencil type magnet to remove/install check balls, pins and springs. Use the barrel of a Sharpie to place forward and upward force on pins and balls while you manipulate the shift shaft until the ball/pin jumps into place. It is the perfect size and shape for this tricky job. TAKE LOTS OF PICTURES AT EVERY STEP, FROM EVERY ANGLE.
Last edited by wireguy; 09-22-2014 at 07:47 AM. Reason: add pictures
09-22-2014, 06:30 AM
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Those would be nice to see (get a free hosting account, like at PhotoBucket).
Your description is excellent, but all-words are hard to get started with.
might help people get oriented to your version (you may have seen even better ones.)
Your description is excellent, but all-words are hard to get started with.
09-22-2014, 02:03 PM
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Great journey. I too am still a little intimidated by manual transmissions but after replacing the front bearing on one and seeing it tore apart really does help one to understand how and what needs to do to repair one. Great to hear it is running great for you and was probably a great experince looking back for you. Great job!!!
10-01-2014, 06:53 AM
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Here are pictures of the old fork. On one side you can see the remainder of the pads. That's the second gear side. On the first gear side you can see the fork is worn completely to the center line. It is effectively gone.
Again, a year ago this transmission brought me home from Oregon, from the Rogue valley across the mountains and down 395, across numerous passes above 7 or 8 thousand feet, while pulling an extremely heavy trailer, and one would never have known the 1-2 slider was broken and the 1-2 fork simply no longer there. That fork continued to do it's job until there was nothing left.
Again, a year ago this transmission brought me home from Oregon, from the Rogue valley across the mountains and down 395, across numerous passes above 7 or 8 thousand feet, while pulling an extremely heavy trailer, and one would never have known the 1-2 slider was broken and the 1-2 fork simply no longer there. That fork continued to do it's job until there was nothing left.
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10-01-2014, 07:13 AM
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Yup - ALWAYS a good thing to do when wrenching.
Helps thought process, helps others, helps re-sale, etc., ...
My photo-doc vette threads are over 100K hits...
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Helps thought process, helps others, helps re-sale, etc., ...
My photo-doc vette threads are over 100K hits...
Top End Cleanup from A - Z
Delco-Bose Gold Front Panel MP3 Aux Input
Headers / Exhaust Installation w/snappics
DataMaster; Sync'ing w/ ECM
C4 Headlight Repair
Headliner, Glasstop Screen; Repair, Custom Logo Installation
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