Getrag Transmission Fun.

[ScottAndrews]

There is another thread asking about noise in the Getrag 265. I was curious about exactly how that trans worked. There were no good diagrams, so, decided to make one. This is based of a sectional view posted some time ago by @Devinder. I added the colors to highlight the various parts.

Here is the transmission in Neutral:
The input shaft on the left is light pink. The output shaft is purple./blue. The bearings are light blue. Some are rollers, so they are hard to see. The lay-shaft is orange, the shift clutches and syncros are maroon, and the gears are various colors. The gear faces that engage the lay shaft are shown in reddish orange.

The input shaft is connected by its gear directly to the lay shaft. So the lay shaft always turns when the input shaft is turning, and all of the colored gears are also turning, because they re meshed with the lay-shaft. This is what is known as a constant mesh gearbox, because the driving gears do not actually ever not mesh. This means that all of the colored gears are spinning all the time at different rates when the input shaft is turning (note all of them are separated from the output shaft by roller bearings (light blue), and this is why this whole thing works. Shifting is a process of selectively connecting the gears with the output shaft.

Here is the trans in 1st gear. the aft shift fork has moved the aft dog clutch to the left (yellow arrows). This connects the 1st gear to the output shaft, and thus the torque comes in the input shaft, goes to the lay-shaft, and then gets to the output shaft via the first gear.

Here is the trans in 2nd gear. The middle shift fork has moved the middle dog clutch to the right (yellow arrows). This connects the 2nd gear to the output shaft, and thus the torque comes in the input shaft, goes to the lay-shaft, and then gets to the output shaft via the 2nd gear.

Here is the trans in 3rd gear. The middle shift fork has moved the middle dog clutch to the left (yellow arrows). This connects the 3rd gear to the output shaft, and thus the torque comes in the input shaft, goes to the lay-shaft, and then gets to the output shaft via the 3rd gear.

Here is the trans in 4th gear. The forward shift fork has moved the forward dog clutch to the left (yellow arrows). This connects the input shaft to the output shaft to create a 1:1 ratio. Thus the torque comes in the input shaft and goes directly to the output shaft. In this gear the lay-shaft is turning, but it is carrying no load, because none of the gears it engages are connected to the output shaft.

Here is the trans in 5th gear. The forward shift fork has moved the forward dog clutch aft (yellow arrows). This connects the 5th gear to the output shaft, and thus the torque comes in the input shaft, goes to the lay-shaft, and then gets to the output shaft via the 5th gear.

And lastly, here is the trans in reverse. The aft shift fork has moved the aft dog clutch to the right (yellow arrows). This connects the reverse gear to the output shaft. There is a secondary lay shaft (not shown in the diagram) that connects the lay shaft to the reverse gear, and thus the torque comes in the input shaft, goes to the lay-shaft, goes to another lay shaft (thereby reversing direction), and then gets connected to the output shaft via the reverse gear.

I think this is all correct, but if I have misunderstood then please let me know,.

 

[Arde]

Nice drawing and description. Let's now derive a noise throubleshooting guide based on that.
There are 4 bearings to consider, let's designate them UL, UR, LL, and LR based on their location in the diagram Ignoring their real names for now).

1) Transmission is in neutral, car idles, no motion, clutch pedal depressed: No bearings can be making any noise because none should be spinning.
2) Transmission is in neutral, car idles, car rolling forward, clutch pedal depressed: The only bearing that moves is UR, if we hear noise that one is bad. No noise means UR is good.
3) Transmission is in neutral, car idles, no motion, clutch pedal released: UL, LL, LR are spinning but UR is not. Bearing noise can be any of the three. Noise should be proportional to RPM.
4) Transmission is in forward gear, car idles, car rolling forward, clutch pedal depressed: All bearings should spin and any noise should be proportional to road speed and independent of engine RPM.
5) Transmission is in gear, car accelerated, clutch pedal released: All bearings are spinning, UL, LL, LR proportional to RPM, UR proportional to road speed.

Based on the above it is hard to know which of the UL, LL, LR is noisy unless the load is a factor.

 

[Thomas76]

The most complex color by number I've ever seen, thanks for sharing your project!

 

[ScottAndrews]

Nice drawing and description. Let's now derive a noise throubleshooting guide based on that.
There are 4 bearings to consider, let's designate them UL, UR, LL, and LR based on their location in the diagram Ignoring their real names for now).

1) Transmission is in neutral, car idles, no motion, clutch pedal depressed: No bearings can be making any noise because none should be spinning.
2) Transmission is in neutral, car idles, car rolling forward, clutch pedal depressed: The only bearing that moves is UR, if we hear noise that one is bad. No noise means UR is good.
3) Transmission is in neutral, car idles, no motion, clutch pedal released: UL, LL, LR are spinning but UR is not. Bearing noise can be any of the three. Noise should be proportional to RPM.
4) Transmission is in forward gear, car idles, car rolling forward, clutch pedal depressed: All bearings should spin and any noise should be proportional to road speed and independent of engine RPM.
5) Transmission is in gear, car accelerated, clutch pedal released: All bearings are spinning, UL, LL, LR proportional to RPM, UR proportional to road speed.

Based on the above it is hard to know which of the UL, LL, LR is noisy unless the load is a factor.

Hi Ariel;
This is exactly why I did this! Good work!. I think load is a factor. Also, while I agree there are 4 ball bearings, there are also seven roller bearings (along the output shaft), although I doubt any of these would cause the noise. These would be under load depending on what gear was selected.

I general, in ANY gear, with the clutch pedal released, the lay shaft will be turning and under load. Every transmission I have rebuilt has had lay shaft issues (although none were as complex mechanically as the 265).

Scott

 

[starcruiser]

Great illustration!

 

[Arde]

I general, in ANY gear, with the clutch pedal released, the lay shaft will be turning and under load. Every transmission I have rebuilt has had lay shaft issues (although none were as complex mechanically as the 265).

Scott

Except that in 4th gear the layshaft carries no load, a 4th gear noise test has to be very useful for determining if the LL,LR bearings are noise or not, but not sure how.

Next topic would be to understand dog clutches, as smooth shifting is as important as as smooth gears...

 

[ScottAndrews]

Since we are exploring the 265 trans, I thought it might be useful to go into the actual shifting process. I assume many of you are already familiar with this, but I hope it might be instructive for those who find gear boxes somewhat mysterious.

Some background: I was semi-fortunate that my dad gave me a car for my 16th birthday. The unfortunate aspect of this was that it was a decrepit Morris Minor 1000 convertible. It belched smoke and 2nd gear was non-existent. So I spent the spring and summer of 1969 pulling and rebuilding the engine and trans. I drove that car all through highschool and part of college. Wish I still had it.. It was cute..

Anyway, rebuilding a transmission from only the exploded diagram causes you to learn a lot!!

You can see in the diagram below the colored gears (input shaft gear, green, yellow, magenta, brown, and pink) are positioned in pairs with a dark purple shifter between them. These gears are also always meshed with their corresponding gears on the lay shaft (also called a counter shaft, since it turns counter to the input shaft). Shift forks (darker green) fit into grooves on the shifters. You can see some actual shift forks in the photo above posted by @Thomas76. One of those is still engaged in its shifter (center left). These forks are actuated by the shift rods (shown uncolored at the top of the image below) so that they slide fore and after depending onthe position of the gear shift lever. The shifters slide on splines on the output shaft (indicated in red). The shift forks are interlocked by small balls that allow only one fork to move at a time (see added anecdote below for a good story!).

Between each shifter and each of its two adjacent gears is a dog clutch (shown in gold). There are six of these, one for each gear-shifter interface.

When a shift fork causes a shifter to slide toward a gear it first engages a conical mating surface (these are not really shown well in the diagram) - this is the synchro cone. This cone causes some friction between the shifter and the corresponding gear causing them to spin at more-or-less the same rotational speed. As the shifter slides into position, the shifter engages the dog clutch. The dog clutch has a large number of small teeth that mate with corresponding grooves in the shifter, thereby locking them together, so they spin at the same speed.

It is important to remember that the lay-shaft is driven by the input shaft gear, so it is always spinning when the input shaft is spinning. Since it is constantly meshed with each of the colored gears, and each pair of lay shaft gears and colored gears has some defined gear ratio, the colored gears are all spinning at different rotational speeds.

When the transmission is shifted "into gear", what is really happening is that a shifter is locking one of the spinning colored gears to the output shaft, thereby connecting the input and output shafts together through some rotational ratio determined by the specific combination of gears involved (in all cases other than 4th gear, via the lay-shaft).

So here are a few more detailed diagrams of the torque path in various gears:

I'll leave 2nd and 1st as exercises for the reader...

So for those who read this far. here is the anecdote: When I disassembled my Morris trans, I put all the parts in a big box, and then carefully figured out which parts went where when I re-assembled it. When I was done there was one part left in the box. A single small ball bearing ball. I did not recall any of the bearings themselves missing any balls, and this one was smaller than those anyway. I scoured the exploded diagram I had (which had been copied onto that horrible thermal copy paper we used back then...) to no avail. I finally decided that it must have been in the box from some other project. So I put the trans back in the car and hopped in to take it for a spin. I drove to the Sav-On drug store at the nearby shopping center to get a celebratory ice cream cone (this was pre-beer, of course!). That all went fine, but when I went to drive home, I shifted into first and headed off, shifted into second, and when I let out the clutch there was a horrible crunch and the car stopped. I called my mom from a pay phone (remember those?) who came down in the VW bus with a rope, and we towed the car home. Out came the trans, and I opened it up. My brand new lay-shaft was destroyed.. Apparently the ball was supposed to sit in a small detent between the two shift rods, so that when one was engaged, the ball prevented the other from moving, and vice versa. It was supposed to be removed and installed by removing a small bolt onthe side of thew housing. Apparently it had fallen out unseen when I pulled the shift rods out. Without the ball, the shift forks moved the shifters to engage both second gear and 4th gear, and when I let out the clutch something had to give.. My dad was kind enough to buy me a new lay shaft and I rebuilt the whole trans again.. That time it lasted for several years until I sold the car to buy an MG... So the moral here is never assume a left over part is not important!!

 

[ScottAndrews]

Except that in 4th gear the layshaft carries no load, a 4th gear noise test has to be very useful for determining if the LL,LR bearings are noise or not, but not sure how.

Next topic would be to understand dog clutches, as smooth shifting is as important as as smooth gears...

HAH!!! you read my mind!

As explained above, the shooting is performed by the dog clutches, but built into them are the synchros which get things rotating at the same speed , so the dog clutches don't grind when they mesh.

And yes, in 4th there is no load on the lay shaft.

 

[ScottAndrews]

Here's a photo of a typical dog clutch and synchro. You can see that the clutch dogs will engage the corresponding dogs on the other part while the synchro cone will get the two parts spinning at the same speed, so the dogs are not moving fast relative to one another.

 

[Thomas76]

@ScottAndrews let me know if you want more pics for illustration purposes, I still have a 265 completely torn apart.

 

[ScottAndrews]

@ScottAndrews let me know if you want more pics for illustration purposes, I still have a 265 completely torn apart.

OOOOHH! Interesting!

Yes, can you show a pic of a shifter, dog clutch and gear showing what they look like apart and how they mate together? I think that would be very instructive. Maybe the assembly on the right side of the image you posted.

Are you rebuilding the 265? If so, where did you find parts?

 

[stphers]

I don't have any tranny's apart in the shop right now but something else that would be helpful to people would be to show some worn out parts, specifically, where they wear and why There are 2 different kinds of synchro rings, one with serrated steps on the inside to help grab the next gear and ones that have a rough sandpaper type of feel to them, wear in the dog teeth on the gears, wear in the shifter sleeves and on the shift forks just a few things

Thanks, Rick

 

[ScottAndrews]

I don't have any tranny's apart in the shop right now but something else that would be helpful to people would be to show some worn out parts, specifically, where they wear and why There are 2 different kinds of synchro rings, one with serrated steps on the inside to help grab the next gear and ones that have a rough sandpaper type of feel to them, wear in the dog teeth on the gears, wear in the shifter sleeves and on the shift forks just a few things

Thanks, Rick

Yes, that would be great to see, if anyone has such pics! Thanks for the suggestion!

 

[eriknetherlands]

Great, great work.

Having an unknown condition 5spd under my workbench, I'd be interested to have some pics of (commonly) failed/worn parts, and their 'pass/fail' ctiteria.

This would be helpfull for anyone without Gertrag knowledge to be able to rip it open, check and correct what would be needed and reseal. Provided you have to guts to open it up and deal with all those gears...

 

[Arde]

... I'd be interested to have some pics of (commonly) failed/worn parts, and their 'pass/fail' ctiteria.

This would be helpfull for anyone without Gertrag knowledge to be able to rip it open, check and correct what would be needed and reseal.

The tree of Getrag knowledge is said to be in the midst of the Garden Of Eden, and the serpent says you can just go ahead and eat its fruit...

 

[Thomas76]

Pic of the synchro clutch material and the inner race it rides on.

 

[Thomas76]

OOOOHH! Interesting!

Yes, can you show a pic of a shifter, dog clutch and gear showing what they look like apart and how they mate together? I think that would be very instructive. Maybe the assembly on the right side of the image you posted.

Are you rebuilding the 265? If so, where did you find parts?

I am not ambitious enough to attempt a rebuild! I was given a bad trans to rob the shift rod. It was fun to take apart, now I have spare parts.

 

[ScottAndrews]

OK, Like I said in the title: Getrag Fun!!

I have been working 12 hour days for about 2 weeks on a patent trial in DC. Did these (the shifter post and this one) on the plane ride home. Needed to do SOMETHING different!!!

Here is an analysis of the gear ratios. I don't know exactly how many teeth are on each gear, but knowing the ratios of the 265/6 and 265/5 (CR), and looking at the relative gear sizes in the diagram, I worked out the analysis below. Here we have the output shaft rotational speed as a function of the input shaft rotational speed. Based on the actual published ratios for these two transmissions, we can at least work out the ratios of the number of teeth on each gear combination.

If someone has the gear teeth counts for the lay-shaft and the input shaft (@Thomas76 ??), we can work out the tooth counts for the rest of the gears.

I found it interesting to note that the CR trans has a 1:1 5th, which means that all of the gears in the 256/5 (CR) are larger than their corresponding lay shaft gears. In the 265/6 the 5th gear is smaller, and the other gears are larger. And, of course the shift pattern is different.

 

[ScottAndrews]

Thanks to @Thomas76 for posting the great photos of the innards of the trans.

The photo below really clarifies how the dog clutch works, which was not super clear in my colored drawing.

You will notice that the shifter (the thing with the circumferential groove) is actually two parts. The outer part engages the shift fork. This slides right or left on an inner part that has a set of short trapezoidal cut teeth. That part is splined to the output shaft. These teeth are the same size as those on the bronze piece, and the same as the teeth on the gear. In the photo, the gear on the left is not engaged. The gear on the right is engaged (because the shifter has slid over the bronze teeth and the teeth attached to the gear, locking all of them together.

Normally these pieces are all nestled up close to one another, with just a little space between them, so when the shifter is between the two gears both gears can rotate freely, independent of the shifter.

The bronze piece is the synchro. There is one on each side of the shifter. It has a conical surface inside that engages a mating surface on the inner part of the gear, and basically floats between the shifter and the gear.

When the shifter slides, it moves the synchro up against the gear synchro surface, causing the gear and the shifter speeds to match. This avoids a lot of gear crashing. As the shifter slides further over, it engages the dog teeth on the gear (which is now spinning at the same basic speed, and locks that gear to the shifter, which is locked to the output shaft, and the gear shift is complete. To shift to the other gear, the shifter moves the other way, disengages the dog teeth on one gear, and presses the synchro on the other side toward the other gear, and then eventually engages the dogs on that gear.

It is interesting to note that since all of the shifters in the trans are splined to the output shaft, they all turn at the output shaft speed. Since all of the gears are engaged with their corresponding gears on the lay shaft, they are all spinning at different speeds (some ratio times the input shaft speed (see my post above on this)). So we have lots of parts, all spinning at different speeds inside this box.

Remember, since the output shaft is connected to the differential, it is rotating at a speed determined by the speed of the car, and it is not going to change easily because of the momentum of the car. When the gears are changed, the main clutch between the engine and the input shaft is disengaged, so the synchros actually slow down or speed up the gear, which in turn slows down or speeds up the input shaft to match. Any difference between engine speed and input shaft speed is then addressed by the main clutch as the driver releases the clutch pedal. Presumably the engine speed has dropped a bit since the driver lets off the gas (in an up shift) or speeds up the engine (in a down shift), so everything sort of matches up and then you head off in the next gear.

 

[ScottAndrews]

The tree of Getrag knowledge is said to be in the midst of the Garden Of Eden, and the serpent says you can just go ahead and eat its fruit...

And then, for most to do so (i.e., cracking open their Getrag), the serpent bites them and they die a horrible crunchy death generally preceded by much whining!!