Alright folks, here it is...
This applies to all of you with what I believe is the 2002MY Getrag M86/M94 and later as well as some 2001 and earlier transmissions especially those which have had the TSB fix for gear rattle in 1st and 2nd gear following the Saturn overfill TSB#02-07-29-001
TSB information as per GM Doc ID #1337141
GM produced a TSB for Gear rattle in first and second gears on the M86/M94 manual transmissions in early 2002 with the fix for one particular noise of overfilling with a different lubricant. This was described as a gear rattle in first or second gear that could be exacerbated by making a sharp left turn and eliminated by shifting to 3rd gear or making a sharp right turn. This did not fix complaints for some units and GM revised this in early 2003 with another bulletin to fix the rattle noise. This TSB instructed technicians that if the vehicle was to be repaired there needed to be an additional thrust load on 1st and 2nd gears. They accomplished this by installing a wave washer between the blocking rings and the speed gears for
3rd and 4th gear This through the gear set layout fixed the rattle issue however I believe in mid to higher mileage units, has caused another problem far worse than noise.
To understand the issue, for those who do not understand the concept of synchronizers and how they work, you need to see what I'm referring to.
In this example we will use the gear towards the left of the photo, Part number 5.
Observations
Observe, Gear number
5 has two parts, a cone assembly that is machined as part of the gear (part number
6), and the dog teeth that are also cast as part of the gear. In between the gear and the synchronizer assembly (part number
1) is a blocking ring (part number
7). Many refer to these as synchronizers, the correct term is blocking ring. The synchronizer is the hub assembly and is part number 1 in this photo. Try to keep that straight in your head.
Moving on, the action of the synchronizer assembly (
1) and blocking ring (
7) is to bring the shafts that the gears are mated to up to speed as you move the transmission into gear. This is extremely important and is the reason that it is so easy to drive a synchronized gear box as opposed to a non synchronized box.
So with that, the tough part.
The cone on the speed gear, in this case (
5) is a direct mate to the internal cone that is cut into the inside diameter of the blocking ring (
7) This allows the blocking ring (
7) to actually act upon the speed gear (
5) and shaft when the cones mesh. There is a relative large amount of friction at work here and if you have ever held a blocking ring and mating speed gear in your hands you will see what I'm talking about.
Shifting
When you go to shift gears, the transmission is not "in gear" until the synchronizer assembly (
1) has slid all the way over on the shaft and interlocked with the dog teeth on the speed gear (
5). If we did not have blocking rings (
7), when the synchronizer (
1) slid over, it and the speed gear (
5) would be moving at such a different RPM that the dog teeth on the speed gear (
5) would mash and grind until the RPM was matched, at which point the synchronizer hub (
1) would finally interlock and go into gear. Instead, the synchronizer assembly (
1) has pointed teeth protruding from it facing the dog teeth on the speed gear (
5) These teeth are very important since they correspond with a similar pattern cut into the front of the dog teeth on the blocking ring (
7). When the synchronizer (
1) slides over, it pushes the blocking ring (
7) with it in a sort of slipping motion across the face of the teeth. Study the synchronizer ring from the Getrag on the input shaft to better understand this concept.
The triangular pointed teeth I'm referring to are at the edge of the synchronizer, barely visible and are good size, cut at about a 45 degree angle. <
When the synchronizer assembly moves towards the blocking ring (
7) it forces the ring against the mating cone of the speed gear, thereby bringing the shaft up to or down to the speed of the gear, and allowing the dog teeth on the gear to mesh properly with the synchronizer assembly without grinding.
Now that we have that out of the way, if your still lost, there are videos online that demonstrate this... Its really much easier to understand if you can hold it in your hand but this is the best I can do.
Now, back to our TSB...
GM's fix was to install wave washers between the blocking rings and the speed gears, remember? Here is my 2002 MY Getrag M94 input shaft again, confirming that MY2002 + M94 and M86 units already began to come with these wave springs installed from the factory.
You can barely make them out, being wavy, in between the rings and the speed gears of third and fourth.
I believe this is the cause of our third and fourth gear blocking rings going out, and subsequently causing our issues with 3rd and 4th gear grinding on mid to low mileage getrags.
My Diagnosis
Basically from having it on the bench and rebuilding it with a bearing kit only at my junior college when I first got the transmission I determined all the blocking rings were fine and need not be replaced. I reassembled it and it went in just recently as part of my conversion... With the wheels off the ground, or on the ground going into 3rd and 4th it would grind, pretty horribly. Drove like this for a week and pulled it out the very next weekend to go after this issue. In fiddling with the shaft on the bench I found the wave washers between the blocking rings and speed gears are so heavy they do not allow the blocking rings to engage the cone of the speed gear enough to actually bring it up or slow it down to the proper speed. This basically eliminates synchronizer action and causes the grinding issue.
My fix
Ditch the wave washers... I pulled them out, and after inspecting the blocking rings on 3rd and 4th decided it would be a safe bet to replace those as well as they had taken a beating in the short week I drove the vehicle. Threw the trans back in, started it up, and voila!, No more gear grind.
I have since been driving on this fix for over four weeks, the wave washers are sitting in my tool box and the trans shifts smooth as butter. No noticeable gear rattle either, so obviously it is light enough to be drowned out by an exhaust... Either way, its in no way detrimental to the unit and really is not annoying whatsoever. A manual trans is going to make noise, it is the nature of the beast.
The culpret
The old blocking ring...
Hope this helps some of you who are tired of going through getrags like Candy, this is a good transmission, just needs some love.
Peace!
Alex
Buildin' n' Boostin for 08' - Alex Richards
