wrp
02-26-2008, 10:17
Fixing broken things has given me an opportunity to study a lot of the subsystems that comprise our cars. In particular, the T56 transmission is an interesting piece of gear. I've watched shifter wars rant and rave over the past few years. I wanted to take a moment to share some of the things I have learned about the shift guide plate on the T56 and how it relates to the shifting rods/forks and the shifter. I don't claim to be an expert and welcome criticism or corrections.
Of course you are aware that the shifter itself has an arm or shaft that has a ball shaped end and fits down into a receptacle in the transmission. It doesn't take a lot of deduction to understand that movement of the shift lever moves the shaft and the mechanism that the ball is sticking into is then forced to move in essentially the opposite direction and that motion is what results in the transmission shifting.
http://img2.putfile.com/thumb/2/5622251266.jpg (http://www.putfile.com/pic/7746462)
The shaft sits in a cup that is attached to the shift rail which pivots as the lever is manipulated. http://img2.putfile.com/thumb/2/5318113451.jpg (http://www.putfile.com/pic/7727435)
The rear of the shift rail where the shifter shaft connects is in the transmissioin extension housing while the shift guide mechanism is actually in the transmission housing.
http://img2.putfile.com/thumb/2/5318113361.jpg (http://www.putfile.com/pic/7727425)
In the illustration, the shift guide plate is the piece with the shift pattern tracks and holes in it. You are looking at the rear top portion of the transmission housing.
http://img2.putfile.com/thumb/2/5318113357.jpg (http://www.putfile.com/pic/7727427)
If you look really close at the shift guide plate you can notice a couple of things. The shift pattern is exactly opposite of the way it would look on a hurst shift ball. Also, there are a series of round indents forward of the shift tracks and they correspond to the shifter position in each gear and reverse. Note in the middle between the two indented rows that there is a slot that goes from side to side but there is also a centering hole/indent.
http://img2.putfile.com/thumb/2/5318113451.jpg (http://www.putfile.com/pic/7727435)
The shift rail that the cup the shifter shaft is inserted into runs forward into the main casing so that it can engage the shifting forks.
The Front Offset Lever is the larger piece in the photgraph and it slides onto the shift rail. The ball detent and sppring are fitted into a slot in the Front Offset Lever and they fit into the shift guide plate. looking at the bottom of the Front Offset Lever you can see where the ball sticks down into the shift guide plate detent holes and the little tit on the back fits into the shift pattern tracks of the shift guide plate. When the shifting mechanism reaches an appropriate gear, the tit guides it there along the track. The detent ball clicks out of the hole being left and snaps down into the hole corresponding to the gear the shifter was positioned at. The race in the middle is why when in neutral the shifter handle rockes back and forth left and right but centers when released.
http://img2.putfile.com/thumb/2/5318113351.jpg (http://www.putfile.com/pic/7727429)
I just thought it would be interesting to consider this. The question it brings up is, what does the shifter really add? If the shifter itself positions the shift rail and overrides this guide plate is it forcing the shift rail to positions that cause internal damage to forks and synchronizers? Conversely if the shift just takes up the normal slack that exists in this assembly, what are the effects in the long term on the shift rail, forks and shifting fork pads?
No real answers here, just a look at what I see and some thoughts on how it works.
Of course you are aware that the shifter itself has an arm or shaft that has a ball shaped end and fits down into a receptacle in the transmission. It doesn't take a lot of deduction to understand that movement of the shift lever moves the shaft and the mechanism that the ball is sticking into is then forced to move in essentially the opposite direction and that motion is what results in the transmission shifting.
http://img2.putfile.com/thumb/2/5622251266.jpg (http://www.putfile.com/pic/7746462)
The shaft sits in a cup that is attached to the shift rail which pivots as the lever is manipulated. http://img2.putfile.com/thumb/2/5318113451.jpg (http://www.putfile.com/pic/7727435)
The rear of the shift rail where the shifter shaft connects is in the transmissioin extension housing while the shift guide mechanism is actually in the transmission housing.
http://img2.putfile.com/thumb/2/5318113361.jpg (http://www.putfile.com/pic/7727425)
In the illustration, the shift guide plate is the piece with the shift pattern tracks and holes in it. You are looking at the rear top portion of the transmission housing.
http://img2.putfile.com/thumb/2/5318113357.jpg (http://www.putfile.com/pic/7727427)
If you look really close at the shift guide plate you can notice a couple of things. The shift pattern is exactly opposite of the way it would look on a hurst shift ball. Also, there are a series of round indents forward of the shift tracks and they correspond to the shifter position in each gear and reverse. Note in the middle between the two indented rows that there is a slot that goes from side to side but there is also a centering hole/indent.
http://img2.putfile.com/thumb/2/5318113451.jpg (http://www.putfile.com/pic/7727435)
The shift rail that the cup the shifter shaft is inserted into runs forward into the main casing so that it can engage the shifting forks.
The Front Offset Lever is the larger piece in the photgraph and it slides onto the shift rail. The ball detent and sppring are fitted into a slot in the Front Offset Lever and they fit into the shift guide plate. looking at the bottom of the Front Offset Lever you can see where the ball sticks down into the shift guide plate detent holes and the little tit on the back fits into the shift pattern tracks of the shift guide plate. When the shifting mechanism reaches an appropriate gear, the tit guides it there along the track. The detent ball clicks out of the hole being left and snaps down into the hole corresponding to the gear the shifter was positioned at. The race in the middle is why when in neutral the shifter handle rockes back and forth left and right but centers when released.
http://img2.putfile.com/thumb/2/5318113351.jpg (http://www.putfile.com/pic/7727429)
I just thought it would be interesting to consider this. The question it brings up is, what does the shifter really add? If the shifter itself positions the shift rail and overrides this guide plate is it forcing the shift rail to positions that cause internal damage to forks and synchronizers? Conversely if the shift just takes up the normal slack that exists in this assembly, what are the effects in the long term on the shift rail, forks and shifting fork pads?
No real answers here, just a look at what I see and some thoughts on how it works.