C5 T56 rebuild - 5th/6th Extension Shaft Details
11-02-2011, 09:48 AM
#1
Tech Contributor
Thread Starter
C5 T56 rebuild - 5th/6th Extension Shaft Details
My purpose for this thread is to provide detailed information for assembling the 5th/6th gear extension shaft for a Corvette C5 T56 transmission.
I just finished an overhaul of a M12 T56 transmission that will be swapped into my '99 FRC. My original MN6 lasted 236k miles, but the 4th gear synchronizer started acting up two months ago at a track day. After doing some research on the forums, I decided to tackle the transmission rebuild myself. A friend had a M12 core with a bad 5th gear synchro that he donated to my cause. My parts list included a C5 synchro ring kit (blocker rings, seals, c-clips; synchro keys, fork pads); a steel 3/4 shift fork; bronze fork pads; 3/4 synchro billet keys; 5/6 synchro assembly; and a new 5th gear. Total cost of new & upgrade parts was ~$1,000. Note, a base C5 T56 rebuild "kit" will be a minimum of $550, but I also had to replace the worn 5th gear parts and I upgraded to billet keys, bronze pads, and steel 3/4 fork.
Disassembly of the transmission went fairly smoothly by following the many well written articles on forums and using the Tremec T56 manual. I won't go into detail on the 1-4 main shaft and shift linkage since it is already well documented and similar between f-body and Corvettes. I found the shift rod a little tricky, but after a couple dry runs on assembling the case & aligning the 2 bolts it became a lot easier. Be sure to practice before you break out the gasket sealer.
My biggest challenge was to find information for the Corvette 5th/6th gear extension shaft assembly. The online Tremec manual doesn't show the extra spacers that are used in the Corvette's synchronizer. I wasn't able to find decent pictures, so I decided to add some to the forum in payment for all the help I have received.
Here are the parts that make up the 5th/6th gear extension shaft in a C5 Corvette T56:
These are the Corvette blocker rings - one set for 5th and one set for 6th:
Here is the 5th/6th synchronizer assembly. While you don't typically have to replace these hard parts, my transmission had a lot of wear on the "teeth" on the 5th gear side:
And this is the 5th/6th synchromizer hub with the 3 keys and one of the two springs that hold the keys on each side of the hub. The 1st/2nd synchro keys come from Tremec already solid but the 3/4 and 5/6 and reverse keys are stamped steel and can be a weak link. I upgraded my 3/4 keys to billet but didn't figure my 5/6 or reverse would need to be upgraded:
This picture shows the 2 sets of blocker rings used in the 5th/6th synchro. Notice the spacer for each set that looks like a star washer. These spacers are specific to the Corvette transmissions. Don't leave them out.
Assembly of the extension shaft starts with the 5th gear, followed by the synchronizer. The synchro hub will have to be pressed onto the splined shaft. I finally figured out that the synchro has to be pressed down far enough to hit a shoulder on the shaft. This picture shows how far the synchro should be pressed on:
And here is the extension shaft with the 5th gear, 5/6 synchro assembly , and the c-clip.
The remainder of the 5th/6th assembly is to slide the 6th gear on, add the shift fork, and slip it down into the transmission.
Thanks to all that went before me on this forum and took the time to add pictures and good information. Maybe this thread will in turn help someone else. In hindsight I'm glad I took the opportunity to build my own transmission. It took me a while, but it's a good learning experience, and will likely pay off in future "opportunities" on my car or friends cars.
I just finished an overhaul of a M12 T56 transmission that will be swapped into my '99 FRC. My original MN6 lasted 236k miles, but the 4th gear synchronizer started acting up two months ago at a track day. After doing some research on the forums, I decided to tackle the transmission rebuild myself. A friend had a M12 core with a bad 5th gear synchro that he donated to my cause. My parts list included a C5 synchro ring kit (blocker rings, seals, c-clips; synchro keys, fork pads); a steel 3/4 shift fork; bronze fork pads; 3/4 synchro billet keys; 5/6 synchro assembly; and a new 5th gear. Total cost of new & upgrade parts was ~$1,000. Note, a base C5 T56 rebuild "kit" will be a minimum of $550, but I also had to replace the worn 5th gear parts and I upgraded to billet keys, bronze pads, and steel 3/4 fork.
Disassembly of the transmission went fairly smoothly by following the many well written articles on forums and using the Tremec T56 manual. I won't go into detail on the 1-4 main shaft and shift linkage since it is already well documented and similar between f-body and Corvettes. I found the shift rod a little tricky, but after a couple dry runs on assembling the case & aligning the 2 bolts it became a lot easier. Be sure to practice before you break out the gasket sealer.
My biggest challenge was to find information for the Corvette 5th/6th gear extension shaft assembly. The online Tremec manual doesn't show the extra spacers that are used in the Corvette's synchronizer. I wasn't able to find decent pictures, so I decided to add some to the forum in payment for all the help I have received.
Here are the parts that make up the 5th/6th gear extension shaft in a C5 Corvette T56:
These are the Corvette blocker rings - one set for 5th and one set for 6th:
Here is the 5th/6th synchronizer assembly. While you don't typically have to replace these hard parts, my transmission had a lot of wear on the "teeth" on the 5th gear side:
And this is the 5th/6th synchromizer hub with the 3 keys and one of the two springs that hold the keys on each side of the hub. The 1st/2nd synchro keys come from Tremec already solid but the 3/4 and 5/6 and reverse keys are stamped steel and can be a weak link. I upgraded my 3/4 keys to billet but didn't figure my 5/6 or reverse would need to be upgraded:
This picture shows the 2 sets of blocker rings used in the 5th/6th synchro. Notice the spacer for each set that looks like a star washer. These spacers are specific to the Corvette transmissions. Don't leave them out.
Assembly of the extension shaft starts with the 5th gear, followed by the synchronizer. The synchro hub will have to be pressed onto the splined shaft. I finally figured out that the synchro has to be pressed down far enough to hit a shoulder on the shaft. This picture shows how far the synchro should be pressed on:
And here is the extension shaft with the 5th gear, 5/6 synchro assembly , and the c-clip.
The remainder of the 5th/6th assembly is to slide the 6th gear on, add the shift fork, and slip it down into the transmission.
Thanks to all that went before me on this forum and took the time to add pictures and good information. Maybe this thread will in turn help someone else. In hindsight I'm glad I took the opportunity to build my own transmission. It took me a while, but it's a good learning experience, and will likely pay off in future "opportunities" on my car or friends cars.
11-05-2011, 10:09 PM
#4
Tech Contributor
Thread Starter
I swapped in this rebuilt M12 transmission today, and am happy to report it is working well. It's nice to have all 6 gears again. It's a little stiff shifting right now, I will likely add a shim on the detent (anti-venom mod).
My failed 4th gear synchro turned out to be a broken key. I'm glad I upgraded the new 4th/3rd keys to billet.
My failed 4th gear synchro turned out to be a broken key. I'm glad I upgraded the new 4th/3rd keys to billet.
08-23-2017, 09:26 AM
#7
Burning Brakes
Damn it all the photos are broken...
