Hi James...
Sorry to hear You are having similar problems. I started this post a few years ago, but only last month pulled the gear box to get to the source of the problem. I separated the casings, and found the problem just as I suspected. The interlock pin between the 1st/2nd selector shaft, and the 3rd/4th selector shaft was missing! This caused the 3d/4th lock pin to jam up its own shaft from selecting those gears. I pulled all of the selector shafts out of their respective bores in the clutch/differential side of the transmission casing. At the bottom of the 3rd/4th selector shaft bore, was the missing interlock pin. Who ever swapped out my differential, and put in the Quaife Limited Slip, for what ever reason, was not diligent in making sure all of the pins were in their respective locations. What is interesting about this mistake, is that when the transmission is out of the car, you can sometimes shift it through all the gears. This is because, out of the car, the angle of the lock pin gallery causes the 3rd/4th lock pin to fall back to its normal position inside its shaft. In the car, the angle of the gallery causes the pin to jam. Dave Bean Engineering Inc. still has some of these pins, or You can check with Mark at El Grove Isuzu, (info below). Hopefully, the pins on Your transmission will all be there, like mine were.
http://www.davebean.comphone: (209)754-5802
fax: (209)754-5177
I decided to replace all of my synchro rings while I had the box open. Its not too big of a job if you have a 12 ton press, and the DTSBK194AWS rebuild kit from Drivetrain.com. Here is the link...
http://www.drivetrain.com/parts_catalog ... 3_mk7.htmlI took some pictures of what I did on this project. They are okay and I can post them if anyone is interested. I found a site with better pictures of a GM/Isuzu MJ1 transmission, which is almost identical to our transmission for all the important parts inside the case. Here is the link to that...
http://www.j-body.org/forums/read.php?f ... 41&t=47066Picture #18 shows the exact pin in the location between 1st/2nd and 3rd/4th selector shaft bores where mine should have been. I found mine at the bottom of the bore to the right of where the pin is in that picture.
I was also able to source the 5th gear input/output shaft nuts and some other clips for the 5th/reverse selector shaft assembly. Here is the contact info for that. This is actually an Audi dealership in Elk Grove, South of Sacramento CA. They still have access to some Isuzu parts. call them and ask for "Mark"...
Dealer Name:
ELK GROVE ISUZU (ask for Mark about Isuzu parts)
Phone: 916-421-9267
Contact Email:
erins@elkgrovevw.comHere is some further information to supplement the transmission section of the M100 manual...
https://dl.dropboxusercontent.com/u/131 ... sembly.pdfhttps://dl.dropboxusercontent.com/u/131 ... sembly.pdfhttps://dl.dropboxusercontent.com/u/131 ... 0Specs.pdfI hope this helps anyone considering doing their own work on this transmission.
Michael