As I understand, the 5 speeds up to mid '79 build date had the 3.9 ratio - it then switched to the 3.45:1 in the TR7's
The underside of the diff "pumpkin" will be stamped (using 3/4" tall letters as I recall) with the axle ratio identifier. Note that you will almost definitely need to wire-brush the underside to see the stamped letters, but they will be there. Not to be confused with any raised cast letters on the diff if course - they are definitely stamped into the housing....
CH = 3.9 ratio. You may also find a patch of red paint as a factory identifier
CL = 3.45 ratio. You may also find a patch of yellow paint as a factory identifier
CM or CK = 3.08 ratio. You may also find a green/white paint patch.
I find the easiest way to get a diff out of an axle was to run a disc-cutter around the axle tubes just outside the center member. Once cut through, the halfshafts and axle outers can be pulled out (and set on the scrap pile). Setting the unit over a 5-gall pail makes it relatively easy to drain as well....
Of course, if you'd prefer to pull everything and send me just the CWP, that'd be great as well... I can swap for a 3.08 if anyone needs one.
I should have several kicking around here if you are willing to ship. I can pull the gears fairly easy, but then its up to you to reset them in your axle. Why 3.9? They top out extremely quick. In a TR8, top speed is only around 110mph depending on tires. Tried them in the race car, but ended up shifting gears too much on all of the tracks around here. Get towards end of straight and be maxed out in 4th, just to upshift to 5th for 200 to 300 yards, and then brake. With the 3.45s I could stay in the lower gears until the corners. Every track had one or more places where I got stuck doing this, and the tracks with longer straights like LRP and Pocono, they absolutely would not have worked because of top speed limitations. Where are you located? I may be about to embark on a road trip with an empty truck and trailer to retrieve another wedge. Advertise the 3.08 on one of the wedge facebook groups. Bet you get $300 for the CWP.
Like Todd, I would think that the 3.45s would be ideal.
We ran a 3.45 in our TR6 race car & were banging on the rev limiter at the end of the straightaway. We did not have the luxury of a 5th gear, though.
SD1 racecar with T5 trans, and 17" wheels is the intent. Running the numbers, a 3.9 is way more suited than a 3.45
Well, Todd Kishbach stopped by and dropped off a 3.9 axle on a recent road trip. Totally stand-up guy right there!
Todd wouldn't take any money for the axle, so I made a donation to the site instead.
Cheers!
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Thanks, Dave & Todd!