Quadratrac Speedo Calibration

[79qtrac]

I hate asking relatively dumb questions like this, but I have looked all over and not found anything. I would like to re-calibrate my speedo because my tires are oversized. I have the BW1339 quadratrac tcase. I imagine I just need to find a new speedo gear to fit on the output shaft, but I can't find anything about doing this other than for the newer Wrangler cases. Does anybody know if you can re-cal the speedo like this and if so, where to find the gears? My local dealer just laughs at me whenever I call and try to find parts with them.
Thanks for reading this newbie post!

[tgreese]

May not be ideal, but Stewart-Warner makes (used to make?) a little transmission that you put inline with your speedometer cable that had interchangable gears. Many different ratios were available.

Oddball parts for a BW 1339 will be a problem. Maybe someone here has a gear from the ratio you need, or knows about interchangability.

[carrotman]

On my 76 with a T18, the speedometer cable is on the transmission. If yours is on the trans, it is probably a GM 400. Any GM dealer should have different gears. If it's on the transfer case, bring it to a Chrysler dealer. Their older cars used Borg Warner manual trans, and they might have different drive gears.

[g503]

well simple math ,take your new tire diameterdivided by your old tire diameter,and then times it by your shown speed limit,the number you get will be your actual speed ,say you put 35's on and had 31's.and go driving at 55mph.divide 35 by31 then times by 55 = 62mph,works both ways,

[g503]

oh and does your cable hook to the tranny or the transfercase?i havent been under a quadra for a while

[79qtrac]

Thanks for the help guys. The cable hooks into the rear output of the tcase, not the TH400. I know I can use simple math to know what speed I am going, but I would rather just fix it to be accurate if possible. If anybody has ever messed with this before, please let me know.
Thanks!

[J4GRAND]

79qtrac,

I have the same problem in my 73; 33" tires makes the speedo read 20% low. No replacement speedo gears available anymore for the QT. Try to find a speedo shop that can put a converter inline in your speedo cable to recalibrate.

[79qtrac]

Thanks, that was what I had figured after much searching. I guess I will just live with it. No big deal. Thanks for the input everybody.

[jc turtle]

HI 79, I had a similar situation with my 55 chevy when I added an automatic trans and a different rear end. you can have someone follow you with a known accurate speedo and note your speed at a certain sign from the other car,ie, they flash their lights when they are going 40,50,etc. compare their speed with yours as a ratio. if they are going 50, and yours says 45,you are about 10% slow. you need a driven gear in the t/c that has a 10% difference in teeth. 33 teeth vs. 30 teeth. I think that less teeth speed up your speedo, more teeth slow it down. i hope this is right, i always get confused by this, but this is what you have to do to get it right. email me with your info and I will see what you need for a tooth count. get the color and tooth count from the driven gear, and the approximate size of the gear. good luck, John