I've been lurking here for awhile and have seen some good information on T5 transmissions so now I have my own T5 question. I have a jeep T5, actually being used in a jeep, and the 5th gear ratio is .76 as far as I can tell (both ID tag decoded and physically counting teeth 53 and 23). From my reading the Jeep T5 was only available with 2 5th gear ratios .76 and .86. I'd love to get a little bit more overdrive, do any of the other T5's have compatible 5th gear sets like the S10 or Aerostar etc? I would like to get up to a .67or so overdrive. I know it doesn't sound like much but a few hundred rpm in the jeep on the highway makes a big difference. Any ideas? Thanks Bill
I run two of them with the .76 gears set. It's a nice step from 1.1 Drives real nice that way. The ones with higher ratios that I've riden in have a huge drop in RPM which makes sometimes 5th too high and 4th too low. Both of mine are with 4.11 rear gears.
Since I'm running a straight six, it doesn't want to rev to much so my .76 is just a tad high. I know other 5th gear sets exist for other T5s but I was unclear if the Jeep T5 gear-sets that were unique to the Jeep box or if there were crossovers in terms of fitment from other T5 gearboxes.
The 5th gear sets can be mixed-n-matched with some limitations. Both 5th gears must be matched (out of the same ge****t T5) and both must be from a like-cl*** box (WC w/WC and NWC w/NWC, but no mixing). So, you can use the 5th gear set pair from any NWC box in your Jeep. To my knowledge, the Jeep ONLY came with .86 as it ONLY came with the 4.03 ge****t. You can't tell the ratio by simply dividing/multiplying the two gears outside the case, you have to use compound gearing because your input gear and first gear on your countershaft are part of the equation. So, you need to know all of the gear teeth...or at least those four gears. For example, if you use the Jeep 5th gears on a 3.50 ge****t, you'll get about .69, IIRC. I did this research for a Frankenstein T5 I was working on a while back, but is now on hold for a while. Here's a thread where I had to figure this out: http://www.jalopyjournal.com/forum/showthread.php?t=254912
Thanks for the post Ernie, I just read through that thread. I find a lot of different info on the jeep boxes, some say only the .86 ratio, some say both .76 and .86 and some say only .76. The only real way is to count gears it sounds like. Most jeep vendors offer either a 53/23 tooth set like you had or a 51/25 tooth set. Doing the math from the other thread it sounds like you may have had the .76 gear set in your Jeep T5 as well. And a 51/25 tooth set would give the .86 ratio you were looking for, ***uming you had the same 4.03 first gear set. Those equations are good to know though, I forgot all about needing the input gear set in the equation. I'll have to physically count those teeth as well and do the math myself. But that is good news that the non-world cl*** 5th gear sets are interchangeable. So I just have to look around until I find a NWC box like an S10 or Astro that has a set closer to 61/25. Thanks again Ernie, great info
And I just stumbled onto this site: http://home.roadrunner.com/~schickling/1940Chevy/T5.html He essentially built two custom ratio T5's one a close ratio box and the other is exactly what I want, a 4.03 1st gear and .72 5th. Well maybe not exactly. I guess it depends if my existing 5th gear is .86 or .76 but either way it will drop the revs a few hundred rpm.
There is no application list for a Jeep with anything but the 4.03 ge****t. The 4.03 ge****t always has the .86, so I'm not sure where the .76 is coming from. Only the 3.76 ge****ts have that ratio - it's a function of the first gear. That said, nothing surprises me anymore with T5...
I'll try and find the sites that listed the .76 as an option. But there are numerous Jeep vendors that sell two different 5th gear sets for the Jeep CJ T5 box, which indicates to me that it was available with two different ratios for 5th. But like you've said nothing is surprising when it comes to T5's so I could be totally wrong. Good news is a I have a spare gearbox out of my jeep sitting on the bench right now, so I can dig into it a do a tooth count myself and report back here as to what it had.
I know this is an ancient thread, but I have reason to be playing with these Jeep T5s at the moment, and I have some info to add that will possibly clear-up a couple of mis-conceptions. First of all, there are TWO accepted Jeep 5th gear ge****ts.......23/53, and 25/51. The KEY thing you MUST KEEP IN MIND about these ge****ts is that the SMALL diameter mainshaft gear in ANY of these OD ge****ts can only be used on a mainshaft with the SAME number of splines matching it's transmission of origin. Jeep MAINSHAFTS have 23-splines. Ford shafts have 28-splines, and the Chevys have 27-splines. So unlike what was stated earlier, ya canNOT just swap ANY matching ge****t. The small gear's internal spline count MUST match the spline count on the intended mainshaft. In MOST cases, you can swap mainshafts between brands (Ford, Chevy, Jeep) if you stay within the NWC or WC types. Hope this'll help clear-up some questions about these diverse transmissions and the fine-tuning possibilities of their numerous OD ratios. DD
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