If I were to change out my dying l43 tranny with marlins R151 with 5.15 1st gear would I need to re- gear my stock diff ratio of 3.90? Im still debating on whether to run 33's or 35's . Im thinking 4.88 gears would be a good choice overall but im a cheapskate so.....
Hey guy,
The main problem is that your 3.90:1 ratio is so high due to the fact that your truck doesnt have 5th gear, and your engine is carburated = not a whole lot of power for cruising in 5th gear.
Playing around with the
speed calculator I wrote back when I used to be the webmaster (thank god Chris is doing it now!), it looks like:
Traveling at 65 MPH: | 3.90:1 | 4.88:1 | 5.29:1 |
| 4th Gear w/35" | 2,436 rpm | 3,048 rpm | 3,304 rpm |
| 5th Gear w/35" | 2,070 rpm | 2,591 rpm | 2,808 rpm |
So as you can see, if you keep your stock 3.90:1 (4spd) ring and pinion ratio, then upgrading to the 5 speed tranny will only be like upgrading to a stronger 4 speed (except for the 5.15:1 1st gear factor), since you would never be able to use 5th gear on the highway. I know 22R's are known for their amazing bottom end torque, but no carb 22R is going to be able to pull 35" tires at 65 MPH at 2,000 rpm!!
You know, if you are tight on money, why do you want to upgrade to the most expensive transmission available? It's going to cost you a R151F core ($650 / becuase you dont have a core to return) + the cost of the rebuild ($849) + the cost of the imported 5.15:1 gear set ($650) which equals = $2,149 !!!!!!!!!!!!!!! Plus the cost to modify your drivelines since the R trans is 4.5" longer then your L!! I think you would be MUCH MUCH happier if you found a junkyard L52 5speed (so that its the same length as your L43), let's say $250 for that, then install some 4.88s or 529s (same price), lets say ($169 for gears, $99 for setup kit, $50 labor for your buddie to set one up) x 2 = about $600, then you can get a Marlin Crawler Dualcase adapter kit MC07-K21 for $329, find an extra transfercase at a junkyard for $100 and build your Crawl Box, and then get a Marlin Crawler 4.70:1TS-21 total spline gear kit for $449, and do the install your self.. You would still need to have your drivelines modified, but Im not including that price (around $100-$200 depending on shop) because you would have to do this with the longer R151F trans anyways, so no matter what you will have to get this done, so the price cancels each other out, so im not calculating the cost of it here.
That would take your truck to a 5 spd with either 4.88s or 529s and a complete Dual Case Ultimate with a Crawl Ratio ratio of 223:1, all for only $1,728.
Now in my opinion, I could do A WHOLE LOT MORE with an Ultimate Crawler + 5spd + new gearing than just installing a Turbo 5.15:1 transmission without anything else, which remember is gonna cost ya just over 21 bills. So you could be set up as an Ultimate and yadda yadda yadda for around $1,700 and still be about $400 LESS than the 5.15:1 trans ALONE. Then take the $400 and get a new paint job and wa-la. Complete Transformation-
BigMike
