onunez65falcon Posted August 27, 2012 Report Share Posted August 27, 2012 Is there a 5 speed tranny that will fit my J13 engine on 520 truck? also, what will be a good replacement for the rear end diferential. Thank you. Quote Link to comment
datzenmike Posted August 27, 2012 Report Share Posted August 27, 2012 Sorry, only 4 speeds were made for the J engine. A 4.375 from a '70 and up 521 (with L16 motor) or any standard 620 except the '79 (it had a 4.11) will work. 720 trucks have an engine tag that lists the differential gearing on it. They came with 3.364, 3,545, 3.70, 3.889, 4.11, 4.375, 4.625. Avoid 4x4 diffs. Quote Link to comment
onunez65falcon Posted August 27, 2012 Author Report Share Posted August 27, 2012 Thanks for the imformation, I drive my truck for abouth 5 miles on the freeway and it take a lot of guts for on thetransmission and the rearend to keep up at 55 pmh. and my only solution will be to change the tranny and the rearend. Quote Link to comment
zenndog Posted September 1, 2012 Report Share Posted September 1, 2012 Why the transmission? Just change the rear end gears, there is a great deal of information on the forum about rear end gears. Find out what you have and then see if you can put a "taller" gear in. Find a free gear ratio calculator, measure your tires, enter speed you want and then see what rear end ratio you need, assume that your 4th gear is 1 to 1, or look it up on this forum and see. Good luck. My L320 has the same issue and a rear end gear swap is what I plan to do. Quote Link to comment
datzenmike Posted September 1, 2012 Report Share Posted September 1, 2012 The 520 with the J13 had a 4.875 ratio rear end. This was selected because of the small J13 motor and the one ton cargo rating. You will never blow a J13 at freeway speeds. They will rev no problem. I know it sounds worse than it is but don't worry these trucks were around when the highway speeds were at least 60MPH. For only 5 miles per trip I wouldn't waste the time swapping anything. Quote Link to comment
520datsun Posted September 9, 2012 Report Share Posted September 9, 2012 I did freeway once...never again lmao never again 1 Quote Link to comment
KFunk740 Posted September 13, 2012 Report Share Posted September 13, 2012 Got a J13 in my L320, along with 4.88 gears. I use it to commute to work 33 miles each way on the freeway. I've put about 13000 miles on it since I got it in June of last year (stays in the garage in winter). It's not remarkably comfortable on the highway, but I don't mind. I don't spend much time in the fast lane, and keep it around 60 to 65mph. If there were a good 5-speed option, I'd try it. The benefit of a 5-speed over a rear-end gear swap would be that the 5-speed could add overdrive without giving up bottom-end power in the lower gears. Quote Link to comment
wayno Posted September 13, 2012 Report Share Posted September 13, 2012 Got a J13 in my L320, along with 4.88 gears. I use it to commute to work 33 miles each way on the freeway. I've put about 13000 miles on it since I got it in June of last year (stays in the garage in winter). It's not remarkably comfortable on the highway, but I don't mind. I don't spend much time in the fast lane, and keep it around 60 to 65mph. If there were a good 5-speed option, I'd try it. The benefit of a 5-speed over a rear-end gear swap would be that the 5-speed could add overdrive without giving up bottom-end power in the lower gears. Unless you can come up with some kind of adapter and figure out the throw out bearing, you are stuck with changing the rear gears, as there is no 5 speed transmission for the J13. I say this, but keep in mind that the MG folks have someone that figured it out for them, as they are using the 210 5 speed on there older blocks, so maybe you would be the one to figure it out. Quote Link to comment
KFunk740 Posted September 13, 2012 Report Share Posted September 13, 2012 Unless you can come up with some kind of adapter and figure out the throw out bearing, you are stuck with changing the rear gears, as there is no 5 speed transmission for the J13. I say this, but keep in mind that the MG folks have someone that figured it out for them, as they are using the 210 5 speed on there older blocks, so maybe you would be the one to figure it out. I'm in no rush myself. I just got done swapping a 320i 5-speed into my BMW 2002, so that shall take over for my commuting duties. B) Quote Link to comment
69srl311 Posted September 13, 2012 Report Share Posted September 13, 2012 I swapped a roadster 3.90 into mine and it will cruise on the freeway comfortably at 70+ mph. There needs to be no wind though! Quote Link to comment
KFunk740 Posted September 13, 2012 Report Share Posted September 13, 2012 Also, if you're a real high-roller and have $3K+ to spend, then you can figure out how to use an aftermarket overdrive unit. I'd assume it requires cutting/balancing the driveshaft, figuring out a way to mount the box, etc. http://www.gearvendo...m/agmanual.html Quote Link to comment
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