sm420 thought on driveshafts

[Joey]

I have looked at so many conversions for FJ40 3spd to SM420 4spd that I can't even count all of them. The one thing that I have yet to see, and I saw it first hand today was the stock driveshafts being way way off and not being able to be used without modification. The movement of the tranny backwards was only about 2" max, but the front driveline would not even reach- ie, the yolk was about 2"s from even reaching the splines on the other section. The rear shaft looks like it will be too long also.

From everything I have seen the stock shafts should have fit. What gives?

Also I have not heard of the rear mounts for the tcase-the AA cross member- having to be moved either. This one they had to be moved about 1 1/2-2" back and moved up and down because of the tilt of the tranny now.

I thought the LC 3spd and the SM420 were similar in length, especially when using the plate adapter for the tcase.

Info really appreciated because I will be finishing mine this weekend and just would like to know if this is something that was just failed to be mentioned or if it was a freak thing.


Movement of the brackets and modifying driveshafts may not be that big of a deal for those of you that have welders and know how to weld, but I just got welder and am not very confident at it yet so this is a pretty big deal to find out when it came time to mount the whole tranny/tcase up. Especially the driveshaft thing, what a freakin bitch-it is Friday and now it will be a wait until Monday and a trip to the metal shop to get them done. Was hoping to do a little wheelin with the new setup this weekend.

[DCruiser138]

both of the stock d-lines are too long and must be shortened. as for the front, i had just done soa and the sm420 very close and hadnt had one made for the forn yet soa...so i dont know about IT. as for the aa mounts...if the tranny moves the t-case back..wich it does..then of course you have to re-do the mounts. so im pretty sure thats normal.

[Eric]

using plate adapters......

The stock 3 speed tranny is shorter than the SM420, therefore the stock 3 speed front drive shaft will be too short, and the rear too long.

If you were replacing a stock 4 speed tranny, you don't need drive shaft modifications. You only need to swap out the front slip yoke for a 3 speed one with the small hole pattern.

For 3 speed applications, you need to get your hands on the long sectins of the stock 4 speed drive shafts and then change yokes.

[flexing40]

Originally posted by Joey
........ The movement of the tranny backwards was only about 2" max, but the front driveline would not even reach- ie, the yolk was about 2"s from even reaching the splines on the other section. The rear shaft looks like it will be too long also.

From everything I have seen the stock shafts should have fit. What gives?

You should be able to substitute the rear drive shaft with the original front driveshaft. Then have the original rear drive shaft lengthened for the front.
Mike

[Jason M]

Originally posted by DCruiser138
both of the stock d-lines are too long and must be shortened.

Shorten the front driveshaft to go on the rear and lengthen the rear drivesahft and put it on the front. It is always cheaper to shorten a DS than it is to lengthen a ds...


You end up having a slightly longer drivetrain than before. And it is just a bit easier to lengthen DS than anything else.
The only real way to do this tranny swap and not have to alter DL's is to stuff a V8 in at the same time and position it so that no DL mods are necessary...