4 speed trans swap
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Senior User
Joined: Mar 2007
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4 speed trans swap
I bought a t18 in descent shape to swap for this 3 speed RAT...could use a new shifter lever, boot and luxuries like A ****, 1-2/reverse slider a bit chewed up but i think it'll be ok. Btw the bell housing should work since both trans have a butterfly pattern.
Now i measured the original trans and driveshaft and the t18:
The rat3speed w/ tail housing is 27.5 in, driveshaft is 56.5 in ====> 84 in driveline
The T18 is 18.5 w/ tail housing (12 w/o) so im looking at a total length to make up for to the rear end of 64in...now these measurements are a little crude but does 64 in driveshaft ring a bell to anyone? anyone got a swb with a t18 or np that can measure his? I think the Np435 and T18 are the same length. Has anyone done this kind of swap? Im trying to get my ducks in a row b4 i tear into it.<!-- / message -->
Now i measured the original trans and driveshaft and the t18:
The rat3speed w/ tail housing is 27.5 in, driveshaft is 56.5 in ====> 84 in driveline
The T18 is 18.5 w/ tail housing (12 w/o) so im looking at a total length to make up for to the rear end of 64in...now these measurements are a little crude but does 64 in driveshaft ring a bell to anyone? anyone got a swb with a t18 or np that can measure his? I think the Np435 and T18 are the same length. Has anyone done this kind of swap? Im trying to get my ducks in a row b4 i tear into it.<!-- / message -->
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Joined: Apr 2006
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From: mid-MO
Yes and no. Depends on how your fab skills are. I assume its a 2 wheel drive. Look on your crossmember that holds the tranny in place. Is it slotted to allow forward and backward adjustment? If so, that might gain you a little bit of adjustment, but probably not the 2 inches you are looking for. The other option is to fab up your own crossmember and make it so it bolts through the from from the outside with some angle iron and then drill some new holes in your frame. If you don't want to go this route then yes, you will need your driveshaft shortened or lengthened.
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Thanks for the idea on the crossmemeber but I'm not so worried about the cross memebers really, but the problem is the total lenght of the driveshaft would have to be 84 in due to the shorter t18 total legth in comparison to the 3speed rat. see earlier post.
Elder User
Joined: Apr 2006
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From: mid-MO
Not familiar with a "RAT" transmission. Why do you not want to lengthen/shorten your driveshaft? So you would have a 7 foot long driveshaft. Big deal. It is a 2wd truck, right? It really doesn't cost that much to have it modified. One other thing, I don't know if there were different tailshaft lengths of the t-18 and different rear housings. I do know a 4x4 tailhousing is different than a 2wd housing, but not sure of the lengths. Is it possible you got hold of a 4x4 tranny with a shorter tailshaft?
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