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Thread: SM465 to 700R4 trans swap?

  1. #1
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    SM465 to 700R4 trans swap?

    I have a 78 Chevy K25 4x4. I am replacing the SM465 trans with a 700R4.

    What I am removing; SM465 trans, SM465 trans to NP205 adapter, SM465 to Chevy 350 motor bell housing.

    What I am installing; 700R4 trans, TH350 to NP205 adapter.

    When I measured from the bell housing motor face to the cross member mount bolt holes the 700R4 and TH350 adapter was 1 3/4 ? longer than the SM465 and adapter. Can any confirm that this? Will I have to drill hole in my frame to relocate the cross member? There is a second set of hole on the frame, but I haven?t measured how far back they are to see if they will work yet.

    Also when I measure the overall length, bell housing motor face to t-case mount face the 700R4 and adapter was 1 ? ? longer than the SM465 and adapter. SO I am thinking I will have to have my rear drive shaft shortened 1 ?? and the front remade 1 ? ? longer.

    Any suggestions and info would be helpful. Also if you have done this swap or know of any headaches or problem I might run into that you could help me avoid would be greatly appreciated. As the saying goes, ?The best mistakes to learn from are of not your own, but of others.?

    Thanks and this forum is the best.

    Caleb
    K-Man -~

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    Hey Caleb,

    I can't really tell you about the measurements. I do know that in some cases the hard core guys run 2 cross members one for the trans and 1 for the t case. It helps stiffen the frame and support the drive line. As for drive shaft lengths you seem to be in the ball park on that one.

    - Jason
    "Ask not what your country can do for you - ask what you can do for your country." -JFK

    2004 K1500
    1987 Suzuki samurai

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    The 700r4 trans will definitely be longer than the SM465. Did you also check to make sure the input gear of the t-case matches the splines on the trans output? I believe the SM465's are usually 10-spline coarse, versus 27 spline on the 700r4???

    For the crossmember I would guess there is a good chance the second set of holes will match up, but not certain.

    For the driveshafts, definitely wait until you have the new trans installed to measure, but I'm guessing you are on the right track.
    Brad
    '90 Blazer - 6.2 diesel, 700r4, Dana 60, 14 bolt, locked, 39.5" Super Swamper TSLs, winch, rollcage, yada, yada, yada......

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    Quote Originally Posted by Brad View Post
    The 700r4 trans will definitely be longer than the SM465. Did you also check to make sure the input gear of the t-case matches the splines on the trans output? I believe the SM465's are usually 10-spline coarse, versus 27 spline on the 700r4???

    For the crossmember I would guess there is a good chance the second set of holes will match up, but not certain.

    For the driveshafts, definitely wait until you have the new trans installed to measure, but I'm guessing you are on the right track.

    Brad, you are correct, I do have to swap the input gear, (forgot to mention that in my parts list) and I all ready have it. It is a TH350 type input gear. My 700R4 is a 91 and it has the larger 31 spline input/output shaft. At least I think the output shaft is the same as the input? Doesn't matter how many splines it is, I do know that the coupler I have fits, which is all that really matters.
    K-Man -~

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    Sounds like you have it covered. I just wanted to make sure because I have seen some people try to bolt the stuff up in the truck before they realize the splines are wrong.
    Brad
    '90 Blazer - 6.2 diesel, 700r4, Dana 60, 14 bolt, locked, 39.5" Super Swamper TSLs, winch, rollcage, yada, yada, yada......

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    I did run into a pit of a problem. Since I am basically swapping a TH350 for a 700R4...... since I swaped the SM465 adapter and t-case input gear to fit a th350...... when I bolted up the 700R4 the output shaft is to long and sticks put past the TH350 adapter. So I have ordered a replacement output shaft from Advance Adapters.

    So, when swapping a TH350 for a 700R4...... you need to change the output shaft.

    I also had to drill holes for my cross member. The second set of holes were about 1" to far back.
    K-Man -~

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    Drive shaft

    I will need to shorten the rear drive shaft 2" and the front will need to be remade 1.5" longer.
    I also had to midify the transmission pan to clear the front drive shaft.

    this has been fun........
    K-Man -~

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