Turbo 400 or SM465?

[Mattchu60]

Have been reading a lot about SM 465 swaps lately. I really like durable stuff and both the Turbo 400 and SM465 are very durable transmissions. Thought I would see what people think about the two trans and the pros/cons of each as I may swap my 700r4 out in the future for one of these - I don't seem my 700r4 surviving forever as I pull loads with it a lot and also have a 355 which is making more than the factory hp in front of it - someday I'm going to need to either have it rebuilt or replaced.

SM465 seems like the most "fun" choice - I know they are slow shifting - I don't drag race anyways. But there is something fun about just going through gears.

The TH400 seems like the easiest route - and if you do get on it, it would probably reach 60 mph faster than the manual would. Plus they can be built to take a lot of abuse.

What are thoughts on the two? My thoughts are the SM465 would be neat to have, and also it would probably have better mileage than the Th400 since there is less power/rpm loss through the trans.

[mongocanfly]

The sm465 is basically a 3 speed tranny with a granmaw gear 1st..like you stated its not a trans you can speed shift .depending on your rear gears and tire size the 1st gear is basically usless unless your moving heavier loads...the turbo 400 would be a better choice since you already have a auto in your truck.remember neither of your choices will have the overdrive that your 700r4 has...if you are set on a manual I would recommend a nv4500..if you go manual don't forget to factor in that you'll have to come up with the whole clutch apparatus...and driveshaft lengths are subject to change

[Mattchu60]

One of my thoughts was to buy a donor truck with a SM465 in it to get parts from. There are quite a few on CL it seems.

Never done it - but does the tunnel swap out on these cabs (are they bolted on) or do you have to cut holes for the SM 465 shifter?

[mongocanfly]

Yes the tunnel should swap..if you get a donor truck it should have what you need in it with the shifter hole already there.simple bolt in..

[mongocanfly]

I swapped my sm465 out for a nv4500..with my 4.10 gears I was turning about 3000rpm at 65mph...with the nv it dropped to around 2200 rpm at 65mph

[Tom]

All this to hold up behind a rebuilt, what I'm assuming is at least mostly stock, 350 small block? Rebuild the 700R4 when the time comes and enjoy still having overdrive.

[Alex V.]

Each are very tough - really just depends where your priorities lie. Both have the same 1:1 high gear ratio and will probably last just as long with any kind of maintenance. If put through a contest of ultimate abuse I'd have my money on the SM465, but a prudent driver and an adequate trans. cooler should keep the 400 from having any issues for a long time. Probably right about the manual having less parasitic loss, but it will certainly lose a drag race to the 400 purely because of shifting.

If the TH400 was any less as good a unit than it is I'd have seriously considered an SM465 swap in my '85 C3500 instead of rebuilding its original TH400, but it's really a nice truck the way it is and being a 2WD with power everything I really think the turbo is fitting equipment and it makes a darn good pulling truck as it is.

[GRADYS Performance]

Keep the TH700/4L60 transmission or swap to a 4L80E. The fuel mileage drop to the non overdrive transmission will be considerable, think 25% range. Unless you are towing heavy loads all the time the TH700/4L60 is your best choice. With a TCI 376500 shift kit and a Corvette servo the trans is pretty strong without much expense.