Q's about transmissions

[BIG*RED]

My current set up is a '82 K-5, with a Vortec 350 H.O. backed by a SM465 transmission, followed by a NP208 transfercase, turning 38 inch tires, with 3:73 gears in the axles.

I love the low gear of the SM465, but i don't have the opurtunity to get out and really use it that much anymore. So I am trying to make my blazer a little more "streetable". So I want to convert to an Automatic transmission.

I have narrowed my choices down to: a TH400 or a 700R4.

Which of these would be the better transmission to go with? I know the 700R4, will give me overdrive, which would be nice with the cost of fuel. I also know the TH400 can be a pretty stout transmission. I also know the TH400 should have the same output shaft spline count as my SM465.

What do those of you who run these transmissions think?

Also what all is needed to convert to auto? I know the 700R4 would require some minor wiring to get the overdrive, and there are several companies that make a kit for this.
But will i need to change my crossmember? Will I have to relocate my crossmember? Also what tourque convertor should i run? (stall speed).

And for the dumb question of the day: will my NP208 just bolt up to a 4wd automatic transmission? or do i need to locate an adapter? (Sorry i know dumb question, but i have always run manual trannys n 4x4s, and have never actually looked at an automatic setup in a 4x4)

Thanks.

 

[George_Pimpdaddy]

if your no looking for highway mileage id go the TH400 route but if you like to go faster and thinkin about DD it or going for trips then the 700R4 is great just look for a later model one i beleive its 87-91 for the better version

 

[BIG*RED]

Thanks for the tip

 

[lectric80]

There is also a size difference between the auto and manual tranny's, so the driveshaft lengths will probably need to be changed.

As George said, if you are looking at DD type duty, the 700r4 is a great choice. But, that being said, make sure it is a well built tranny. Also make sure you run a good cooler with the 700, they don't like heat at all.

I plan on removing my th350 and replacing with the 700, but that is mainly because mine gets driven on the street more than on the trails. If it was more trail, I would be sticking with the 350 or going to a 400 for the strength.

 

[Chevy305]

I think you're crazy for making a manual to auto swap. I DD my truck with the 465/208 and 35"s without any problems at all. You will miss that third pedal. Also you're going to need a well built trans or those 3.73 and 38s will tear it up.

 

[cabledawg]

I agree with Chevy305. If you end up using the 400, you havent gained anything as you still have only three speeds with no OD, but now you have a steeper first, so you'll be lugging off the start and the 465 is going to be spinning a few hundred RPM's slower than the auto. And you wont need wiring for the OD to work on the 700. The wiring is actually for the TC lockup (if equipped). I've ditched the 700 for 465's in both my Suburbans, so I dont know why anyone would go the other way.

 

[dyeager535]

Just some quick numbers @ 60MPH w/3.73's:

1979RPM's w/465/38's
1385 w/700/38's
1698 w/700/31's.

Your RPM's are close enough to stock, I'd leave well enough alone. You won't gain anything but automatic shifting unless you get crazy with rear axle gears and/or tire size reduction, both of which simply add more cost to the swap.

Got a hydraulic, diapghram style clutch? Light years ahead of the mechanical setups if not, and makes driving the truck SO much nicer.

 

[BIG*RED]

Got a hydraulic, diapghram style clutch? Light years ahead of the mechanical setups if not, and makes driving the truck SO much nicer.

No, I have the manual clutch. is there really that much difference between the manual and hydraulic clutch, other than not having to adjust it?

 

[dyeager535]

Please click one of the Quick Reply icons in the posts above to activate Quick Reply.

 

[Chevy305]

Please click one of the Quick Reply icons in the posts above to activate Quick Reply.

 

[pauly383]

350 with Vortecs or not , you need something a little lower than 3.73's out back when you go to Auto trans , otherwise you'll have a Vortec 350 that thinks its a 2barrel 305 from a 77 Disco Nova .