Keep 4 speed or put in Automatic

[Grande Rojo]

I got a 1986 SWB a few months ago. It has a 305 4 speed granny gear 273 geared rearend.
I am putting a 400hp 355 in it soon. Should I keep the factory 4 speed or put a th350 auto in it?
If I keep the 4 speed how long do you think it will last before I blow it up?
Or should I just sell the 4 speed and go with the auto now?

what to do, what to do, I need a new hobby (not really)

[lilpup69chevy]

go for a super t10 borg warner 4 spd ditch the granny low slap some 3.73 gears in and add rear tires weekly lol

[84 400]

i love the manual. keep it nothing like shifting your own

[wedgemon]

Being 2wd Ya may want to go Auto or 5 speed. Because, you ain't never gonna blow up that SM465.

- Dave

[benoit454]

I'd leave it stick shift, for sure. I'd love to have standard shift in my 86 4x4.

[Grande Rojo]

So are the sm465's worth anything if I was too sell it? I would sell everything needed to do a swap.
Thanks for the input guys!!

[79Silv4x4]

Originally Posted by Grande Rojo

Should I keep the factory 4 speed or put a th350 auto in it?

Depends on what you want out of this truck. . .

Originally Posted by Grande Rojo

If I keep the 4 speed how long do you think it will last before I blow it up?

That depends on your driving habits. . .

Seriously though, what is your intent with this ride? ? ?

[edman87]

You aren't going to blow a sm465 with 400 horses and 2wd, but you won't enjoy the slow, long shifting in a high perf street truck.
No, they aren't worth much, especially in 2wd form, way too common.
Bottom line, if you want to stoplight race it, go with another tranny, if you want to pull, definately keep your 4 speed.

[benoit454]

How easy is it to convert them to a 4wd tranny? I can't find any transmission for my 86 here and I'd rather not rebuild the junk auto.

[Grande Rojo]

Thanks for the input guys. Im going to pull it(4sp) and put in a th400 that I have.

[Russell]

You'll notice that it will be slower with an auto, just becuase they suck so much more power than the standard does... That said, there is still a certain amount of convenience of not having to worry about shifting though

And as mentioned, you wouldn't possibly break an SM465 with a meer 400 hp. You'd need more than 1500 ft lbs of torque to break that beastie...

Benoit -- Switching them to 4x4 is very easy. Just need to take the top off, pull the mainshaft bearings, slide the mainshaft out (make sure you don't loose the needle bearings between the two peices of the mainshaft!), then toss the output half out, and put a new 4x4 output half in, and slap it all back together. All you need for special tools is a bearing puller, and if you want to make things easy, a hydraulic press. A couple blocks of wood and a big hammer will suffice though!

Wear gloves too, gear lube takes just as long to come out of your skin as it does to come out of your clothes, after I rebuilt my SM465, nobody would come around me for weeks...

Consider replacing your shift forks, and the springs for them too, and make sure to check the shifter as well. Should prevent the 3rd gear (L123) popout, and make the shifter a lot less sloppy.

[piecesparts]

The standard will give more MPG, if driven within their gear range. The upgrade to a 5 speed will give an overdrive ratio, but change your final gear ratio requirements, so that will be in the future. A 2.73 rear end gear is GM's way of trying to get MPG out of a 4-speed, so the ratio would have to change to a 3.42 or 3.73, so that the motor would work in a good RPM power band, with an overdrive tranny. If you put in an auto without the OD, then I would consider a 3.08 geared rear end.
The TH 400 is a heavy duty tranny and will stand up to a lot of punishment, HOWEVER; out of all of the GM trannies, it and it's omputer based brother (4l80E) are the most power robbing ones they have. The slippage within the design of an automatic (any automatic) will cost you about 1 to 2 MPG in general useage. The auto will give you a better more general useage and ease of driving in any traffic. I would put a good external tranny cooler on to protect it. Just a thought.

Oh; by the way, I have a complete (includes the brake drums, shoes, axles and all)3.08 geared, 10 bolt rear end sitting outside my shop, that came out of my son's 86 Chevy 1/2 ton. I am looking for someone that needs one. We took it out and installed a 3.73 12 bolt posi for a better alignment with the 700R4 tranny that I pput in his truck.

[Jonboy]

I vote 700R4 and 3.42 gears. Lower 1st gear, and still great for the highway.

[mhicks]

Like they said above, it depends on what you want to use it for.

[84 400]

glad to see you made a choice. If it ewere me i would keep it manual sice everything is auto these days and i love shifting plus they don't burn up like autos do. I am really wanting to put a 4 speed in my 1984 c10 but i heard the conversion from auto to stick is a real pain. ahh well maybe some day or maybe a 3 on the tree.

[piecesparts]

The conversion to a manual is not that bad. The clutch assembly can be taken from any truck and it should mount easily in the cab. The tranny and crossmember should come from the donor and the speedo gears are easy to find. You would have to make a driveline, that isn't hard either.

[Grande Rojo]

Originally Posted by Jonboy

I vote 700R4 and 3.42 gears. Lower 1st gear, and still great for the highway.

My 77' stepside had a 355/700r4/4.10 geared 12 bolt last year. It ran 13's and I could drive it everyday if I wanted too. It now has a 468BBC th400 and a (soon) 9 inch ferd rearend.
At the time I had 31" tall tire in the rear and it ran down the hiway great.


I guess my main concern with the 4 speed was "is it very strong?" from what you guys say it is but I know how I drive and I think an auto is best for me.

[84 400]

Originally Posted by piecesparts

The conversion to a manual is not that bad. The clutch assembly can be taken from any truck and it should mount easily in the cab. The tranny and crossmember should come from the donor and the speedo gears are easy to find. You would have to make a driveline, that isn't hard either.

when you say drive line what do you mean. not a drive shaft right. do thease have a clutch booster on them. i ask cause i found a 85 gmc at a local yard with a 3 speed on the colum. the guy is very nice and would let me grab it all for cheap. would the 3 speed work on my 84? i was just wondering. do you think it could stand up to the sb 400?

[benoit454]

I wished I was closer to snatch up the 4 speed for my 86.

As far as stick shift conversion you need the pedals, upper push rod, lower push rod, z bar or cross shaft and the z bar/cross shaft frame bracket, with two ball studs. If it's a complete stick shift truck you can get it all from that truck. I'd grab the crossmember and driveshafts also. Not sure if they'd be different or not. I have a saginaw 4 speed here from a 74 or 75 camaro but something's not right with it I don't think. The 3 on the tree can also be changed to floor shift pretty easy with one of thoose indy shifters from hurst or mr. gasket for like 75-125 bucks I think. You'll need the trans itself, bellhousing, flywheel, and bolts(thicker then auto) then you'll have the clutch so you'll know what size to buy. I'd say buy a new clutch kit, throwout bearing, and pressure plate, all that stuff, and have the flywheel resurfaced.

Now on a side note, my 76 c10 short bed had a 3 on the tree factory and straight 6, it was converted to floor shift, and eventually had a very mild 350 in front of it. it worked good. It was a saginaw 3 speed, and we swapped it out for that saginaw 4 speed I mentioned, which bolted right in place, same driveshaft and all. No mods, other then a new shifter. THEN, I pulled that out due to the whole truck having serious cancer, and dropped it in my 85 monte carlo ss, which had a th350, and v6 stock but was replaced with a 350/350 setup. I mention this because the saginaw 4 speed came out and I put in a th350 short tail, the saginaw 4 speed was the same length as the th350 short tail, and used the same driveshaft and trans. mount.

So.. I think if you have a short tail th350 now, and it's a stock saginaw 3 speed the driveshaft you have and crossmember even tranny mount should all bolt up and work fine. Not posative 100% but pretty sure it would.

[84 400]

thanks i did not mean to highjack but i have been wondering for a long time

[82c10]

i say put the auto in it, you can still shift it manually, so good choice

[84 400]

you could but whats shifting with no clutch????

[benoit454]

crapppy IMO. I run a th350 in my monte carlo behind that very mild 350 I had in my 76, the 76 was 3 speed converted to the floor and you could really bring it alive, NOTHING like this lazy old auto. I plan to do a shift kit, then later a rebuild with stall in it. Right now I'm going to put in a good rear end. Shifting a manual is alot better then an auto IMO.