auto tranny question

Chevyjoe · Jan 17, 2009

wonderin whats the best automatic gm tranny for wheelin out of the th350, th400, or 700r4? all the 4x4 versions of course and why which one is the best for wheelin and why? lowest 1st gear, overheating issues, etc ... any information would be greatly aprreciated! thanks :awesomework:

TreeClimber · Jan 18, 2009

There is no one best tranny. Each has advantages. I prefer TH400s behind V8s. With enough motor, you don't need overdrive as you can power thru slightly lower (numerically) gears (4.56) and still maintain a decent RPM at 70 mph. It's stronger than the others, although they each can be made plenty strong themselfs.

Chevyjoe · Jan 18, 2009

thanks for the info treeclimber! the set up im plannin is either a 400 sbc or 350 sbc, 205, 60 front, 14 bolt rear and 40's for tires. what would be the best gearing and and tranny combo for that? mostly gunna be a trail rig but would like to cruise down the freeway (70 - 75mph) if i had to. thanks

Fordzuki · Jan 18, 2009

Low first gear+OD= 700R4
Strength=TH400

Chevyjoe · Jan 18, 2009

ok so definitely not the 350? can you make the 700r4 strong? are both the th400 and 700r4 aluminum?

Corey Y · Jan 18, 2009

TH400, they are really strong and simple, no electronics or cables.

wazz · Jan 18, 2009

Its pretty hard to kill a mildly built TH350 w/ a small block

The 700R4 is by far the weakest one. But like stated before it has better gearing.

wazz · Jan 18, 2009

Crazy Daze said:
TH400, they are really strong and simple, no electronics or cables.

Yep, only real issue is hooking up a good electronic kick down switch can get to be frustrating, and it seems there is way less adapters out there for the TH400 then the TH350's

Chevyjoe · Jan 18, 2009

so whats the difference between the th350 and the th400? which one, if you could have the one you wanted, would you put in your rig? looks like the all have their advantages and disadvantages but one has to be the best right?

wazz · Jan 18, 2009

TH400 is considerably beefier, but it will rob a little horse power to turn that extra internal mass.
A lot of the equation depends on what T-case and adapter you want to run.

Chevyjoe · Jan 19, 2009

im gunna be runnin a np205 for tcase with stock internals or the 3:1 low kit. everything else is stated above. is there any one to make the 700r4 strong? does the 700r4 have an electronic kick down switch also?

454k30 · Jan 19, 2009

you should be aware that there is no 3:1 kit for a 205. There is a 3:1 205 case available but it is an entire case that is custom made just for that gearing. I think you mentioned you already had a sm465/np208 setup in your truck. You should stick with that if you want my $0.02. If a slushbox is in your future than I would go with a th400/np205 or np208 setup. Since you are only running a sbc engine then you could go with the th350/208 and be just fine. With 40 inch tires you are gonna want steeper gearing than 4.56. I have 4.10's with 37's and wish I had 4.56. You might want to look at 4.88s to make life on that transmission a little easier.

wazz · Jan 19, 2009

86chevyjoe said:
im gunna be runnin a np205 for tcase with stock internals or the 3:1 low kit. everything else is stated above. is there any one to make the 700r4 strong? does the 700r4 have an electronic kick down switch also?

I'm guessing you have found an adapter that will mate a 205/700R4? I ask cause I cant say that I have ever come across a stock one.

To answer the question about beefing up a 700R4 I would say no, there is no way to make it as strong as either the 350 or the 400. The visual that sticks with me is there is a dual clutch and drum set in it that's clutch disk spline's are a piece of stamped sheet metal, it even looks weak & cheesy. imo
Of coarse if your only talking a 3000 pound rig with 5<something gears then sure it will probably hold up fine.

Chevyjoe · Jan 20, 2009

you should be aware that there is no 3:1 kit for a 205. There is a 3:1 205 case available but it is an entire case that is custom made just for that gearing. I think you mentioned you already had a sm465/np208 setup in your truck. You should stick with that if you want my $0.02. If a slushbox is in your future than I would go with a th400/np205 or np208 setup. Since you are only running a sbc engine then you could go with the th350/208 and be just fine. With 40 inch tires you are gonna want steeper gearing than 4.56. I have 4.10's with 37's and wish I had 4.56. You might want to look at 4.88s to make life on that transmission a little easier.

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yea im aware of that, just pronounced it wrong :redneck: lomax makes a 3:1 case. right now i have an 86 chevy k10 as my daily driver that has the sm465 with 208 but have a perfectectly rebuilt sm465 with 205 that i was wonderin if i could just swap in the stronger 205. have already had that answered in the other thread. im plannin a build up of a 75-78 3/4 chevy with dana 60 front, 400sbc, np205, 14 bolt rear, 5.13's, and 40's. im not sure which auto tranny to run as i want it to wheel well but still be able to go down the freeway at 70mph if i had to. from the looks of it, im leanin to the th400? is this a good choice? why or why not?

I'm guessing you have found an adapter that will mate a 205/700R4? I ask cause I cant say that I have ever come across a stock one.

To answer the question about beefing up a 700R4 I would say no, there is no way to make it as strong as either the 350 or the 400. The visual that sticks with me is there is a dual clutch and drum set in it that's clutch disk spline's are a piece of stamped sheet metal, it even looks weak & cheesy. imo
Of coarse if your only talking a 3000 pound rig with 5<something gears then sure it will probably hold up fine.

no, i havent found a stock one, just figured somebody made one (advanced adapters). well, looks like the 700r4 is out of the question then, as the trannys gunna be in a 3/4 chevy. debatin between the 350 and 400. whats the difference between the two (beside strength)? thanks

Corey Y · Jan 20, 2009

Do a 400 sbc, TH400/ORD203/Lomax 205, 4.10s, 40s. I have built alot of Chevys like you are planning, and this is what I would suggest.

T-case reduction would be 1:1, 2:1, 3:1, 6:1

Craw ratio would be 61:1, and you could still do 70mph with 40" tires.

wazz · Jan 20, 2009

Crazy Daze said:
Do a 400 sbc, TH400/ORD203/Lomax 205, 4.10s, 40s. I have built alot of Chevys like you are planning, and this is what I would suggest.

Sounds like a good mix to me,

Back in the day I ran a 77Chevy SWB, SBC400 to Th350/203 on 38/16/16.5s' and 3/4 ton 3:73's.

for street mud drags and general wheelin.
The SBC400 = kick ASS (best small block to work with)= best bang for the buck (they like the smaller intake valves and the longer 5.7" connecting rods). imo

I never killed the th350 but I really didn't use the hell out of it that much either.
I have had a few TH400's in some rigs, w/stage2 shift kits, in a variety of rigs now, and absolutely no complaints there at all (keep in mind the 400's I used were all built well and all 3 of them after dialed in, would second gear scratch w/no problem).
Getting a well built TH400 is not always easy.

454k30 · Jan 20, 2009

X2 to the th400/lomax and 203 doubler for a drivetrain. of course putting all of that together is gonna run into the $3,000 range or even higher. If you've got that kind of pocket book then go for it and let the rest of us chevy guys drool!

Corey Y · Jan 20, 2009

Here is what I was working on today. 454/TH400/2.72 Klune/NP205. I will be into this about $3000, and @80 hours of labor

. The ORD/Lomax would have been better.

Chevyjoe · Jan 21, 2009

Do a 400 sbc, TH400/ORD203/Lomax 205, 4.10s, 40s. I have built alot of Chevys like you are planning, and this is what I would suggest.

T-case reduction would be 1:1, 2:1, 3:1, 6:1

Craw ratio would be 61:1, and you could still do 70mph with 40" tires.

that sounds awesome and all, and i do plan to put a little money into it, but for washington, with a fullsize, i dont think i'll need the doubler. thats why i was gunna run the 5.13s and just a detroit in the rear. maybe true-trac up front but probably just leave open. was lookin at one of those r&p ratio to tire size charts and 5.13's seem to be the perfect fit for what im gunna do :stirpot: as for trannys and engines, who builds good 400 sbc's and th400's that can get them "dialed in", in the northwest? thanks :awesomework: