Education needed......TH350 tranny versus 700r4 tranny

[whiskymaker]

Hi folks,

can anyone help explain to me what the benefits/differences would be between these two transmission please?

Is it worth me putting a 700r4 into my 1955 2nd series 3100?

At the moment she is running a TH350 mated to a 350 engine....


is it an easy straight forward swap or am i in for a load pain if i went for it?


Many thanks in advance


Mario

[Kim57]

The 700r4 is basically a TH350 with an extra gear.
It shouldn't be that bad of a change over as I don't think its electronically controlled.
The length may be different so you'll need your drive shaft modified.
Kim

[whiskymaker]

Originally Posted by Kim57

The 700r4 is basically a TH350 with an extra gear.
It shouldn't be that bad of a change over as I don't think its electronically controlled.
The length may be different so you'll need your drive shaft modified.
Kim

ah thanks Kim....

it was the shaft i was worried about.....where i live there is no one that does these sorts of vehicles,so i feel it will end up being more hassle than i really need.....

thank you for taking the time out to reply

[1-ton of fun]

I think it's about 1.25" longer (the 700r4) so you may need the driveshaft shortened

[_Ogre]

depends on how much you drive your truck and how much you like paying to fill the tank
with 25,000 miles on truk i think i have justified the extra expense of swapping from 350 to 700r4

the 200r4 is the same length as the th350 and will bolt right in
the 700r4 will need the x-member moved and driveshaft shortened
either one you need to find the right years, early years were unreliable, later years had computers

you'll need to control the lockup on either one, many vendors have kits that can do this
both also have a tv cable rather than the kickdown cable, the tv cable needs a bracket and mount on the carb
again universal kits available to mount the tv cable

[whiskymaker]

Originally Posted by _Ogre

depends on how much you drive your truck and how much you like paying to fill the tank
with 25,000 miles on truk i think i have justified the extra expense of swapping from 350 to 700r4

the 200r4 is the same length as the th350 and will bolt right in
the 700r4 will need the x-member moved and driveshaft shortened
either one you need to find the right years, early years were unreliable, later years had computers

you'll need to control the lockup on either one, many vendors have kits that can do this
both also have a tv cable rather than the kickdown cable, the tv cable needs a bracket and mount on the carb
again universal kits available to mount the tv cable

we dont do a lot of miles in the ol girl...so i think i would be best using my money on other things for the truck.....

thank you for giving me all that info Ogre

[Highsider]

Ok, what does the "tv" mean?

[56 3100]

tv cable is throttle valve I do believe. the tv cable on the 700r4 have to be set up on carb end and adjusted correctly for them to shift right and last. the electronic ones are the 4L60E (E for electronic) ,if you have low rear axle gears 3:73,3:90 4:11(3:90 is in 55-59 trucks) and small diameter rear tires an overdrive definitely will help drop cruIse rpm. 3:73 gears in OD will be like 2:73-3:08.

[_Ogre]

[Highsider]

Originally Posted by _Ogre

Oh, good...I have MILES of that stuff!

[56 3100]

lol wont shift very good with that tv cable .probably get lots of channels though.

[4544speed]

Ogre, That is funny..... I really like that "tv" cable

[tmoble]

I had a bunch of that tv cable stuff, so I took Ogre's advice and installed it in my truck. A very nicely coiled section, on the floor right above the tranny. It didn't work, the TH400 shifts just like it did before and disappointingly, still no OD. So, IMO it's now proven conclusively that it doesn't work.

[Donaldo]

57 channels and nothing to watch !

700r4 'early' trannys had mechanical shift, later are computer shifted. Some 'early' have mechanical speedometer drives, later ones are for digital speedometers, can be interchanged with corresponding parts..

[_Ogre]

the early ones with tv cable and mechanical shift are also the best for use in our old trucks

fwiw... i've never paid for cable tv, can't justify paying for commercials

[Donaldo]

""the early ones with tv cable and mechanical shift are also the best for use in our old trucks ""

That's what we put in the '51 - rebuilt with red line clutches and a thicker shift plate, and a frame mounted cooler.

[1project2many]

Originally Posted by tmoble

I had a bunch of that tv cable stuff, so I took Ogre's advice and installed it in my truck. A very nicely coiled section, on the floor right above the tranny. It didn't work, the TH400 shifts just like it did before and disappointingly, still no OD. So, IMO it's now proven conclusively that it doesn't work.

Ahh... did you have it connected to hotrod tv? That option allows entire body swaps in just four scenes...

[72freak]

If it is an around town periodic cruiser and the TH350 is already in it just stick with it. You wont need overdrive. If you are going to turn it into a pro tour truck or an interstate driven daily driver DO THE SWAP!

In addition a few thing to think about:

If your truck does scream at higher RPM's it is way easier and cheaper to change the rear end to a higher gear ratio. If you are running the original rear and it was a 6 cyl truck its probably a low gear. Slap a car/truck 10/12 bolt in it from a junk yard or craigslist with a 3.08 or even a 2.73 and your golden. Your "off the line starts" will suffer slightly but now top end will be better. You will need to do the research to see what is the correct width rear. This could be done depending on brake condition for $100 to $300 and possibly a little perch welding and brake work.

If you go with a 700R4/4R, you will need to find or build a good transmission, buy and or do the lock up kit, move back the transmission cross member or buy a new one, shorten the drive shaft, acquire a TV cable bracket and most importantly, if you know nothing about TV cables, have a local trans shop set the cable for you. You can burn up a 700 quickly if your shift points aren't set correctly. $700-$2000

As usual the above is just this mans opinion and we all know about opinions!

[Lowlyfe]

My 56 doesn't have a power train in it yet but I have a th350 in the shed, and a friend offered me a good 700r4 for $150. I'd need to have the drive shaft shortened and build a cross member either way I go. Would it be silly to pass up the offer or stick with the 350? My truck will mostly be a weekend cruiser but will see the highway occasionally.
Sorry if I'm jacking this thread but I figured I'd ask it here since you're all on the subject already.

[Highsider]

Originally Posted by Lowlyfe

My 56 doesn't have a power train in it yet but I have a th350 in the shed, and a friend offered me a good 700r4 for $150. I'd need to have the drive shaft shortened and build a cross member either way I go. Would it be silly to pass up the offer or stick with the 350? My truck will mostly be a weekend cruiser but will see the highway occasionally.
Sorry if I'm jacking this thread but I figured I'd ask it here since you're all on the subject already.

When I think of Montana, I thinks of open spaces with high-speed roads.
700, for sure.
Maybe, 3.23 gears too, like Ogre.

[1project2many]

I'd use the OD transmission. It will work well, even in Helena.

When I lived in Hardin I had a '79 Monte with a 455 Buick, a THM400, 235/75 15" tires, and a 2.26:1 rear gear. That was a good combination for the highway.

What's really important though is what condition is the trans in? Is it an early trans that doesn't have any upgrades? Has it been used for 200k and in need of overhaul? Has it been worked hard and put away wet too many times? IOW, be confident that the work to install the trans is worth it, and that you're not going to be replacing the unit shortly after the truck's on the road.

[_Ogre]

Originally Posted by Lowlyfe

Would it be silly to pass up the offer

ogre thinks you'd be silly to pass on it, but...

depends on your mpy (miles per year) and your expectations out of your truck
weekend cruiser up to glacier or weekend cruiser to the local burger joint?
60 mph weekend cruising or 95 mph weekend cruising; face it, you live in montana
i prefer the option to do both; cruise to glacier at 95 mph, if i so choose
even michigan is thinking about bumping the freeway speeds to 80 mph

either one needs the same basic mods to fit in a task force truck and again... but,
the 700r4 will need modifications as in the lock up kit, there are a couple of versions of the 700r4;
one has a tv cable and controller (good) the other is full computer controlled (bad)

[1project2many]

there are a couple of versions of the 700r4;
one has a tv cable and controller (easy install) the other is full computer controlled (much more work to install)

Fixed it for ya.

[_Ogre]

thanks 1p2m
my wife says i'm a man of few words
all the wrong ones

[Lowlyfe]

The condition of the trans is truly unknown, my friend bought a 90s caprice with the LT1 in it and crashed the car shortly after he got it. I drove the car and seemed to shift fine but it's been a few years. I'll go with the 700r4, too many votes and I know I'll regret it later on. For $150 for a working trans and I'll have to install either trans anyway, it seems like a no brainer. Even if I have to rebuild it later on that would be OK, I'm doing a fresh complete build on my vortec 350 too. Shall be like a new-old truck when I'm through