Better Tranny

[chanclas90063]

Good morning Group, I have a 1970 C-10 with a 350ci engine and 350 tranny. The tranny has been slipping and I was considering having it rebuilt but while I was at the mechanic's shop, he offered me a 400 tranny which he claims is better than my 350. I would appreciate any advice offered on this board. Much appreciated...

[leftybass209]

Your 350 is most likely fine. The 400 is a stronger transmission, if you plan on throwing a lot of torque in the mix.

We would need more info about your motor, and your plans for your motor to truly tell you which would be better for your application.

[hamjet]

I haven't checked but are they the same length? if not, more money for drive shaft change, plus are they going to make sure you have the correct speedo gear too?

[davepl]

TH350s were $75 twenty years ago, and while I have no idea what they're worth now, if you swap to the stronger 400 you'll run into crossmember and driveshaft length issues.

If your truck has the small floor hump, I'm not actually sure it'd fit in the truck.

[71meangreenc10]

You will need to change the Driveshaft Yoke and probably adjust the lenght on it. Along with what is mentioned above how do you plan on getting the kickdown to work?

Smitty

[Stocker]

TH400 trans is designed for the extra torque of a big-block. So yes they are stronger, but they also rob horsepower -- can't recall the exact number but I think I have read it's 40-50 HP. If you have a typical small block, the TH350 is plenty good as well as less expensive. If you're gonna change the trans anyway, why not upgrade to a 4-speed or OD trans?

[chanclas90063]

Many thanks to this group for the responses. The engine is from a late 70s Camaro and according to my mechanic, is in good shape. I would like to put a little more power into the motor, but I prefer to find me a good mechanic locally that can advise me on upgrades. Anyway, based on the comments here, I think that I will forego the change of tranny and stick with the current 350. Thanks again folks, you responses are much appreciated...

[hugger6933]

Your looking at uneeded expense to change to a 400 trans when a 350 will be plenty strong for what your gonna do.For the cost of the stuff needed to change it over to be right, you could have the 350 rebuilt. Jim

[chanclas90063]

Originally Posted by hugger6933

Your looking at uneeded expense to change to a 400 trans when a 350 will be plenty strong for what your gonna do.For the cost of the stuff needed to change it over to be right, you could have the 350 rebuilt. Jim

Thanks to you all, after reading the comments here, I made the decision to stay with the 350 and if I decide to change later, I will consider a 700R4. I appreciate all of the comments they came in handy in making my decision. Thanks all

[special-K]

The TH350 is about as good as automatic transmissions ever got.

[BCOWANWHEELS]

350th is tons better than the 700r4

[chanclas90063]

Originally Posted by BCOWANWHEELS

350th is tons better than the 700r4

WOW!!! I am really surprised, I was told that the best tranny for my truck is the 700R4. Guess he was just trying to make a sale... Thanks for the info...

[MARKDTN]

700R4 got a bad rep because of the weak front pump and some internals in the early ones. Then they got a bad rep for retrofits because people did not hook up or adjust the TV cable. There is nothing wrong with a good 700R4. It is the basis of the current 4L60E. If you use a 700R4 you must properly adjust the TV cable.

TH350 is an OK transmission. I would not swap to a TH400 just because I could get one cheap, HOWEVER the TH350 with some power in front of it will eventually grenade and when they go they basically self destruct. In your case with a stock engine, I would rebuild the TH350 that is there. If you later go to a blown 454, don't expect it to last forever.

[leftybass209]

Originally Posted by chanclas90063

WOW!!! I am really surprised, I was told that the best tranny for my truck is the 700R4. Guess he was just trying to make a sale... Thanks for the info...

The best transmission for your truck is the one that suits your needs and driving style. If you do a lot of highway driving, and you like lots of low end torque for stoplight acceleration, then yes, an OD would provide the biggest benefit. Saying the 350 is tons better than the 700 is very subjective with no proof or comparison to warrant otherwise. A 350 is just a more user friendly transmission for those that don't know or want to know how to make a 700r4, or any other OD trans work correctly. When looking at transmissions, it's never cost effective to swap to or from one another to gain a particular trait, because the investment rarely ever nets a profit (mostly when talking about gaining gas mileage by swapping to an OD trans).

However, it can be beneficial when the original transmission is already shot. Time and time again we discuss the OD trans swap. It's too expensive to warrant the swap without the right rear gearing, and I never recommend dropping in a junkyard OD trans to save a dollar.

My truck came with a 700r4 when I bought it. Had it a Th350 when purchased I would never have made the swap unless the trans went out. I'd always suggest a comparison between the 2004r and a 700r4 when considering an OD trans because they are geared differently and one may benefit the owner more.

Since you've already considered keeping the 350, truck along with that idea. It's a cheap rebuild/replacement, and you know it already bolts right it. Best of luck!

[kehstr]

a 700r4 is just a turbo350 with overdrive

[leftybass209]

Originally Posted by kehstr

a 700r4 is just a turbo350 with overdrive

No, that is an inaccurate comparison.

gear ratios are as follows:

700r4 1st, 3.06, 2nd 1.62, 3rd 1.00, 4th 0.70, reverse, 2.29

TH350 1st 2.52, 2nd 1.52, 3rd 1.00, 4th x.xx, reverse, 1.93

Only 1 gear has the same ratio. The cases are shaped different, and there are different weights due to the difference in an extra gear.

A TH350 is 21 5/8" long with a 6, 9 or 12" tailshaft. A 700r4 is 24" long with a 6" tailshaft.

[kehstr]

i stand corrected, but the general idea is that it's a 350 with overdrive

[Gimme Jimmy]

The t400 is much tougher but the gearing is slightly higher.

[jocko]

You can easily beef up the TH350 for a mild small block, if you feel the need. But, stock is probably fine. In your case, TH400 too much of a headache. If you don't mind extra work or paying for extra work - get a 2004R. Overdrive at approx. same length as TH350 (no driveline mods, just some trans tailshaft mount re-wickering). Your mechanic probably has a TH400 ready to go, perhaps that is why he's pushing for it. If he thinks it's the same amount of work to put in as the current TH350, I'd find another mechanic, then the transmission.

[Chrisbeds82]

I have good strong 350 with a mild shift kit that I'm going to be taking out of my truck in the next couple weeks if you're interested. I was told it was just rebuilt a couple years ago and doesn't have many miles. Let me know. What area are you in? I travel a lot and may even be able to deliver.
Only pulling it out for an LS swap with a 4L80