Recommended Transmission for 5.7L 350 V8

[Auroch]

Hey forum,

considering upgrading my current setup (TH350). I'm torn between the TH400 or the 700r4. I plan on doing some towing and would like to keep the rpms a little lower on the highway.

[jocko]

Pretty much everyone gets torn on this question at some point.
TH400 alone would be an HD upgrade without a reduction in highway rpm.
700R4 would be a reduction in highway rpm without the strength required for an HD application.

Assuming you want to stay with an automatic, the only (or perhaps just the best) way to accomplish both goals in a single upgrade is to upgrade to a 4L80E. (or something like that)
Another approach that will be more expensive in the long run is to upgrade to TH400 and Gear Vendors over/under drive behind it. But by the time you upgrade all that stuff, you probably could have worked a 4L80E swap...

So, what are you going to tow?

If a BIG trailer, I'd go with :
- TH400 and just accept the highway rpm
- TH400 with GV
- 4L80E

If a tiny trailer:
- retain the TH350 and add a GV for your reduced RPM highway use.
- or perhaps go with a well built 700R4 (check Bow-tie Overdrives site).

What kind of truck? C or K / 10 or 20

[Auroch]

Originally Posted by jocko

Pretty much everyone gets torn on this question at some point.
TH400 alone would be an HD upgrade without a reduction in highway rpm.
700R4 would be a reduction in highway rpm without the strength required for an HD application.

Assuming you want to stay with an automatic, the only (or perhaps just the best) way to accomplish both goals in a single upgrade is to upgrade to a 4L80E. (or something like that)
Another approach that will be more expensive in the long run is to upgrade to TH400 and Gear Vendors over/under drive behind it. But by the time you upgrade all that stuff, you probably could have worked a 4L80E swap...

So, what are you going to tow?

If a BIG trailer, I'd go with :
- TH400 and just accept the highway rpm
- TH400 with GV
- 4L80E

If a tiny trailer:
- retain the TH350 and add a GV for your reduced RPM highway use.
- or perhaps go with a well built 700R4 (check Bow-tie Overdrives site).

What kind of truck? C or K / 10 or 20

Thanks man! Nice recos. Might be leaning towards the 700r4. I have a 1970 c10. As for what I'll be towing; a medium size fishing boat / medium sized trailer.

[truckster]

I would go with a built 700R4 if for the C10 - it's not designed to haul heavy loads anyway, and with a fairly stock 350 you're not likely to overstress it as long as you keep it cool.

BUT - I have to ask what your rear gear is and how heavy the load is. You may be throwing money at a problem that doesn't really exist.

[Auroch]

Originally Posted by truckster

I would go with a built 700R4 if for the C10 - it's not designed to haul heavy loads anyway, and with a fairly stock 350 you're not likely to overstress it as long as you keep it cool.

BUT - I have to ask what your rear gear is and how heavy the load is. You may be throwing money at a problem that doesn't really exist.

Yeah I've considered sticking with the th350. Don't think I'd top 3500lbs in tow weight. I'm not sure what rear gear I have, I assume it's the stock gear that comes in a 1970 short bed. Have to check on that and get back to you.

[Mike C]

The GearVendors makes zero sense behind a TH350. The $3000 cost of admission is still limited by the strength of the trans.

A TH700R4 can be built for moderately heavy towing. At least as much as a 1/2 ton truck should be pulling. The 700 is based on the TH350 so the overall strength is about the same but both can be upgraded. IMO, if you need to do a trans and you can't rebuild it yourself I would go to the TH700. I am more of a fan of the TH200 4R, but you are looking at spending a good chunk to get one to hold up under a lot of weight. I'm saving my nickels to get an ExtremeAutomatics TH200 4R for my '69 short step I'm putting a 427 in.

[jocko]

Originally Posted by Mike C

The GearVendors makes zero sense behind a TH350. The $3000 cost of admission is still limited by the strength of the trans.

It depends. The TH350/GV statement was specific to the case of towing a 'tiny' trailer - in which case strength isn't the problem trying to be solved. In the OP's case, towing something light reduces the problem to just addressing highway rpm. Price of admission is high with either approach considering what a well built 700R4 will cost along with the time (and/or additional cost) of moving the engine forward or t-case backward, TV-made EZ kit for most folks, line pressure check capability, and the resultant driveshaft changes. GV install is quite a bit simpler. But I do agree, a GV approach is still likely going to be the more expensive route. A GV unit is more easily reversible than an O/D trans swap (for those that have a thing for the ability to return a truck to an all original numbers matching config - I'm not one of them, but some do care about that). It's also a gear splitter, so, O/D in all 3 gears - a 6 speed of sorts. That's more a bonus than an actual utility, but some might like that aspect of it.

On the other hand, if strength was the goal, why choose a 700R4 at all over a 4L80E?

Now here's a question that might help tip the scales toward a 700R4 over a 4L80E... does a 4L80E fit in a low hump truck? Any mods required for a high hump? That's territory many would rather avoid (myself included, if I can help it). I don't know the answer, am curious.

[AussieinNC]

4L80E behind a 350 in 67 low hump cab...no issues with clearances in my build....

[Mike C]

Originally Posted by jocko

It depends. The TH350/GV statement was specific to the case of towing a 'tiny' trailer - in which case strength isn't the problem trying to be solved. In the OP's case, towing something light reduces the problem to just addressing highway rpm. Price of admission is high with either approach considering what a well built 700R4 will cost along with the time (and/or additional cost) of moving the engine forward or t-case backward, TV-made EZ kit for most folks, line pressure check capability, and the resultant driveshaft changes. GV install is quite a bit simpler. But I do agree, a GV approach is still likely going to be the more expensive route. A GV unit is more easily reversible than an O/D trans swap (for those that have a thing for the ability to return a truck to an all original numbers matching config - I'm not one of them, but some do care about that). It's also a gear splitter, so, O/D in all 3 gears - a 6 speed of sorts. That's more a bonus than an actual utility, but some might like that aspect of it.

On the other hand, if strength was the goal, why choose a 700R4 at all over a 4L80E?

Now here's a question that might help tip the scales toward a 700R4 over a 4L80E... does a 4L80E fit in a low hump truck? Any mods required for a high hump? That's territory many would rather avoid (myself included, if I can help it). I don't know the answer, am curious.

I automatically default to what will work best for the least amount of money to be spent. A $1500 TH700 should be more than capable of the work required for a 1/2 ton truck IMO. And if it were mine I would be towing with converter unlocked in 3rd gear.

If I wanted a 4L80E in a truck, I would buy a 2500HD that had one it along with a 6.0 V8 and swap it all in using factory electronics. The aftermarket trans controller is a big expense with the 4L80.

It won't be long before we don't talk about these 4 speeds at all as the 6 and 8 speed trans will start to be the more common swap when price starts coming down and that will be the bomb.

In my own truck I plan on running the TH200 4R. My reasoning is that it has the most logical gear spread of any of the 4 speed automatics. The TH700 has too low a first gear and too wide a spread between first and second from a total performance standpoint (Once again, these are all my opinons...) and the 4L80E suffers from insufficient first gear, IMO. But the TH200 4R has an almost ideal split on the 1-2 gears and more overdrive than either of the other two. But the drawback is cost. In my case, it's worth the $3500 or so that it will cost to make this happen.

As usual, YMMV.

[jocko]

thanks, good to know

[jocko]

I like your work best for least money approach. And as I read back thru my comment I realize I mixed some of my own truck's considerations into the OP's discussion (i.e. moving eng fwd or t-case backward, etc - that's a 4x4 consideration (i.e. mine), not the OP's (sorry about that Auroch!) I like the 2004R also - specifically because the 1st gear is not as deep, but also because of its overall dimensions, not sure why it always seems to get less press than the 700 most of the time. Have you looked at the high perf 2004Rs at Bowtie Overdrives? I haven't looked recently, but I don't recall them being much more expensive than the 700s.

[Mike C]

I'm putting an L36 427 in my truck with a Nitrous grind hydraulic roller which should be 450hp and 500lb/ft so a trans that will hold up runs around $3500 by the time you are all in.

Bowtie Overdrives does not have as good a reputation as Extreme does. And my buddy has an Extreme that had issues when he got it (as autos can and will have) and they were very prompt in taking care of it including shipping both ways.

You mentioned TV cable adjustment earlier, and just to add to the knowledge in this post check out constant pressure valve bodies. You still need to have TV adjusted correctly for shifting, but the eliminate trans failure from misadjusted TV.

http://www.tciauto.com/tc/valve-bodi...-pressurehtml/

[Auroch]

Originally Posted by jocko

I like your work best for least money approach. And as I read back thru my comment I realize I mixed some of my own truck's considerations into the OP's discussion (i.e. moving eng fwd or t-case backward, etc - that's a 4x4 consideration (i.e. mine), not the OP's (sorry about that Auroch!) I like the 2004R also - specifically because the 1st gear is not as deep, but also because of its overall dimensions, not sure why it always seems to get less press than the 700 most of the time. Have you looked at the high perf 2004Rs at Bowtie Overdrives? I haven't looked recently, but I don't recall them being much more expensive than the 700s.

Haha all good Jocko, I'm learning a ton from you guys. This has definitely opened my eyes to other possibilities. I hadn't even looked at the TH700 or the 2004R.

[PepperTreeGarage]

Gear Star Transmission website works great for some comparison shopping.

https://gearstar.com/

[GASoline71]

TH350's are stouter than people give them credit for. Even in stock form.

What RPM are you turning? Most people nowadays are spoiled with modern EFI and OD transmissions. If you're worried about parts and longevity... a 350 with a TH350 is made to take the RPM's and live. However, your wallet may not be able to with fuel consumption.

Gary

[Auroch]

Originally Posted by GASoline71

TH350's are stouter than people give them credit for. Even in stock form.

What RPM are you turning? Most people nowadays are spoiled with modern EFI and OD transmissions. If you're worried about parts and longevity... a 350 with a TH350 is made to take the RPM's and live. However, your wallet may not be able to with fuel consumption.

Gary

Yeah, I'm probing the options. I was reading an article on the TH350 that actually gave it very high praise and I can understand why. But yeah, saving on gas would be nice. I've done a few upgrades that I think help me out on fuel economy, carb, exhaust and new intake manifold. So I might have a good balance (maybe). If the transmission starts failing I'll definitely upgrade it to a 4 speed, just not sure which yet. Probably the 700R4 from what I've gathered so far. I also like how light the TH350 is in comparison to the rest, while putting out respectable performance.

So about the RPMs, it's my fault, I have a lead foot... I push the truck too much on the interstate. I don't have a tach on my truck yet, by the sound, I'm guessing I must be doing 4000 rpm on average; that sound right?

[tdangle]

You may really want to find out what gear ratio you have before doing anything. According to the documentation I see, a 70 C10 with the optional 350 and TH350 trans, the standard ratio is 3.07. You shouldn't be seeing 4000 RPM on the freeway unless your driving 90+

Also something to consider is you may never recoup the money to put a OD automatic in improved gas mileage unless you drive a lot. I put a 2004R in my truck since I have 4.10 gears. My mileage improved from about 9.5 to 13.5 MPG.

[WorkinLonghorn]

Originally Posted by tdangle

You may really want to find out what gear ratio you have before doing anything. According to the documentation I see, a 70 C10 with the optional 350 and TH350 trans, the standard ratio is 3.07. You shouldn't be seeing 4000 RPM on the freeway unless your driving 90+

Also something to consider is you may never recoup the money to put a OD automatic in improved gas mileage unless you drive a lot. I put a 2004R in my truck since I have 4.10 gears. My mileage improved from about 9.5 to 13.5 MPG.

tdangle; I can see getting better mileage with an overdrive and 4.10 gears but if he does indeed have the stock 3.07 gears then he will probably LOSE mileage with an overdrive and a carb'd engine.
But if he is guessing 4000 RPM then he either has a much lower ratio or he is a madman. -BA

[tdangle]

Originally Posted by WorkinLonghorn

tdangle; I can see getting better mileage with an overdrive and 4.10 gears but if he does indeed have the stock 3.07 gears then he will probably LOSE mileage with an overdrive and a carb'd engine.
But if he is guessing 4000 RPM then he either has a much lower ratio or he is a madman. -BA

I agree he may lose mileage. Years ago I had a 84 dodge 1/2 ton with a 318 and auto trans with 2.94 gears. I changed them out to 3.55 and actually got a couple of miles per gal better.

[GASoline71]

Originally Posted by Auroch

So about the RPMs, it's my fault, I have a lead foot... I push the truck too much on the interstate. I don't have a tach on my truck yet, by the sound, I'm guessing I must be doing 4000 rpm on average; that sound right?

I have a TH350 and a snotty 355 in my rig with 3.73 butt gears. I turn right around 3,400 at 60mph on the interstate. At 70mph i'm close at about 3,900 RPM's. My truck gets 6 to 8 mpg no matter what.

I don't tow or haul with it... except haul a$$. It's also not my DD so it's okay if it sits around.

Gary

[WorkinLonghorn]

I have a TH350 and a snotty 355 in my rig with 3.73 butt gears. I turn right around 3,400 at 60mph on the interstate.

GASoline71, that seems too high. Either you have 23.23" tires or your tach is off if I am using this calculater correctly (assuming 5% TC slippage); http://www.wallaceracing.com/calc-gear-tire-rpm-mph.php

I have 3.73 gears but with a manual and 31" tires and I spin 2500 at 60. -BA

[GASoline71]

I have 26" tall tires.

Gary

[geezer#99]

http://www.advanced-ev.com/Calculators/TireSize/

Your numbers say 22 inch tall tires.

[HO455]

T350's are good. We have have one our 64 GTO with a destroked 455. It has pulled 450 + pound feet of torque on several chassis dyno's and runs in the low 11's. We only have run it on street tires and no trans brake. Which i am sure has keep it alive. At 3200 lbs it is lighter than your truck but I wouldn't think twice about running one with your plan.