Turbo 350 Gas vs Diesel........Confused!!!!

[gregg72340]

Hi guys, have read on here a bunch of previous posts about a gas Turbo 350 vs a diesel Turbo 350. So here is my dilemma I have a gas 305 with a Turbo 350 and the trans is shot. I have a diesel parts truck with a 350 Diesel and a Turbo 350 behind hit that has the dual pattern housing on it (BOP and Chevy). Can I use this trans in my gas truck? I Guess basically what mods or adjustments would need to be made to make this shift right behind the gas motor? Also the parts truck is an 81 so would an 81 diesel have a lockup trans in it or would it be just a regular th 350?

My other dilemma is I can get a 79 parts truck that has a good gas th350 in it but would that be a lock up as well or just a regular one? Because the 79 the only thing really good it would have for me is the trans and thats the only reason I would get it as the rest of the truck is a real tired POS.

I have read the other posts n this idea and it just confused the crap out of me on it so hopefully any responses will point me in the right direction

Thanks in advance
Gregg

[codydubb]

From what i understand the diesel th350 has a different valve body in it to make it shift correctly with the diesel engine's rpm range, ive seen one matched up to a gas engine in a friends truck and it shifted horribly way too early, you might be able to switch out the valve bodies and it could work but ive never personally seen it done or know what it would take so dont quote me on it.

[lindstromjd]

The TH350 from the diesel should work just fine; it's the torque converter that controls when the transmission shifts. You'll notice the difference when you pull it apart. Run a diesel engine with a gas TC (if you can even make it work; you'd have to change flywheels too) and it will shift totally wrong. Run a gas engine with a diesel TC and it will give you a lot more low-end power, but no serious difference in top end. I know guys who run diesel TC's because they like the extra low-end power. But the bolt patterns are different on the two TC's; make sure you match the TC with the flywheel.

I know this because I swapped a 6.2 diesel into my pickup with a TH350, and had to get myself a new TC to match the engine. But the trans worked perfectly fine; no wierd shifting at all.

Best way to check if it's a lockup TC is if the trans has an electrical plug on the driver's side. If it does, it's a lockup. If it doesn't, then it's not.

[gregg72340]

Originally Posted by lindstromjd

The TH350 from the diesel should work just fine; it's the torque converter that controls when the transmission shifts. You'll notice the difference when you pull it apart. Run a diesel engine with a gas TC (if you can even make it work; you'd have to change flywheels too) and it will shift totally wrong. Run a gas engine with a diesel TC and it will give you a lot more low-end power, but no serious difference in top end. I know guys who run diesel TC's because they like the extra low-end power. But the bolt patterns are different on the two TC's; make sure you match the TC with the flywheel.

I know this because I swapped a 6.2 diesel into my pickup with a TH350, and had to get myself a new TC to match the engine. But the trans worked perfectly fine; no wierd shifting at all.

Best way to check if it's a lockup TC is if the trans has an electrical plug on the driver's side. If it does, it's a lockup. If it doesn't, then it's not.

So I was wrong in assuming that the governer controlled when this shifted?

[lindstromjd]

Yeah. The internals of a diesel transmission are slightly different, yes, but it's so that they can handle the extra torque of the diesel engine vs the gas; not for when they shift. You shouldn't have any problems by using it.

[spudz]

Originally Posted by gregg72340

So I was wrong in assuming that the governer controlled when this shifted?

no your not wrong.

[lindstromjd]

I stand corrected.

[spudz]

i think all you need to use a diesel trans in gas is converter and governor. The rest is compatable. If you use diesel governor, the shifts will be to fast. The converter doesnt control when the trans shifts, just the stall speed.

[Dieselwrencher]

The only big difference is the torque convertor. I highly doubt any of the internals are different other than maybe a few more clutches in a drum here or there and maybe the govonor. The valve body is the same, maybe with different springs. But the torque convertor for the diesel is heavier duty as in the stator fins are stronger, and they generally have less stall than a gas convertor. Since it sounds like you're in a pinch, you could use that trans and torque convertor behind your 305 and be fine. The stall speed may not be what you prefer, but it should be drivable.

[spudz]

I agree. Thumpin455 put a diesel 700 in his truck and left it alone.
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[billnorman]

Man, I hope you're right. I have a friend with a diesel suburban with a 700r4 that I could sorely use behind my 4.3 with a 3.70 rear. I better see if i can get it from him before he junks it out.

[spudz]

Originally Posted by billnorman

Man, I hope you're right. I have a friend with a diesel suburban with a 700r4 that I could sorely use behind my 4.3 with a 3.70 rear. I better see if i can get it from him before he junks it out.

I think the 700 torque converter had different bolt pattern then gas but I think he just drilled it. I dunno, he used to post on here often. maybe pm him

[lindstromjd]

Originally Posted by spudz

I think the 700 torque converter had different bolt pattern then gas but I think he just drilled it. I dunno, he used to post on here often. maybe pm him

The torque converter has the same bolt pattern on the flywheel; but it's the input shaft that's different between the 700's and 350's. 350's have 27 teeth, and 700's have 32. Just get a gas torque converter and you should be fine.

[Dieselwrencher]

The biggest difference between a TH350 & TH400 torque converter from a 700R-4, is the 700R-4 has a clutch in it for lock up just like a torque converter for a lock up 350. They are not interchangeable with TH350's & TH400's either.