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Deisel to gas trans swap questions

rfda_454

rfda_454

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So i have a th400 out od a deisel blazer, i am swapping it into my 88 k5 with a tbi 350, im not sure if the flax plate is the same or it this is going to require a torque converter and govener change? any one have any info on this, did a search but nothing for sure,
 
rfda_454 said:
So i have a th400 out od a deisel blazer, i am swapping it into my 88 k5 with a tbi 350, im not sure if the flax plate is the same or it this is going to require a torque converter and govener change? any one have any info on this, did a search but nothing for sure,
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Flexplate is the same but unless you are putting it behind a 454 I would suggest you change the TC and governor
 
also dont forget a new vacuum modulator as well. only about 12 bucks.

also might want to check your output shafts as well, i believe the 350 has 27 spline and the th400 is 32 unless you also got a new transfercase in which case you are good to go.
 
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New vacuum modulator, torque converter and a gas governor. Just went threw this myself last fall. Flex plate will bolt right up with three bolts
 
Why change the converter? They bolt up. I called the trans shop to buy a converter when I swapped my CUCV 400 into my K5, he said he would sell me one, but the one I had would work exactly the same. Same stall speed and everything.
 
I happened to have a gas converter given to me to put in, so I used it. from what I was told the diesel has a lower stall??? Can always use the diesel one and if it seems to low take a day and swap a gasser in. Thinkin back the diesel one was a tad bigger in diameter than the gas one I put in...
 
mill5471 said:
I happened to have a gas converter given to me to put in, so I used it. from what I was told the diesel has a lower stall??? Can always use the diesel one and if it seems to low take a day and swap a gasser in. Thinkin back the diesel one was a tad bigger in diameter than the gas one I put in...
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Yes the diesel TC is lower stall, that is why I said if you were putting a 454 you would be OK because it produces a lot of torque at low RPM, but it would kill your 350 take off power.
Yeah it will bolt up like cruz89k5 said but it will not run good.
 
Mine ran fine. What's the stall speed of both converters? I tend to believe the local trans guy that their stall speed is the same. Based on the way that mine drove and the fact That old man has forgotten more than I'll ever know about transmissions.

Edit:

I'd like to know for sure in case Im giving bad information. I dont intend to come off as an ass. After re reading I know it sounded that way. I know I ran the same internals with the stock diesel converter and a stock gas converter and noticed no change in drivability, which is why I think his information was accurate.
 
ok the one think im still ot 100% on is, is the flex plate off the 6.2 going to work on my sb350 the k5 had a 4 speed in it befor so i was just going to use the flex plate that came off the 6.2
 
I'm preety sure the 6.2 uses a different flex plate,you'll have to get one off a gas engine.............................I have read where GM installed the lower stall speed torque converters on gas engined trucks as a fix when they had some problems with shudder on some trucks ,and I know more than one person who stuffed a diesel TH400 right into a car he was building and he liked the way it felt with the lower stall speed............................................also know guys who bought used trannys from salvage yards out of gas powered trucks and put them behind a 6.2 and just used three out of the six bolts on the flex plate,and haven't noticed any big difference driving the trucks...the govenors on diesels are calibrated to upshift a bit sooner,but probably not enough to make a huge difference really--same with the stall speeds,they are only a few hundred RPM's lower on a diesel version...they sell low stall speed torque converters for towing use that have less slippage than the usual ones,that are probably the same as a stock diesel one or close to it...
 
I just put my th400 out of my diesel suburban behind a tbi 350 in another burb. Just bolt up the three converter bolts that match the 350 flexplate and it will work fine. I didnt change the converter or governor. My th400 has an aftermarket low stall/towing converter for the diesel, and is very noticeable behind the tbi350. I have towed with it quite a bit (with the 350) and suspect that it would pull better with a stock converter, but it does a good job of keeping temps down and keeping rpm down. At 65, if I floor it rpm only goes from 2600 to maybe 2750. As far as the governor, my shift points are fine.
 
MNorby said:
Is the diesel internal or externally balanced?
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The flex plate will not work on a gas engine.
Each engine has a different flexplate.
Even if the engine is internally balanced, the crank will have a different bolt pattern.
 
imiceman44 said:
The flex plate will not work on a gas engine.
Each engine has a different flexplate.
Even if the engine is internally balanced, the crank will have a different bolt pattern.
Click to expand...

This info is not.exactly correct being as I have seen the same flex plate bolt to a 350 454 ant a tall deck 427. Not run that way but pulling one engine n swapping parts was put on by mistake but still bolted right on. I plan to.compare the 350 and the 6.2 flex plates because they look identical.
 
so you are saying that both your tbi 350 and 6.2 flexplates have no weights? I just looked at my tbi 350 and 6.2 flexplates, and they do have weights.
 
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