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Discussion in '1982-Present GM Diesel' started by 55Willy, Sep 5, 2005.
is the only thing different between a diesel th400 and a gas th400 is the torque convertor?
does the same hold true for a th350 and 700r4???
What is the difference? stall speed?
Diesel torque converters have a lower RPM range . If swapping transmissions you need to swap governers . The Diesel one has a lower RPM for shifts .
I believe the shift modulator is different also. I have a built gas turbo 400 in my 6.2 burb. It works, just shifts at higher RPMs than the diesel 400 normally would. Mine seems to shift out of first at about 35mph and into 3rd at 55mph. I kinda like this for normal driving because you get up to speed faster, but it sucks if speed limits are 25-35, never gets a chance to get out of first.
just installed a 350 in place of a 6.2 and it looks like the TQ bolt holes dont line up to a 350 flywheel.
This is on a 700r4
dual bolt pattern??
Perhaps the flexplate has 2 sets of bolt holes?--most GM's have two,one set fits the TH350 and the other fits the TH400 and others..never looked at my 6.2 convertor,so you could be right!..
86 DieselBurb--I think the modulators might be listed as "different" in the parts catologs,but are basically the same thing as a gas tranny uses--the spring inside MIGHT be a hair less or more tension..its likely the GOVENOR in your tranny being calibrated for a gas engine thats causing your "late" shifts..a modulator "'adjustment" screw only varies the speed of the shift about 5-10 mph and the "firmness" of the shift from one end of its adjusment range to the other...
I ran the vacuum directly from the vacuum pump to the modulator on my TH400 in my 82 K20--the "VRV" valve (Vaccum regulator valve) was shot on my truck,it regulates the amount of vacuum sent to the modulator,so it mimics the vacuum a gas motor has(a diesel with a vacuum pump makes vacuum at ALL speeds,and INCREASES as the RPM goes up--just the opposite of a gas motor,and that valve bleeds off the vacuum to the modulator as rpm increases)...
I had to screw the adjustment screw on the modulator IN all the way to compensate for the excessive vacuum,(at the advice of an experienced tranny rebuilder,this is what he does in cases like mine)--and it still shifts a bit too soon and soft for my liking--I'd replace the valve,but GM no longer sell it,and junkyards wont "break up" a running motor,or they are junk like mine already ..I'm hoping it wont shorten the life of my tranny--I plowed 25 bad storms last winter,and so far its holding up fine--hope it stays that way!
They should line up my tranny came out of a gas 350 and thats all I changed was the govenor
Alright maybe its a year to year difference thing. The tranny is in a 1984 model c-10 with a 6.2 it has 6 bolt holes in the TQ convertor(700r4)..... the block is a rebuilt 4 bolt main out of a 90 model 3/4 ton.....was in front of a th400....thinking about it now I bet thats where the difference is, if i remember right though that was a 6 bolt hole flywheel as well
6 bolt converters?
Only 6 bolt torque converter I ran into on a GM was in a chevy van that had a 292 straight six in it,I think it was a TH350,but I'm not sure(long time ago!)..We bolted it to a 3 bolt flexplate ,the three holes lined up..just left the other 3 empty!--not sure if you can do this in your case..
My th400 has 6 bolts as does my 4l80...both diesel units.
All GM converters had 6 bolts remans have 3 go figure ????
not true, you can get remans with 3 and 6. it depends on the application. almost every diesel has 6 bolts while almost every gas has 3. there are a few that crossover, but not many.
so whats the lock up rpm for a diesel convertor? i may just run it if it will match my engine, probably not though.
a diesel converter usually stalls around 1000-1200. the lowest gas converter stalls around 1400.
There are some gas TC that lock up at 1250 and the diesels are 950 to 1100.
All diesel TC have six bolts.
You need to change the governor and the TC that is all.
I ahve doen some of those swaps and I have talked to tranny builders, some claimed it was more and then I started asking them questions, specific questions about what and why and I explained what you would only need those 2 items and they eneded up saying oh well you could do it that way but we have different part numbers for GAS and DIESEL.
question... I'm using a caddy 472 engine with it's early torque curve, and using a TH400 out of a M1008. which parts should I switch to get the best economy? I have both the caddy 400 and convertor, as well as the diesel one.
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