New to me C20 questions - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ajcan · 03-29-2009, 09:23 PM

Hi All

I am new here and to Chevrolet's.
I just picked up a 1970 C20 Camper special.
It has the 350/350 setup.
I would like to have overdrive so it is not screaming at highway speeds.
My first of many future questions is,
Is the turbo 400 transmission the same as the 350 but with overdrive?
If it is what is involved in a swap?
I know it will bolt up to the engine.
What is involved in the linkage and everything else?
I know from looking there is a short tail and a long tail.
Mine is short,
So if I get a 400 transmission with short tail is the driveshaft re useable?
Thanks for any help you can give.

AJ

72BlckButy · 03-29-2009, 09:44 PM

AJ, let me be the first to say:

the board from Mid-MO!!!

It looks like you picked up a great looking C20.

I'll let someone else chime in on changing out the tranny, but best of luck on with your truck.

**Green Machine** · 03-29-2009, 09:55 PM

Hi - and WELCOME !! Best place ever for the info you need. Turbo 400 is not an overdrive, just a beefier version of the Turbo 350. What you are looking for is likely a 700R4 trans. Go to the top op the page in the google search and type in 700R4 and select this site. Lots of good info on the swap.

willyCJ · 03-29-2009, 10:20 PM

Green's advice is correct, you likely want a 700R4. It should be longer than your TH350 currently in place.

I'm in a somewhat small town and we have 2 shops that do driveshaft work. Getting a shaft shortened isn't too expensive. ($50-100)

rico7769 · 03-29-2009, 10:29 PM

Piggybackin on everyone else, the TH400 is a stronger tranny. The biggest difference is going to be the fact that your kickdown cable doesn't exist as it would on the TH350. It is replaced with an electronic switch/silenoid on the driver side of tranny that regulates the kickdown based on pedal location or throttle position. Also, your vacuum modulator is on the pass side instead of the rear of the tranny. Have it checked out really well as the TH400 trannys were notorious for difficult 2-3 shifts. Good luck with the new project! You are in good company here!

Steve

Critter · 03-29-2009, 10:39 PM

Also, there is such thing as a 200R4 OVERDRIVE transmission that you should consider. Some say they are easier to swap in place of a TH350 than a 700R4. They are harder to find though. Here is some good info...

http://67-72chevytrucks.com/vboard/s...d.php?t=188948

ajcan · 03-30-2009, 06:29 PM

Thanks for the warm welcome and the replies.
I guess maybe in the future I could look for a 700R transmission and maybe a switch for lock-up.I was told today that the lock-up is the only thing electronic involved.
Thanks again.I will be back for more help in the future I'm sure.

AJ

jbarron · 03-30-2009, 07:15 PM

The 200R4 is the same size as the th350 and requires no change to the drive shaft. If you are not building some monster motor than the 700r4 is not needed. A properly build 200r4 is plenty strong enough. You do need to setup the newer trannys(700/200) right or they will burn up really quick. I now what you mean about rpms at highway speeds the campers usually had 4:10 gears.

Also if you put in a 200 the transmission cross memer will still work from the th350, since ther is another set of holes in the frame that match up perfectly for the mount on the 200.

If you are going to find a 200 in a junk yard you will need to find one for a grand national or montecarlo ss. Not all 200 are made to handle the same stress.

You have to ask if it is worth the cost. I get around 15mpg on the highway with a 200 in the same truck as yours. It drops the rpms to around 2200 at ~70. I usally don't use the overdrive in town, but it s nice on the highway.

My th350 lost 3rd so it was worth doing at that time. Either trans will cost much more than a 350/400.

ajcan · 03-30-2009, 08:18 PM

jbarron,
I will be keeping this engine stock.Should something happen to this motor down the road it will just get a crate motor.
With that being said the 200r4 should fit the bill fine.
A transmission upgrade probably won't happen till later down the road.
This truck runs and drives but needs a lot of work.
Many leaks and other problems.

My next question is,
My oil pressure guage reads about half way up when driving but drops down near "L" when at idle.Is this reason for concern or does it sound right?
Thanks.

AJ

03-29-2009, 09:23 PM	#1
ajcan Registered User Join Date: Mar 2009 Location: Covington Georgia Posts: 87	New to me C20 questions Hi All I am new here and to Chevrolet's. I just picked up a 1970 C20 Camper special. It has the 350/350 setup. I would like to have overdrive so it is not screaming at highway speeds. My first of many future questions is, Is the turbo 400 transmission the same as the 350 but with overdrive? If it is what is involved in a swap? I know it will bolt up to the engine. What is involved in the linkage and everything else? I know from looking there is a short tail and a long tail. Mine is short, So if I get a 400 transmission with short tail is the driveshaft re useable? Thanks for any help you can give. AJ Attached Images

03-29-2009, 09:44 PM	#2
72BlckButy Tot Roddin' Join Date: Apr 2005 Location: Mid-MO Posts: 24,461	Re: New to me C20 questions AJ, let me be the first to say: the board from Mid-MO!!! It looks like you picked up a great looking C20. I'll let someone else chime in on changing out the tranny, but best of luck on with your truck. __________________ -Nate 1969 CST SWB - Project Blank Slate (4.5/6" ECE Static Drop, 6-lug disc brake upgrade (manual), Billet Specialties Vintec 20x8.5 255/40 (F) 20x10 295/40 (R), 250 I-6) 1960 AMF Skylark - Tot Roddin' (Lowered with custom frame; soon to include custom push bar and interior) 2008 Silverado CrewCab 1LT (5.3L, 3:73, 4x4, LT1, Z-71, Towing Package)

03-29-2009, 09:55 PM	#3
Green Machine Senior Member Join Date: Jul 2004 Location: Estherville, Iowa Posts: 3,371	Re: New to me C20 questions Hi - and WELCOME !! Best place ever for the info you need. Turbo 400 is not an overdrive, just a beefier version of the Turbo 350. What you are looking for is likely a 700R4 trans. Go to the top op the page in the google search and type in 700R4 and select this site. Lots of good info on the swap. __________________ 1968 C10 307 3spd Long Fleet ------ http://67-72chevytrucks.com/vboard/s...d.php?t=201103 1970 C10 305 Super T10 Long Fleet --- http://67-72chevytrucks.com/vboard/s...d.php?t=202285 1971 C20 383 TH350 Dana Posi ----- http://67-72chevytrucks.com/vboard/s...d.php?t=206894 2001 GMC Sierra 1500 C3 6.0

03-29-2009, 10:20 PM	#4
willyCJ Registered User Join Date: Mar 2009 Location: Lafayette, IN Posts: 37	Re: New to me C20 questions Green's advice is correct, you likely want a 700R4. It should be longer than your TH350 currently in place. I'm in a somewhat small town and we have 2 shops that do driveshaft work. Getting a shaft shortened isn't too expensive. ($50-100) __________________ 1970 Shortbed C10 Parts I need: Headlight Switch, Headlight retainers, Bezels (found, thanks jc) wiper arms, wiper switch (found, thanks jc) Carpet (blue/black preferred) about half the e-brake cables (for a shortbed truck)

03-29-2009, 10:29 PM	#5
rico7769 Hybrid67 Join Date: Jan 2009 Location: Martinez, GA Posts: 195	Re: New to me C20 questions Piggybackin on everyone else, the TH400 is a stronger tranny. The biggest difference is going to be the fact that your kickdown cable doesn't exist as it would on the TH350. It is replaced with an electronic switch/silenoid on the driver side of tranny that regulates the kickdown based on pedal location or throttle position. Also, your vacuum modulator is on the pass side instead of the rear of the tranny. Have it checked out really well as the TH400 trannys were notorious for difficult 2-3 shifts. Good luck with the new project! You are in good company here! Steve

03-29-2009, 10:39 PM	#6
Critter Future TOTM Winner Join Date: Aug 2006 Location: Bulverde, TX Posts: 2,692	Re: New to me C20 questions Also, there is such thing as a 200R4 OVERDRIVE transmission that you should consider. Some say they are easier to swap in place of a TH350 than a 700R4. They are harder to find though. Here is some good info... http://67-72chevytrucks.com/vboard/s...d.php?t=188948 __________________ 72 Chevy CST K5 HIGHLANDER BLAZER Getting a 6.0,NV4500,NP205,14BFF (Currently laying all over the place in little pieces) 72 Chevy swb step-side "LS" 6.0 Here's a build thread of sorts 2002 HD2500 Crew Cab, 8.1L Allison 4x4 Daily Driver Check it out www.lsdyno.com

03-30-2009, 06:29 PM	#7
ajcan Registered User Join Date: Mar 2009 Location: Covington Georgia Posts: 87	Re: New to me C20 questions Thanks for the warm welcome and the replies. I guess maybe in the future I could look for a 700R transmission and maybe a switch for lock-up.I was told today that the lock-up is the only thing electronic involved. Thanks again.I will be back for more help in the future I'm sure. AJ

03-30-2009, 07:15 PM	#8
jbarron Registered User Join Date: Apr 2006 Location: Spring, Texas Posts: 167	Re: New to me C20 questions The 200R4 is the same size as the th350 and requires no change to the drive shaft. If you are not building some monster motor than the 700r4 is not needed. A properly build 200r4 is plenty strong enough. You do need to setup the newer trannys(700/200) right or they will burn up really quick. I now what you mean about rpms at highway speeds the campers usually had 4:10 gears. Also if you put in a 200 the transmission cross memer will still work from the th350, since ther is another set of holes in the frame that match up perfectly for the mount on the 200. If you are going to find a 200 in a junk yard you will need to find one for a grand national or montecarlo ss. Not all 200 are made to handle the same stress. You have to ask if it is worth the cost. I get around 15mpg on the highway with a 200 in the same truck as yours. It drops the rpms to around 2200 at ~70. I usally don't use the overdrive in town, but it s nice on the highway. My th350 lost 3rd so it was worth doing at that time. Either trans will cost much more than a 350/400. __________________ '72 3/4 Cheyenne Super 402/TH400 Gear Vendors '72 3/4 Cheyenne Super 350/200R4 '50 1/2 Chevy 3 Window

03-30-2009, 08:18 PM	#9
ajcan Registered User Join Date: Mar 2009 Location: Covington Georgia Posts: 87	Re: New to me C20 questions jbarron, I will be keeping this engine stock.Should something happen to this motor down the road it will just get a crate motor. With that being said the 200r4 should fit the bill fine. A transmission upgrade probably won't happen till later down the road. This truck runs and drives but needs a lot of work. Many leaks and other problems. My next question is, My oil pressure guage reads about half way up when driving but drops down near "L" when at idle.Is this reason for concern or does it sound right? Thanks. AJ



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