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TH350 to 700R4

magik235

magik235

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I have a RV on a K30 Chevy Van chassis. It has a 350 with a TH350. Is the list below all I need to change the transmission to a 700R4?

700R4 transmission
700R4 torque converter
TV cable and bracket

My current TH350 is a locking transmission. Is a locking transmission better? Should I get a locking 700R4?
What else is needed if I go with a locking 700R4?
 
I am pretty sure ALL 700r4's have a lock up torque converter--only a few years of the Th350's had them,like early 80's versions..A lock up converter does aid in fuel mileage and reducing internal heat by eliminating any slippage inside it once it locks up--but they have been known to be problematic sometimes...personally I'd prefer a TH350 over a 700R4,they are more reliable,but the 700R4 does have the advantages of a lower first gear,the overdrive saves fuel and engine wear,but in stock form I consider them weaker than a Th350...

You say you have a "k30" chassis,but its a VAN??..I think you meant maybe a "P" series step-van chassis or a "G" 30 van (both 2wd)..if so,the tranny swap wont be that complicated--a 4wd would be more involved,as I think the overall length of the tranny case is different (700R4 is longer than a TH350 if I remember right)..you may have to have the driveshaft length altered to fit in either case..we'd need more detailed info on exactly what your doing the swap on,the year,model,2 or 4wd,etc in order to help more..
 
if going 700 in a big heavy rv get a built tranny from someplace like bowtie overdrives.

and possible driveshaft move or modify the crossmember for mount position. and def a cooler and temp gauge install.
 
Thank you for the responses. Here is more information as requested. It is a two wheel drive 1985 RV with a 350 and TH350. I currently tach 3000 at 60 and 3500 at 65. I would like to get the rpms down so the .7 overdrive of a 700R4 would help. I was debating changing the gearing but I think the 700R4 would be more effective and provide greater flexibility.

RV.jpg


diesel4me said:
I am pretty sure ALL 700r4's have a lock up torque converter--only a few years of the Th350's had them,like early 80's versions..A lock up converter does aid in fuel mileage and reducing internal heat by eliminating any slippage inside it once it locks up--but they have been known to be problematic sometimes.
Click to expand...
Is a lock up converter computer controlled?

diesel4me said:
personally I'd prefer a TH350 over a 700R4,they are more reliable,but the 700R4 does have the advantages of a lower first gear,the overdrive saves fuel and engine wear,but in stock form I consider them weaker than a Th350...
Click to expand...
I agree that is why I have a TH350 in my Jimmy

diesel4me said:
if so,the tranny swap wont be that complicated--a 4wd would be more involved,as I think the overall length of the tranny case is different (700R4 is longer than a TH350 if I remember right)..you may have to have the driveshaft length altered to fit in either case..we'd need more detailed info on exactly what your doing the swap on,the year,model,2 or 4wd,etc in order to help more..
Click to expand...
I have changed drive shaft lengths before and have a good source for this operation.

sweetk30 said:
if going 700 in a big heavy rv get a built tranny from someplace like bowtie overdrives.

and possible driveshaft move or modify the crossmember for mount position. and def a cooler and temp gauge install.
Click to expand...
Is bowtie overdrives a better source than TCI?
 
By the time you're done buying a BUILT 700R4 you could just as easily buy and install a gearvendors overdrive on your existing trans which would now give you the advantage of having six gears instead of four if you went with a 700R4. http://www.gearvendors.com/mh3speed.html
 
ya better check that out.

square pan with 45* notch off corner = th350
texas shaped pan =th400

1ton should have th400 for sure from factory .

and bowtie overdrives better options / levels of tranny and also lots of guys here had good luck with them.
 
First: if it is a th350 and has lock up, it's not computer controled, they called the Th350C and it's not the best th350 they ever made.
The earlier non loc up are much better.
If you want lockup and overdrive go with a 700R4.
Now I doubt that your RV has anything but a th400, even if it came with th350 from the factory, the outfit that built the RV would not put a th350 in such a heavy truck.
I second the Gearvendor overdrive for any 2wd heavy vehicle, you will love it after you get over the $$$ you spend on it.
If you insist on a 700R4, go with bowtieoverdrive for sure.
 
I have a TH350 in my Jimmy. I had to remove it, have it rebuilt and install it. See the pictures below. The RV's tranny looks the same.

DSC01403.jpg


DSC01407.jpg


DSC01408.jpg
 
my buddy had a g-10 half ton with 4.3 and had a deep pan th400 in it. :eek1:

i also had a c-10 with a 4.3 and th400 in it. :dunno:

best to look and verify just to be 100% sure.

and drw dana 60 rear in gm ? sure its not a 70 ?

but it is a van cab & chassie and also 80's era when thay were getting rid of a lot of old stock .
 
I had a 1979 Rockwood motor home based on a G-30 chassis,it had a TH350 and a 350 engine!..I too was surprised not to see a TH400 under it,but I guess some RV manufacturers used them..I never had any trouble with it either...had a large aftermarket cooler plumbed up to it along with the factory one in the radiator..

That RV used to wind out pretty high on the highway too,it had 4.10 gears in the rear end I think,possibly even lower!..I drove it to Nashville once,and at 65 mph the engine was tached out at 3400 rpm,at 70+ mph it sounded like it was screaming...it was no champ on gas mileage thats for sure...if I had kept it it would have got an overdrive unit from Gear Vendors...but I sold it to a friend only a year after I got it..
One think I disliked about it was the fact it was built on a 110" wheelbase,a stupid choice,as it had a good 4 feet of overhang behind the rear wheels,it would drag its butt climbing up a steep driveway and felt too light in the front end,felt like you could pull a wheelie with it if you tromped on it from a dead stop!..the ride kind of sucked too,it felt like the 1 ton coil springs up front never had any "give",it took bumps pretty hard...my 81 G-10 with a 125" WB was a caddy compared to how that thing rode..I also didn't like the rear half of the camper behind the cab being wider than the nose,I almost wedged it between buildings in an alley in TN and between trees at campgrounds because I'd forget it got wider behind me!..

If your camper were mine,I'd go with a TH400 and an add on overdrive unit..
 
If your 350 uses a 4 pin connector for lock-up control to the trans then it will plug right into the 700R4. All factory 700R4's were lock-up, but the internal wiring varies between years and models. It is fairly simple to re-wire the 700 for 4th gear lock-up and compatibility with your factory lock-up control functions. Your driveshaft will be the same length for both the 9 inch tail 350 and the 700R4 and they share the same yoke spline. The crossmember will need to be moved back about two inches. If equipped with the original quadrajet carb, you can use the existing kickdown cable bracket and just pick up a universal tv cable and hook it right up and adjust it. The factory carb has excellent tv geometry so you won't have to do anything special.
 
Greg Ducato said:
If your 350 uses a 4 pin connector for lock-up control to the trans then it will plug right into the 700R4. All factory 700R4's were lock-up, but the internal wiring varies between years and models. It is fairly simple to re-wire the 700 for 4th gear lock-up and compatibility with your factory lock-up control functions. Your driveshaft will be the same length for both the 9 inch tail 350 and the 700R4 and they share the same yoke spline. The crossmember will need to be moved back about two inches. If equipped with the original quadrajet carb, you can use the existing kickdown cable bracket and just pick up a universal tv cable and hook it right up and adjust it. The factory carb has excellent tv geometry so you won't have to do anything special.
Click to expand...
Excellent reply. This is the information I needed. Thank you.
 
imiceman44 said:
This only shows that you could have either the 350 or the 400.
I know your Van is a G series, but my G series 1 ton GM came with a th400.
Click to expand...

A TH350C is a lock up convertor and the manual clearly shows 350C as an option.
 
4X4HIGH said:
A TH350C is a lock up convertor and the manual clearly shows 350C as an option.
Click to expand...

I know, I said that earlier, but here I was just pointing out that the manual says it could have either and that the post didn't prove it was a 350 :waytogo:

imiceman44 said:
First: if it is a th350 and has lock up, it's not computer controled, they called the Th350C and it's not the best th350 they ever made.
The earlier non loc up are much better..
Click to expand...
I think though I may have made a mistake, since 85 they did have a CCC and ESC which meant computer controled, so the th350C may in fact be computer controled.
I know they started using these in 81
 
The TH350C in both my Rockwwod camper and the '81 G-10 van had a vacuum/electric switch that controlled the lock up converter...later years may have had it controlled by the computer..
 
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