Automatic conversion

[Johnl48]

I'm doing a complete nut and bolt restoration on a 70 3/4 4x4 with a 350. This is for my wife so she wants it converted to an automatic. She plans on using as a daily driver during the no salt months. I considered the th350 for the simplicity but I fear the gas mileage will prevent her from driving it to work every day

What's everyone's thoughts on the 4L60 with Overdrive ? I know the cross member will need to be moved. Truck has 4.09 gear ratio

[gmc684x4]

Are you going to put efi in the build a 4l60\4l80 need a pcm to control them
for a 3\4 i would recommend the 4l80
or run the t350 and put a gear vender on it

[Accelo]

"What's everyone's thoughts on the 4L60 with Overdrive"

Just to be sure everyone is on the same page.
700R4 and 4L60's are the same transmission. 1982-1993.
I highly recommend the 1987-1993 version be used as the 4l60 went through a major upgrade in 1987.
The 4L60E and it's cousins (4L65E 4L70E) are the electronic versions and are not typically transplanted unless it's with a LSX motor.

The 4L60 makes an excellent transplant. I even ran on behind my 1971 C10 3/4T 396 BBC without issues. Of course I am not 16 anymore and I am assuming you wife drives like wife's do so no extrema duty change over is required unless maybe you are towing.

In Over-Drive the motor will act like it has 2.86 Gears if you were running a THM350 or any old style transmission with a 1:1 ratio in drive. To figure this out multiply the gear ratio by the over drive ratio, in this case it's .7 . (4.09*.7)
You also get a lower first gear which helps get the truck moving. Their are no downsides.

Removing the old manual transmission cross-member is likely the most difficult thing on this conversion. A flex plate, shortened driveline, dipstick tube, torque converter cover, and the automatic cross-member are required. Also the TV cable and the bracket for the intake manifold. Be sure to get the correct bolts for the torque converter as they will be metric. Installing the wiring for the lock-up converter is optional. Expect another 3% increase in highway mileage if you set this up. It is covered in other threads.

I set mine up shift indicator so drive was OD and park and neutral lined up. I just relocated the factory 350thm bracket by moving on leg of the frame adapter. The shift linkage lined up fin after that. The indicator just didn't indicate "manual first gear" which was fine. My BBC went from 10mph to 13mph on my 3/4T with the same gears. That's a 30% improvement. You may get the same 30% but start from a better number than the 10mph I was getting.
You will love it.
Cheers.

[Richard]

Have a 4l60 in my 94 and a 4l80 in my 2000. IMO the 4l60 has better gear spacing and feels better on the road. I did break the output shaft on the 4l60 in my 94. Stock 190 hp motor with real firm shift kit. Major carnage inside the trans. Cost $1,000 in hard parts to repair and I rebuilt myself 100,000 miles ago. Dialed the shift back and it is still in service now. Using the 6l90 in my 72. Final OD is the same, I see the gear spacing should be even better with two more gears.
As said a trans controller maybe needed for the E versions of the transmissions in a swap. Be aware of the cost and installation.

[Bigdav160]

Originally Posted by Johnl48

I'm doing a complete nut and bolt restoration on a 70 3/4 4x4 with a 350. This is for my wife so she wants it converted to an automatic. She plans on using as a daily driver during the no salt months. I considered the th350 for the simplicity but I fear the gas mileage will prevent her from driving it to work every day

What's everyone's thoughts on the 4L60 with Overdrive ? I know the cross member will need to be moved. Truck has 4.09 gear ratio

I am running a 4L60 in my 4x4 Suburban. It truly makes it drive like a modern truck. There's a bunch of small modifications to be done when moving the motor mounts forward. Exhaust is too short, hoses too long, gear shift linkage has to be moved, factory fan shroud doesn't fit, front drive shaft clearance issues etc.....

Still I think it's a better solution than moving the transfer case member back and dealing with driveshaft and TC lever modifications.

[Johnl48]

Originally Posted by Accelo

"What's everyone's thoughts on the 4L60 with Overdrive"

Just to be sure everyone is on the same page.
700R4 and 4L60's are the same transmission. 1982-1993.
I highly recommend the 1987-1993 version be used as the 4l60 went through a major upgrade in 1987.
The 4L60E and it's cousins (4L65E 4L70E) are the electronic versions and are not typically transplanted unless it's with a LSX motor.

The 4L60 makes an excellent transplant. I even ran on behind my 1971 C10 3/4T 396 BBC without issues. Of course I am not 16 anymore and I am assuming you wife drives like wife's do so no extrema duty change over is required unless maybe you are towing.

In Over-Drive the motor will act like it has 2.86 Gears if you were running a THM350 or any old style transmission with a 1:1 ratio in drive. To figure this out multiply the gear ratio by the over drive ratio, in this case it's .7 . (4.09*.7)
You also get a lower first gear which helps get the truck moving. Their are no downsides.

Removing the old manual transmission cross-member is likely the most difficult thing on this conversion. A flex plate, shortened driveline, dipstick tube, torque converter cover, and the automatic cross-member are required. Also the TV cable and the bracket for the intake manifold. Be sure to get the correct bolts for the torque converter as they will be metric. Installing the wiring for the lock-up converter is optional. Expect another 3% increase in highway mileage if you set this up. It is covered in other threads.

I set mine up shift indicator so drive was OD and park and neutral lined up. I just relocated the factory 350thm bracket by moving on leg of the frame adapter. The shift linkage lined up fin after that. The indicator just didn't indicate "manual first gear" which was fine. My BBC went from 10mph to 13mph on my 3/4T with the same gears. That's a 30% improvement. You may get the same 30% but start from a better number than the 10mph I was getting.
You will love it.
Cheers.

I actually have the crossmember out for painting. It's just a bolt on. So I will need a completely different one ? Do you know of a source for these ? I contacted monster transmission to see if they can set me up, waiting to hear back

[tim_mc]

I didn't want to mess with a electronic transmission controller, so I went with a rebuilt 700R4 ('92 from a Caprice). It was "upgraded" with an older style valve body that has hydraulic converter lock-up, so no lock-up solenoid or wiring needed. I'm really happy with it, especially since swapping my 3.08 gears to a 3.42 posi. The C10 frame was set up for a TH350, so I just had to slide the crossmember back about 1" (I think) and drill new holes in the frame rails using a long bit. I'm not sure about a source for a cross-member. There's a guy here locally in St. Charles, MO that deals specifically with 67-72 C10 parts that I've used in the past, so maybe there's someone within a reasonable distance from you that may have one.

[tutone]

I will agree on the 700r4 posts, unless you go with a computer, it is the only way to go, but keep in mind since yours is a 4x4, there is the xfer case adapter coupling issue. I havent done this on a 4wd , but it's easy on 2 wheelers.Transmission and case length won't kill you, it will be some drilling at worst. Some oddball adapter couplings are hard to find. Having one machined could get expensive.

[MARKDTN]

I have an '83 K20 that was factory 350/700R4 that I bought from my uncle in 1991. It has 3.42 gears. It got in the 14s for mpg. Hauled many a trailer with it. It was always sluggish on the hills and you really had to get into the throttle to maintain speed at times. In 2004 a cam lobe went down. I swapped in a bone stock '91 Corvette Tuned Port 350 (yes Corvette with aluminum heads). The difference is amazing. Mileage jumped to 17+ and I have gotten over 20 on the road. Hit a hill and just barely touch the pedal and it goes. Tuned Port has fallen out of favor the last few years for LS. I like LS but if you have/want a basically stock 350 then TPI is really a nice option.

Anyway, OP, 700R4 is a great choice. The later units built right are good. It is very important to adjust the TV cable before you run it even 1 time. But the 700R4 combined with the TPI with such nice low rpm torque is even better IMHO.

[RichardJ]

<<But the 700R4 combined with the TPI with such nice low rpm torque is even better IMHO.<<

Corvette L98 TPI 350. Wow. Didn't expect to see that on a transmission thread, but I do agree.
IMO, the L98 was the last and very best of the factory 1st Gen SBC. Alum heads, roller cam.
People generally overlook any statement about "low end torque" when mentioning this engine.
The 700R4 overdrive was mated to 2.59 rear gears. The engine was actually a stump puller, loafing around town at barely over 1k rpm.

The replacement LT1/LT4 2nd Gen SBC had more top-end , but after only 4 years of production was buried in history.

http://67-72chevytrucks.com/vboard/s...d.php?t=645958 L98 Thread

[dz1087]

The PO converted my truck from a column shift manual, to a Th350. Used the same manual column, too, so I don't have any gear indicator on the column or reverse lights...

[Accelo]

I missed the 4x4 part. Is the 350 the motor or transmission. Seems it's the transmission. I would consider using the aluminum transfer case that came mated to the 4L60.
However, the original transfer may bolt up. The shift handle will be further back unless you modify it. You need to confirm that as I have converted a few 2 wheel drives but never a 4x4. I know the manual transfer case will not as it has a different spline count on the input shaft than the automatic.

[Johnl48]

Currently it's a 350 engine with a manual transmission

[cj847]

Since you are not concerned about using the original parts, I would recommend a light resto-mod. My suggested choices:

-5.3 or 6.0 LS/4L60E swap; if you like your t-case see Novak adapters or Advanced adapter website. To save money, you could switch to the T-case that came attached to 700R4 from 1984 to 1991 K trucks, blazers, and suburbans. It should bolt right up. (Since 1992 all Chevy 4x4's are driver drop hence the requirement to adapt or change t-case). Or change the front axle to driver drop.

-350 SBC with EFI, 700R4 and T-case from a late 80's K truck.

I highly recommend an LS swap especially if it is going to be driven. I am now driving my 1960 Willis Wagon with this swap (still in primer waiting on a painter). It is an absolute delight to drive. Much more fun than my 1971 with 350/350.

[Johnl48]

Originally Posted by cj847

Since you are not concerned about using the original parts, I would recommend a light resto-mod. My suggested choices:

-5.3 or 6.0 LS/4L60E swap; if you like your t-case see Novak adapters or Advanced adapter website. To save money, you could switch to the T-case that came attached to 700R4 from 1984 to 1991 K trucks, blazers, and suburbans. It should bolt right up. (Since 1992 all Chevy 4x4's are driver drop hence the requirement to adapt or change t-case). Or change the front axle to driver drop.

-350 SBC with EFI, 700R4 and T-case from a late 80's K truck.

I highly recommend an LS swap especially if it is going to be driven. I am now driving my 1960 Willis Wagon with this swap (still in primer waiting on a painter). It is an absolute delight to drive. Much more fun than my 1971 with 350/350.

Don't think that's in the budget unfortunately

[Richard]

Originally Posted by Johnl48

I actually have the crossmember out for painting. It's just a bolt on. So I will need a completely different one ? Do you know of a source for these ? I contacted monster transmission to see if they can set me up, waiting to hear back

I have purchased parts from them in the past but highly suggest you do extensive research on them before purchasing a complete trans.
Wanted to add In my experience with the th350 you will be at 10-12 mpg, 4l60 will be 12-14 mpg. Just changed gears from 3.42 to 3.73 in my 94 (5.7), better pickup now but zero change in mileage.

[cj847]

For just the transmission (regardless of engine). Buy a 700R4 with the transfer case from an 85-91 K10. $200 or less for core. $800-1200 for rebuild and components to adapt. Sell your 203 T-case for $200-300 ish.

[Accelo]

cj847 has given good advice.
However, I am unsure of the shift linkage conversion issues.
The new transfer-cases are lighter and leak free compared to the 205's.
Just be sure to watch for the swing of the transfer case as they lean both to the drivers side and passenger side depending on the year. If you can find an complete assembly you will be better off. I would get the newer cross-member and convert it to fit your truck.
If you want to use your original manual transmission transfer-case the input shaft collar will have to be changed to a automatic style as they are splined differently, 10 splines on the manual and 26 on the automatic.
Let us know how you work it out.

[Johnl48]

Originally Posted by Accelo

cj847 has given good advice.
However, I am unsure of the shift linkage conversion issues.
The new transfer-cases are lighter and leak free compared to the 203's.
Just be sure to watch for the swing of the transfer case as they lean both to the drivers side and passenger side depending on the year. If you can find an complete assembly you will be better off. I would get the newer cross-member and convert it to fit your truck.
If you want to use your original manual transmission transfer-case the input shaft collar will have to be changed to a automatic style as they are splined differently, 10 splines on the manual and 26 on the automatic.
Let us know how you work it out.

So if I took the simple way out and bolted up the th350 do I still need to change the transfer case spline ?

[57taskforce]

I skimmed over the OP’s post and see nothing about him mentioning a 203. Factory equipment would have been a 205. Changing The legendary 205 to a modern aluminum case is a HUGE downgrade in my honest opinion. This thread has got a good dose misinformation in it, between thinking it’s for a 2wd and getting the cases mixed up. OP I’d suggest to Post up in the 4x4 section and we will get you taken care of. Long story short; you can put a 205 pretty easily behind a 700R4 or a 4L60/4L80E with the right conversion parts and some minor machine work to the input bearing hole on the 205 if going with a 4L80E. Don’t get rid of the 205 is my strong opinion.
As a dedicated 4x4 guy with a K20 I would take that 700/R4/4L60(not E) and throw it as far as you can into the bottom of a lake and leave it there for fish habitat. They are far from the strongest or most reliable in a heavier 4x4 truck especially with mods. My personal opinion of course most will probably disagree. They have bitten me more than once. My favorite was to skin this cat is not an OD transmission swap. It’s a gear vendors overdrive. Lots more gear choices and cool things you can do with the Gear vendors.

[Accelo]

57taskforce
I agree with you on the 4L60. Not the best for hard core wheeling. This is a rig for his wife to drive to work. Difficult to beat the 4L60 for adding overdrive for the cost.
Thanks I edited the transfer-case information.

So if I took the simple way out and bolted up the th350 do I still need to change the transfer case spline ?
Yes you will have to change the input on the transfer-case to match the thm350 output.