Turbo 350C to 4L60E

[Guardian]

I am looking to swap out the current 350C tranny for something a bit stronger and was considering an overdrive like the 4L60E. Has anybody done this? It is for my 86 C10 with the new engine. The final drive is 3.08.

 

[HotRodPC]

I am looking to swap out the current 350C tranny for something a bit stronger and was considering an overdrive like the 4L60E. Has anybody done this? It is for my 86 C10 with the new engine. The final drive is 3.08.

Keep what you got buddy !!! You don't need OD with 3.08 rear gear ratio. And you don't really want to do a 4l60E cuz unless you're ready to deal with all the electronics involved. Now the 700r4 is the NON electronic version of the 4L60-E, BUT, it's not stronger than the 350C. Of course the Th350 is even stronger than the Th350C but the only weakness is the front shaft and the torque converter. If you were running a 3.73 or 4.10 rear end gear, then the 700r4 and it beefed up might be an OK option, but for now with 3.08's not worthy at all.

 

[Guardian]

I appreciate the advice. Maybe I will start looking for a TH 350 or 400 to rebuild. I have never had a 4L60E with much horsepower in front of it and did not know if it would handle much.

 

[HotRodPC]

You can work them over the handle some hp, but you have to do very little to a Th350 or Th400. You can likely build 3 maybe even 4 Th350's to one 700r4 when it come to cost of parts and mods. And the Th350 WILL last longer and take more abuse.

 

[Guardian]

I have already abused this 350C and it ain't liking it. lol
It is starting to give me trouble so I started looking and had a 4L60 offered to me and wanted to find out if it was worth the headache. I can live without the overdrive. that is why it has two tanks, for trips!

 

[HotRodPC]

And honestly, with a 3.08 gear ratio, the OD isn't going to help your mpg hardly at all if any. Now if you had a 4.10 or a 3.73 lower rear gear, then yeah, you might squeeze a couple mpg out of it. Only because the lower gear is taking strain off the motor, then you have the OD to compensate for the lower gear when on the freeway to get the rpms down a bit.

 

[Guardian]

I had thought about changing the gears but got the wifes truck down right now so....
I am still thinking this thru and being easy on the tranny!

 

[HotRodPC]

What are they symptoms on the Th350C?

 

[Guardian]

It picked up a minor vibration and has a soft 2-3 shift. It happened right after a hard launch, so I am pretty sure the torque converter or pump is hurt.

 

[HotRodPC]

Could be, and I'd jump underneath it and make sure you didn't lose a converter bolt.

 

[Guardian]

It is worth a look, maybe all it is. Thanks.

 

[Guardian]

HotRod, I did an inspection of the torque converter and all the bolts are installed and tight. I noticed a leak from the tailhousing and driveshaft so I replaced the seals and bushing in the tailhousing including the o-ring for the driveshaft. I noticed the output shaft had some play in it. I have driven it for a couple of days and the leak at the driveshaft has returned. How much play should that output shaft have with the tailhousing off? Could that be a problem?

 

[HotRodPC]

It could be. You will be having a little walking around with the tailshaft off but not excessive. There is a bushing in the back of the case that the rear planet sun gear rides, that is connected to the output shaft. I wonder if an out of balance driveshaft or bad Ujoint caused the rear tailshaft bushing to go bad, left alone it also wore the rear case bushing. But it would seem to me that a new tailshaft bushing, if the yoke fits it right and the yoke isn't wore down now that is should at least longer than a couple days of driving. But sure, you're vibration can certainly be coming from the back end too. So the leak has come back, but what about vibration? It could be that the yoke is wore and even a new seal can't fix that. I wish you were closer, I have another yoke, you'd just have to buy a new U joint to put it on.

 

[Guardian]

I have not had the shaft spun but it is a good idea. The u-joints are new, I replaced them a couple of months ago when I had it out. I did not notice a worn area on the outside of the yoke, but I guess it could have worn splines.

I will find someplace local to spin the shaft and I will make sure the diff saddle is holding the u-joint centered, I have seen that once before. If the yoke splines are jacked up I may give you a shout. Thanks for bouncing ideas around, it helps.

 

[Joshua8336]

Keep what you got buddy !!! You don't need OD with 3.08 rear gear ratio. And you don't really want to do a 4l60E cuz unless you're ready to deal with all the electronics involved. Now the 700r4 is the NON electronic version of the 4L60-E, BUT, it's not stronger than the 350C. Of course the Th350 is even stronger than the Th350C but the only weakness is the front shaft and the torque converter. If you were running a 3.73 or 4.10 rear end gear, then the 700r4 and it beefed up might be an OK option, but for now with 3.08's not worthy at all.

WRONG!!! all you'd need for the 4l60e to work in your truck is a PCM out of a 98-02 chevy truck, or corvette, camaro, trans am equipped with the 4l60e. you'd need the dakota digital vss buffer box, and you'd need to run your shift solenoids to your computer and have vats turned off... piece of cake, if the wiring bothers you send me a PM i'll be glad to help.