78 C10

[WiskyBadger]

Hi all, I bought a 2wd 78 C10 this last fall and as the weather gets warmer will start wrenching on it. It has sat for 10 years with a blown small block. Amongst the long list of things to do is trans fluid and read diff fluid. It has a Turbo 350 trans with a shift kit and a 12 bolt posi rear end. For the trans what would you use? I have been debating on one of the Dex 3/ Merc type trans fluids or maybe a Dex 6. Worried a Dex 6 might not be the greatest for the old Turbo 350. What say you? Also for the rearend a regular old 80w90 or something of a newer spec, maybe with a additive. I'm newer to the older stuff so I'm looking for some help. Thanks in advance.

 

[mazdamonky]

I currently have a 77 C10 in the yard with a 350 and turbo 350 trans. It is currently running and happy with a Dex 3 supertech high mileage fluid. I am unsure whether I would go with anything beyond a dex IV fluid.

 

[WiskyBadger]

Originally Posted by mazdamonky
I currently have a 77 C10 in the yard with a 350 and turbo 350 trans. It is currently running and happy with a Dex 3 supertech high mileage fluid. I am unsure whether I would go with anything beyond a dex IV fluid.

Thanks, I figured I'd stick with a regular old Dex 3 but didn't know if there was any reason for a Dex 6. I wasn't sure how the trans would respond.

 

[Linctex]

I'd run the cheapest Dex you can find - check Rural King or Atwoods Farm & Ranch

 

[Chris142]

Dex 3. What engine will you put in it? Do you have emission testing?

 

[mazdamonky]

Originally Posted by WiskyBadger
Originally Posted by mazdamonky
I currently have a 77 C10 in the yard with a 350 and turbo 350 trans. It is currently running and happy with a Dex 3 supertech high mileage fluid. I am unsure whether I would go with anything beyond a dex IV fluid.

Thanks, I figured I'd stick with a regular old Dex 3 but didn't know if there was any reason for a Dex 6. I wasn't sure how the trans would respond.


I would probably be comfortable with Something like Valvoline Maxlife ATF, but beyond that, I would be hesitant.

 

[WiskyBadger]

Originally Posted by Chris142
Dex 3. What engine will you put in it? Do you have emission testing?

I have a built 355 going in. Thumper cam, headwork, airgap intake. No emission testing.

 

[slacktide_bitog]

Dexron VI can be run in all GM automatic transmissions with no problems. It is backwards-compatible

If your transmission doesn't have a drain plug, get an aftermarket pan that has one. This will make future ATF changes much easier.

 

[clinebarger]

You might as well pull the trans & build it right, Commercially available performance TH350 shift kit's are pure garbage!

A TransGo SK-350 kit along with Internally Dual Feeding the Direct Clutches with High Rate Return Springs is far superior to the warp/leak prone sandwiched transfer plate found in performance shift kits!

 

[ka9mnx]

Dex VI is the only fluid now licensed and is a replacement for all older Dex fluids. Mercon was always compatible with the old Dex's but is now not licensed. Mercon V replaced Mercon. I used Mercon V when I replaced the fluid in my 4Runner in the Summer of 2017. Works just fine.

 

[4WD]

Know a Mechanic/owner who still tows which those … swears by Mobil 1 ATF to take the heat …

 

[Egg_Head]

Sounds like a nice rig & fun project.

I have a 1978 K5 with the same tranny. Whatever you do drop the pan and change the filter, you won't believe what you'll find in the bottom. I bought an aluminium aftermarket pan with +2 qt. capacity and it had a drain plug. Dex III is just fine. Any brand of gear oil is fine just use a Fel-Pro gasket on the rear end and take your time laying down the sealer.