C6 may be toast, need some wise opinions

So I had some time to some odds and ends on the truck. Decided to change out the vacuum modulator in the C6 because it has always shifted kinda early and hard. It came with a purple stripe modulator so I ordered a black strip modulator (supposed to hold the shifts longer). Both are adjustable.

Put the black stripe in and it shifted very early and every shift had a lot of slippage. Felt like I was driving an ATV with a CVT trans (lol not good). A lot of slip in reverse. Okay, so I tightened the adjuster down significantly. Barely any change, eventually bottomed it out. Topped the fluid off. Same problem. I put the purple stripe modulator back in and also tightened down the adjustment. Big whoop, wasted $12 on a modulator, not my worst life decision.

Well took the truck down the road, exact same problem. Uh oh. That's no bueno.

Let me preface what I'm about to ask. For several years I accidently ran the trans with too much fluid. Whether it was a dipstick error or the dipstick holding the dipstick, I know not. Serviced the trans a few years ago when I figured that out. Fluid looked like someone poured a pound of glitter in it. Not good. changed the fluid, new filter, run it till it gives up. Well, it may have given up now.

I have also noticed it leaking from the front seal and pan. And after it sits over night it takes some time to build up enough line pressure to actually move. I'm gonna verify 100% its in need of a bench job. I've already had it rebuilt once and it's okay if I have to do it again. I just want to put this out there in case worst case scenario happens so I'll have a good idea of what I am going to do.

Here is my question where I need some wise advice. I can rebuild the C6, wouldn't bother me. I like the trans. But I also have an E4OD sitting on my shop bench. 150k miles on it. Pulled it out of a totaled truck that had been sitting for awhile, 1995 model. I have that truck so I have all the parts needed to swap it in and some really good buddies that know much more than me that would help me do it.

 1) I would buy a controller for the E4OD trans, replace the filter, add a speed sensor to my speedo cable and send it. Don't feel comfortable spending more money to fully rebuild it, an extra $800 in parts or $1,500 for a shop to do it. Sound like a good idea? Would it be foolish to run the trans without going through it? Too big of a risk?

2) Or I can just rebuild the C6. Is that a better idea?

Both are comparable in price. Just need to be convinced to go one way or the other.  

If they are comparable costs, then the question I'd want to ask is how you are going to use the truck.  If you are going to put many highway miles on it I'd vote for the E4OD due to the lock-up torque converter and the overdrive gear.  That will save you $ in fuel awa.

The truck does spend most of its time on the highway. It definitely would increase the mpg and be easier on the motor. I think the biggest thing holding me back would be putting the E4OD in as is. It hasn't had power to it in a long time. I know it'll be a risk just don't know how big of a risk....

WAIT!  Is your lift frame or body?  The E4OD is so long that the t-case will hit the floor on a regular cab truck w/o a body lift.  Been there and had to cut the floor out and graft a piece in on Dad's truck.  

It is a suspension/frame lift. I remember you saying that on a different post. Thankfully I have the cab the E4OD came out of so I can graft in that little section so it would clear. Or I can body lift, the body mounts need to be replaced anyways.

Any swap that isn't just putting another of the same thing back in is alwayd a lot more work that most people think up front.  If you're looking for a project, the E4OD is a good trans to end up with.  But if you're looking to get your truck back on the road for a reasonable cost, the C6 isn't a bad trans either.  And yes you'll save money on fuel with the E4OD.  But odds are you won't save what the swap ends up costing.  That's just not the way those kind of projects tend to turn out.

So should you go with the C6 or the E4OD?  I feel like if you have to ask you should stick with the C6.  But if you're going to do what you want, and if you want to use the E4OD, I think you'll be happy with that choice.

Nothing Special wrote

Any swap that isn't just putting another of the same thing back in is alwayd a lot more work that most people think up front.  If you're looking for a project, the E4OD is a good trans to end up with.  But if you're looking to get your truck back on the road for a reasonable cost, the C6 isn't a bad trans either.  And yes you'll save money on fuel with the E4OD.  But odds are you won't save what the swap ends up costing.  That's just not the way those kind of projects tend to turn out.

So should you go with the C6 or the E4OD?  I feel like if you have to ask you should stick with the C6.  But if you're going to do what you want, and if you want to use the E4OD, I think you'll be happy with that choice.

Wise words!

Absolutely. I went through all that when I put and later model 351w and efi in my truck. Took 5 times longer than I was expecting and little details drive up the cost significantly. As much as I can dream about it going smoothly I know it won’t.

What has me on the fence is that when I did service the C6 a few years ago the amount of metal I found was scary. So I’m just figuring in having to replace everything from the converter back. I don’t want to pull it back out later because I was cheap or worry something else my break. It’s not gonna be a simple bench job or cheap. The E4OD is a good core to rebuild and I have all the necessary hard parts. Crossmember, driveshafts, tcase linkages, floor pan parts, etc. BUT there will be things I don’t see and it will take much longer.

If I’m only looking at a 1 mpg increase then it’s not worth it to me. 3 mpg? That would be more convincing. Make the effort worth it. Especially if gas prices start coming back up. Does anyone have any experience on mpg gains with an OD conversion? I’m getting about 13 mpg, 70 mph at 2,700 rpm. Rolling on 33s and 3.50 gears.

A stock 95 f150 351w E4OD is only rated at 16 mph highway. But I know that people rarely reach that in 351 equipped trucks.

And thank y’all for responding. It’s nice to be able to bounce ideas around with people that know what they’re talking about!

You remember the modulator rod? I saw a video on this the other day... there's a rod in the vacuum modulator that if you loose, you'll loose your tranny pressure (and eventually burn the transmission to the ground. The pin can be remade from some TIG filler rod or other thin rod of the appropriate diameter

Bit about the Vacuum Modulator and the easily lost rod of doom (and how to make a new one):

https://youtu.be/bta6XSsJy7k?t=250

Another relevant video (same guy, different C6 rebuild)

https://youtu.be/g9cMArvgJQ4?t=245

If you lost the pin, hope you didn't burn it up...

Bingo! The new modulator didn’t come with a new rod and when I pulled the original the rod flew out and I didn’t see it. I was watching some C6 teardown videos and came across the exact one you recommended. Saw his warning about the rod. Pulled the modulator, no rod. Searched around in the driveway and there it was. Got it in and it’s much better.

The fluid is very dark and the transmission still has issues but now I have some more time and don’t have to rush to a decision.

Glad you fixed it. Hope it holds you by for a while.

Good info! Glad you found it!

Thank y’all! As much as I would love a new tranny with all the toys it is saving me some money!