Hello everyone.

After some internet research and inner soul searching, I've decided to rebuild my dad's C6 transmission from his 1978 F-250 4x4 w/ 400.

First, a little background...

He bought the truck knowing it had been abused for a lot of its 110,000 mile life. The (we assume) original 400 had two or more cylinders not firing. It barely run, and barely made it up the drive into his garage.

We thought it just needed a new head gasket, but it had been run so long with a damage head gasket, that the combustion had eroded the steel in the gap between cylinders. It was too deep to just have the heads and block re-surfaced.

We obtained a low-mileage 400 from a 76 LTD that ran good, dropped it in and fixed it up, and the truck ran great (for a 40yr old truck).

While the engine was out, we put new (TYPE F) fluid in the transmission and a new pan gasket & filter.

A short while after the truck was functioning again, the C6 tranny started acting up. After running to a pizza joint, when he started it back up to take off, and shifted to drive, the truck wouldn't roll, or barely wanted to. After some shifting and revving, he managed to get it to engage, and got it home quickly.

At that point, the tranny is stuck in drive. You shift to park, and you can tell the engine is still under load, the truck trying to drive forward when you gas it, unable to rev up much. It was the same in all of the letters on the column. Even in reverse.

Some internet research said that it could be loose linkage (that checked out), the shift rail could've slipped from it's slot on the linkage inside the tranny (nope, that was good too). If not those things, then forward drive clutch pack is seized up.

We pulled the tranny pan. Fluid looked and smelled fine as far as we could tell. The pan was thoroughly cleaned when we put in the type F fluid earlier, but it had a layer of dark grey goo lining it that we felt shouldn't have been there this quickly after a fluid change.

I apologize, but we didn't think to take a picture of the goop in the pan.

We took the valve body off, and took out all of the valve that we easily could to make sure they were sliding smoothly. All appeared well there.

We put it back together with fluid, and symptoms were unchanged.

So we dropped the tranny and t-case. I bought the C6 videos from www.badshoeproductions.com/c6 as recommended by many others.

I disassembled the tranny, taking over a hundred pictures (linked below). And 3 or so frictions & steels were seized up in the forward drive clutch. We had to use a screwdriver to pry them apart. The belleville spring was cracked as well.

Everything else in the tranny looked fine, according to our best judgement as well as what the videos explained.

I've ordered this ATC Pro King KS-28 rebuild kit: ATC Pro King Automatic Transmission Rebuild Kit KS-28 - Read Reviews on ATC Pro King #KS-28

And I found a later version belleville spring on Ebay.

While I'm waiting on the parts to arrive, I'd like any of you experts to look at these pictures below, and point out anything I might've missed, as well as give a first time tranny rebuilder any needed advice.

Thanks in advance.

Here's a link to the picture gallery: https://postimg.org/gallery/lhphc532/

Click on the thumbnails below to see the large version:




























































photoupload

 

Some quick comments for reference & discussion:

So I forgot to mention earlier that the transmission endplay between the pump thrust washer and first drum was approx 0.060", after ensure the drum was fully seated rearward. According to ken's videos, spec is 0.008" to 0.044".

After reassembling with new clutch frictions, steels, and seals, endplay measurement was virtually unchanged.

The kit didn't come with any thrust washers, so we decided to go ahead and go with what we got.

Additionally, the belleville spring in the forward clutch drum was cracked, and was of the thinner variety. Spec for this year range of C6 was for a thicker version. I can't remember the two different thickness specs right off hand, something like 0.076" & 0.093"

The belleville spring wasn't in the kit either, and while I found several of the thinner version online, I only found one place for the thicker version, some guy on Ebay. We ordered one and replaced the cracked one.

On I believe the forward drum, I had to remove the wave spring to make room for all of the clutch steels & frictions. Ken's video made this appear optional. I remember the gap spec being a little on the high side afterward (going off memory, I believe 0.055"). The spec is 0.021" to 0.050". I thought the rebuild kit would come with different snap ring thickness to adjust for this, but it didn't, so we rolled with what we had.

My rebuild kit came with teflon sealing rings, while the tranny had metal ones. They leave a lot of gap in the grooves compared to the metal ones. My limited reasearch on them says this is fine...
The bottom ring on the forward drum was having a lot of force put on it. A bur had built up all around it's bottom edge.

We replaced all of the metal rings with the new teflon ones. We almost messed up the teflon rings on the pump when installing it into the c6. Definitely use grease or vasoline to get them to stay sucked in their groove. Metal rings would've been much easier.

Also, the piston in the forward drum had a lip type seal on its circumference. The rebuild kit only came with a square-cut seal. The piston was clearly made for the lip style, as one half of it had a smaller diameter to make room for the lip.

We asked a local tranny shop about using the square cut seal on a piston designed to use a lip seal, and he said it would work just fine. Looking at it, I'm inclined to believe him.

Valvebody teardown, cleaning, and rebuild went smoothly, except for one detail: THERE WAS NO GASKET PRESENT BETWEEN THE TWO VALVE BODY HALVES! Only the separator plate was there.

I'm not sure how important that was, but I matched up the correct one of two that came in the rebuild kit, making sure no holes in the plate were covered, and put it back together.

Overall, everything went better than I would've expected. The C6 is really a pretty simple thing, once you understand how it works, how the power is transferred through its gears and clutches.

We have yet to drop it back in the truck. My only concerns at this point are the following:

Will having a square cut seal on a forward drum piston designed for a lip type seal cause any issues with forward clutch engagement or slippage?

Will leaving forward clutch pack clearance 0.005" over spec cause any issues?

Will leaving transmission endplay the same at approximately 0.060" cause any issues?

The truck that this C6 belongs to is just a beater work truck, with a plain stock 400. So I'm guessing that everything will be just fine

Any comments or thoughts?

Here's more pics, click the thumbnails for large versions:


























print screen windows 7

 

Its real important to make sure you disassembled and cleaned the governor and clean out the cooler.

 

The governor was disassembled and cleaned thoroughly, and the valves moved freely.

Good point about the cooler, I forgot about it.

 

Well, everything is back in the truck and it is driving (well, shifting) perfectly as far as we can tell!

Anything specific we should do or watch for driving with a newly rebuilt tranny?

 

What does the dip stick say to use for fluid. I though by 1978 they where using mercon in these transmissions. Type F and Mercon have very different friction coefficients.

 

it says cj something spec (I don't rememeber), but I do remember that it equated to either dexron II or III.

I see a lot of people online recommend running type f anyway, for firmer shifting, less slipping, and a cooler and longer running c6.

I've been tempted to switch out the fluid in my other nicer truck for type f. It only has <70k miles on it, tranny has never been rebuilt, but has had a fluid change at least once or twice. Runs fine, but is super soft shifting.

 

Please delete

 

 

Posted to wrong thread...please remove.

 

Posted to wrong thread...please remove.

 

posted in wrong thread sorry