Back story 1971 F100 360 went kaput. Motor was pulled from 68 mercury, 390 and C-6. NO idea on miles. LOTS. Dropped in truck with no rebuild or anything. Truck pulled a 1000 gallon water tank on trailer for lots of years after. A testament to the C-6 no doubt. Truck was retired 15 years ago or so. I resurected truck with basically a carb and HEI ignition and comlete brake system. Truck runs, drives, shifts fine just leaks lots of trans fluid and went tink tnkly tink occasionally. Pulled trans and found soft plug for band servo pivot pin hole came out and got ground up in fly wheel. Added 2 new plugs with silicone and peened around plug hole. Replaced all external seals. Put trans back in. Truck was run with Dexron 3 Mercon forever because we knew no better. Having now decided to be "correct" I put type F in after my seals. Filter was clean. Pan had very little sludge in it which was shocking. OK now the weird part....
trans no longer leaks fluid. HOwever first time it is put in drive it goes in fine. Wether drive or manual 1st it goes fine. After it warms it gets slower and slower to engage, but only drive. Reverse goes right in firmly. Wehter drive or manual 1st it takes maybe 30 seconds or more to engage. Once there it is fine for a while. Seems firm pulls hard. Then after driving further it sort of slips into 1st and occasionally seems to be a soft slippy shift to second. And now my tink tinkly tink seems to be back.

1. Fresh fluid in an old trans finished it off? (or is that a myth?) so rebuild
2.It does not like type F so go back to decron mercon
3. complete coincidence and trans is just tired so rebuild
4. What would cause those soft plugs to push out?!!! That has me totaly baffled

And one more question, I have a C-6 for a 1980 f250 4x4 that was rebuilt 200 miles before I rolled it. Can I take the guts out of the 1980 and put them in the 1968? I know the converter snout is deifferent so I would have to do something there and I would have to remove transfer case and put short tail shaft on. Just curious if anyone had some certain info before I started gutting and swapping. Thanks in advance. Just really dont have any money right now, Christmas, it is basically a sentimental truck. I mean I have another but I love this truck.

 

1. Meh..
2. no
3. perhaps
4 dunno on that one. Pic of plugs?

Yes you can move the guts of the '80 to the old FE bell unit. but may be as much work as rebuilding the FE unit anyhow.

 

No pic at the moment. It is just a 1/2 inch drive in plug like a "freeze plug" that fills the end of the hole where they drill for a pivot pin. It goes in right by the front pump just a bit low and off to the side.

I am definitely not just itchinig to tear 2 apart to piece one together, but I am also wanting to drive my truck. I have rebuilt trans for myself and others in the past...... but I guess I got lazy as the last one I needed done I paid a shop. $850 carry in with a warranty is not bad in my book if you got the cash. PLus I am building 2 sheds and trying to redo 2 maybe 3 corrals at the moment so I do not have a whole lot of time to work in trans fiddling LOL

Thanks for your input

 

First a mid 1977 and older C6 should be filled with type F. Unless it was rebuilt. Then it would depend on what fluid the rebuilder had soaked it's friction discs with. Changing to a different fluid can cause loss of friction on the discs.
Next I'll ask if the tranny has the correct amount of fluid? You are checking the fluid with the engine running, tranny up to operating temp, and on level ground, correct? Are there air bubbles on the dipstick when hesitating? Air bubbles in the torque convertor or front pump can cause cavitation.
If it does have the correct amount of fluid then check the fluid pressure (line pressure) in the tranny. There is a threaded port on the driver's side of the C6. Front of the shift linkage. About where the front pump behind the bell housing.
Tranny in neutral, engine idling, brakes applied the pressure should be 50-80 psi.
In drive, 2, or first engine idling, brakes applied the pressure should be 50-95 psi.
Reverse engine idling, brakes applied, the pressure should be 60-150.
Take this test when cold and then again when it starts to hesitate when going in drive.

 

It has had dexron mercon III for 25 years or so that I know of. Drive til it acts like it goes in neutral when you go around a corner.. add 3 qts. Repeat. Yes it has been neglected.

Check idling in park but not always at temp. Added a quart just to see cuz it acted like it was low....sort of. So it is some overfill now. Yes I did see a few bubbles last I checked the fluid after it started acting up..

The cavitation makes sense.. I just can't believe it is a friction disc issue because last test drive after adding a quart,, I drove it mile.. done a burn out.. drove 2 miles and done another burn out. Just to see how hard it was hooking up. Drove 3 more miles and stopped. Drove a few feet. Stopped. Put in nuetral and then pulled back to drive. Took a few seconds to then slip softly into 1st and start moving then when shifted to 2nd it slipped again.. slip more when more throttle applied.. I can't believe it is a friction issue if it will do burnouts and then barely move. Let sit over night and boom it is good again. Farther I drive the more it slips so that could mean more driving equals more air equals more likely to cavitate. I will drain some fluid and see how it acts. I was about to pull it and swap guts out with 80 model but then I read in my book that old has no reverse check ball in VB and newer does have. So now I am hesitant to go swapping stuff.

I appreciate the info. I believe I have seen those numbers in my book but have not got a gauge. Can I just get a hydraulic type gauge and plumb it in that port or do I need something special?

Not sure if it is related but the throttle valve or kickdown if you will feels like it is stuck in the VB. Like the lever moves back and forth but the rod it pushes in the VB does not. I noticed it when I had the VB off replacing the shift shaft seals. If it is stuck in the "kickdown" position it should have extra pressure, correct? And have more harsh shifts not soft.

Appreciate everyone's help. Building 2 sheds, a corral, and work 40 hrs a week. Plus it is deer season so.... gonna be a slow process lol

 

So I drained some fluid out, went for a test drive. May have been marginally better. Got home, checked fluid level.... not even on the stick. OOPS too much. Going to add back gradually until I get proper level and re-evaluate. But I am starting to doubt the cavitation/dirty fliter/sucking air theory as it goes quickly/firmly into reverse every time. Almost has to be in the forward clutch. And since it hooks so firmly for the first few miles, I am doubting friction issue and leaning more toward leaky seal or loosing pressure in the apply passage somewhere. But this is all based off of what I can imagine in my head is going on in there so.... Need to get a gauge hooked to it and check some pressures I suppose.

 

you can use an oil pressure gauge to check trans line pressure

 

Quick update:
Let me preface this with "I do not believe magic in a bottle will fix anything or renew worn parts"

I put a jug of Lucas trans fix in it, in hopes that it would possibly soften seals (or that stuff is thicker than honey so perhaps it might thicken the fluid and make the pistons seal better)? Anyway, 2 weeks or so later, so far so good. May be a Band-Aid but if it gets me past Christmas, I am considering it a blessing!