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Discussion Starter · #1 ·
Hi everyone,

I own a 1971 Lincoln Mark 3, 460 engine with C6 transmission, got its transmission rebuilt 2 months ago because of bad seals, so I decided "well, might as well have a full proper rebuilding while I'm here"
Replaced all the seals, o-rings, clutch plates and steel disks, bands and so on (I gave the transmission to a trusted mechanic to do the job)

Once the trans was back on, it worked fine as it should have, but it had some funky shifts while going from 2nd to 3rd, by that I mean that while the transmission was ice cold, it worked perfectly, 1-2 and 2-3 shifts were smoother than modern days transmissions, then by the time the tranny warmed up a bit, it did not want to engage 3rd gear, it did only if I let go completely of the gas, the moment I put the slightest pressure on the gas pedal, it downshifted to 2nd gear, then once the tranny is nice and warmed up to temperature, it does engage 3rd gear but with a pretty long upshift, kind of consistently
The 1-2 shifts works perfectly no matter the temperature

Up until today I didn't really pay much attention to it, but today I did a slight pull, going WOT from 10mph to 70-80mph (all at operating temperatures) and when I let go the gas it seemed as if the car braked, not just common engine brake
Stopped the car, put it in neutral, put it in drive and it all worked fine after this
Worried for this, I got home and checked the trans fluid level (put the car in neutral after going through the gears) and it had a burnt smell coming from the dipstick tube and has some bubbles on the dipstick itself... and noticed that the fluid level was decently above max on the dipstick

Could the problematic 3rd gear engagement and bubbles/burnt smell from the fluid have been caused by the overfill?
Thanks in advance, everything helps!

Also, forgot to add, when I got home, when I put into reverse it did a double "clunk" like if it engaged twice, a first clunk and then a consecutive one later, other than that reverse engages fine, no slip
 

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Based on your description, the trans was never right from the start.
A rebuilt trans should never have "funky shifts while going from 2nd to 3rd" when hot.
This indicates a pressure leak to the high/direct clutch.
It worked cold cuz the oil is thick(er) and covers up the leak.

Now, a burnt smell means likely the high/direct clutch is cooked and the trans will have to come out again.
Unlikely the overfill caused this issue.
Someone goofed up on the rebuild.

The double clunk into reverse is also an indicator that the high/direct clutch has a problem.
It may not seem to slip now in reverse, but if you keep driving it with these issues,
it will eventually completely lose 3rd and reverse.
 

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Discussion Starter · #3 ·
Based on your description, the trans was never right from the start.
A rebuilt trans should never have "funky shifts while going from 2nd to 3rd" when hot.
This indicates a pressure leak to the high/direct clutch.
It worked cold cuz the oil is thick(er) and covers up the leak.

Now, a burnt smell means likely the high/direct clutch is cooked and the trans will have to come out again.
Unlikely the overfill caused this issue.
Someone goofed up on the rebuild.

The double clunk into reverse is also an indicator that the high/direct clutch has a problem.
It may not seem to slip now in reverse, but if you keep driving it with these issues,
it will eventually completely lose 3rd and reverse.
Damn this is unfortunate... what could have gone wrong? Forgot a seal/pinched it while assembling?
 

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Damn this is unfortunate... what could have gone wrong? Forgot a seal/pinched it while assembling?
LOTS of things can go wrong...
Seals, rings, sticky valves, wrong VB gasket, servo etc. Not to mention human error.

Get a shop manual for it and put a pressure gauge on it to help diagnosis.
Human error during rebuild is one of the hardest things to diagnose.
Part failure, (cracked something, check ball missing, etc) can also be tricky to diagnose.

Pull it out and tear it down,
Does your trusted mechanic have experience with these transmissions?
If he's new at this, find someone that is familiar with the C6 to do the repairs.
 

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Discussion Starter · #5 ·
LOTS of things can go wrong...
Seals, rings, sticky valves, wrong VB gasket, servo etc. Not to mention human error.

Get a shop manual for it and put a pressure gauge on it to help diagnosis.
Human error during rebuild is one of the hardest things to diagnose.
Part failure, (cracked something, check ball missing, etc) can also be tricky to diagnose.

Pull it out and tear it down,
Does your trusted mechanic have experience with these transmissions?
If he's new at this, find someone that is familiar with the C6 to do the repairs.
He said that he's worked on some C6's, I was "lucky" finding this mechanic because he was the only one willing to work on my car since he is specialized in vintage american cars, and by "specialized" I mean it in "italian standards" since here in italy such cars are pretty uncommon
So finding anyone with more experience than him would be extremely hard
Regarding wrong gaskets or seals, I bought the rebuild kit that he used on Summit Racing, it's a late '67 to early '76 kit so it should be all good, theoretically that is

Other than that, he said that he cleaned the VB and I confirm that because I visited him in the moment he was cleaning them
 

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Aside from the advice above, if you bought the rebuild kit from Summit, there’s a good chance the clutches were the same type as the original which means you need to run type F auto transmission fluid. The newer stuff can cause problems (but not as bad as you indicated).
 

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Discussion Starter · #7 ·
Aside from the advice above, if you bought the rebuild kit from Summit, there’s a good chance the clutches were the same type as the original which means you need to run type F auto transmission fluid. The newer stuff can cause problems (but not as bad as you indicated).
I’m basing this on the first advice that was sent in this thread, going by elimination, the VB gasket should be the correct one (or at least so is stated by Summit), I doubt it has anything to do with the servo because 2nd gear engages fine, the valve body itself was cleaned by the mechanic who did my rebuild, I’m guessing it’s either seals or sealing rings in the high/reverse drum
 
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