Automatic C6 And a Diff Ratio.

[freeline95]

I have a 1969 f-100 custom cab with a 360 in it and I swapped the three speed on the column for an automatic c6 and I was wondering if it would have changed my speedometer because i noticed that everyone was passing me when I was already doing 5 mph over the speed limit???

I just installed the transmission yesterday and I bought it from some guy that had an add in the paper and he said that it was a good transmission but it kind-of shifts quite harder that it should i thought about putting lucas in it but im not for sure if i should or not but i do know that i am going to put a b&m shift kit in it. Any ideas on why it would be shifting hard?

I also was wondering what would be a good gear ratio for my rear differential? I would like to have a good take off but still yet also have a good top speed? I kind of want something in the middle.

[MadMaxetc]

It is posible that the internal gear on the C6 is a differant size than the one in the 3-speed.

Most of the time the Autos have a lower rear gear than the manuals. 3.5 (auto) vs 3.7 (man)

[Hawkrod]

The gear for the speedo cable is different for a C6 than a 3 speed so you will need a correct one for a C6 with your rear ratio. You also will need to know which speedo drive gear the trans has as there are more than one and the trans you got may have the wrong one in it. If you got a trans with the wrong one you are going to have to wing it or take it apart and change it. Hawkrod

[freeline95]

Thanks guys for the reply's I guess that I'm going to wing it as "Hawkrod" said but what about to hard shifting do you guys think that I should try lucas because I think that sticking valves is what causes hard shifting.... am I right about that???

[DuckRyder]

Thanks guys for the reply's I guess that I'm going to wing it as "Hawkrod" said but what about to hard shifting do you guys think that I should try lucas because I think that sticking valves is what causes hard shifting.... am I right about that???

Before you wing it see if you can install the correct cable drive gear, that is easy to do.

Do you have the kickdown linkage hooked up?

Did you change the transmission fluid and filter when you installed it?

Did the seller mention any modifications (Shift Kit)?

Is the modulator hooked up, functioning and properly adjusted?

[freeline95]

Before you wing it see if you can install the correct cable drive gear, that is easy to do.

Do you have the kickdown linkage hooked up?

Did you change the transmission fluid and filter when you installed it?

Did the seller mention any modifications (Shift Kit)?

Is the modulator hooked up, functioning and properly adjusted?

Yes the kickdown is hooked up.

No I havent had time to change the fluid and filter but the fluid in it looks brand new.(added 4 quarts when put in do to loss of fluid from being removed and installed)

The seller mentioned no modifications.

yes the modulator is hooked up and it shifts at the right time when driving. But I didn't know that you could adjust it I just thought that you could only replace it I have never heard of being able to adjust it point me in the right direction on how to adjust it. If you think that is the problem with the hard shifting.

Thanks a lot.


I had a 98 dodge ram with a 316 in it and it had about 100,000 miles on it and it started shifting real hard so we put a quart of lucas in it at it straightened right back up and has never done it since and it now has 290,000 miles on it. what are your thoughts about trying lucas if you don't think that its anything else such as the modulator.

[michael69]

If it is shifting hard now and you don't like it why would you want to put a shift kit in it to make it shift harder?

[freeline95]

If it is shifting hard now and you don't like it why would you want to put a shift kit in it to make it shift harder?

good point but what I was saying is that it has never been modified so i didn't think that it should be shifting as hard as it is without modification.

[fordman]

hard shifts can come from hard seals inside the transmission. if its never been apart then its probasbly needs to be done then. or you could try to change the fluid and get by for a while.

[mmerlinn]

If your C6 has a bolt-on flange, all you will need to do is change your driven speedometer gear to suit, as all drive speedo gears are the same.

If you have a slip yoke C6, you MAY be able to do the same thing, but ONLY if the toothcount for the drive speedo on the shaft is correct. If it is wrong, then you must dismantle the whole transmission to change to the correct shaft. Shafts come with 6, 7, 8, OR 9 tooth speedo gears CUT into the shaft.

[DuckRyder]

Most c6 modulators are adjustable, you remove the vacumme line and you will see a small valve inside the nipple. Also make sure the line to it is metal with short rubber sections. The rubber line can collapse and restrict flow.

You really need the speedo working to make sure the shift points are correct.

I'm not a big fan of additives, but if its worked for you in the past.

[sideoilerfe]

I had a 98 dodge ram with a 316 in it ...

you mean 318. 5.2L