C6 Shift Points

[dieselfuelonly444]

Hi all, first post on Oil Burners, I just rode in my buddies 1984 6.9 C6 auto, it shifted into second at around 25-30ish if I remember right, and then into 3rd at around 45-50. I have a 86 F350 with a 7.3IDI the C6 but I shift into second gear at FIVE miles an hour and third at FIFTEEN, this thing screams when im cruising down the highway, any input as to why it shifts so early? Thanks

 

[Garbage_Mechan]

More than likely the VRV (vacuum regulator valve) on the injection pump is not set right, telling it you have a very light throttle opening, and to shift early. If you look at the platic valve on the side of the injection pump, you can see it rotates when the throttle is opened. Make yourself a reference mark, then loosen it up and rotate about 1/8 inch in the direction that will make it move sooner when the throttle is opened. This should raise shift point. There are specs for this but I have had great luck sneaking up on it. You went too far when it hangs and you have to let off the throttle for it to shift.

 

[Wyreth]

If you have a vacuum gauge, it's really pretty easy to check. Towcat just posted the testing/setting procedure in this thread over here:

http://www.oilburners.net/forums/showthread.php?65757-Help-with-C6-diagnosis-please

Personally I like how mine shifts, sitting at idle it measures 18hg. Babying it, it hits 2nd about 10-15, and 3rd 28-35, but seems to delay them sufficiently when flogging it harder.

 

[hallgren87idi]

or you got 4.10 gear ratio and he had higher. if you peg it to the floor will it still shift at 5? if i give mine a little gas it shifts at 5, but if i peg it itll do like 20-25 in 1st

 

[dieselfuelonly444]

If I floor it it'll have later shifts but my friend checked the axle codes or whatever they were on the door and said it had 3.55 gears unless someone had switched them out for some reason over its lifetime

 

[jayro88]

The previous owner had set mine to shift like you are stating.....almost into 3rd instantly. It made my van very doggy and was always bogging. I just started adjusting my vrv until I got it where I wanted it. It shifts prior to the governer, but I can run the rpms up in first and seconds pretty well without having to floor it (think constant half throttle). It is also nice that when I come out of a slow 90* corner in town I am now in 2nd instead of bogging in 3rd.

As far as it screaming at hwy speeds, all you can do about that is add a Gear Vendor Over Drive, switch transmissions or change your rear gear (which I wouldn't recommend). I like the simplicity and durability of the c6, so I am going to add a GV.....even though the non locking torque converter makes the mpg suffer. I usually set the cruise between 60-65mph....I have 3.54's.

 

[dieselfuelonly444]

I'll try adjusting the vrv to get it better once my truck is running again but hopefully I'll have a ZF-5 in my truck sometime soon. What exactly is a gear vendor od, is it just like an auxillary trans?

 

[jayro88]

I'll try adjusting the vrv to get it better once my truck is running again but hopefully I'll have a ZF-5 in my truck sometime soon. What exactly is a gear vendor od, is it just like an auxillary trans?

It is an OD that bolts to the back of the trans. It also works like a spliter for your gears. So it makes the c6 a 6 speed trans. You end up with 1st, 1.5, 2nd, 2.5, 3rd and OD(3.5). If you are going to put in a ZF-5 then don't bother with the GearVendor.