Shifting hard

[IHdiesel]

Hello all, I am new to this website and to the 6.9 diesel (owned a 6.7 Cummins). I just bought a stock 84 F250 6.9 4x4 with a C6 auto. Love it. But the transmission is shifting real hard. It doesnt have a tach on it but it sounds like it gets into really high RPM's before shifting. When it does shift, it is real hard and puts you back in your seat. It is the worst in from 1st to 2nd. Is this normal for these or is there a problem? I checked the tranny fluid and it was fine, not burnt or low. I hope this was descriptive enough. Thanks for your time and help,

Jeff

 

[DaveBen]

Sounds like someone installed a shift kit. This is a mod to the valve body.

Dave

 

[bike-maker]

There is a vacuum modulator on the trans. On one of my past trucks, the vacuum hose that went to it would fall off, and create the conditions you are describing. Takes alot of RPM to shift and shifts really hard, regardless of throttle input. This was on a 460/C6 truck, however.

 

['94IDITurbo7.3]

I don't know if the C6 has a TPS like an E4OD does but my tranny shifted like that when i first got my truck & all i had to do was adjust the TPS.

 

[HammerDown]

For years my C6 shifted high and neck snapping hard >turned out to be a bad VRV on the side if the IP.

 

[Brianedwardss]

VRV on the side of the IP is most likely bad. May just be out of adjustment tho.

 

[Brianedwardss]

Try this post:

http://www.oilburners.net/forums/showthread.php?t=47459&highlight=Adjust

 

[Squeaky_Wheel]

For years my C6 shifted high and neck snapping hard >turned out to be a bad VRV on the side if the IP.

I agree with Hammer. I had the same issue only I found out the hard way hence my C6 to ZF5 swap.

 

[sparkymichigan]

I also had this problem when I replaced the C6 in my 85. Turns out a slight adjustment of the VRV on the side of the IP fixed it. I also don't have a tach. So I set it be ear and feel. Simple fix if this is the problem. Also insure the vac line from there is connected and in good condition. I guess I should have first asked if your vac pump is working properly?

 

[HammerDown]

I agree with Hammer. I had the same issue only I found out the hard way hence my C6 to ZF5 swap.

And one trany shop(I knew the fella too) said I would need to have the C6 rebuilt...luckily I went to another trany shop (actually grew up with this guy) and he said BS, no rebuild needed it was the VRV > a HUGE TO Max's Tranny Repair in Sharron Hill Pa
I did originally set the new VRV up to proper procedure specks with a vacuum gauge and gauge block etc. but then went ahead and moved it to where I liked the shifts > NOT TOO SOFT THOUGH!