Adjusting shift points on C6???

[Classicfordguy]

So I finaly have this 1984 Van/truck machine all painted and ready to sell (6.9 with C6), However it seems like it waits too long to shift to second gear. Is there a way to adjust it? Can I fiddle with the vacuume modulator on the trans, which way should I turn the screw?

Heres a link to the Vuck (van truck)
http://i486.photobucket.com/albums/rr224/classicfordguy0/IM004779.jpg
http://i486.photobucket.com/albums/rr224/classicfordguy0/IM004780.jpg

Thanks guys,

-Rob

 

[69oiler]

you can turn the VRV on the IP (black thing with vac hoses going to it) to adjust shift points.

 

[sassyrel]

after the vrv is adjusted right--you can talor the shift point more by the adjustment of the mod valve on the right rear of the trans---

 

[Classicfordguy]

Great, thank you. Any idea what which way I turn the VRV to make second come in sooner? From what I gathered from my dads 86 service manual the vacuume modulator adjusts the harshness of the shift but not the shift point, does that sound correct?

Thanks,

-Rob

 

[sassyrel]

they are somewhat tied together--

 

[02AutoWag]

So what is the appropriate RPM for a 1-2 shift change in a C6 under normal pedal pressure?

Is this 1-2 shift always a "violent" shift? My issue is that it shifts hard during the 1-2 shift when cold, but it's acceptable when the truck is warm.

I checked fluid level when the truck was warmed up and while it was running. Level indicates proper fill at the upper hashmarks.

The most rearward rotation of the VRV will get me harsh 2200-2300 RPM shifts between 1-2 when cold.
I rotated the VRV toward the front (about a dime's width) and it then began shifting at > 2600.

Pulling the vacuum hose on the vaccum modulator (the one on the rear passenger side of trans) and turning the screw outward (counter clockwise) did not change anything. Is there a worry about backing this screw all the way out? I'd like to try backing it out more, but want to be sure I can put it back without damage.

 

[Classicfordguy]

Same thing with this one, fist 1-2 shift when cold you have to be screamin, after it warms up a bit it works much better but still a bit high. This one doesn't have a tack but I know its getting up there before it shifts, I run it up then let off and it shifts.

-Rob

 

[02AutoWag]

I initially backed the modulator screw outward 2 turns without any affect. Another complete turn (3 total) has eliminated the "violent" shift change when cold. It'll still shift at 2200-2300 RPM, but with much better manners.

I don't know where the modulator was set before I began turning, so the final position is unknown. I ask again, is there any concern with this thing backing all the way out? I'd like to experiment with backing it out more, but don't want the thing to fall out and not get it put back together again. Yes, I'm paranoid.

 

[suv7734]

after the vrv is adjusted right--you can talor the shift point more by the adjustment of the mod valve on the right rear of the trans---

VRV adjustment from Dieselmann:

Vacuum Regulator Valve--C-6
Remove the throttle cable and return spring. Reinstall the return spring to hold the throttle bellcrank at wide open throttle (engine off). Remove the vacuum modulator hoses from the VRV; install a vacuum gauge on the lower (output) port and a vacuum pump on the upper (input) port. Apply vacuum and maintain 20 in/HG on the gauge; cycle the bellcrank from WOT to idle position 5 times. A gauge block for the throttle lever can be improvised using the 13mm head of an 8mm bolt. Insert the head of the bolt between the flat boss on the right side of the injection pump and the throttle travel screw. The vacuum gauge should read 6-8 in/HG. If it does not, loosen the VRV screws and adjust the VRV so the gauge reads 7 in/HG. If this reading cannot be achieved, replace the VRV and restart this procedure. After adjusting the VRV, remove the spring, apply and maintain 20 in/HG of vacuum to the VRV and cycle the throttle 5 times. The vacuum gauge should read at least 13 in/HG at idle position. If it does not, replace the VRV and repeat this procedure.

 

[Classicfordguy]

Great, thank you guys for the info.

-Rob

 

[HammerDown]

After I installed a new VRV and set it up with a vacuum guage like Dieselmann's post I still wanted to 'firm-up' the shifts a tad on my C6...when looking at the VRV from the drivers fender, rotating it counter clockwise .030 did the trick

Note, few years back when my original VRV was found to be bad it always shifted 1-2 high and hard, sometimes I had to lift off the throttle and get a neck snaping 1-2 shift...not fun!