c6 shifting problems

[fixxer]

Well I am needing some help. I recently picked up a 70 f100 with an inline 6 and automatic c6 tranny. The previous owner said there is a shift kit in it. Its been rebuilt by a reputable shop as well. I was told by the seller that I would need to adjust the kickdown. But I have noticed when in Drive it will take a while to shift into 2nd and do the same for 3rd. It pretty much just hangs there at whatever rpm it is and then decids to shift. I have read the shifting issues are sometimes adjustable and fixable without pulling the tranny and going through it. If someone could chime in and guide me through some steps to adjust it and eliminate things that could be wrong I would greatly appreciate it.

[BobbyFord]

Fisrt of all, make sure you have a good, leak-free vacuum source going to the vacuum modulator valve and make sure the modulator valve is not leaking fluid out of the vacuum hose nipple. If the vac source is good then remove the vac line from the modulator (there is a small screw inside the vac nipple) and insert a small screwdriver into the vacuum nipple and turn the screw counter-clockwise one full turn. Next take it out and drive it to see if it's better. You may need to adjust the screw further to suit your expectations.

[fixxer]

I will try that and report back this afternoon. Thanks bobby

[Donnie]

Everything that Bobby said is solid info....If these tips do not cure your problem, post back with the color stripe on your modulator & the amount of vacuum available at your mod., engine idling in park..Best to have an assistant in the truck when you are under it doing this test to hold the brakes, just for your safety.........Do you know whose valve body program was used during the rebuild ?

When it does shift, are your shifts firm? I assume that they are as your only complaint was late, correct? Donnie

[fixxer]

I do not know what brand of components were used. And when it does shift it is very hard and solid. Hard enough to jerk mine and my passengers head back into the rear window almost. I thought that hard shifting ment something wrong but a friend of mine said that's the shift kit doing its job

[fixxer]

When checking vacuum.. where do I put the gauge at and about how much vacuum should I be looking for?

[BobbyFord]

Sounds like a B&M kit. Vacuum at the mod valve should be above 15 inches, 18-20 ideally.

[fixxer]

Ok, before adjusting that set screw you had talked about Bobby, I first did a vac check and it was roughly at 14 at idle. I checked the line over and sure enough the nipple on the manifold in the engine that the vac line went to, pulled out. I used some permatex 300 form-a-gasket and buttered the nipple some and put it back on. I am now waiting for it to dry so I can re-instal the line and check vac again. I will report back within the hour. Also when I pulled the line from the vac modulator nothing came out. I did however forget to check the stripe color on the modulator

[fixxer]

Vacuum is now at 19 and it did excellent during the test drive. Shifted on time through all gears. My next question now is, is it normal for it to slow itself down hard and quick like it has an internal brake? When I let off the gas like I am approaching a stop sign, you feel it catch a gear to slow it down. I am assuming that is the shift kit working? I tried tracking down some info on the components and the previous owner said he would like to think the guy told him it had a B&M street/strip kit in it but he is not 100% sure.

[BobbyFord]

Depending on the rear end gear ratio, it can have some engine braking. Certain shift kits will result in more noticeable downshifts when coming to a stop.

[fixxer]

Good to know, I imagine its just normal engine breaking. Everything should be good then, thanks for the help Bobby.

[Donnie]

Fixxer, if your shifts are firm at lite throttle, like driving around town, you probably have as Bobby said, a B&M valve body program.
glad you found your vacuum leak...........19 inches is good... Donnie