Vintage Mustang Forums banner
  • Hey everyone! Enter your ride HERE to be a part August's Ride of the Month Challenge!
1 - 7 of 7 Posts

Discussion Starter · #1 ·
Can you believe my luck with transmissions?!

Let me tell everyone what I have, then I will ask some questions.

351C C-6(Just rebuilt) TCI 10" converter(3000 stall I think) TCI manual-reverse valve body.

The car seems to shift fine under minimal load. 1st gear is strong, and the shift from 2nd to 3rd is very strong. The problem is with the shift from 1st to 2nd. Under 3/4 to full throttle, slipping occurs. If you briefly let off the gas it will engage, and hammering it again it stays engaged. The shift from 2nd to 3rd is very strong and instant, no slipping. If you have it in 3rd and downshift and a good rpm, so that the rpm's are high in 2nd, it shifts fine, and holds good. It is just slipping from 1st to 2nd under medium to heavy loads.

Now for some questions.
Should the vacuum modulator be hooked up on a manual valve body tranny? (it is not)

What controls the line pressure if the modulator isn't hooked up? I know in a normal valve body, the vacuum controls it. Is it not needed in a manual valve body?

If it is not needed, what should the pressure read when measured? Does it run at full pressure all the time? If so, isn't that bad on the seals?

My tranny guy and myself test drove the car tonight, and the above observations were noted whim him driving the car. He doesn't know much about the manual valve body, and neither do I.

Why is 2nd slipping? He is positive that he did the band adjustment correctly, although we will check this Thursday, along with checking the line pressure with gauge.

Help me out here guys....... Please!!!

Full Throttle

Discussion Starter · #3 ·
You described in a few words what it took me a paragraph to say....dragged out 2nd gear shift.

That is what is happening. My friend the tranny guy also mentioned that this servo piston did not come new in the rebuild kit, so he re-used the old one. What goes whong with them, or is it a seal?

Full Throttle

10,588 Posts
Nothing wrong with using the old servo piston over as long as the seal surfaces and the plunger are ok...

But he should've put new seals on it....there's two that go on the piston and a third to seal the servo cover to the case...

Your control circuit pressure should be in the 160-190 range with the modulator disconnected...I still run a modulator in my race car trans and it has a manual valve body....

Here's some info on C6 service...

Since your 2-3 is OK, it may be a scheduling problem....or shifter your shifter adjustements and re-install a vacuum modulator and note changes, if any

Good luck!


Discussion Starter · #6 ·
So by hooking up the modulator, I keep the pressure from being full pressure all the time, is this correct? If so, then I think I will hook up the modulator(It is currently plugged off).

Full Throttle
1 - 7 of 7 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.