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Author Topic:   transmission help

Posts: 73
From: Pocahontas,IL USA
Registered: Aug 2000

posted 03-24-2001 10:07 PM     Click Here to See the Profile for 73429MACH   Click Here to Email 73429MACH     Edit/Delete Message   Reply w/Quote
The C6 trans. in my Mustang seems to be slipping as it shifts from 2nd to hi.(I have to let of the gas before it will shift) From 1st to 2nd it's fine. I had the trans. rebuilt back in '91. I parked the car in '93 with about 4000 miles on the trans. It had been sitting until now. I drained the fluid, changed the filter and installed it back in the car. Its all stock except for a B&M shift kit. I've checked the fluid level and its fine. Does anyone have any ideas what would cause the slipping? Does the vac. modulator have anything to do with this? Please don't tell me I need to get it rebuilt again. Thanks, Ryan.

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Posts: 279
From: Memphis, TN
Registered: Feb 2000

posted 03-24-2001 11:56 PM     Click Here to See the Profile for 65hoss   Click Here to Email 65hoss     Edit/Delete Message   Reply w/Quote
It sounds like the clutches in the high gear drum are bad. Mine did the same thing and this was the problem. You can check the modulator valve, but since 1 to 2 is ok, I would doubt it.

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Posts: 499
From: Gadsden, Al
Registered: Aug 99

posted 03-25-2001 12:29 AM     Click Here to See the Profile for Dave_C   Click Here to Email Dave_C     Edit/Delete Message   Reply w/Quote
It is the sealing rings on the servo. Positive about that. With only 4K miles on it and sitting that long the rubber seals on the servo have hardened up. If it was the clutches it would still shift but slip all the way into gear. Letting off on the gas shows it is the servo

The servo works like this. It applies 2nd gear on the 1-2 shift. But the kicker and what many people don't realize is that it must *release* 2nd gear before 3rd can apply.

The piston (in the high gear drum) is trying to apply 3rd gear. The band is still holding onto 2nd so the high gear clutches slip. The valve body diverts fluid to the back side of the servo to make it release. The servo still has pressure on it from the front side. But the seals are leaking and it doesn't move fast enough. Or as fast as the high gear piston applies the high clutches.

When you let off the gas it reduces the fluid pressure to the servo. Under less pressure the fluid isn't blowing by the seal as bad, the servo releases the band and 2nd gear and it shifts to third.

Fairly simple to fix. You can do it with the trans in the car. Loosen the locknut on the adjuster, tighten the band all the way down. If it's loose the adjuster mechanism may fall off inside the trans when you remove the servo from the other side. Unbolt the servo cover, remove the servo. If your trans is original it will have rubber o-ring type seals on an aluminum piston. If it is a later model trans it may have an "n" servo. Looks like a hockey puck on a stick. No o-rings, just the entire piston is covered in rubber. In that case replace it ~$10. Replace servo, re-adjust band.

Been through this on 2 C-6's of my own and one in a friend's car.


David Cole

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