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Subject: 400 Turbo shifts too fast

Original Message
Name: Randy L.
Date: July 20, 1998 at 15:05:45
Subject: 400 Turbo shifts too fast
I have a 400 turbo installed in my 67SS 396. It's not the original tranny, and I'm not real sure what it came out of. My problem is that it shifts from 1st to 2nd too soon. Also from 2nd to 3rd too soon. By the time I get to 20 mph I'm already in 3rd gear. I've been told that it may be the modulator valve. Is there an adjustment for this? If so, how is it done? Thanks.

Response Number 1
Name: Alan F.
Date: July 20, 1998 at 17:12:35
Subject: 400 Turbo shifts too fast
On the passenger side of the transmission, the vacuum modulator is connected to the engine with a 3/16" rubber hose to a metal tube. Slip the rubber hose off of the nipple on the vacuum modulator. There should be a small flat-head screw. Turn it clockwise to increase the shift point and firmness and vice-versa. I would suggest making adjustments in increments of two complete revolutions on the screw as you may not otherwise notice the change.

Response Number 2
Name: Shannon
Date: July 20, 1998 at 17:32:47
Subject: 400 Turbo shifts too fast
I have the same prob. w/ my TH 350 in my Z28....shifting to soon and not real firm. I did the shift kit myself by drilling the factory plate several years ago, and noticed quite a bit more firmness in the shift. But it doesnt shift as hard any more. I have always assumed that my 3.73 gear ratio was the reason for it shifting so soon.......but it still shifts all the way thru third too soon. Do you adjust the 350 modulator valve the same way you do the 400? Is the screw inside the nipple when you remove the vaccuum hose?
Thanks Randy for bringing the subject up and thanks Alan for your response.......I thought my trans was on its way south....hopefully Alans advice will help.


Response Number 3
Name: Schurkey
Date: July 20, 1998 at 20:18:32
Subject: 400 Turbo shifts too fast
TH 400 and TH 350 can use the SAME modulator.

Keep in mind that adjusting the modulator is NOT the proper way to change the shift points. The modulator affects shift firmness, and the shift timing as a "side effect". Modifying the modulator raises the pressures inside the transmission and makes life tougher for the rubber seals and the pump. There is a better way!

The proper way to adjust shift timing is to modify the governor. This can be done by lightining the weights with a drill bit, being carefull to drill the same size holes in both weights at the same location, so as to preserve the balance. A better way is to buy the B&M governor kit, and just follow the instructions.

Response Number 4
Name: safak
Date: July 20, 1998 at 22:41:26
Subject: 400 Turbo shifts too fast

I recommend using B&M shift point kit. It contains weights for major changes and springs for minor changes. But your max rpm where upshifts occur and your downshifting character will also change. So be careful and don't exceed your rpm limit. It would be a good idea to change the springs first.

Response Number 5
Name: Greg
Date: July 28, 1998 at 09:31:30
Subject: 400 Turbo shifts too fast
not all modulators are adjustable from the factory. I also agree that this is not the proper method. Use the governor kit. The governor controls the upshifts in conjunction with the modulator. Use the modulator to fine tune only.

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