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#1
03-25-2003, 07:51 PM
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I fired up the car recently and took it out for a drive (first time since December), and the transmission wouldn't hold low gear and then began to slip. I turned around and limped it home only to discover that the line to the vacuum modulator had fallen off. I reconnected it and took it out for a test drive and everything appeared fine. Well drove it again the other day and the trans. would not hold low gear again-it shifted into second by itself. Not only that, but when I use the 'His' part of the His/Hers shifter, the car begins to shudder in first gear. The trans. is a T-400 that was rebuilt about 1 year ago by ATI. Any suggestions? Could I have damaged the trans. by driving without the modulator hooked for about 2 blocks? Could it just be the modulator not working correctly? Thanx for your help!
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#2
03-25-2003, 07:51 PM
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I fired up the car recently and took it out for a drive (first time since December), and the transmission wouldn't hold low gear and then began to slip. I turned around and limped it home only to discover that the line to the vacuum modulator had fallen off. I reconnected it and took it out for a test drive and everything appeared fine. Well drove it again the other day and the trans. would not hold low gear again-it shifted into second by itself. Not only that, but when I use the 'His' part of the His/Hers shifter, the car begins to shudder in first gear. The trans. is a T-400 that was rebuilt about 1 year ago by ATI. Any suggestions? Could I have damaged the trans. by driving without the modulator hooked for about 2 blocks? Could it just be the modulator not working correctly? Thanx for your help!
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#3
03-26-2003, 05:46 AM
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To see if the modulator is not leaking, pull vac. line at vac. source and see if there is any trans. fluid present. Replace all vac. lines on car. If the line can fall off by it self replace lines for sure, they're all bad. When my 400 modulator line fell off the modulator, it got about 10 - 20 degrees hotter, and would not shift, but that was on my chevy RV. Remember there are 2 rubber vac. lines to the modulator, 1 at the trans. and 1 at the vac. source. good luck
  BIGGERISBETTER-15 yrs in NHRA tech ret.
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NHRA tech. "Its just a 412, I swear it". Pontiac tip of the year, quit those damn cigarettes. 
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#4
03-29-2003, 05:29 AM
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Running without the modulator for a short distance would hurt nothing. The modulator is simply used to send a vacuum signal to the trans to help it with gear selection. Without the modulator hooked up the car will have high upshift speeds and no braking effect when you let off the throttle. The slippage in low gear is from one of the applied components not holding. Use a tech pub and and follow the flow charts for slipping in low gear. More than likely the trans will have to come out for repairs, but not always, troubleshoot first......Cliff
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If you can read this, thank a teacher. If you can read this in English, thank a Veteran! https://cliffshighperformance.com/ 73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile), |
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#5
03-29-2003, 09:46 AM
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Cliff, it doesn't actually slip in first gear (once the vacuum line was reattached), it's more like a chattering or hesitation then a slipping. It's definetly in the drivetrain and not in the motor. The chattering only occurs with the shifter in the 'His' side of the Hurst dualgate (which doesn't really make any sense because the tranny gear selector is positioned the same as in the 'Her' side of the shifter. Plus, as mentioned previously, the tranny is designed to remain in low gear as long as the shifter is held in low. However, now when the 'His' side is selected, it shifts out of first by itself.
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#6
03-30-2003, 04:22 AM
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No experience with the His/Her shifters. Not sure how they work or effect manual gear selection. The TH-400 trans should upshift to 2nd gear even if held in manual low unless you modified the 1-2 shift valve. Shuttering, chattering or vibration are indications of slippage within one of the components in the trans trying to hold for that particular gear...Cliff
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If you can read this, thank a teacher. If you can read this in English, thank a Veteran! https://cliffshighperformance.com/ 73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile), |
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