: '73 SDV Early 2-3 Upshift @ WOT, Late Part-Throttle Upshifts

08-20-10, 08:36 PM
Hey all,

I searched these forums & google, and the only information I found vaguely pointed me toward the vacuum modulator... Found a lot of info on TH400's hanging onto gears @ WOT, but not early upshifting.

As a comparison, years ago I had a '71 Fleetwood; at WOT it shifted 1-2 @ ~45mph, & 2-3 just north of 80mph. I'd put a tach on it, and both shifts occurred at just a hair over 4000rpm, maybe 4100rpm.

The '73 DeVille I have now has the same WOT 1-2 upshift speed, but at WOT 2-3 happens @ ~67mph. I haven't put a tach on this one (yet), so I don't know if the 2-3 upshift is occurring at a lower rpm than the 1-2. But, it certainly sounds & feels like it is.

I was wondering what might be causing this. A friend of mine suggested maybe my '73 has deeper rear gears than the '71 did. While I haven't found out yet what gears it has (probably 2.93's), I thought that if the gears were deeper, *both* upshifts would be earlier than my old '71.

Also, the part-throttle upshifts seem to happen late, like the trans is hanging onto 1st & 2nd a few hundred rpm too long. Other than this, the trans seems fine. No juddering or slipping or other weird behavior. I was wondering if anyone here could help point me in the right direction before I start gettin' greasy...

Anyway, thanks for reading this everybody. I'm looking forward to any replies.

08-20-10, 08:50 PM
Check the fluid for the correct level and/or being burnt. If the fluid is ok, replace the vacuum line to the modulator. The modulator is probably alright as a symptom of a bad one is white smoke in the exhaust (a bad modulator will suck transmission fluid into the engine).

08-23-10, 02:07 PM
Thank you for the reply. The fluid is fresh & the level is fine, but I did notice some smoke as you described. I'll replace the modulator and the lines, & see if that takes care of the problems.