The Turbo 400 in my '70 GS455 is the original, numbers matching tranny that has been rebuilt sometime prior to my buying it and the shift kit is unknown. Upshifting is fine in all gears and passing gear also works fine. Problem is the shift from neutral (or park) to either drive or reverse is very harsh when the car is idling at only about 650 RPM. Is this likely a tranny issue or perhaps somewhere else in the drivetrain? If in the tranny is there a fix?
That's odd. The only thing that comes to mind is the vacuum modulator? Maybe double check the line? It's a weak theory, I know... Is there a clunk audible when you shift? If so, a universal joint in the drive shaft is likely.
Also check fluid level and condition, but most likely a “tight” torque converter. Does it sit at a light in drive pretty tame or does it feel like it wants to go and your holding it back more than normal?
Grab the yoke going into the differential and see how much backlash there is. Gotta be in neutral to check it...
Does it do this from park to in gear as well or only neutral to in gear? If the external checks come out good, if during the rebuild they left the wave plates out of the direct and forward clutch packs and used line pressure you would get this for sure
I think I'll start by putting it up in the air and checking the universals and backlash. How much backlash is normal?
Proper backlash in the rear on average is .007 to .010 over movement measured at the ring gear holding the pinion perfectly still So basiclly if rocking the pinion there should be basiclly very little free movement........ Normally if a backlash issue there is a clunck herd when engaged not just a very firm feel
You would want to look at line pressure on the trans, to see if some builder jacked it way up. Take it to any trans shop, and have them check the line pressure at idle, in park..should be about 60psi. Buick used two strategies to soften the "hit" from putting it in gear. The first was the much hated by hot rod guys, tube in tube driveshaft.. the driveshaft was actually two tubes, one smaller than the other, that were pushed together, with an adhesive rubber material injected between them, much like what was used between the two pieces of the harmonic balancers. This allowed just enough flex to eliminate the "bang" when you put it into gear.. The other thing they did was use a waved steel plate in the forward and direct clutches, eventually some later transmissions use it in the intermediate also. This waved plate slows the clutch apply speed down, to facilitate buttery smooth shifts, as well as lessening the bang when it goes into gear. A lot of builders automatically throw the waved plates away, and most A body driveshafts were the solid shaft design, so you may be suffering from the affects of not having either.. good news is, the small diameter converter your talking about buying from me, will soften that feel, as it will absorb some of the shock. Those who have installed that converter, and went away from the big 13" unit, can attest to the difference in feel. JW
Referencing the driveshaft, here's the one in the car now. It doesn't look original. Is it perhaps the solid version? Also, can the line pressure be turned down conveniently?
Line pressure can't be turned down as your thinking....there is no adjustment screw.......but the pan can be dropped and pressure regulator spring can be accessed and changed without dropping the trans out of the car......but it can be fun to get it all back in if never done b4
