HELP WITH SUPER TURBINE 400 SHIFT PROBLEM

Have a '64 Riviera (all stock), was parked for several weeks, shifted without any problems before being parked. Now it won't shift from first (out of first) to 2nd gear and will just "freewheel" without any compression or engine breaking when the rpms are increased. I have changed the fluid, the filter, added Seafoam, changed the vac modulator, checked for vacuum (18+), and removed, cleaned, and checked the governor; still won't shift?
Who has any other suggestions or can offer a diagnosis?,,,

 

Well, the engine is at 18+ inches of vacuum and I measured the line going back to the modular from the line going back to it from the firewall, it held more than 18 inches without dropping; thanks for your reply,,,

 

If a trans was even half that age, I would have it apart and refreshed for service.
Rubber ages even on low miles. Bruce Roe

 

If it had no vac at the modulator it could still shift into 2nd, just be very late. This is what happens every time we floor the car and it makes a 1-2 shift.

Sound to me like one of the rubber seals on the intermediate piston finally broke. It sold like everything leading up to the shift is working (valve body, gov, etc) I draw this conclusion because you are a drastically different feel when you should have second.

I assume the transfer does the same thing when letting it shift it self as when in drive, and when you manual shift through from 1 to 2. If so it is almost certainly a clutch piston seal broken, which may or may not have burnt the clutches for second. If when in manual you feel a little more like the gear is trying to work it would point to burnt clutches.

We had a 4l80e, basically the same transfer with od do the same thing. We could actually run 1st longer, higher up the rpm, the shift to drive, back off the gas the gov would up shift from 2nd to 3rd and we could go on, from there when we pulled down into 2nd you could feel some tring of engine braking

But even if it's just a .25 cent oring, the transfer still has to come our and apart. At that time I would add a HD intermedate sprag, (about 75 bucks doubles the holding power of 2nd gear, and your 64 transfer should have the smooth sprag drum needed for this) I would also dual feed 3rd gear. It's as simple as leaving a Oring off the instead of direct piston and or leaving the 2nd sealing ring off the center support ( I do both ) and installing a 7/16th plug cup into the reverse passage in the case right beside the center support bolt. This will give twice as much fluid to 3rd gear.

There are several other free mods to do like drilling out the seperator plate in 2nd and 3rd to allow for faster firmer shifts if wanted, several accumulator springs that could be removed this also speed up and firm up shifts, basically what they do for a shift kit without spending the 75 bucks.

 

Thanks for your advice; can any of all of this work be done by a good mechanic or is a trans specialist with special tools needed?,,,

 

The only really "special tools needed to rebuild a 400 are the tool's needed to install the lipseals (you can get plastic ones online for under 50 bucks), a good press and adapters needed to replace the bushings inside the parts( I bet 90% of the time you could do a rebuild with out replacing them with no side effects) I torque wrench, dail indicator to measure end play, and a feeler Guage set to check clearances or clutch packs and planetaries.

A lot of ppl don't want to do transmission, there are a lot of parts in them. Sometimes it's better to pay the pro then save a little on someone who has never done one.. but that's a choice for you to make

 

is it possible the kickdown switch is sending voltage to the transmission all the time? I had something similar happen years ago and this was the problem

 

If nobody mentioned it, a stripped governor gear could keep you from
upshifting. Don't know how this was for 64, but later years used plastic
gears and it isn't unusual in a TH425 (including mine).

Seems to me, if it isn't the kickdown, vac modulator, or governor, no
need for more speculation, just get that trans apart. Bruce Roe

 

You say you changed the modulator , did you make sure the valve moves freely in the case ? Stick a magnet in the hole and move the valve in and out?