Manually Controlled Lock Up 904

[340inabbody]

Anyone here controlling their lock up manually with a 12V switch?

I am asking because I’m thinking of using a lock up 904 in place of my 1970 non-lock up 904 for the following reasons:

Lower gear ratio
Steel planetary gear sets
5 clutch bands
Partial kickdown

I just don’t know anyone doing this and wanted to know how it’s working for them. I assume if I controlled the 12V lockup solenoid that I could lock it up when in cruise. Otherwise is should perform the same as a non lock up unit out of the gate. I therorfe could take advantage of the stall then have a quasi overdrive.

Comments?

 

[memike]

Interesting. Watching

 

[Professor Fate]

I'm not going to re-write everything, but same reply as in the other thread.
Will A904 parts swap into A999
The one thing I don't recall offhand is whether 12v applies the lockup, or bypasses it... it's been a couple years since I wired one up. If you cornered me on it, I'd have to say 12v prevents lockup. Still gets wired the same either way.
Works fine, just make sure you use ATF+4 in it- helps prevent lockup chatter.
And while it may not be an issue on your B body (although I'd still strongly suggest a trial fit), there is one other thing about this swap to be aware of on A bodies-
If you have the later style trans with the reinforcement ribs in the tailshaft housing, things can get kind of cozy with the '67 and up A body trans crossmember. It'll fit, but every car combination is just a bit different, so your clearances may vary.
However, on early As ('66 and earlier) those ribs will require significant grinding on those ribs to clear the much more restrictive early crossmember, as well as removing that rubber "pad" at the top of the hoop.

The access plate for the tailshaft snap ring was also moved from the bottom of the housing to the side of the housing, and also gets very close to the early A crossmember.
Nothing insurmountable, just a couple of points to keep an eye on.

 

[str12-340]

I use a manual switch for both the overdrive and the lock-up in my 904 based A500 (RH42) trans. It's worked just fine for about 16,000 miles so far. You just have to remember to hit the switch when you roll off the interstate up to a stop sign. After a few thousand miles I pretty much started hitting the buttons without really thinking about it.

 

[340inabbody]

I use a manual switch for both the overdrive and the lock-up in my 904 based A500 (RH42) trans. It's worked just fine for about 16,000 miles so far. You just have to remember to hit the switch when you roll off the interstate up to a stop sign. After a few thousand miles I pretty much started hitting the buttons without really thinking about it.
View attachment 1716511520View attachment 1716511519

So 12V to the switch deactivates or activates LU?

 

[str12-340]

Actually the wiring for an RH42 has one hot wire into the trans and 2 ground wires out (one for OD & one for Lock up), so the switches actually cut the ground side of the circuits for each. If I put a switch in the hot side it would control OD & LU simultaneously. I presume the lock up only circuit has a hot wire in and a ground wire out so you could put the switch anywhere in the circuit. I used fancy switches that are lit with the dash lights too.

 

[Professor Fate]

Actually the wiring for an RH42 has one hot wire into the trans and 2 ground wires out (one for OD & one for Lock up), so the switches actually cut the ground side of the circuits for each. If I put a switch in the hot side it would control OD & LU simultaneously. I presume the lock up only circuit has a hot wire in and a ground wire out so you could put the switch anywhere in the circuit. I used fancy switches that are lit with the dash lights too.

Lockup only just has a single wire in- it's internally grounded.
You just put it on a toggle. Actually, you put a toggle on a fused relay to feed it- those solenoids draw a lot of juice and can fry a toggle.