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M46 P-Type Overdrive Rebuild...tips tricks?

oifish

I'm feeling extra zazzzy
Joined
Jul 30, 2014
Location
Indiana
The time has come to rebuild my overdrive. Last year I had issues with it randomly disengaging, which turned out to be faulty wiring. I also replaced the relay for good measure. Now after being in overdrive for ~5-10 min it kicks out and drops to 4th gear. The "5th Gear" light stays lit. If I disengage the OD then re-engage, it will stay in 5th for about 10 seconds before popping out again.

If I'm in 4th gear, I always get the OD to engage and hear the relay click, so the 4th gear switch is working correctly. OD does not engage when in any other gear.

I checked the fluid level, which was ~1/2qt low, and topped it off. But the problem still persists. I'm assuming OD is unable to maintain pressure and needs new o-rings and seals.


The unit needs new gaskets anyways to stop the leaks, so I figure while it's out I might as well service the entire thing. I was looking at getting this kit: https://www.ipdusa.com/products/7348/115283-overdrive-mini-kit

Is there any information I should know before tearing into this thing? Thanks!
 
Also, if you have the old style pistons with the thin o-ring and Teflon backer, you'll need to update the pistons. FYI, the updated pistons come with the o-ring.

overdrivepiston2.gif
 
Also, if you have the old style pistons with the thin o-ring and Teflon backer, you'll need to update the pistons. FYI, the updated pistons come with the o-ring.

good to know. I'll get the thing apart first before ordering anything. Any chance you have a part# or know where I could get these if needed?
 
Just to clarify, in hiperfauto's photo-- the blue ones are the style that needs to be replaced with the simpler (thicker) o-rings and matching pistons.
Don't overtorque the piston holdown plates!

Handle carefully the new round thin paper gasket between the OD and tranny. If it seems a bit too small, don't force it-- you'll break it. Instead, soak it in a pan of water for several hours.

And: Most Important Preparatory Step (you'll regret it if you don't) is to kill the engine by dumping the clutch while in reverse, to loosen the deathgrip on the OD shaft. Otherwise, good luck separating the OD unit from the tranny.
 
And: Most Important Preparatory Step (you'll regret it if you don't) is to kill the engine by dumping the clutch while in reverse, to loosen the deathgrip on the OD shaft. Otherwise, good luck separating the OD unit from the tranny.

I got overzealous and already removed the driveshaft with the car up on jack stands. Think it'll still kill the engine w/o being connected to the rear end?
 
meh, takes 10 min to bolt it back up. I'll do that tonight. Sounds like a real b**** to separate the trans and OD w/o doing that.
 
Did an M41/J type rebuilt a few years ago. The thing was shipped here from Kansas and of course was stuck together. After some Google searching I found the unit can be pressured up with a hand operated hydraulic pump, the solenoid "clicked" and the thing will just fall off.
At the risk of loosing my man card I'll admit to not owning a hand operated hydraulic pump.
However I do have a grease gun or two.
On my J type a 3/8s bolt fit the pressure port so I just drilled a short bolt, tapped it and put a Zerk in it, along with the copper washer off the OEM plug.
First attempt with the G gun filled with straight 30W didn't work, not enough pressure I guess.
Second attempt I pumped grease in it whilst "clicking" the solenoid on a battery did it. There was a loud enough click or bang that I could hear it and the OD unit slid right off.
Only down side to the grease method is cleaning all the dammed grease out of all the little passages. But you gotta clean the dammed thing anyway.
Grease might actually work better if the unit has bad Orings however that was my first and last time redoing one of these things so I can't say for sure.
It's still working!
 
I've got the transmission out (I plan on doing the clutch and RMS as well). Now I'm trying to remove the OD solenoid. It looks like people have ground down a 25mm (1") open end wrench or crowfoot to fit in the small gap. I'd rather buy something thinner than ground down a thicker tool. Does anyone know of a thin 25mm wrench that will fit in that gap? I've found some super flimsy ones on amazon, but everything else looks to bee too thick.

I saw this: https://www.amazon.com/Channellock-...rd_wg=6MhG6&psc=1&refRID=FFEJ6MJDK3NMQK68GHPA

But using an adjustable wrench to loosen a tight nut/bolt usually doesn't end well...
 
For disposable tools I go to Harbor Freight. (AKA Horrible Fright, and others...) Get the appropriate wrench (1") and slowly grind it to size. Don't heat it up too much while grinding, and don't be tempted to cool it off in a water bath...:nod:
 
For disposable tools I go to Harbor Freight. (AKA Horrible Fright, and others...) Get the appropriate wrench (1") and slowly grind it to size. Don't heat it up too much while grinding, and don't be tempted to cool it off in a water bath...:nod:

That's what I did. No Hazard Fraught store in town but we got the Cheap Tool Store over by Wally World. Got a set of combination wrenches from about 3/8 to 1 1/4 for 20 ish bucks. Then spent the afternoon slowly grinding the 1" to fit.
Obviously buying the proper tool is better but delivery takes time and with any luck I'll never rebuild an overdrive unit again.

Here's the link for Hazard Fraught. https://imgur.com/gallery/JcG3B
 
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