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Old 09-09-2020, 04:02 PM   #1
Drunk_Babies
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Default M46 od

Just installed this transmission, the OD functions as expected until about 10-15 minutes into a drive.

Going down the highway running through gears 1-4 feels great, I press the clutch in and shift into OD and I can see my revs drop as I re-engage. At about 70mph in OD I'll be at around 3k (3.73 gears). After 10 or 15 minutes of cruising it seems like OD is dropping out- my revs will jump back to what it would be in 4th gear and my revs drop/rise very quickly, almost as if I was revving with the clutch disengaged.

Probably OD piston seals?
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Old 09-09-2020, 04:52 PM   #2
Cwazywazy
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Yeah, in my experience that happens when the unit is on deaths door. Thicker fluid can help (10w30 instead of ATF) but that's just a bandaid and won't last.
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Old 09-09-2020, 05:14 PM   #3
planetman
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It does sound like you may have some internal hydraulic issues and that can usually be fixed with a basic overhaul.

The majority of overdriives that we rebuild usually require a basic overhaul which entails about $50.00 in gaskets, o-rings and seals and 3-4 hours of labor.

When the O/D was working, did you hear any bearing noise?
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Old 09-09-2020, 05:52 PM   #4
tintintin
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Is it actually a time-based issue (you state 10-15 min. into a drive), or could it be a fluid temperature-based issue (trans fluid warms up and OD doesn't engage until cooled down again)?

If actually a time-based issue you should be able to re-engage the OD for another 10-15 minutes. Repeatedly. Can you?

If fluid temp-based, then yes, that points to the somewhat common piston seal failures, as the hot fluid is thinner and more able to leak past the failing seals.

Another possibility: Cold solder joints on the relay. Does going over a bump seem to disengage the OD?
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Old 09-09-2020, 06:58 PM   #5
hiperfauto
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I would try a known good solenoid before pulling the overdrive.
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Old 09-15-2020, 08:30 PM   #6
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Id try a solenoid change if you can find one. But I do agree with someone else up there. The OD working for a short amount of time (best when cold and non existant when warm) is a pressure issue. I have this problem with my OD and ks.more than likely the o-rings on the pistons. If you haven't messed with them or if your sure the OD hasent been cracked open already, I'd bet that that is your issue. You can also perform a pressure test. Assuming you have the J type OD, rnon-engaged pressure is around 21 PSI and I think the engaged pressure is 560 to 600 PSI.
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Old 09-15-2020, 11:52 PM   #7
Mr. V
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If you decide to remove, inspect and repair the overdrive be sure to follow the correct procedure when shutting off the engine.

If you do it wrong the OD won't come out.
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Old 09-16-2020, 01:35 AM   #8
tintintin
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Quote:
Originally Posted by Mr. V View Post
If you decide to remove, inspect and repair the overdrive be sure to follow the correct procedure when shutting off the engine.

If you do it wrong the OD won't come out.
Yup. Brakes on hard, dump the clutch while in reverse. This relieves the opposing (deathlock) grips on the splined shaft, allowing the OD to slide out without resorting to excessive prying and hammering.

We told you.
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