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What actually tells the OD to engage (AW71)?

Donny

Donny

New member
Joined
Jan 24, 2005
Location
Delray Beach, Florida
I ask this because I just changed the O2 last night on my 765 and now today the OD is craping out on me. This morning it didn't engage for about 20 minutes. I guess it could just be coincidence that it decided to go the next morning.

The relay is working, I actually cleaned the contacts up a little and the arrow light comes on and off with the switch. I can hear it operating in the cab.
 
I can't speak for all of them, but I find the overdrive on mine to be fascinating. It engages after 3rd gear, period. It completely ignores the switch, and even removal of the relay. It must be a conspiracy!
 
Three Fat Tigers said:
Does sound like your relay is fine and that the wiring to the solenoid is good (as otherwise the dash light would not work). Odds are you need another solenoid, this is the same part used on all AW70/71 trans (240/700/900).
Click to expand...

So the wiring that frequently goes bad would be the problem if the solenoid never engages? Since mine works after 20-30 minutes you think the solenoid is bad?
 
Captain Reclino said:
So the wiring that frequently goes bad would be the problem if the solenoid never engages?
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If the wiring was bad, then yes it would likely cause the solenoid to never engage. However if that were the case then the dash indicator light would not come on either as on you car this lamp grounds through the OD wiring and the solenoid itself.

Captain Reclino said:
Since mine works after 20-30 minutes you think the solenoid is bad?
Click to expand...
Yes, from your description odds are the solenoid is bad, this is not to say it couldn't be something else such as a defect inside the transmission, but the odds favor the solenoid.

If you want to try a test: run a fused wire directly from the battery, down the transmission tunnel and connect to the solenoid wire. If the OD works right off the bat, then you do in fact have some sort of wiring/relay issue where insufficient amperage is getting through, at least when these parts are below operating temp.
 
It could maybe be a sticky kickdown cable. Shoot some WD40 into it up at the top and let it sit for a few, never know, that happend to me and the car wouldnt get out of second.
 
OD solenoid, go under at the drivers side, mounted on the side of the tranny facing down. Looks like a small lump on the side of the tranny, has a wire going from it. two 13mm bolts hold it on ( 13 or 14, cant remember). wire connects above its location, simple clip to another wire.
 
The night before the OD started acting up I noticed the accellerator cable had gotten out of it's groove. It actually had been that way for a while, it slowly added LOTS of drag to my accellerator but it hapened gradually. Eventually I was like... something is really wrong with my accellerator cable. Once we fixed it I noticed a bit of slack on the kickdown cable at rest. I didn't think this was the problem because it does kick down. It just doesn't shift into OD. I will go try some spray on the cables, maybe some PB. I'll report back my findings.
 
Nope. I was just hoping for a quick fix. I will just grab a few solenoids from the JY and swap em out. The car is kinda fun to drive without the OD anyway.
 
Three Fat Tigers said:
The solenoid may have been modified into a permanent bypass position, or the it's simply stuck.
Click to expand...
Nah, if it was simply stuck or permanently engaged it'd be working on 1st and 2nd as well.
 
Three Fat Tigers said:
Not in an AW70 or 71.
Click to expand...
Why do you say that? It's located after the main transmission. If it was stuck on as you claim, it would be engaged in all the gears.
 
What you are describing is an 4 speed manual transmission with a J type OD, otherwise known as the M46. The subject here is an AW71 4 speed automatic, IMO "OD" is not really a correct nomenclature to apply to this transmission. On the AW71, the solenoid is normally on all the times unless you manually turn it off, so bypassing the solenoid, or a stuck open solenoid, will simply not allow you to manually turn off 4th gear (aka OD).
 
Very impressively written! Unfortunately, it's completely wrong.

The ZF transmission is the 4 speed unit. The AW transmissions (both the 70 and 71) are conventional 3 speed planetary geartrain units. They are just like a Ford C-4, or a GM Turbo 350 in their 3 speed planetary geartrain design.

A separate overdrive is used by the AW71, and inhibited in operation to only third gear. This overdrive lives within the transmission case, but is distinct and separate from the rest of the transmission.

The electrical circuit to the overdrive solenoid on the transmission is not normally energized, it is normally off. It is only energized when the solenoid closes the contact, providing electrical power. This event only happens when the transmission is in third gear, and the shifter electrical switch is closed, causing the relay to close. Then, and only then, is electrical power provided to the overdrive solenoid, engaging it.

If the overdrive unit were to somehow "hang up" in the engaged mode, the transmission would no longer shift to four distinct gear ratios, but would engage only the conventional three, at the higher overdrive enhanced ratio. This would be most noticable in 1st gear, as it would be a much taller ratio, resulting in substantially slower acceleration.

I hope this information helps you to understand how these transmissions and overdrive units actually operate. Further information on this subject can be obtained from a factory service manual, wiring diagrams, and examination of the transmissions themselves.
 
I assume you know how to read a factory wiring diagram?

If you will observe the power flow section below:
AW71od2.jpg


The force is strong with this one, but you are not a Jedi yet.
 
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