My 1988 vert runs great with 47k miles, the 4 speed is clunky but shifts fine just like it did from the factory. My 2 Speed Overdrive unit when activated would be slow to engage (may take up to a minute) then when it did engage it would drop out then engage then drop out then maybe engage again. When it finaly engaged it would stay, anytime i would floor it the OD would drop out as it should then take its good old time reengaging, then maybe drop out a couple times b4 it would stay engaged. Keep in mind the OD dash lite was on the whole time the OD would engage and disengage.

I pulled the single wire at the Od unit that sends the 12vdc thru the case to the pressure switch. With the ALDL shorted pins A-B I would get battery voltage, the wires were fine no burns or shrinkage of the insulation. this tells me when I select OD the signal get to the OD unit as it should.

After Dropping the OD pan there was plenty of fluid, the filter looked fairly clean, the magnet was coated with debris(it was no big deal to clean it). The wires from the case plug to the pressure switch was in perfect condition as were the wires from the pressure switch to the solenoid and the solenoid to its own ground.

I shorted the battery voltage to the solenoid to check its operation. The solenoid was slow to engage and I was able to move it with my finger with voltage on it(this should not happen to a good solenoid). A good solenoid should engage fast and should not be disengagable with the push of a finger.

Using my FSM!!!! to remove the valve body. Testing the pressure switch I used 70 PSI air using a rubber tipped blow gun, it shorted out. By the way this switch is normaly open.

Again I played with the solenoid removed from the valve body. It was still slow and weak, It appeared my problem was the solenoid. Then I ohmed the coil, it was 17 ohms. I decided to take the solenoid apart to see if I could clean it. Physicaly the solenoid assy looked fine.

This is when it occured to me, this is a magneticly actuated solenoid!! my magnet in the pan was coated with debris why wouldnt this get coated with debris. If this was coated with metalic particles wouldnt that degrade the magnetic field it applies to the plunger?!?! Taking this solenoid appart was no big deal just a C-clip, then i cleaned it out with carb cleaner. After putting it back together the action was fast and positive, i could no longer move it with my finger.

Then I took the vlave body apart and cleaned all the plungers and springs and reassembled it. I put it all back together, using RTV Black on the pan I waited overnight for it to set up b4 filling it wih dexron III type ATF.

In the morning I filled it with 2 quarts of fluid and checked for leaks(none), Then test drove my work. The OD shifts firmly into gear when commanded, does not fall out of gear, and it operates as intended according to the manuals Ive read.

At 123 degrees of coolent temp my dash OD will light and my OD will now engage immediatly and stay engaged. In 4th gear when I floor the gas the OD drops out and I accelerate. After letting up on the gas the OD then reengages and stays.

Lesson learned: there is a magnet in your pan that collects metalic particles and dust. There is a solenoid that uses magnetic properties to move a plunger that engages your OD. They BOTH collect magnetic particles. They BOTH need to be cleaned periodicaly. When the solenoid collects metalic dust floating in your tranny fluid it has a weakening effect on the solenoids ability to attract the plunger to engage your OD and hold it under pressure. CLEAN YOUR SOLENOID.

 

Thanks for the tip. Glad your car is running better.

 

Man, I don't know what to say except...Wow! I have a 6spd so I don't have to worry about it though. That's some kind of troubleshoothing. Wish the Air Force had people that could do that more often.

 

I've got an 86 conv with 5k actual miles and I'm having a problem with the Overdrive not wanting to lock in. Do you think this could be the same problem? With the low mileage I wouldn't think there should be enough wear to cause this...I bought the car out of storage 5 yrs ago with 3K miles and everything worked perfect regarding the od until just recently.


ncdlee

 

I couldn't tell you, but I have some info from my 86 manual.
http://members.shaw.ca/agent86/Overd...iagnostics.pdf

http://members.shaw.ca/agent86/OverD...Electrical.pdf

 

cleaning the valve body and solenoid is free. you dont even need to buy a gasket. wit a car below 5k miles i just dosent make any sense that it would have a mechanical problem.
first question to ask is whether or not the dash light is on when the OD drops out if it is on then make sure you got battery voltage to the terminal on the outside of your tranny.
Check this by shorting out the A-B on your ALDL and using a volt meter. dont forget to inspect your wiring.

 

in the words of the immortal CC

Pull the pan off and inspect.......

Did you pull the pan yet??? No???

Pull the pan off and inspect.....

To the OP, I am sure you uncovered

A) why we are now changing the fluid every 10k miles
B) the source of many owners getting unneeded 'rebuilds'

 

Okay, let me start first by inspecting and cleaning the valve body and soleniod. How hard are they to access...and where are they located...on the underside? I'm not an experienced mechanic but I do have all the tools and I'd like to take a crack at it before taking it to a garage. I really appreciate your help!

The dash light come on but only when the od finally engages. Also once it does engage and I switch the od off it won't relock until ~ 5-10 minutes later.

 

After spending money to replace the OD switch on my 86 coupe, with no change in behavior, I discovered that there is a matched pair of relays piggybacked to the firewall between the brake booster and the distributor. the one closer to the firewall (on my 86) is the relay for the fuel pump; the other is the relay for the OD. The relay costs less than $20 at NAPA. I dismounted the old one and put the new one in place in about 15 minutes, and my OD has behaved beautifully ever since.
A $20 relay is an easier place to start than digging into the tranny case.

 

You have to start by shorting the A-B pins on your ALDL then turning on the key.
then checking for battery voltage on the connector at the driverside of your OD unit.
If there is no voltage there then you need to check your relays on the firewall.
there is no easy answer, you must start troubleshooting. Before you start troubleshooting you must study the circuitry and its locations in the FSM.

Is the dash light on when the OD wont engage? if it its on and the OD wont engage, then start by looking for battery voltage at the OD case. if the light is not on then start troubleshooting at your switch on your shifter.

 

Thanks Guys

Yes, the light in the dash doesn't come on when I switch the od on at the shifter, but once the od does engage (sometimes not a all and sometimes 10-15 minutes later) the light on the dash does illuminate. From what I heard this might indicate that I have a problem on the switch side?

 

I realize this thread is 13+ years old but it sent me down the right path of getting my OD working again. Was getting an OD light but no OD. Replaced the relays, changed the fluid and still nothing. Pulled the valve body and the solenoid did nothing with direct power. Might have been jammed? Cleaned it with some carb cleaner(I can't say it looked very dirty honestly) and the OD works again!

 

Great work. About 6 months too late for me. This may have been what was wrong with mine. I got pissed and replaced it with a LT1 T56. Enjoy the fruits of your labor!

 

Any special tools/tricks needed to remove/clean the valve body and solenoid? Seems like this may solve my problem.
I have an '87 and I've bypassed the ECM and have my OD actuated by a switch I installed on the console. Recently, when going over 70mph, I'll engage OD, it may work for a little while, then it will engage/disengage a couple times and I'll just turn it off to not cause damage. Functions fine in the 60mph range and below though, which is odd.

Thanks

 

It was pretty straight forward but MESSY. There are two ***** in the valve body you need to keep track of. One is operated by the solenoid and the other sat on top of the valve body. The solenoid was a slight pain to get back in as it holds a spring loaded plunger in place also. You need to keep that compressed while trying to get the screws started. I think it took me about an hour start to finish.