jerander

I think that my overdrive died. I was driving along in overdrive, I got out of the overdrive to pass a couple cars(got up to 108 mph). Then I tried to get back into overdrive when I got back to 70 mph and only the overdrive light came on, but the overdrive did not work. I tried putting it on while I did not have the clutch in(I usually hear a click or feel it engage when it comes on) but nothing happened.

Will I have to get mine rebuilt. or will I have to get one from a junk yard and how much would it cost? Or could there be something else wrong?

thanks for the help
jerander

CentralCoaster

Hold up there.

Was it ever intermittent before then? If so, it's probably low fluid. If it just went all at once, the overdrive plug may have fallen off. Both of these have happened to me twice. If the plug is on, I'd drop the pan and do a flush and filter change before giving up on it. There's an internal pressure switch that won't let the overdrive operate if the pressure drops, such as from the pump sucking air with a low fluid level.

These are really the only two ways to lose overdrive and still have the light come on, except for mechanical failure. Supposedly this makes it impossible to drive in reverse, so I'd test that too.

Also, when you go over 110 mph, it forces the car into overdrive even with the switch off.

jerander

never was intermittent before in the last year(when I first got it). i just looked at the fluid last week, it looked old but it was full(I'm going to change it when I can find a new filter). when you say overdrive plug to you mean a plug to keep the fluid in or an electrical plug? It went into reverse just fine when i parked it(so that is a relief).
the only time I had it over 110mph(it was at 116mph) that I remember I don't think the overdrive kicked in. If it did there was not a dramatic change in rpms(but it is hard to remember anything but the speedo saying 116 and the rpms being around 5000).

CentralCoaster

It's the single prong electrical connector on the right:




When the overdrive indicator is on, this plug gets 12 volts.

Downstream of that... on the brown wire, is the pressure switch in the top of this pic. If the pressure switch is closed, the pink wire sends this 12V to the solenoid. If all this and the solenoid works, but still no overdrive, only then would I'd say you're looking at a rebuild.

jerander

I will check that tomarrow morning. If that is the problem hopefully it just fell out and is still in good shape.

thank you very much for your help

jerander

is there a way to check to see if the overdrive is getting power if the car is just sitting. Is it possible to run a wire a 12v wire from the battery to the overdrive if it is just sitting to see if it is the overdrive or the wire going to the over drive.

I would prefer not to have to set up a test light that i have to run up to the cab to check while I'm going down the road

CentralCoaster

I ran a wire from my fog light switch to the overdrive relay, to force it on with that switch.

For all the trouble, just put the rear end up on jack stands.

Then you can put the car in 2nd gear and mess with it that way.

Oh... and shorting diagnostic leads A&B on the ALDL port under the hush panel will send 12V to the overdrive even with the car off. Then you can crawl under the car and check for 12 V at the plug, that'll tell you if your wiring is intact.

If the indicator lights up, the relay is good, so that's not your problem.

88espo

I agree that the fluid is likly to be the problem. Mine is an 88 and the relay by the battery was the problem with mine not working all the time. 10. dollar part.

jerander

where is a good place or website to get a new pressure switch and/or solenoid if I find out they are bad. Also where should i go to get a new overdrive filter and what is the part number for them( i really need to get a drivers manual and the helms manual for this car).

with college have not had any time until tomarrow to work on the problem.

CentralCoaster

Have you verified that you're getting 12V to the side of the OD case yet?


jack up the drivers side and go under there with a test light or voltmeter. short pins on terminals a & b on the aldl diagnostic connector under the dash, and that should put 12 V to the solenoid and light up the 'overdrive' indicator on the dash.

The pins you need to short together on the aldl are the two right ones on the top row, just bend a paper clip and stick it in there, then turn the ignition key to on, but don't start it. Thiis port is under the drivers side dash on the right side.

it's easy as pie, shouldn't take you more than 30 seconds to check after you jack the car up.

test light is maybe $2.


overdrive filters have to be ordered from one of the vette catalogs, ecklers or tld or midamerica, or zip or...

I doubt any of them will have theh o/d solenoid or pressure switch though.

There's a slim to none chance that a parts store might, but they sure as hell won't know how to find it in their computer or on the shelf, so good luck there.

Your best bet is probably the GM dealer.

Ask Scorp508, he might know where to find these parts. But as i said, Check for 12V at the o/d before you bother with any of this!

CentralCoaster

If you are getting 12V, then get a little plastic fluid pump and top off the o/d unit with some ATF and then try driving it. The fill plug is on the drivers side. In fact, buy this stuff anyways then you can do it while you're under there if you need to. You are going to end up needing that stuff anyways when you change the filter.

Easy stuff first...

Keep us updated.

VQT88Vette

Damn it Centralcoaster! Is there any dirty grease on your car. Everything is so clean.

jerander

It is getting 12v to the overdrive and it is topped off. I will order a new filter tonight and next saturday I will replace that and see if the solenoid and pressure switch inside the overdrive are ok.
thank you very much for your help. I will keep posting here what I find out.

CentralCoaster

I tested my pressure switch by hooking it up to a compressed air source, I just happened to have the right fittings laying around. I think it took something like 80 psi to close it.

You can test the solenoid by just looking at it once you have the pan off. when it gets 12v you'll see the disc move. You'll probably have to short across the pressure switch to feed it 12V.

Its unlikely that either of them is the culprit, sad to say... and if those don't fix it, then it's gonna get $$.



The ONE other cheap failure I can think of, that happened to me, the grommet on my od filter cut itself and the od pump started sucking air, which opened the pressure switch. Even with a full level of atf it still wouldn't operate.

Take a close look at the rubber grommet when you do the filter change. The metal opening in the filter is sharp, and the grommet is a little tricky to get on there right.