You now know more about the overdrive unit than every Chevrolet dealership in a 100 mile radius.

 

Well I'm gonna see this thread through to the end. Maybe I can be helpful to next poor slob that has to go through this.

All the threads I googled using the keywords "Corvette pressure Switch" (of course this thread was the number one return) terminated with the original poster leaving to put in a Switch and solenoid. They never reported back after that.

 

Update, I ordered the pressure switch from SK. $39 + shipping (2 day) He has a $75 minimum but let me slide do to me being in a Jam.

He told me...and I am writing it down for future reference.

The Clutch plates will be exposed once you drop the pan to install the pressure Switch. If the plates appear dark brown or black then it the OD unit is fried. If they are still reddish Brown you should be ok.

He also told me that there was no way to check the pressure switch without conducting a destructive test. Sorry CC, He didn't like the Air pressure idea.

Another tip from a retired Vette Guru from Anaheim, Gary Leonheardt, Go to Pep boys and purchase an oil pan drain plug. This is a plug that has a two sided mount with an o-ring (use RTV instead). You punch or drill a hole in the bottom of the pan. Then install the drain plug. Now, you can drain the ATF and refill it every time you change your Motor oil. Only a Quart or so will come out.

The Common theme here from everybody....and I have spoken to quite a few about this 4x3 OD unit....is regular maintenance, meaning clean fluid and filters. The fact that the General failed to provide this info is what is killing these units prematurely. That coupled with the fact that there is no dipstick under the clamshell means the unit is usually neglected.

More info as it is gathered.

 

Destructive testing? You simply remove the pressure switch from the car, send air pressure to it, and check for continuity. No different then what happens to it while on the car. I know this because I did the test myself and it did exactly what it was supposed to. The FSM will tell you what pressures it closes and opens at.

It seems like you're hesitant to pull the pan. Just pull the pan already, it takes 5 minutes. Might take some effort to pop it loose. See if you can get a blade into the sealing flange to seperate it, or try a mallet and wood block. If you have to pry on the pan gasket surface, make sure it's with a wide tool to spread the force out, otherwise you'll bend the pan or damage the sealing surface.

It would be pointless to replace the pressure switch and seal everything up without having identified the cause. For that reason you have to test the original pressure switch anyways.

While the pan is off, you will then also check the ohms across the solenoid, or just send power to the solenoid to test it, using the diagnostic mode and bypassing the pressure switch.

 

I think installing a drain plug in the pan is not really worth the effort. If you do regular maintenance on the OD by changing the fluid and filter, the drain plug isn't a necessity. The cost of the fluid and filter is cheap; $6-8 for the filter and about $6 for two quarts of Dexron II/III

There is not a lot of fluid involved when draining and with a wide drain pan, you should easily catch all of the fluid when you take the pan bolts out. Leave one or two bolts in the highest part of the pan with just a couple of threads holding the screws and pop the seal at the lowest part. That will allow most of the fluid to drain out and won't allow the entire pan to drop off.

 

(A.) I'm listening............I'll try it when I get to that point. I didn't Say "I" don't like it. I've never seen the switch. I have no way of picturing what you are saying to do....not yet anyway. I just want a new switch there when I do get into it.

(B.) I am hesitant to pull the pan, your observant and patient. Mainly because I can't get up under the car, No real Jack at the moment. My Bud has a lift, I just have to wait for it to be open. We'll get there Friday.

(C.) That is True. I'll try to figure out what you are saying when I get the switch. Sorry, please don't lose patience with me. I know your mind you are thinking that it is so easy, but with me I have a hard time just pulling **** apart when I haven't a clue what I am trying to do. This instance I really have no choice and with your gentle prodding I'm getting there.

(D.) Checking the ohms across the solenoid from the inside will be the proof in the pudding. I can't do this properly and since the opportunity passed by last Friday. I have to wait.

Thanks again. You are Huge I really really appreciate you.

 

Are you putting a new filter in there every 3000 miles? The guy that told me about this idea told me that He was changing his ATF fluid at the same time as the Motor oil and with the same frequency.

I'm not questioning to be a Jerk, rather I'm trying to learn.

 

I am going with 12,000 miles on the fluid and filter. For typical street driving, this should be enough. Although I autocross my car, the OD unit is not engaged so I don't think that type of use is a big issue.

I recall reading about other 4+3 owners using synthetic ATF like Mobil-1 (maybe it was Scorp??). Not sure if that's a good idea or not, but the synthetic fluid might help if the tranny is subject to extreme use.

If you really want to install a drain plug for frequent fluid changes, I would not use RTV to seal that plug assembly. Either get a nut that matches the threads of the drain plug and braze it to the pan just like the block oil pan or braze the drain plug female portion. Be careful to not use a lot of heat so the pan won't warp or maybe risk burning thru the thin sheet metal.

Learning about the 4+3 is important for the owners to get a better understanding of this tranny. There are those on the Forum who don't seem to care for the tranny, but they do work if you pay attention to them. Reeves Callaway didn't seem to have issues with them as he used them behind his twin-turbo motors

 

Closing and opening pressures for the switch are shown on the right side of this pic:



Also I have photos of the pressure switch with p/n, and the whole underside of the overdrive on my home pc. There's probably some universal pressure switches that'd work as well.

 

The clutch plates are not exposed when you drop the pan. See here:

http://www.rbartick.com/vetwork/pics/clutch_015.jpg

I doubt your switch is bad. I tried to replace that switch on mine before I pulled my O/D.

See here for some pics:

http://www.rbartick.com/vetwork/clutch.html

 

 

I recall you have to remove the whole valve body to see any part of the clutch plates.

It's no big deal to do.. disconnect the TV cable, remove the long bolts, and make absolutely sure you don't lose track of any ball bearings!

 

That web page is something else.

If the OD just stopped working all at once with no warning, why would you think mechanical failure over electrical???

 

that is a great shot. You went home and jacked yours up and pulled the pan this evening to get that shot didn't you?

 

Just a hunch because that is what mine did. Drop the pan and check the fluid color. You will know that you have a problem if it is dark and burnt.

 

The fluid that came out was not clean by any means but not dark, and it didn't have that burned smell.

 

Got the Switch......UPS and SK come through.

 

This is overly simple, but it happened to me on my '85.

I had the OD light come on, with no overdrive. It happened a few times and was really frustrating. I too felt that "Oh no, it finally went!" feeling in the pit of my stomach.

It turned out that the electrical connector at the OD was coming loose. I cut the plastic connector off (it was partially melted anyways), got a spade connector from NAPA, spliced it and reconnected it. I used some vacuum hose to put over the wire and the connection on the OD. I think it was something like 5/8" inner diameter but I'm going from 2 years memory on this.

The OD has been fine ever since.

BTW, these units get a bad rap. If maintained, every 10k or so fluid and filter changes, they'll last.

 

My connector shrunk with age and I had to zip tie it to keep it on.

These units earned their bad rap. I haven't come across an owner of an 84-85 unit that still has the original unit. It seems most were dead by 25-30K miles. That aside, I enjoyed driving it with the stick shift and the auto kick-down. (the only cool part about an automatic)

 

I haven't given up yet on this thread or this project. I've just been busy.

Updates are on the way.

Thanks everybody.