1984 Corvette Overdrive prob. I was told that the Transmition has been rebuilt. Sometimes it does not want to go into overdrive(when it is hot, after driving for a while, after sitting in the sun all day in the afternoon) I have had it to shift down out of overdrive once but, mostly If I press the switch for the overdrive when it is hot it will work most of the time. Is there a senser on the engine that I could check out that will cut the switch off and on so I can not use the manual switch and that could be the problem or? Also is this overdrive supposed to downshift using the detent cable, if not what is the reason for the detent cable. I can see that it would be very nice for it to downshift and upshift without having to use the clutch and change gears. Is this how it is supposed to work? Thanks, jjohnson@pdxinc.com

1984 Overdrive problems for "Jjj": Overdrive in 1984 cars will only work if the car is above 175 degrees F. Sometimes temperature sending units go bad and the car gets a bad signal. The cable is not a kickdown cable. It is a throttle pressure cable. Basically the more you are into the throttle the firmer the OD will shift.

Overdrive operation is commonly misunderstood. Everytime you use your switch on the console you send a request to the ECM for overdrive and it determines if you should have it or not by checking load, speed and throttle position. So make sure all throttle position sensors ar at the proper voltages.

Yes is can upshift and downshift on it's own if all sensors are working correctly.... just like an automatic.

I have a 1988, Z-51 option, coupe with about 34,000 miles. Lately, I have notice that shifting the 4+3 transmission out of overdrive and back into the direct drive mode requires several attempts. I use the button on the shift lever and also clutch when shifting in and out of overdrive. This morning I had to press the button 4 times before it would go back into direct drive. Any ideas as to what is wrong and what should be done.
Thanks,
Gary

Tip for Gary Chiodo's 88 vette 4+3. This is a common switch failure. The computer in 1988 has Overdrive mode defaulted on. The only way you get go back into direct is stop the car or mash the gas pedal when a switch goes bad. So if you can even shut the car off and as soon as you pull 2nd gear OD should come on... if you can't get it back off with the switch, floor the gas pedal... if it kicksdown replace your switch.

Last year I purchase an 88 with Z51 with 18K miles on it. It now has 33K and I want to change the fluid in the both the standard transmission and the OD unit.

I've changed AT fluid on other cars, but I'm not sure if there is enough room to get the AT fluid and the 4speed fluid back into the transmission without having a lift. I have a set of 4 good jack stands and can get the car off the ground 20 inches or so.

Also, the GM manual doesn't really show which plugs to remove to drain and fill the transmission.

Also, as I race sever times a year, how frequently should the trans & OD fluids be changed??

On Al Higgins' 4+3 oil change problems. The fill plug on the overdrive is located on the driver's side of the unit next to the single wire connector. The drain and fill plugs on the 4 speed are located on the passenger side. We recommend 85-90WT gear lube ( Valvoline) in the 4 speed and Dextron III in the overdrive. Use no sythetics! Oiland filter changes should be done every 10,000 miles. You can change the oil with the car on stands. I use a hand pump for both oils which is available in any auto parts store. You can also use a oil can.

I have an 84 Vette with the 4+3. The overdrive unit went out and I needed some information on what it would take to go to a different transmission whether it be an automatic or a manual. Also, I would like to know about how much something like that would cost. This would help me decide if I should have my overdrive unit rebuilt or not. Thanks.

To Jose Lomas: I advise that you stick to the 4+3 overdrive. Once they are rebuilt properly with all the updates they are a fine unit. Most 6 speed conversions will cost approx. $3000 dollars. Try and be realistic about the situation. The car is not worth that expense and also is 14 years old. Most 6 speed cars are now seeing problems in a smaller time frame than yours.

I have had an 86 convertible for 4 years. It has about 90,000 miles and the 4+3 transmission. I do not abuse the car and have no major complaints about the 4+3 transmission. The only thing I don't like is a very hard shifting out of o/d. To avoid that I shift only when going very slow and use the clutch. I have driven a friend's 85 and shifts a lot smoother. What can cause this problem; and is it easy to fix?

Greetings from Puerto Rico.

I have a 1985 coupe (120K miles)and the overdrive unit was stuck in overdrive. The switch in the shifter was taken apart and the wires soldered back on and worked fine for a month. Now same problem. I have a new switch from GM and intend on replacing it. Any other things I ought to look at? Do not know if the transmission has been up-graded or not. Does operating the car in overdrive all the time do any damage?

Thanks,

Jim

I am in the market for a '88-'90 Corvette with low miles, and all of my sportscars have always been stick. Would the '88 4+3 Nash be reliable if the equipment is all original, or would I have less trouble going with an '89 or '90 6 speed? I can't afford costly repairs or a lot of downtime, since this car will be my only daily driver. How will either of these transmissions compare in maintenance costs and/or RELIABILITY compared to the Corvette automatic?

Thanks,

John M.

86 Corvette, 45000 miles. Recently the OD has been erratic. It doesn't always goe into OD when pushing the gearshift button, and twice has jumped out of OD while in high gear. The trans shifts beautifully, and there is no strange noise from the trans/OD unit. I changed the filter, but was unable to fill up to proper fluid level cause the fill plug is ABSOLUTELY FROZEN in place, so I got in as much as possible by removing the ATF cooling line and filling through that orifice, but of course the OD case fluid is low. What kinds of problems will this cause me? How can I get the darn plug out?

To Jon Height: When you have erratic shifting in the overdrive take a look at the OD indicator light. If the light is going on and off with the OD unit then it is a computer/ecm related problem. If the light stays on but it kicks in and out ( called hunting ) it usually means that the OD unit is slipping.

On that plug. You must only remove them with an 8 point 9/16 socket. If you have stripped it, drop your pan and push out the electrical connector, right next to the plug. Fill the unit thru the connector hole and snap it back in.

John Meyer asks whether a 4+3 is a better choice than a ZF 6 speed. Here are my views. We are now seeing alot of broken 6 speeds and problems in 5 year and older vettes. There are NO SERVICE PARTS offered from GM for these transmissions. There never was. I personally will never purchase any car from any company that doesn't offer service parts for assemblies such as engine or transmissions. GM just discontinued service parts for the 4+3 overdrive and we are busy making alot of these components. The current 6 speed repair proceduce is the unit is removed and validated as a Corvette 6 speed then boxed and shipped to ZF North America. Minimum cost to inspect the unit is $500 plus freight. Average repair costs are $2500.00. Average repair costs on an overdrive 4+3 are still $1150.00

i have a 1984 corvette with 37000 miles on it. recently the car got stuck in reverse and would not come out. at first the shop told me it was a linkage problem. they adjusted it and the car would shift but would also grind in reverse. they took off the rear drive portion of the transmission housing and now claim that i have a worn reverse idler gear and a worn reverse gear among other thigs. they also tell me the parts are no longer available from gm. please help!!!

i have a 1984 corvette with 37000 miles on it. recently the car got stuck in reverse and would not come out. at first the shop told me it was a linkage problem. they adjusted it and the car would shift but would also grind in reverse. they took off the rear drive portion of the transmission housing and now claim that i have a worn reverse idler gear and a worn reverse gear among other things. they also tell me the parts are no longer available from gm. please help!!!

About Paul Pensabene's reverse problem. If a transmission grinds trying to go in reverse that means the transmission is still turning. Gears don't grind against each other unless they are moving. It's wierd to see that shops don't understand this simple tell tale sign that a clutch is not releasing properly. If you are in neutral with the car idling and you press down on the clutch pedal and wait 6 seconds... the transmission should not grind going into reverse. If it grinds then it is still turning thus the clutch has not relesed it from the engine.

I purchased a 1988 corvette with 88 k miles The overdrive light comes on and the transmission will free wheel but will not up shift I have no noise and can turn the light and free wheeling on and off with the switch. Also what makes this tranny shift so hard.

To Walter Meyer. If the light comes on and the unit freewheels that means the overdrive is burned up. This is a common symptom. The clutches for the overdrive are slipping so it reverts to a direct mode with a freewheel condition since the sprag in the unit is not locked.

Is it possible to put an automatic overdrive gearbox on a muncie 4 speed tranny? If so, which spline? Also, why is it not recommended to use the overdrive on street rod applications?
bobby lee gentry

I have a 1985 Corvette Coupe 4+3 with 68,000 miles. The transmission and overdrive unit work just fine; no problems in the year and a half I've owned the car. However, I have noticed that when the car is hot, and has been driven for 1/2 hour or more, the trans makes a whining noise in 2nd or 3rd gear, without the overdrive engaged. It does not make the noise in 1st or 4th gears. I don't think it makes the noise in those gears with the overdrive engaged, but I ususally take it out of overdrive when stopping or slowing anyway, and rarely if ever drive it with overdrive engaged around town. The noise will subside with slight manipulation of the gearshift while driving. What is the noise, and am I looking at problems shortly? Thank you!

Hi i just brought a 88 vette and am experiencing problems with the 4+3box. When decellerating in second it jumps out of gear, all the other gears are fine in fact accelerating in 2nd is fine i hear no clunks or anything. I suspect a linkage problem, any ideas ?

For Pete: Jumping out of second gear on a decel. is caused by worn 1-2 slider and shift fork. We get this all the time and it is a common problem. You should do a full rebuild on the transmission and change all the bearings and rings. Install special locking sliders that prevent jumping out of gear and new shift forks.

Dear Paul,

I have a friend with an '85 4+3. He claims that he
does not have a TV cable going to the O/D. He
said he raised the vehicle and looked at the
passenger side of the O/D case near the cooler line
and did not see a TV cable hookup. He has no
TV cable stuff near the throttle body.

Is it possible that his 4+3 O/D does not need a TV cable?

I have an 85 Z-51 4+3 with 90,000 miles with two problems in the transmission. The overdrive would only kick in eratically after turning on the switch. It seemingly would decide when or not to bless me with it presence without warning or pattern. A Corvette shop couldn't ID the problem after 2 days of searching. The engine has many modifications and makes about 340 hp now and has a a hypertech chip. The shop figured the computer must be getting unusual readings from the modified motor that were not allowing normal operation. They then (at my request) converted the switch wiring to operate the unit manually and it works perfectly now whenever I switch it on. Why wouldn't the unit work as designed?

Also the transmission was rebuilt at 75,000 and seemed to work fine until I installed a new clutch. After the new clutch was installed, there is an intermittant terrible grinding and groaning sound from the transmission just as the clutch is being released. It seems to happen more frequently when hot. Re-depressing the clutch once or twice again seems to allow the noise to pass and the trans and clutch work together silently and correctly. The shop that did the clutch said the noise is coming from the transmission. What could this problem be? Will it necessitate another trans rebuild?

After all this, I am about half inclined to pull the Doug Nash and put in a Richmond 6 speed (lthough I am not crazy about the idea of cutting out the old shifter and tunnel). Any Suggestions?

Thanks!

I have a 87 corvette 4+3 with 10k miles and plan on changing the o/d fluid-filter and gearbox oil.
1- How much AT fluid does it hold and what type of fluid is the best?
2- How much should the pan bolts be torqued or is snug good enough?
3- What type of gear box oil and should I add any type of additive?
Thank's

I have a 1985 Corvette with a 4+3 transmission. Question....Is the transmission, when in overdrive, supposed to "kick down" when the gas pedal is mashed down? My does not. It only reverts back to manual (higher RPMs) when I mash down from 4th gear while in overdirive. Do I have a problem? If so, any ideas? Thanks for the help.

Jim

Are there any aftermarket ('85 Corvette) 4+3 overdrive transmisson parts available?

To Lori L. Briggs: We stock all the overdrive parts. Just visit our page on this website www.5speeds.com/dne.htm.

I want to replace the 4+3 transmission in my '84 vette. What is a good replacement that doesn't require a lot of modification?
Would appreciate what others have done...Thanks

Hi. I own an '88 with 190,000 miles. Recently the seal between the manual and the overdrive unit went bad allowing 90wt to leak into the overdrive and dissolve my friction discs. I took apart the unit and replaced the seal and clutch packs, but while I was putting it back together I snapped the piston while compressing the springs. I was using three nuts and bolts for a puller. My question is was I using the correct procedure or are the springs supposed to be compressed using some form of press. Thank you.

I am looking to buy a corvette and I always see the cars with 4+3 trans are always cheaper. Are the OD problems with the automatic, manual, or both?

I recently purchased a 1984 Vette. The trans and overdrive seem to work great. I was told I should put a trans cooler and filter in an easy to reach place. Do you have any recomendations?

By Tony Wysocki on Monday,March 10,1999-7:15pm.I have a 1986 Vette.It is a former Valley Chevrolet showrooom stock car. The 4+3 trans. works great,the overdrive is locked out by the custom E-prom until I engage it.This modification is good for road racing or a hot street set-up. The only problem is, on the highway you have to remember to engage it. Also,the only lubricant to use in this trans. is GM Goodwrench stuff.

I have a recently rebuilt 4+3 transmission with an unlimited mileage, 2 year full warranty from the All Tune Transmission franchise chain.....come and get it for $1850+shipping. Joe Camacho work (757)686-7266/home(757)460-5445 e-mail camacho4@aol.com.

how does the 4+3's work how do i put one in my s10

Hi,
I recently bought an '87 Vette with a 4+3 trans and 80,000 miles. At times when shifting from 1st to second it seems notchy going into second. In other words I have to use more pressure to get it in second. The shift from 3rd to 4th seems to be fine. Not driving any other Vette to compare it to, is this normal? It's so tight I wouldn't even attempt to speed shift it let alone power shift it. There is no noise like grinding when I do this, just hard to get in. Any suggestions you may offer would be appreciated. Thanks for your time. Dan

My project is an '84 Corvette with 4+3. It pops out of 2nd gear on deceleration (synchros?) and whines in OD. It whines less since doing OD maintenence. Slated is a 406 SBC (Hi torque Low rpm) and the 350 will be put in storage. Clutch and associated hydraulics to be replaced. What is the best approach? Thanks.

Greetings...Bought an 84 with 50k miles, which was stuck in reverse, towed it home, reset the linkage to get it out of reverse, changed tranny and OD fluid and filter, which had a good amount of bronze shavings. Problems-(1) Little to no reverse gear to move the vehicle, accompanied by a rolling, grinding noise, which also is present in nuetral, kinda like a throw out bearing noise. (2) When placed in 1st gear (key off), vehicle will roll, as if in nuetral. (3) After a long drive, OD unit would not disengage. Have been advised by 2 techs that all problems are in OD unit; by another tech that it's the reverse idler gear. Would a rebuild of the OD unit give me back reverse gear? Your help is greatly appreciated!!! Kirk

Hello i recently purchased a 1984 vette it all seemed fine untill i tried to reverse up my shops not to steep driveway....the transmission was in reverse,car was slowly moving and when it got steep the car stopped ane the engine freereved...now i can only renerse on really flat ground...is this a common problem with the 4+3 trans.if so is it repaired without removing the trans??? is it eletricial??? any help would be appricated greatly Thank You!!

where do u get parts for the 4+3 trans???? also the overdrive unit??? if anyone can help please e mail me......thank you...Bmars@aol.com

I have an '86 4+3 with 54,000 mi. The O/D became erratic and now only comes on at random intervals. We drained the O/D unit and both the fluid and the unit looked good. We found that applying external voltage to the electrical connector of the unit caused it to shift on and off with the current. Any suggestions as to where to look in the control circuitry ? ( the temperature sending unit to the computer was changed with no effect )

To Larry Little,

I had the same problem. I changed the 1st gear O/D lock
out switch and that fixed it. The switch is on the 4spd
by the 1st/2nd shift rod. You will need a crows foot socket to get it off because there is no room for a wrench or full socket.

I have an 89' aoutomatic with 123,000 miles on it. Recently it revs pretty high and then finally clunks into gear. Also there seems to be a bit of hesitation when I step on the gas. I have yet to find a trustworthy shop. Any suggestions?

i have a 1986 corvette with the 4x3 trans. the car has 86,000 miles. the o.d. unit will not shift into overdrive unless the car is coasting with no load. the fluid is burnt and has a lot of material in it. i have purchased a rebuild kit. will this solve the problem? is this a job for the do it your selfer?
does anyone provide step by step instructions on this job? any help is greatly appreciated

Hi! I have a Corvette 87 with the 4+3, my overdrive doesn't work. I get 12 volt to the switch on the
side of the overdrive unit when the OD lights on in the cockpit. Anyone got an idea? When i manually put 12 volts on the switch nothing happens, should it "click" or ??

i live in Denmark, noone knows anything at all about vettes, so any help will be appreciated :-)

Rgds, Erik

I own a 1984 vette with the 4+3,the problem is when
i shift into 4th gear,the car will start "bucking"
after a few minutes!,i have to shift down into 3rd overdrive to stop this.
Is it an electrical problem? I would like to know if anyone else has heard about this or experienced it.
Also,can anybody share any power tips,nobody seems to
want to touch the crossfire engine or even market any power parts.
Thanks for any help
Steven B

Hi. You guys recommended me to SKSpeed to purchase an overdrive unit, which I did because ya'll were out of stock at the time. Only thing is, their website isn't up yet.... Help!!!!!!. Ok, I got the unit in. Took it for a test drive. And the O/D light would never go off. But my 85 Corvette never got above 165 degrees. Is this my problem? I don't want to damage the unit. So I won't drive it until I have a solid answer from the experts. Which is why I'm asking you.

I have a 85 Corvette that shifts into overdrive at 142 degrees. It will shift into direct drive when accelerating, or when the temp drops below 142. Other than that, the only way to get into direct drive is to hold the overdrive swith down. It shifts right back into overdrive as soon as I letup on the swith. Suggestions?

1985 Corvette
L98 Engine
Manual 4+3 Transmission

Need a valve body throttle valve cable GM part # 14082734. I recently had
the transmission replaced and found the cable to be bad also. GM has
discontinued this part, and my mechanic cannot locate one anywhere. Any help
would be GREATLY appreciated.

Hi I am looking at purchasing a Corvette, and like the C4 1986,87 body style, so far all the vettes I have looked at have the 4+3 transmission, am I buying trouble?

What is the average re-build cost, and can I do the re-build myself?

85 vette... shifter is very unpositive between the 12 and 34 gates it is quite worn..
aparently this is first design with the od switch on the console..
for trans and od...
correct fluid should be what for trans... seems someone said not to use synthetic in trans or od...
use dexron III in od...
best recommendation..
the shifter problem is getting real annoying...anybody who can get this tightned up for me i will be grateful to.
robert
P.S. personal ques
anybody know what trans came in 73 ss454 chevelle?? factory of course.. have one sitting around...

Since this site isn't well maintained, it would be great if you post your solutions to the problems you had. There's alot of people with the same problems you have and would like to know what it took to fix it.
Thanks.

In that spirit, I found a dual engine and trans cooler in the Summit catalog. The main problem with the OD is that it is mounted between exhaust pipes. Keeping the OD fluid cool is the cheapest and best way of babying your 4+3.

I have just purchased an 86 vette with 22k miles. I want to change the direct drive tranny and OD's oil. Can you tell me what type of oils are used and the quantity of oil needed for each unit. Also where are the drain plugs and fill holes located one each unit? I have a filter and gasket purchased from Eklers.

I've been running Redline MT90 gear oil in the manual section and synthetic ATF in the OD for years. Someone on the Vettenet pointed out to me that you recommend 85-90 Valvoline and Dextron III. Can you tell me why you recommend against synthetics? I have 125k on my system and it's still working beautifuly. Neither the gearbox nor the OD have been rebuilt.

For Bob Quaid. Your overdrive switch is bad or the wrong type. This is the switch in your shifter. If you have to hold it to stay in OD it oviously is bad. I have new switches in stock

Oil and lube questions: I only recommend Vavoline 85-90 gearlube in the 4 speed section and DextronIII or a Synthetic equal of Dextron in the OD. Synthetic in the gearbox will usually result in oil leaks and abnormal shift fork wear as well as cracked synchro rings. I don't care who brags about what has worked or knows of someone who swears by this stuff. I've seen more of these boxes then most people will ever see and these are the COMMON problems.

I set out to change the fluids in my 1984 4+3 and OD unit this week end. Did the OD with the Dextron III. But when I went to drain the transmission, out came what I believe to be ATF. I bought the car from a friend and have the service records back to day one. About a year before I bought the car he had the Chevy garage replace the transmission and the OD unit with the upgraded 4+3 setup. Would they have used the ATF?

I put in gear oil, and everything seems to be OK and may even shift a little easier. Can I run into problems if there is a little ATF left in there? Should I flush it out somehow? And put what back in?

Lately, I've been having problems with my 1985 4+3 going into overdrive mode completely at random, even if the overdrive rocker swith is turned off and the the coolant temp is below 141 degrees. It seems to drop out of o.d. when I mash the throttle down however. The gearbox and auto overdrive seem to be functioning fine mechanically and are doing just what they are being signalled to do. Could it be something simple like a loose or chafed wire be causing this or something more serious like an ECM/Black Box problem?

To Bryan: If your OD switch is off and it still goes into overdrive....well the switch is broken.

To Mr. Cangialosi:
A broken rocker switch on the O.D. sounds like an obvious fault if the O.D. is stuck on. However, no matter if the switch is on or off, the O.D. should never come on until the coolant temp has reached 141 degrees, and not while the transmission is in first gear or reverse. The problem is that the O.D. is staying on, despite the conditions listed above.

To Bryan Snyder: What you need to do is look at your OD engaged light. If the light works in sync with the od coming on or off then the fault is not in the OD unit. A bad 1-2 switch on the side cover as well as a bad temp sensor can cause this. If your OD is on whether or not the light is on or off do the following....unplug the OD and see if it stays in OD. If it does then the shift valve in the OD is hanging up or has a restriction in it.

Mr. Cangialosi:
Thanx again for your reply. Yes, the OVERDRIVE ENGAGED light on the dash is going on and off with the actual engagement of the O.D. unit. If I could press you again for one more question, what is the 1-2 switch? The car is currently in the shop and the serviceman is having a tough time figuring it out and perhaps this will point him in the right direction. Thanks again.

To Bryan Snyder: The 1-2 switch is located on the side cover of the transmission screwed into the 1-2 shift lever boss. If your light is in sync with the OD going on or off then something is telling the ecm to drop and apply power to the OD relay. If the 1-2 switch or coolent temp switch get buggy the logic is totally screwed up and wierd things like this can happen.