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C4 4-3 reverse problem

Heyblue

Well-known member
Joined
Aug 8, 2015
Messages
50
Location
Felton, CA
Corvette
1984
Been repairing things as I discover them on project car. I have been riding with the OD off until I could check the levels of fluids. Yesterday went to get oil change and check and top all fluid levels. They claimed "transmission level fine". When I asked which "transmission manual or OD automatic" I got a big quiet spell.
That all said. Backing out of the parking stall I thought I heard an odd sound. All the way home it appeared the OD was engaged, the tack readings were all quite a bit lower in top 3 gears, even when down to 1000 rpm in forth gear going about 30+mph. Got home and later needed to go out to store. Went to back out of car port, fairly level and no reverse. Kind of a wearing sound but not even trying to move. I read on different sites that no reverse with this set up (4-3) means the OD unit failed. I am guessing the default state has to be OD in the off state, since the pump is on the output shaft, so couldn't shift until there is some forward motion.
Maybe my OD just took a dump and has nothing to do with the work done during the oil change and fluid check, or is there something that could have been done while on the rack. Knock out a wire connection, linkage, vacuum other?
If the problem is the OD unit, does it come out from the bottom without removing the manual part of the transmission?
 

forrest

Well-known member
Joined
Aug 9, 2014
Messages
86
Location
new port richey FL
Corvette
93 polo green
Been repairing things as I discover them on project car. I have been riding with the OD off until I could check the levels of fluids. Yesterday went to get oil change and check and top all fluid levels. They claimed "transmission level fine". When I asked which "transmission manual or OD automatic" I got a big quiet spell.
That all said. Backing out of the parking stall I thought I heard an odd sound. All the way home it appeared the OD was engaged, the tack readings were all quite a bit lower in top 3 gears, even when down to 1000 rpm in forth gear going about 30+mph. Got home and later needed to go out to store. Went to back out of car port, fairly level and no reverse. Kind of a wearing sound but not even trying to move. I read on different sites that no reverse with this set up (4-3) means the OD unit failed. I am guessing the default state has to be OD in the off state, since the pump is on the output shaft, so couldn't shift until there is some forward motion.
Maybe my OD just took a dump and has nothing to do with the work done during the oil change and fluid check, or is there something that could have been done while on the rack. Knock out a wire connection, linkage, vacuum other?
If the problem is the OD unit, does it come out from the bottom without removing the manual part of the transmission?


I would start by getting the car off the ground a give a good look at what they may or may Not have done and work from there, I will warn you the 4+3 (Gear oil in T-10) (ATF in the O-D unit)O-D oil if not serviced regularly will stink like 90 weight gear oil, it may be coincidence that it is acting this way, but I am sorry is sounds like it could be more.:ugh

Transmission removal
The transmission and the O-D are one piece that come out together and are separated at rebuild time.
 
Last edited:

tnovot

Active member
Joined
Jan 14, 2011
Messages
44
Location
Streator, IL 61364
Corvette
1975 pearl white 4 speed convert with 355 HP ZZ4
4+3

Been repairing things as I discover them on project car. I have been riding with the OD off until I could check the levels of fluids. Yesterday went to get oil change and check and top all fluid levels. They claimed "transmission level fine". When I asked which "transmission manual or OD automatic" I got a big quiet spell.
That all said. Backing out of the parking stall I thought I heard an odd sound. All the way home it appeared the OD was engaged, the tack readings were all quite a bit lower in top 3 gears, even when down to 1000 rpm in forth gear going about 30+mph. Got home and later needed to go out to store. Went to back out of car port, fairly level and no reverse. Kind of a wearing sound but not even trying to move. I read on different sites that no reverse with this set up (4-3) means the OD unit failed. I am guessing the default state has to be OD in the off state, since the pump is on the output shaft, so couldn't shift until there is some forward motion.
Maybe my OD just took a dump and has nothing to do with the work done during the oil change and fluid check, or is there something that could have been done while on the rack. Knock out a wire connection, linkage, vacuum other?
If the problem is the OD unit, does it come out from the bottom without removing the manual part of the transmission?

A quiet spell? That's scary! Just another reason to do things yourself whenever possible or at least anticipate problems and give specific direction to the service people. Hope you find the problem and it is easily cured.
Terry
 

Heyblue

Well-known member
Joined
Aug 8, 2015
Messages
50
Location
Felton, CA
Corvette
1984
I have 0 experience with a automatic OD unit, so looking to understand before I get radical and pull it out. First thing that confuses me is the no reverse issue. Since car is not moving the OD should be in the 1:1 mode, which if I understand correctly means no hydraulic pressure so one set of clutch plates are engaged via 1200 lbs of spring tension. If they are slipping why not in forward also? The other issue when I last drove it; the OD seemed to be stuck in OD mode. Could that be the reason for no reverse? Though I guess I do not know how it would be stuck in OD mode without forward motion to run the hydraulic pump while backing up.
Another question. When I was getting my break/light/smog checks to get it registered, the shop that did that work reported I had steering, valve cover and "transmission" leaks. Could my problem be simply low transmission fluid? I will be jacking it up later to do a visual and will attempt to check the levels which may or may not have been checked the other day.
Thanks in advance for any insight anyone can make.
 

forrest

Well-known member
Joined
Aug 9, 2014
Messages
86
Location
new port richey FL
Corvette
93 polo green
I have 0 experience with a automatic OD unit, so looking to understand before I get radical and pull it out. First thing that confuses me is the no reverse issue. Since car is not moving the OD should be in the 1:1 mode, which if I understand correctly means no hydraulic pressure so one set of clutch plates are engaged via 1200 lbs of spring tension. If they are slipping why not in forward also? The other issue when I last drove it; the OD seemed to be stuck in OD mode. Could that be the reason for no reverse? Though I guess I do not know how it would be stuck in OD mode without forward motion to run the hydraulic pump while backing up.
Another question. When I was getting my break/light/smog checks to get it registered, the shop that did that work reported I had steering, valve cover and "transmission" leaks. Could my problem be simply low transmission fluid? I will be jacking it up later to do a visual and will attempt to check the levels which may or may not have been checked the other day.
Thanks in advance for any insight anyone can make.

The no reverse condition can be caused by the failure of what I believe is a part called the Spag Bearing. when you reverse it binds to the out put shaft and makes it possible to reverse, when going forward free wheels with O-D operation.
 
Last edited:

forrest

Well-known member
Joined
Aug 9, 2014
Messages
86
Location
new port richey FL
Corvette
93 polo green
Been repairing things as I discover them on project car. I have been riding with the OD off until I could check the levels of fluids. Yesterday went to get oil change and check and top all fluid levels. They claimed "transmission level fine". When I asked which "transmission manual or OD automatic" I got a big quiet spell.
That all said. Backing out of the parking stall I thought I heard an odd sound. All the way home it appeared the OD was engaged, the tack readings were all quite a bit lower in top 3 gears, even when down to 1000 rpm in forth gear going about 30+mph. Got home and later needed to go out to store. Went to back out of car port, fairly level and no reverse. Kind of a wearing sound but not even trying to move. I read on different sites that no reverse with this set up (4-3) means the OD unit failed. I am guessing the default state has to be OD in the off state, since the pump is on the output shaft, so couldn't shift until there is some forward motion.
Maybe my OD just took a dump and has nothing to do with the work done during the oil change and fluid check, or is there something that could have been done while on the rack. Knock out a wire connection, linkage, vacuum other?
If the problem is the OD unit, does it come out from the bottom without removing the manual part of the transmission?


Here is a article written by a very good friend of mine that I have trusted and relied on for years. on how to work on 4+3 transmissions found here in the archives of the forum

1984 - 1987 Corvette: Technical Article: Rebuilding the Doug Nash 4+3 Overdrive Unit
 
Last edited:

AussieCorvetteNut

Well-known member
Joined
Dec 19, 2010
Messages
189
Location
Gold Coast Australia
Corvette
1984 Two-tone Blue Coupe
The 4+3 Death Sign

Experience is that when there is no reverse, it is transmission out and time for a rebuild.

I took mine out and am in the middle of a Tremec TKO 600 install (as well as a few more upgrades).

I figured my non-overdrive issue still may not have been addressed if I had an electrical issue and as I am changing the Crossfire Injection to FAST Multipoint EZ EFI which has its own ECM, I figured it was time to ditch both.

Rebuild Kits are available, I got some for mine and they shipped to me here in Australia.

:beer

Tony
 

Heyblue

Well-known member
Joined
Aug 8, 2015
Messages
50
Location
Felton, CA
Corvette
1984
Thanks Forrest and Aussiecorvettenut;
I am in the process of pulling the transmission. Last things are the cooler lines, TV cable and the C-Beam. The bolts on the C-Beam were not so bad, but it is still in the car. Removed the drive shaft, and the beam is kind of flopping around but will not be come out. Read all the different posts on this and tried them with no success. One poster said he removed the transmission first. Hopping that can be done, depends on how far out the transmission needs to come before dropping out. Will find out this morning.

I read over the write up Forrest posted, probably shouldn't have until I got into the job a little. I have rebuilt large automatic transmissions in the past just pulling parts and laying across the floor in the order they came out then just reversed the order while replacing parts from a rebuild kit. I am hoping one of the first steps of applying pressure with the "tool" bolts can be done with just 3 metric ones. Anyone had experience with that?

I though about replacing with a 6 speed, but seems past my budget. Let me rephrase that (Wife to husband) Quit spending any more money on your mid life crisis.
 

forrest

Well-known member
Joined
Aug 9, 2014
Messages
86
Location
new port richey FL
Corvette
93 polo green
Thanks Forrest and Aussiecorvettenut;
I am in the process of pulling the transmission. Last things are the cooler lines, TV cable and the C-Beam. The bolts on the C-Beam were not so bad, but it is still in the car. Removed the drive shaft, and the beam is kind of flopping around but will not be come out. Read all the different posts on this and tried them with no success. One poster said he removed the transmission first. Hopping that can be done, depends on how far out the transmission needs to come before dropping out. Will find out this morning.

I read over the write up Forrest posted, probably shouldn't have until I got into the job a little. I have rebuilt large automatic transmissions in the past just pulling parts and laying across the floor in the order they came out then just reversed the order while replacing parts from a rebuild kit. I am hoping one of the first steps of applying pressure with the "tool" bolts can be done with just 3 metric ones. Anyone had experience with that?

I though about replacing with a 6 speed, but seems past my budget. Let me rephrase that (Wife to husband) Quit spending any more money on your mid life crisis.

The clutch pack pressure plate can be caged by bolts like you said the key is you need to fine bolts to thread into the plate with enough thread bite not to strip. than stack washers to fill gap than do your caging 1/2 a turn at a time for about a total of 3 turns or you feel bottom out of plate. when caged you don't want the caging bolts to interfere with the clutch pack.

now the C beam put the most rear bolt back in by the Diff. use it like a hinge with the trans. supported dip the trans down and take a large screwdriver or pinch bar and guide/slide the trans around the C beam (DO NOT PRY AGAINST THE OUT PUT SHAFT IT SELF)and to reinstall just reverse the process, I have found it best to leave the C beam in the car with the 1 bolt in because the rear end's sometimes twist toward the floor making very hard to get the C beam back in. A common step that many forget is to remove the Plenum extension plate (the plate over Distributor) and loosen the Distributor cap more that a few times I seen the cap damaged or in the days of the 1/4 turn spring clamp that the Rotor hits cap when started.
 
Last edited:

AussieCorvetteNut

Well-known member
Joined
Dec 19, 2010
Messages
189
Location
Gold Coast Australia
Corvette
1984 Two-tone Blue Coupe
Thanks Forrest and Aussiecorvettenut;
I am in the process of pulling the transmission. Last things are the cooler lines, TV cable and the C-Beam. The bolts on the C-Beam were not so bad, but it is still in the car. Removed the drive shaft, and the beam is kind of flopping around but will not be come out. Read all the different posts on this and tried them with no success. One poster said he removed the transmission first. Hopping that can be done, depends on how far out the transmission needs to come before dropping out. Will find out this morning.

I read over the write up Forrest posted, probably shouldn't have until I got into the job a little. I have rebuilt large automatic transmissions in the past just pulling parts and laying across the floor in the order they came out then just reversed the order while replacing parts from a rebuild kit. I am hoping one of the first steps of applying pressure with the "tool" bolts can be done with just 3 metric ones. Anyone had experience with that?

I though about replacing with a 6 speed, but seems past my budget. Let me rephrase that (Wife to husband) Quit spending any more money on your mid life crisis.


My trans removal was pretty easy, I have a hoist and used a transmission jack.

I removed the driveshaft, then C Beam.
As Forrest has said, remove the distributor cap or remove the dizzy. I also placed a chock of wood between the engine block and firewall, but the rear of the engine will need to tilt back to get to those pesky bell housing bolts.
I removed transmission, then clutch assembly, then bell, then flywheel.

...only a few more bolts and the engine will come out...I know, you have one of those voices in your ear like mine...stop spending money...but then I get when is the Corvette coming off the hoist...;shrug

Don't forget the spigot bearing, I used a removal tool for this, but there are a couple of YouTube videos on using grease to hydraulic it out.

Can't help with the rebuild, I didn't get that far.

:beer

Tony
 

Heyblue

Well-known member
Joined
Aug 8, 2015
Messages
50
Location
Felton, CA
Corvette
1984
Got the trany out last night. Rolled it to a place to dump the fluid. What came out of the OD unit looked more like old engine oil than transmission fluid. Black thick ugh. Looks like I am on the right path, i.e. rebuild time.
BTW I marked the wires and removed the distributor cover before lowering the engine/transmission. And I left the C-Beam in the car. Left all the bolts out and as I lowered the transmission/engine just pushed it aside and up over the tail of transmission, then after blocking the engine, used my motorcycle jack to pull the transmission.
 

forrest

Well-known member
Joined
Aug 9, 2014
Messages
86
Location
new port richey FL
Corvette
93 polo green
Got the trany out last night. Rolled it to a place to dump the fluid. What came out of the OD unit looked more like old engine oil than transmission fluid. Black thick ugh. Looks like I am on the right path, i.e. rebuild time.
BTW I marked the wires and removed the distributor cover before lowering the engine/transmission. And I left the C-Beam in the car. Left all the bolts out and as I lowered the transmission/engine just pushed it aside and up over the tail of transmission, then after blocking the engine, used my motorcycle jack to pull the transmission.

The Distributor cap Did not need to be removed just loosened, the condition of the ATF in the O-D unit does not surprise me like I said earlier if fluid and filter screen are not serviced regularly the Fluid will be burned and stink like gear oil.


when and if you personally take the O-D units oil pan off you should find a magnet in the pan, it will be covered with a black/silver graphite looking slime it's normal with wear epically in a ill-serviced trans. but if you see bigger chunks of steel or clutch pieces well. it just confirms your path and mission.
 

forrest

Well-known member
Joined
Aug 9, 2014
Messages
86
Location
new port richey FL
Corvette
93 polo green
The Distributor cap Did not need to be removed just loosened, the condition of the ATF in the O-D unit does not surprise me like I said earlier if fluid and filter screen are not serviced regularly the Fluid will be burned and stink like gear oil.


when and if you personally take the O-D units oil pan off you should find a magnet in the pan, it will be covered with a black/silver graphite looking slime it's normal with wear epically in a ill-serviced trans. but if you see bigger chunks of steel or clutch pieces well. it just confirms your path and mission.

One more crucial point now that the Trans is out of the car and we know that the ATF is Severely burned and contaminated it is Very Important that you FLUSH THE TRAN'S COOLER AND LINES failure to do this your just sending a mouthful of mud into your newly rebuilt trans.
 

Heyblue

Well-known member
Joined
Aug 8, 2015
Messages
50
Location
Felton, CA
Corvette
1984
Thanks Forrest and Dave##
I am learning more than I wanted. Having taken it apart enough to see what the problem/s are I find that there are enough "hard" parts damaged to make the cost of me rebuilding it as much as what I can get a unit on the internet. Rebuilt units are $1100-1200 plus shipping. The front bearing went out and caused the inside of the front plate and the front of the sun gear plate to get seriously damaged. Those three parts alone get close to $1000.
I have to believe that since I started driving the car, (only a small amount 2-3 hundred miles) it went from bad to worst because of the following problem.
On 2 occasions when I was in rapid acceleration approaching red line then let off the throttle in second gear I would de-accelerate rapidly in a slight down hill condition, it would pop out of gear. Based on your explanation, the spring loaded plates must have been holding for this to happen. The plates have fair amount of wear, but were in tack.
I will start a new thread regarding the second gear problem. I am considering tearing down the 4 speed unit if the popping out of second warrants.
 

Heyblue

Well-known member
Joined
Aug 8, 2015
Messages
50
Location
Felton, CA
Corvette
1984
As a follow up. I purchased a rebuilt OD unit and rebuilt the 4 speed myself. While trany was out I removed the clutch to inspect. Found both the flywheel and pressure plate had groves. Someone replaced the clutch (because it was not worn down to rivets) without replacing the above damaged parts. Wow who ever owned this car shouldn't be allowed to have another! I looked at u-tubes as to how to remove pilot bushing and tried the wet paper method. Ended up with much compacted paper in the hole. Dug it out and rented a pilot pulling tool that works with a sliding hammer. The hole on this care is too small to insert the puller. I got my handy grinder out and shaved about 1/16 th off the ends so it could fit in the hole. shss don't tell O'Riley but they now have a tool that fits more pilot bushings. Needed to rent a transmission jack to allow positioning to get transmission back in. Since I removed it with the C beam still in car I tried and was able to install transmission with it left in car. Just put in driveshaft before bolting it back in. Should have bought the kit that has the nuts connected. It was a choir to get the individual nuts back on and tightened above the C beam. Hope this helps others thinking about doing the job themselves.
 

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