question about 4+3
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
I recently posted this on another forum. It may be useful to folks here considering a 4+3 car.
I've been driving my 86 with the 4+3 as a daily driver for 3 years now (it has 86k miles). I actually think having 2 sets of 4 gears (1 set for performance and set 2 for better economy(OD)) is kinda nice. OD engages automatically when using light throttle pressures in 2nd, 3rd and 4th, as long as the engine temp is 120 degrees or greater. You can also force shifting in and out of OD with the button. I generally use the clutch when I shift intentionally in or out of OD. It is just a whole lot smoother that way and easier on the OD unit I think. I like to shift, so I don't mind this.
I cannot complain about the automatic shifting of the OD except when it drops out of OD in 2nd gear when too much throttle is applied (intensionally or not) the car launches pretty briskly and my wife gets pissed at me....LOL. She hates speed! I try not to do that when she is in the car. It can also happen in 3rd or 4th gears when you apply a little too much throttle (say on a hill and you want to accelerate a little).
I have no apparent mechanical issues with my OD unit, but I think my 4 speed gear box needs some work. It will pop out of 2nd when compression breaking in 2nd gear. If I avoid down shifting to brake in 2nd I have no big issues with it. It also seems there is drive line play in my unit when you go off the throttle at low speeds (say idling through the neighborhood at 10-15 mph). I have no way of knowing if the play is in the OD or in the gear box.
Don't be fooled into thinking you are going to have 7 gears. It's not like driving a truck with a gear splitter at all. The reason I say this is the ratios the designers have chosen. The ratio of 2nd gear with OD engaged is very close to 3rd gear W/O OD. The same is true for 3rd with OD and 4th W/O OD. Those ratios are very close also.
If all the 4+3 shifters feel the same as mine, then this is an area where GM does not score well with this design. You won't be speed shifting this guy. It is less than smooth in transition between gears. It does not grind or anything. It just feels rough as you slide it from gear to gear (both directions).
Maybe this will help somewhat in understanding how the DNE 4+3 feels/drives for those who have not driven it. Hopefully so!
Tom
PS: Another owner posted that the Super T10 4-speed component of this design will never shift like a modern internal rail design because it has external linkage and the linkage and shifter are more subject to wear. He also stated that the T10 was used in many of the 60s Muscle Cars. If you are familiar with that driving experience, this may be similar.
I've been driving my 86 with the 4+3 as a daily driver for 3 years now (it has 86k miles). I actually think having 2 sets of 4 gears (1 set for performance and set 2 for better economy(OD)) is kinda nice. OD engages automatically when using light throttle pressures in 2nd, 3rd and 4th, as long as the engine temp is 120 degrees or greater. You can also force shifting in and out of OD with the button. I generally use the clutch when I shift intentionally in or out of OD. It is just a whole lot smoother that way and easier on the OD unit I think. I like to shift, so I don't mind this.
I cannot complain about the automatic shifting of the OD except when it drops out of OD in 2nd gear when too much throttle is applied (intensionally or not) the car launches pretty briskly and my wife gets pissed at me....LOL. She hates speed! I try not to do that when she is in the car. It can also happen in 3rd or 4th gears when you apply a little too much throttle (say on a hill and you want to accelerate a little).
I have no apparent mechanical issues with my OD unit, but I think my 4 speed gear box needs some work. It will pop out of 2nd when compression breaking in 2nd gear. If I avoid down shifting to brake in 2nd I have no big issues with it. It also seems there is drive line play in my unit when you go off the throttle at low speeds (say idling through the neighborhood at 10-15 mph). I have no way of knowing if the play is in the OD or in the gear box.
Don't be fooled into thinking you are going to have 7 gears. It's not like driving a truck with a gear splitter at all. The reason I say this is the ratios the designers have chosen. The ratio of 2nd gear with OD engaged is very close to 3rd gear W/O OD. The same is true for 3rd with OD and 4th W/O OD. Those ratios are very close also.
If all the 4+3 shifters feel the same as mine, then this is an area where GM does not score well with this design. You won't be speed shifting this guy. It is less than smooth in transition between gears. It does not grind or anything. It just feels rough as you slide it from gear to gear (both directions).
Maybe this will help somewhat in understanding how the DNE 4+3 feels/drives for those who have not driven it. Hopefully so!
Tom
PS: Another owner posted that the Super T10 4-speed component of this design will never shift like a modern internal rail design because it has external linkage and the linkage and shifter are more subject to wear. He also stated that the T10 was used in many of the 60s Muscle Cars. If you are familiar with that driving experience, this may be similar.
One thing the chart says is there is an automatic upshift at 103 MPH for the 86-88 cars. I have not found this to be true. My '87 is capable of speeds around 125-128 in 4th/no OD. As long as I turn the OD off after starting the engine, the OD unit will not operate at all until I hit the button or shut off and re-start the engine.
Using the clutch for manual OD operation is a good idea. It does save wear on the rest of the driveline and you can get very smooths shifts. The auto kickdown is stiff as is the auto upshift.
There is a way to program the ECM to not have the OD to be automatically ON after engine start. A number of people here have done it and that could make the car easier to drive if you don't want to have the OD kick in.
As far as your issue with the trans kicking out of 2nd on deceleration, that can be due to worn shifter forks, a weak or worn detent in the side cover or some other internal trans problem. From what I remember about Super T-10's, it seems that 2nd gear is the usual problem. Your driveline "slop" is probably in either the u-joints or the differential.
The factory shifter is a pain and I have never really heard of a suitable alternate like a Hurst shifter. Because of space limitations, the shifter is attached to the body with the rods going thru a boot to the trans. Like many shifters that are 20+ years old, they will benefit from replacing the bushings on both ends of the rods and adjusting the gates in the shifter. Cleaning and re-lubing the shifter unit is a help too. The shifter is not fun to remove, but it may help to go thru and clean up everything and replace any worn parts. The short throw levers are definitely a good addition.
I don't think that GM ever made a decent in-house 4-speed shifter. The overall design was bad and the materials were nowhere near as strong as the aftermarket shifters. And their reverse T-handle lockout really sucked especially when the cable broke. Once GM started to use Hurst shifters in their muscle cars (and even in some full-size cars), shifting effort and smoothness got a lot better.
As far as ratios in each gear and the OD, the 3rd/OD and 4thno OD is about a 400 RPM difference in my 87. I usually used 3rd/OD for boulevard cruising at speeds up to about 50. 4th/no OD is good for speeds below 40. The other "splits" are closer in RPM range so there is no real benefit is split shifting unless you stay in a certain speed range over longer distances. GM used two different OD ratios; the Callaway Twin Turbo cars got a .68 OD while the rest got a .62.
Instructor
Joined: Oct 2006
Posts: 246
Likes: 1
From: Elk Plain WA
St. Jude Donor '11
Let me be clear also. I'm getting pretty much out of my 86 what I expected. Even though it isn't perfect in any way, it is still a fun ride. I fool around with several cars in my small older collection. When I get some time and extra cash, I'll likely rebuild the T10 component and see just how it was suppose to feel in 1986. I installed the short shift linkage the 1st year I owned it. Mine know doupt can use a rebuild. My comments were intended to level peoples expectations to a reasonable level.
Last edited by tdf; Mar 21, 2010 at 12:08 PM.
