4+3 Info...any Guidance

[JohnnyD]

Ken,

I hear you have a good link to the 4+3 information. I am interested in the info regarding shutting off the OD and making the car a 4 speed. What other guidance do you have ?

Thanks

Johnny D.:cool

 

[JohnnyD]

Thanks...I knew there was a reason I joined this site!

Thanks again so much.

PS..when you mean jump....that means connect?

Johnny

 

[88canadianvette]

would making a 4+3 a manual o.d., mess up the vehicle speed sensor?

 

[JohnnyD]

thanks again....although one more question...Does the 4+3 have a "typical" whine sound or does it indicate that something might need replacing or adjusting....
:BOW

 

[JohnnyD]

Good one!!

I will need to tell Amy that...(my girl)

 

[muddywaters]

4+3 Transmission

Ken, The 4+3 O.D. trick, jumpering out the 2nd gear switch to fool the puter, that is on the tranny and not the O.D. unit itself. The post is a bit vague saying the most rearward switch, which is on the O.D. unit. Also, the post says jumper the switch. Wouldn't you jumper the plug to the switch ? I'm confused, again. Any input is welcomed, thanks Muddywaters

 

[Ken]

Hey Len, you actually did it. Answer him! :L

_ken

 

[muddywaters]

4+3 Transmission

Len, I did exactly that and had no speedometer or O.D. The post indicates the left side of the tranny ??????? Muddywaters

 

[frost]

Len,

I did that to my 88 and it only works for second gear. If I start out slow 3 gear and 4 will engage OD. The way I normally start it only engages on the 4 gear because my rpm are too high to engage 3rd. So basically it only works on 2nd on my car.
As far as I am concerned this combo of T10 and OD is GM’s version of the YUGO. The OD drops out at a steady rpm on the highway. It feels like it is searching for something. Anything over 63 mph and it could drop at any time. It was interesting when it happened at 96 mph. I have maintained the OD properly, but it doesn’t seem to matter.

Bill

 

[Vettelt193]

;stupid an excellent idea on paper, but didn't quite work out in the real world.... reminds me of that 5.7 deisel GM made for awhile... it sure sounded like a good idea to convert a gas engine, it just didn't work like a good idea!

 

[frost]

Does anybody know of a way to totally bypass the computer. By that, I mean changing the wiring harness to physically bypass the computer so as not to interfere with the OD.
Yes GM does some pretty wierd things.

 

[rrubel]

What I dislike about the 4+3 is when you're cornering in 2nd OD (like coming off a ramp) and hit the gas - the car downshifts out of OD if you accelerate too hard. Last time that happened I almost lost it from the sudden jerk and speed boost.
[RICHR]

 

[omega1940]

4+3

Hi there. I just went to a website I saw mentioned earlier http://www.corvetteobsession.homestead.com/files/html/garage_projects_dougnash.html and discovered the appropriate way to "jump" the 4 speed so that it does not automatically turn on the overdrive at startup.

I think this entire issue is particular to which year Vette is involved. I can only tell you what happened to MY 88.

On the transmission (not the overdrive unit as said by one thread) there is a switch. On mine, one branch of a wire set goes up to the switch on the transmission, and another set goes on to the overdrive unit. Both have two wires.

I disconnected the wires to the switch and tied them out of the way. I then removed the switch. One end of the switch has a small roller ball that is apparently engaged somehow in the transmission. The other end has the connectors, both female.

I bought some male post connectors and made about a 2 inch jumper with 16g wire with one connector on each end. I then plugged in the connectors and reinstalled the switch.

When I started my car, I had to wait until the engine temp reached 126 degrees, because that is when my car normally went into overdrive...automatically. This time it did not! I was thrilled. I shifted into 2nd, still no overdrive. 3rd, no overdrive. When I shiffted in to fourth gear, it dropped into overdrive without hitting the switch. I guess I was expected that it would stay out of overdrive untill I hit the switch on the knob.

I can tell you that it is still a heck of a lot better than the started design. At least now, when doing a lot of errands, I don't have to keep shifting out of overdrive after I restart the car. It stays out of overdrive until 4th gear, and quite often by then I'm going fast enough to go into overdrive anyway. If you hit the OD button after it reaches 4th gear (and is in overdrive) it goes out of OD and never goes back in.

It seems that this is as close as I can get to what I want in my 88. If anyone has a difference experience I'd love to hear about it.

Mike

 

[Ken]

Thanks for clearing that up some more Mike. Seeing as how I haven't actually performed the modification, I was unable to provde assistance when asked questions about it. Now that I run a ROD 6-speed, the DN 4+3 is the last thing on my mind.

Thanks again.

_ken

 

[muddywaters]

4+3 Transmission

Mike, Thanks, I figured it was the tranny and not the OD unit . Tried that Homestead web, can't pull it up. Would you please double check the address . Sometime today I'll jumper the 2nd gear switch on the tranny and let you know how I made out. Thanks again Muddywaters

 

[frost]

Hi,

Mike my experience with the 88 is the same. But if you accelerate slowly it will also engage 3rd into OD.
Len, there are only two plugs on the transmission. One is for the backup light and the other is the one I jumped. I know about the reverse one because I needed to replace it after it failed. It doesn’t so much drop out of OD as it is confused and the decides to drop. By that I mean it goes in and out a number of times before it drops out totally. It happened again this morning. It was on cruse at 76mph and then it went nuts. I had to drop down to 63 before it returned to OD. I then went up to 78 and it was fine for about 3 min. Then it went again. It can happen at any speed over 62.

I had the same problem with the web address.



Bill.

 

[Ken]

Re: 4+3 Transmission

Tried that Homestead web, can't pull it up.

Try it again.

_ken

 

[rwd]

FWIW and for onlookers, it appears the 4+3 is set up differently on different year vettes. On the early C4's, at least through '85, the OD was a separate gear range. With the switch off, you had a standard close-ratio 4-speed. Period. With the switch on, the top three gears ran through the overdrive, but only fourth gear would kick down under acceleration.

The system being described here sounds more like an early CAGS. I don't know when the change was made. Perhaps it can be reversed.

The whine is fairly typical of the tranny with OD engaged. With it out, it's fairly normal.