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4+3 question

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Alan86

Guest
After getting my car out of Winter storage, I decided to take the car for a small run to warm everything up and make sure all joints and bearing are OK. The coolant temp got to 230 and the O/D light came on. BUT.....no overdrive. Cpuld this be a faulty relay or a bum O/D unit???? :cry How can I check the relay to see if it's at fault?
 
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David-F

Guest
On an 86 it the light comes on the relay is working you need to check the connector going into the side of the O/D unit to make sure it's pluged in and making a good contact. Also another thing you can do on your next road test is see if when the O/D light comes on if you loose engine braking, if you do then the O/D clutches are probably burned if not you need to check fluid level and wiring out side and inside the O/D unit.

David Fulcher
 
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Alan86

Guest
Thanks David, I will check out the connections tomorrow.

Alan
 
A

Alan86

Guest
Well.....there's lots of engine braking, no slipping detected. Wiring seems OK and clean connections. I even tried removing the connector from the transmission unit (which I think, lets the ECM know when the transmission is in 2nd, 3rd, or 4th gear), and jumpered the 2 connections on the harness, to try and fool the ECm and by-pass the switch on the transmission. No luck, same problem.
Is it possible that an oil and filter change would help. I had this done 12,000 miles ago.

Alan :crazy
 
Joined
Oct 30, 2001
Messages
2,273
Location
Glen Burnie, MD, USA
Corvette
1986 Bright Red Coupe
David-F said:
Also another thing you can do on your next road test is see if when the O/D light comes on if you loose engine braking, if you do then the O/D clutches are probably burned if not you need to check fluid level and wiring out side and inside the O/D unit.

David Fulcher

I'm a bit confused on this point. Are you saying that when IN overdrive you have zero engine braking if the OD is not engaged properly? I had thought that in OD you should NORMALLY have little engine braking as you want the car to keep moving forward with as little accel pressure as possible. I have what I assumed is a normally-working 4+3 unit and when not in OD (esp. in gears 2 and 3) I get lots of engine braking. However, in 3-OD and 4-OD, I get almost none and the car runs around 75 mph with very little throttle input. OD comes on and off when expected and the RPMs change as expected.
[RICHR]
 
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racecar

Guest
After some exhaust system work, I had the same problem, the light came on, and the OD would not engage. The wire on the side of the trans, near the back was unplugged. If you checked that connection, hmmmm time to get out the book. I have also had to replace the push button switch in the shift lever.
It is a common thing for those to go out.
I'm not sure if that makes the light come on.:crazy
 
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David-F

Guest
Alan86;
If the connector is tight in the O/D unit then what you need to do is put the car in the air and with an ohm meter hooked to the terminal on the side put the car in gear and get the tires moving it should go from open circuit to closed at about 10MPH rear wheel speeds, if it does not then you need to drop the pan and look at the harness inside and make sure the wire is still hooked to everything. I still think you may have an electrical problem.

rrubel;
If the O/D clutchs burn when the apply piston applies(trying to go to O/D) the direct clutches are released and the only thing keeping the car going forward is the sprag(one way clutch) so when you back off throttle there is nothing to drag the car down seeing how the rear shaft in the O/D can over run the input shaft. If O/D worked the input and out put shaft would be hooked up(going through the sun and planets) so nothing more than the O/D ratio speed difference could happen so letting off the gas at high way speeds in O/D would still give you some engine braking not as much as direct(at the same speed).

racecar;
The shifter switch would not make the O/D light come on and not the O/D the only thing the shifter switch does is turn the O/D program on and off the relay supplies power to O/D unit and light on 84 to 86 4+3. The biggest problem you get with a bad shifter switch is unable to control the O/D unit when you want.


Also a 86 only has a back up light switch it does not have gear position switches.

David Fulcher
 
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Alan86

Guest
Thanks David, but there is something strange here.
According to this web page, http://www.gearzone.net/43table.htm, the 1986 model has NO swithes on the tranmission. I have one on the manual, and one on the O/D unit. Is the one on the manual the 1st gear switch, and if so, can I jumper this switch in case it's faulty?

Alan
 
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David-F

Guest
Thats the backup light switch on the rear shift lever.

David Fulcher
 
A

Alan86

Guest
Thanks David, sometimes we forget the obvious. :eek:

Sorry for being such a pain in the a$$, with the continuing questions, but I just don't know anyone up here who knows anything about the 4+3.

Here's the latest...
I raised the car onto jacks and diconnected the harness from the O/D unit. I connected my multimeter to the harness and started the car.
In 2nd gear without the O/D on, I read 64 millivolts.
In 2nd gear with the O/D on. I read 13.4 volts.

Can I assume from this that the problem must be with the solenoid inside the O/D unit? :hb If so. is this an easy fix?

Thanks in advance, Alan
 
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David-F

Guest
Alan;
All you have done so far is check the relay(which we already did with the O/D light coming on) you need to hook the meter up to the terminal coming out of the O/D unit and switch the meter to ohms then get your readings at no road speed and then the next at say 10mph and let's see what you have. Also you might want to use a jumper to hook 12v direct to the terminal on the O/D unit if everything else seems ok just incase you are having a problem with the connecter terminal contact to the O/D unit. And last thisw is not a pain in the a$$ for me I am just glad to be able to help.

David Fulcher
 
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Alan86

Guest
Thanks David, it's really great to have someone who spends the time to help others without compensation of any kind, with the exception of a few thank-you's.
I will try the ohms test either tonight or tomorrow.

Thanks,
Alan
 
A

Alan86

Guest
Well.......No reading whatsoever. It registered unlimited resistance @ 0mph, @10mph, @20mph.
I connected the red to the switch on the O/D unit and the black to ground.
Applied 12 volts directly to the O/D unit. Heard nothing.

Alan - 1986 Vette / 4+0 tranny.
 
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David-F

Guest
You are going to have to drop the pan and take a look inside to check the wiring inside I suspect a wire may have come off inside.

David Fulcher
 
A

Alan86

Guest
Problem resolved: It was the pressure switch inside the O/D unit. Replaced and all is well again.
Many thanks for all of the info.

Alan
 

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