4+3 od @ 80% throttle problem
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Joined: Apr 2000
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From: dfw TX
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4+3 od @ 80% throttle problem
Hey guys! Last time I drove the '85 I had a little OD problem. The OD has had intermittent problems wherein it won't always come on when I flip with switch. Typically once it engages the first time it will successfully work that trip thereafter. I've had the fluids serviced (Brian Alspaugh is da 4+3 MAN so this is as per his suggestion). That helps it engage more smoothly but alas it does not always engage upon immediate switch.
On to the last time I drove it I turned the OD switch to "on" and merged onto the highway. As I was trying to merge I hit the hammer only to find it bog down and the OD did NOT switch off at 80%+ throttle. HELP! Is there a sensor that can be traced? I don't think it's the console switch and it's not the fluids. The light only comes on when the unit is correctly engaged.
Thanks in advance! :seeya
On to the last time I drove it I turned the OD switch to "on" and merged onto the highway. As I was trying to merge I hit the hammer only to find it bog down and the OD did NOT switch off at 80%+ throttle. HELP! Is there a sensor that can be traced? I don't think it's the console switch and it's not the fluids. The light only comes on when the unit is correctly engaged.
Thanks in advance! :seeya
Pro
Joined: Jun 2000
Posts: 686
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From: Crystal Lake, IL USA
Re: 4+3 od @ 80% throttle problem (thrills)
Sounds like something's not right in the valve body. It is the assembly at the end of the oil pickup tube and has a solenoid, several valves and springs that redirect the hydraulic pressure to do the shifting. The fix may be as simple as a good cleaning of all the involved parts. There is an exploded diagram in the service manual.
My first shift into OD in the morning is becoming really slow, so I'm probably in the same boat. After the first time, all is normal again for the rest of the day. This is NOT the major rebuild involving clutches, etc, it has to do with the hydraulics.
It looks like the valve body can be removed for R&R without pulling the trans.
My first shift into OD in the morning is becoming really slow, so I'm probably in the same boat. After the first time, all is normal again for the rest of the day. This is NOT the major rebuild involving clutches, etc, it has to do with the hydraulics.
It looks like the valve body can be removed for R&R without pulling the trans.
Thread Starter
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Joined: Apr 2000
Posts: 11,259
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From: dfw TX
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Re: 4+3 od @ 80% throttle problem (Hendej)
Thanks! I can give this info to my mechanic since they're not typically fully familiar with the 4+3. I'll be sure to carry in my service manual.
Thanks :seeya
Thanks :seeya
Instructor
Joined: Jan 2002
Posts: 221
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From: League city Texas
Re: 4+3 od @ 80% throttle problem (thrills)
The downshifting problem could be as simple as adjusting the TV cable on your throttlebody. On the 85's the cable controlls the downshift not the computer. The intermittant od could be a wiring problem. After installing my ZZ4 motor I found that the od light was on when I started the motor for the first time. I tracked the problem down to the od relay and it's wires. It is the relay closest to the firewall by the brake booster. All the wires going to the relay had their insulation dry and cracked. I repaired all the wires and od function returned to normal. Od operation has been flawless since this fix. Prior the installing the new motor I had a problem simular to what you discribed. Sometimes it would come on and sometimes it would not. Once it came on it would generally stay on for the duration of the trip. Check your relay and it's wires. This is very easy to check and repair and might save you a ton of money at the transmission shop.
Pro
Joined: Jun 2000
Posts: 686
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From: Crystal Lake, IL USA
Re: 4+3 od @ 80% throttle problem (trupp)
Good thing somebody with an '85 spoke up, I forgot about the TV cable for that year. The '85 OD is still electrically operated via a solenoid, but the line pressure is adjusted externally in '84 and '85 instead of internally in '86 and up. Easy to adjust, I hear.
Also noticed that '85 is not supposed to kickdown in 2nd or 3rd gear according to the "4+3 Overdrives" chart at http://www.4speeds.com/ which has always been correct so far. Were you in 4th gear?
If the light and the OD operation are always in sync, then nevermind the valve body discussion. It's when the light is on, but the OD is not engaging, that I would begin to suspect an internal problem. Mine waits a while (about 1") to engage the first time, even though the light is on.
If the light doesn't come on when you should be in OD, then the OD isn't getting power to activate the solenoid (they are wired together) meaning somewhere in the relay, computer, or switch circuits the signal is disappearing. Relay's the usual culprit here, mine had to be replaced recently.
I think I'm pretty much repeating what trupp said...
Also noticed that '85 is not supposed to kickdown in 2nd or 3rd gear according to the "4+3 Overdrives" chart at http://www.4speeds.com/ which has always been correct so far. Were you in 4th gear?
If the light and the OD operation are always in sync, then nevermind the valve body discussion. It's when the light is on, but the OD is not engaging, that I would begin to suspect an internal problem. Mine waits a while (about 1") to engage the first time, even though the light is on.
If the light doesn't come on when you should be in OD, then the OD isn't getting power to activate the solenoid (they are wired together) meaning somewhere in the relay, computer, or switch circuits the signal is disappearing. Relay's the usual culprit here, mine had to be replaced recently.
I think I'm pretty much repeating what trupp said...
Thread Starter
Race Director
Joined: Apr 2000
Posts: 11,259
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From: dfw TX
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Re: 4+3 od @ 80% throttle problem (Hendej)
You guys are a great resource, thanks! I'll print this whole thread out!!
BTW I can't swear I wasn't in 3rd so that may have been it too, but either way I need to fix the intermittent problem.
BTW I can't swear I wasn't in 3rd so that may have been it too, but either way I need to fix the intermittent problem.
