OD 4+3 QUESTION

hmcquade · 10-18-07, 01:42 PM

Could the OD switch on the console of my 84 casue the OD to not enage sometimes? My Mechanic just told me that he ran the Vet on the lift and got it uo to 55 and it went into OD. He said he did check out the switch and he feels it may be shorting out. He is taking it out for a road test as I type.

Thanks,

Hugh

onedef92 · 10-19-07, 08:31 AM

I'm not a 4+3 expert, but others have told me that changing the overdrive filter usually helps.

The 4+3 uses several different electronic sensors to conduct its shifts and if one or more of those are out it can cause this problem.

hmcquade · 10-19-07, 09:14 AM

Thanks for the reply. My Mechanic checked out all of the sensors and found a vaccum leak that he stated was casuing the OD to constantly go on and off, causing the transmission to over heat.

Hugh

onedef92 · 10-19-07, 09:34 AM

Glad you got it fixed. Happy motoring!

hmcquade · 10-30-07, 03:15 PM

found out the vaccum leak was coming from the heater control unit. OD has to be replaced clutches are slipping. Decided to get a new 88 OD should be here this week.

Hugh

hmcquade · 11-04-07, 10:50 AM

Quote:

Originally Posted by hmcquade

found out the vaccum leak was coming from the heater control unit. OD has to be replaced clutches are slipping. Decided to get a new 88 OD should be here this week.

Hugh

Well in the end the OD clutches were going bad so right now I am having a new 88 Od installed.

Hugh

35annv · 11-26-07, 07:06 PM

Quote:

Originally Posted by hmcquade

found out the vaccum leak was coming from the heater control unit. OD has to be replaced clutches are slipping. Decided to get a new 88 OD should be here this week.

Hugh

When you install the 88 OD set it to operate manually. That's what I did on my 35th Anniversary. Got tried of it constantly going on when I did not want it. Now when I wish to use it, such as highway, I push the button.

muddywaters · 11-26-07, 07:34 PM

That's what I did with my 88, now the OD comes in once after it hits 120 degrees,4th gear, I press the button, cancel it and it's gone until I press the button again. Seems to me that it would take alot of wear and tear off the OD if it didn't come in and out needlessly..................

WhalePirot · 11-26-07, 09:26 PM

Not sure where vacuum comes into the picture, except as it might affect closed loop. The ECM allows (or not) O/D engagement under certain conditions, including closed loop, i.e., the engine must be warmed up. Often this occurs at a specific temperature, as mine did, but that number changed with time.

The '84 logic is unique and requires other-than-first gear selected, closed loop, switch ON, 2nd gear below 50mph or 3rd gear below 60 (I think those speeds are accurate) and less than about 3/4 throttle. If the accelerator pedal is nearly 'floored', it will not reengage in 2nd or 3rd until 4th is selected. It may reset if you get back to 1st gear; I don't recall.

I once 'fixed' my O/D (it was cycling On/Off at normal speeds in steady cruise control) by changing spark plug wires. I swear, that is ALL I changed and the fix was immediate and lasting. My understanding is that the poor spark was allowing the O2 sensor to read a rich, or open loop state from my slightly modified engine.

Low vacuum (leak) may tell the ECM to add fuel, as it 'thinks' the engine is under load; that the throttle is open wider. I do not know why the TPS input would not override this, but similar issues arose with an aggressive cam grind, and low vacuum.

In either '87 or '88 the O/D was 'beefed up' with more springs in the clutch pack, etc. When I had my unit redone by the best experts, it was upgraded, after which, I was told that I would not break the it; that it is a tough unit. It now works fine behind my new engine, but as always, I unload it when engaging/disengaging, like when shifting the T-10.

35annv · 11-26-07, 10:31 PM

Quote:

Originally Posted by muddywaters

That's what I did with my 88, now the OD comes in once after it hits 120 degrees,4th gear, I press the button, cancel it and it's gone until I press the button again. Seems to me that it would take alot of wear and tear off the OD if it didn't come in and out needlessly..................

Not sure why it would come into play when it hits the 120 degree mark!?!?! Since the change, mine will not go into OD unless I push the button no matter what the temp.

muddywaters · 11-27-07, 01:42 AM

I didn't mention that I jumpered the rear switch on the trans. to eliminate the OD coming in and out all the time. The 120 degree point is a stock arrangement and the OD will not come in if your below that temp. with or without the jumpered switch. My C-4 is an 88 and I understand that are some differences from earlier years. All I know is that the car is much more fun to drive, I still get kickdown on the highway when it is in OD and in the city, the OD comes in when 120 is reached and your in 4th gear, press the shift knob button and it's gone until you ask for it again..............

hmcquade · 11-27-07, 09:28 AM

Quote:

Originally Posted by 35annv

When you install the 88 OD set it to operate manually. That's what I did on my 35th Anniversary. Got tried of it constantly going on when I did not want it. Now when I wish to use it, such as highway, I push the button.

Thanks, that's what I did, runs great.

Hugh