yokedworkoutbro3

Hey guys i just picked up an 85 with the 4+3 trans. The car is completely stock with 100k on it. It has the overdrive button on the shifter, and when the car is up to temp the o\d lights up on the dash when the button is clicked. But it does not shift into overdrive.
Reverse still works as it should.
When i let off the gas with the o/d switch off, it engine brakes like a normal manual. When i let off the gas with the switch on, the rpms drop like its shifting into o/d, but when i hit the gas the rpms jump right back up.
Any thoughts would be greatly appreciated!
I need to change the filter and fluid soon, no idea how long its been in there...

rodj

Would be the starting point , low fluid will prevent O/d operation
Then to check out if power is actually getting to the O/d solenoid
Dash light shows power is available from the O/d relay but the 1st gear lockout switch on the trans may be faulty or the connector into the O/d unit may be bad ( common problem )

J.Maroon87

Had the same problem wih my 87. Turned out tbe a fuse. Check to see if anything
else is not working. Such as interior lights or door chimes. Check cluster fuse.

ProjectC4

On my 84 the OD light is the last thing in line before the power goes into the transmission to a pressure switch then to the OD solenoid. If there's not enough main line pressure the solenoid won't energize and it stays in low.

Low transmission fluid level can cause this. There's a seal between the OD and the 4 speed trans which can leak and let OD ATF into the manual trans. Check if the OD level is low before you drop the pan. Check if the manual trans level is high before you drain it.

The wire between the OD solenoid plug where it enters the OD and the pressure switch has a spade connector on either end. If they are loose the OD may chatter over bumps. Interestingly the 84 electrical suppliment schematics do not show the pressure switch inside the OD. The repair manual does mention it.

coupeguy2001

Sounds like the clutches are worn, and can't push the car under a load.

yokedworkoutbro3

Hey guys thanks for the responses. I just drained the gearbox and the o/d, both seemed to have about the right amount of fluid. There was a little bit of shavings in the pan, but no apparant sign of atf running into the gearbox. My first gear switch doesnt seem to be working, i believe the switch should have a completed circuit anytime the shifter is not in first (when the ball in the switch is out). Im not getting a closed circuit with the ball pushed in or out.. Also id like to replace the pressure switch in the pan just since im in there. Any ideas where i could get a 1st gear switch and pressure switch?

vetteoz

Brian at www.skspeed.com (631) 957-9525
has been the go to man for 4+3 parts for many years but recent posts about him selling up and getting out of 4+3's
Worth a try