1988 240 Overdrive not working

rpm984 · Post by **rpm984** » 19 Feb 2014, 11:07

Hello,

This is my first post here. I've read over some issues pertaining to the overdrive not engaging on 240s. I will try to detail my issues here as closely as possible to get any advice, which would be much appreciated. I'm really not an expert at all, though whenever I've had issues with this car I seem to be able to figure out what problem is pretty quickly. This one is stumping me.

First off the car is a 1988 240 DL sedan, automatic transmission. I was driving on the highway a few weeks ago when my OD fuse blew; the yellow arrow automatically went on indicating that OD had shut off and I also felt the car shift down---pretty straightforward. I pulled off highway and replaced fuse, it automatically blew when I turned the car on. I drove around for a bit and tried switching it again; it was fine and 4th gear was engaging when it suddenly blew on the highway again a day or so later. Oddly enough at the exact same spot on the highway where it blew days before.

Switched fuse again and has not blown since, but car has not been shifting into 4th gear. I can manually engage and disengage OD on shifter (well, I make it appear that I am though it never engages). I switched the OD relay just in case even though it seems pretty clear that's not the problem at this point (didn't do the trick). There appears to be standard amount of fluid in transmission. Brought it into my mechanic and they replaced wiring for OD harness. This still hasn't done it. Maybe they just didn't catch something first time? Going to bring it back but would appreciate any opinions on what problem could be so I'm mentally prepared in case this is going to cost me a ton...

Thanks!

lummert · Post by **lummert** » 19 Feb 2014, 15:11

Appears to be an electrical problem. IPD sells an overdrive bypass plate for $40. That's what is installed on the AW71 in my 1988 760 Turbo Wagon. Only con with the bypass plate is there is no longer any overdrive lock-out function.

rpm984 · Post by **rpm984** » 19 Feb 2014, 19:05

Thanks!

I was looking into that. Hopefully it works out. I've never used the OD lock, so I don't think I'd miss it. I'm just afraid of screwing up the transmission by continuing to drive on highways...

rpm984 · Post by **rpm984** » 12 Mar 2014, 12:06

Just an update...

Brought it back into shop and they weren't of much help. Basically didn't want to put time/effort into solving issue.

A few days later I was on the highway and suddenly OD started working again and has been fine since.

Perhaps the relentless cold/snow/over salted roads caused a temporary shortage?

Anyway, I am rather happy that I don't need a new transmission!

Post by **rgk** » 13 Mar 2014, 06:04

The fact that 'it fixed itself' sounds like it might be a short in the wiring somewhere between the fuse panel, the ignition switch, the overdrive relay, the OD bulb, and the OD itself. Prepare yourself to battle it again until found.