The Brass Gearbox Plug from Hell Fiasco
(Or how I was a fool---and, yes, you can learn from my mistakes)

My 1987 740 Turbo, M46 manual transmission, exhibited three problems all at once on a drive to and from a local park. On the way to the park, (I) my wife and I smelled smoking brake pads. (II) Hiccups in the engine started to occur again. (III) Also, on our return, shifting gears became more difficult. At home, in the driveway, I noticed that there was no longer a smooth shift from neutral into any of the gears, even with the engine off and the clutch in (disengaged). After trying to switch into the various gears a number of times, the clutch pedal suddenly had no resistance.

Attacking problem (III) first, I surmised it was probably the gearbox oil and the clutch mechanism. Putting the car up on ramps, I went underneath the car and discovered there is no clutch spring mechanism for the clutch fork. The Bentley manual didn't show how my clutch worked and, in my haste, I skipped right over the Haynes material. So, I put my question up on www.volvoforums.com and www.brickboard.com and discovered that I had a hydraulic clutch. Thank you, guys!

I decided to change out the gearbox oil first, since it was over five years and almost 14 thousand miles since I had checked that oil level. Well, previously, I had rounded the upper brass gearbox fill plug, but I continued to reuse it. Big mistake 1!

(For details on the whole fiasco and possible step-by-step remedies, download "How to Avoid the Brass Gearbox Fill Plug from Hell Fiasco.")

  I tried to remove the brass fill plug using a 12-point 13-mm box end wrench. I could not loosen the plug because the head had become rounded (left) and the wrench was slipping. "No problem," I thought. "I'll just use the Craftsman vise-grip tool I have." Big Mistake 2! What was normally a 45-minute job became a 23-day task full of frustration, self-doubt, and the temptation to trade the car in for Cash for Clunkers. This job took up a good chunk of my summer!
  In my misguided zeal and frustration, I had reshaped the hex head into a cylindrical disk (left).

In the end, you can read all about it by clicking "How to Avoid the Brass Gearbox Fill Plug from Hell Fiasco," which includes instructions on how to prevent my predicament, various ways--in deteriorating order--to loosen the plug and, if you fail there, detailed instructions to get oil into the gearbox through the overdrive switch.


J-B Weld is a steel epoxy that mimics the results of a hot weld.
Note that the threads of the brass plug were inadvertently "welded" to the gearbox threads!
Use J-B Weld to fill a sacrificial 13-mm or larger box end to the problem plug head. Big Mistake 3 (biggest of them all)! Be sure to tape off the boundary of the plug threads with that of the gearbox. (I did not and paid dearly for it in time and more effort by trying to scribe and scrape the J-B steel away from the threads.) In the end, I believe the J-B welded wrench would have been able to offer the torque to loosen the rounded plug. I base this supposition on the fact that the popsicle stick I used to mix and spread the J-B Weld was stuck solidly to the cardboard platter and, once set, offered a tremendous amount of torque resistance to rotational motion. In the end, I was not confident that I got enough of the steel out from between the threads. I didn't want to try putting too much torque on the wrench and strip the threads out of the gearbox. After piling one bad decision on top of another, leaving well enough alone was a decision I could live with. In the end, I cut the end off most of the wrench, and then . . .
The overdrive switch plug and connector atop gearbox, passenger side. Easily felt, hard to see.
The 22-mm ZD Mak tool.
I ended up filling the gearbox by going through the overdrive switch plug on top of the gearbox, passenger side. An IPD Tech gave me this hint. He said I would have to drop the transmission a bit to get to the 22-mm plug because space is so confined in there. And space is very tight---too tight for a regular socket and extension. I ended up using a 22-mm crowsfoot wrench from ZD-Mak, which also fits the oxygen sensor socket. I believe other crowsfoot wrenches, shaped like an open end wrench, would be more difficult, or even impossible, to fit in there.


Suggestions from Volvo chatrooms that did not work or I did not try:

1) Use an impact wrench. There was not enough space to fit a normal impact wrench in there.
2) Use a propane torch to heat the plug and then try loosening the plug. Squeezed underneath the car, I decided it was too dangerous to use an open flame.
3) Use a propane torch to heat the plug and touch candle wax alongside the threads so that paraffin can seep in between the threads. Squeezed underneath the car, I decided it was too dangerous to use an open flame. This may have worked if you could get the car up on a lift.
4) Someone suggested going through the gear shifter. I pulled that apart and then talked to a tech at IPD. He said that the M46 had no fill tubes from the gear shifter to the gearbox, a fact I confirmed.
5) I read somewhere (sorry, can't remember, so I can't make attribution) of someone suugesting using a 6 point box end wrench, cutting a slot in the box end, then putting that over the brass plug or bolt head, and fastening a vise grip over the slotted box end to squeeze down on it. Sounds good! Too bad I didn't read about it beforehand.