A few weeks back, on one of the Slipangle podcasts (I believe it was the "Podcast from a truck" episode, with Christian Shipp), I described how my street car, a turbocharged, 2.3L 1990 honda civic, had expoloded the transmission at roughly the top of 5th gear. I went hard for the brakes at somewhere around 150 mph, and I theorized that something let go as the shock load changed in the gearbox. I figured I'd snap a few pictures of what was found as a bit of follow up for those who heard the story, and make a bit of a tech article out of it as well.
This gearbox was a stock 1991 civic transmission with a Quaife differential I installed in it around 8 years ago (I use an adapter plate/flywheel to make this trans to a 2.3L accord F series engine). The little "L3" series trans had been in there for roughly 100 track days, and probably 15-20k street miles over those years. I estimate it saw around 100 drag passes in it's life as well. The gearbox had been making a bit of bearing noise, but nothing too bad, and it was only noticable at highway speed. It was just an RPM-dependant whine , and i liked how it sounded a bit like straight cut gears... but, obviously, it wasnt supposed to be doing that.
On new years day this year I had the afternoon off (a rare thing), so I yanked the trans out and swapped some old junker in temporarily, just to make the car move around under its own power during its planned semi-rebuild that we'll be doing this winter/spring. I'm undecided if we'll keep it turbocharged or make it naturally aspirated. I'm getting older, and have responsibilities. The dumb car might be faster than I need, and I almost don't want the possibility of speed anymore. It crossed the traps in the 1/4 mile at 129 mph on DOT drag tires, and did the standing half mile at 150 on 195 width street tires, running out of gear before the finish line. The turbo/no turbo decision will be made soon. I go back and forth every day. I'd miss the ability to do burnouts in any gear, but does a hamfisted idiot like me need such a quality in a car?
The next step was to answer the question of "is the diff ok?". Quaife builds a simple and strong differential, and many people had told me they can swallow a bit of crap and not be too injured, so I was optimistic. I hadn't driven the car since the explosion, obviously, so not TOO much had gone through it (maybe?).
Cracking the case of the trans is pretty easy on these. Zip the case bolts loose, remove the brackets in the way of a couple of them, and remove the allen head bolt inside the clutch housing, which retains a shift selector mechanism that will hold the gears in place. Next, get the small portion of the case "loose" by breaking the seal of the RTV used the keep the cases from leaking. I lightly tapped a junky, sharpened flat screwdriver into a thicker portion of perimeter, on the top of the case, and it separted immediately.
Next, I zipped the big plug on the end of the case off. It used a 3/8'' socket end , so I just stuck the ratchet into it, and spun it out. Inside, the big clip needed to be opened up, which retains the gear stack. I stuck a couple of flat screwdrivers into it, and forced them apart by jambing a 3/8'' socket extension between them, then a couple of prybars lifted the case up, and off came the case.
The carnage inside revealed I was correct, a gear had expolded, but it was 4th.... so now I'm either miss-remembering when the trans blew, or something odd happened. My current theory is it blew when I downshifted to 4th, but that isn't the memory I have (this was 2 years ago, so, who knows.
No in-car footage unfortunately) . Regardless, this stuff was pretty much junk, and one of the shift forks was shattered as well (before, during, or after?). Next, the important question is, is the diff ok!?!?!?!? Those things aren't cheap!
I stared at the Quaife after removing the gears (a simple pull-and-lift-out procedure) and grabbing the diff out (another "lift it out" thing. easy). It seemed ....ok? These have very few openings in the case, so, maybe a chunk hadn't gotten in. Fingers were crossed.
Next, I popped it in the vice, and started zipping bolts apart. Looking at the outside of it wouldnt reveal the true condition, so apart it must come. I cleaned things along the way, and remembered how it all went together. These are remarkably simple, thankfully. Very little wear appeared to have happened to anything, so I went through it all piece by piece, blasted everything with brake cleaner, and wiped it all down with clean paper towels.
The rest was pretty drama-free. Assembly was the reverse of dissasembly, and there aren't many parts, so it was pretty easy to put back together. The current plan is to install this into my CRX racecar when the transmission is pulle out of it. At Road Atlanta a month ago, I discovered what seems to be a worn out M-Factory clutch-type differential. I'll remove that clutch-type diff, install the Quaife in place of it by swapping the 4.9 final drive ring gear on it and dropping it in the box, and putting the trans back in the car for the spring. The M-Factory piece will be rebuilt, and installed in a trans with better gearing for Mid-Ohio sportscar course, as I hope to qualify for and run the SCCA runoffs there this coming fall.
I guess the moral of this story is, transmissions explode, but sometimes the diff makes it through! If I'd have just been driving a RWD car instead of a FWD snoozemachine, we would'nt have had to worry about this...but gosh I love these dumb little cars. More tech to come, as I try to put this lil thing into another transmission and go racing again!