Spinning Wheels, Full of Teeth

Somewhere back in the mists of time, shortly after our first excursion into the wild world of LeMons auto racing, we realized that our car was far too steeply geared for really spirited performance around the track.  Our best runs, the ones where we hit all the apexes and didn't hit any other cars and had nice, clear racetrack in front of us (OK, admittedly, there weren't that many laps that met that description, but there were _enough_) saw us just barely running out of revs in 3rd gear.  Unfortunately, by the time we could reach for fourth and snake the ridiculously long shifter lever into position, the next turn would be upon us, necessitating a quick downshift back into 3rd.  Indeed, I soon discovered that, at least for me and my two left feet and three center arms, it was a faster way round the track to simply leave it in 3rd and, if the tach reached 5500 (our pre-decided rev-self-limitation, for longevity's sake) to simply hold it there until the next bend. 

But this year was going to be _different_.  We would undoubtedly be faster out of the turns, thanks to our drastically lowered suspension, nice fat wheels and engorged sway bar.  And, as such, if we left the driveline alone, we'd find the pushrod plant spinning up to the redline that much quicker, leaving us with more quick 3-4-3 shifts, sure to be frustrating.  We did some quick calculations and determined that if we swapped the rear gears from a 4.10 ratio to a 4.88 ratio, we could get into 4th much sooner, have more torque going through the turns in 3rd, Stay in 4th much longer, get more top end, and (hopefully) never have to worry about dipping down into 2nd in the chicane- a notoriously hairly dogleg shift into a gear with an already weak synchromesh. 

In the above snapshot, we see Brian illustrating the differences between the old 4.10 gears and the nice, new 4.88 gears.  Just another morning at the office.

Of course, when it comes to old cars, particularly old _foreign_ cars, nothing is ever straightforward.  We had initially been under the impression that our Volvo was equipped with a Dana 27 rear axle, a point that made finding replacement gear sets somewhat difficult.  When I finally did stumble upon a set of the right gears, I had them shipped to me post haste only to find out the ring gear had only 8 bolts holding it to the carrier.  Ours had 10.  Out of desperation, I swung for the fences and bought a set of Dana 30 gears- which were much, much easier to find.  And of course, they matched, and fit perfectly.  One problem solved.  Unfortunately, the next problem followed immediately- we needed to get the bearing off the old pinion (lower one in the above pic) and press it onto the new one- the upper one of the two above.

But first, Brian attempts to....well, crap, I don't know what the heck he thinks he's doing.  I think he thinks he's being clever, and imitating some sort of a monster or tiger or shark or something.  We aren't sharks.  We're Tuna.

The bearing.  Lacking any sort of formal bearing pulling equipment, or any green shreds of paper to trade for some, Rob and Brian and Gary spent the better part of a weekend jury rigging up various Rube-Goldbergian devices with the intent of getting the bearing to yield its hold on the pinion shaft.  Their progress was roughly as follows:

  • 11AM, Saturday morning: Rob begins tapping at the bearing with a chisel, hoping to wedge it away from the pinion gear.
  • 1PM, Saturday:  The bearing has moved approximately .225".  Brian shows up.  Meanwhile, I have mostly finished installing the exhaust system on the car.
  • 3PM Saturday: Gary shows up and the three of them move the bearing another .175".  Anthony, meanwhile, has plumbed most of the fuel system.
  • 6PM Saturday: After trying and discarding approximately 14 different tools, and having budged the bearing approximately .785", Rob goes inside and makes Jambalaya (traditional Mardi Gras dish) for dinner.
  • 7:30AM Monday morning: Rob comes into my cubicle, bearing the bearing and pinion separately, lamenting that we spent 17 man-hours removing a $20 bearing and mumbling something about having found his personal Lord and Savior, Jesus Christ.  No matter, the bearing's off.  Now we just have to figure out how to put it on the new pinion...

My initial plan was to take the bearing and press it onto the new pinion mechanically.  Brian, however, had a better idea- heat the bearing, chill the pinion, and the two should slide together effortlessly.  Rob and I, being the true engineers of the group, got out our calculators and Shigley and Mischke's "Fundamentals of Engineering" and calculated the precise temperature difference that would be required to increase the inner radius of the bearing and decrease the outer diameter of the pinion shaft to the point where they would slide together "effortlessly".  As it turns out, the precise heat the bearing would have to be heated to neatly coincided with the temperature I like to bake a potato at. 

And yes, I know my toaster is filthy.  I would like to think that the remnants of hundred of bagels, hot dogs, potatoes and sundry other foodstuffs encrusted to the bottom combine to impart to the culinary creation de jure complex and varied undertones.  Sometimes they even catch fire, and I end up with Blackened, Cajun-style dishes.

Meanwhile, turns out the precise temperature the pinion needed to be cooled to was the exact temperature I like to keep my Vodka, er, I mean, my _bread_ at. 

Voila!  And I didn't even need that hammer! 

Back in the car, or more accurately, under the car, we had several measurements to make.  After installing the new pinion and ring, the first thing to measure was backlash- how much the ring could rotate back and forth while the pinion was held still.  According to Dr. Dana, this should be 0.006" to 0.010" for the Dana 30.  Of course, Rob being Rob, he only had a dial indicator that measured in millimeters, which required some conversions:

1 hogshead : 113.5 deciliters

7 hands-breath : 1.2 meters

4 Stone : 31.76 kilograms

Or something like that.  Anyway, we moved some shims on the diff carrier from one side to the other and eventually ended up with 7 thousandths worth of backlash.  Next, we had to set the pinion depth, but to do that, first we had to chalk the teeth. 

Mmmm...chalk.  Delicious chalk.  Here we see the teeth chalked, and then rotated a few times through the pinion.  What you want, ideally, is for the area rubbed by the pinion to be more or less even between the root (bottom) and face (tip) of the gear.  As you can see in the above picture, we're already pretty close.

And here, on the drive side, you can see we're not too shabby either, perhaps a little on the shallow side.  After some consultation, we decided to let it be.  Without boring you too much with our decision making process, it basically involved the following logic:

  1. We were not crawling rocks with our Dana-equipped steed.
  2. The 1.8 litre engine in front of our Dana puts out a less-than Earth-moving 108 lb-ft of torque on its best day.
  3. We did not own any pinion shims.
  4. We had some misgivings about our ability to remove, shim, and replace the pinion bearings, which could also possibly lead to needing to re-shim the carrier again, thus leading to pulling the carrier bearings, which was also not-very-much-fun (and possibly tail-chasing)
  5. We were hungry.
  6. Rob's wife had beer.

So we buttoned it all up, went inside and had beer, pork roast, sauerkraut, applesauce, wine, bread, mashed potatoes,and ice cream and cake.  And then Amaretto, Sambuca, Goldshlager, Kaluha...

Sadly, I'm not exaggerating.