Grinding Gears

It's been several months since we've updated the project blog, mostly because the evTD has been out of commission for that long. You may recall that I added a postscript to the last installment of the EVCCON reports about the emergency contactor switch and the trouble that caused. Well, there's more to the story.

Several months before EVCCON, I began to notice a slight vibration or resonance in second gear that started about 3000 RPMs and smoothed out over 4000 RPMs. Then it became more pronounced and showed up in third gear, too. Since it hit the same RPM band in several gears, I was suspicious that the Impulse 9 motor might be the culprit, and asked everyone I talked to at EVCCON for their advice and counsel on the problem. Tom Brunka of Helwig Brushes suggested that I increase the brush spring tension. Bill Ritchie of HPEVS of course suggested I swap out that nasty brushed DC motor for one of his smooth AC 50's. Other opinions included too much brush dust, dry bearings, or a misaligned adapter. The real cause raised it's hand at the drag strip.

On our third run up the strip with John Hardy riding shotgun, I hit the go pedal with the transmission in first gear and heard the most indescribable "fingernails on chalkboard, makes your teeth itch" noise that went away as soon as I upshifted to second. Since I normally start in second, it wasn't too much of an issue in daily use. After we got home and resumed normal activity, everything seemed ok except for that pesky 3000-4000 RPM vibration. Then I put it in first at an uphill stop light and the noise was back, and after that the vibration in other gears got worse, so it was clear the transaxle was at least partially at fault.

Knowing that the one year warranty on the transaxle had expired, I took the car to my favorite mechanics at Pro Automotive (no web site - these guys are old school wrench jockeys, not computer geeks) and placed my trust in them. First off, Robert Juarez re-engineered the rear support frame so they could pull the motor without removing the body. Tearing down the gearbox showed that reverse gear was chewed up pretty badly which meant it was hitting some interference when first (on the same shaft) was engaged. Thus the noise in first. Pro Automotive is right next door to Motor Mania, a VW specialty shop, and they recommended sending the transaxle off to Ken Harvey at German Transaxle of America in Bend, OR. 

Ken was a pleasure to deal with and took the time to walk me though what he found and what my options were. Turned out that the needle bearing on the input shaft had disintegrated allowing everything in the gearbox to wobble around enough to cause the screeching and damage. The ring and pinion showed galling and needed replacement, and Ken recommended replacing the fine-spline gear shaft with a coarse-spline one for better strength. Then during reassembly, he went to tap the front main shaft bearing into place and it just slipped into the hole where it should have been a press-fit - new case needed!

On the recommendation of Jack Rickard and Brian Noto, we went with a 3.44 final drive ratio that makes first gear more usable and makes fourth gear a .88 overdrive. Also added a "Super Diff" for more strength as well.

The trans arrived Wednesday this week and it is a beautiful piece of work. Like so much of the craftsmanship on this build, it will never be seen again once it's installed. First driving impressions are great! It is quiet and smooth, and with the revised final drive ratio it seems faster with less fuss than before. Shifting seems a bit stiff, but I think a little clutch adjustment will take care of that. I think the evTD is happy to be home, although the wife's Prius enjoyed living in the garage while evTD was in the shop.

Now to clean all the shop dust off and get it shined up for the IBM Day Car Show on October 31. Stay tuned ...