June 2012 Chevy High Performance Q&A

Chain Reactions

Kevin McClelland Apr 23, 2012 0 Comment(s)
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Have you ever noticed the number of parts that can be taken out in one shot when we break our hot rods? I have a great example of this. I was racing my roadster at one of our local races here in Fontana, California (luckily, I was close to home). I made my first time run of the day and rolled up to our pits and shut everything off, cooled the car, recorded the weather, and downloaded my data logger. Everything looked great, and we went up to make a run with Daniel’s wagon. I went back to my roadster when they called us for our second-time run. I hopped into the car and fired the engine. When it started it sounded like there were marbles in a coffee can being rattled around in the cockpit. I immediately killed the engine and thought to myself, did it have oil pressure? The RacePak dash in my car has warning lights and nothing lit up. I cranked the car and the pressure was right there. I jacked the car up and looked to the flexplate, hoping to find it cracked or the converter bolts loosened up. No luck. Next, I fired the car again and put the car in First gear. The noise was immediately gone. Well, like I said I was glad that we were close to home since I didn’t have a spare transmission.

1206chp 01 O  June 2012 Chevy High Performance Q A Editor 2/3

This past weekend I finally got a chance to pull the transmission and check out the damage. I had assumed that the planetary gearset had given up. This Powerglide trans had factory 1.76 planetary, with a 4130 carrier and output shaft, which is good for the 850hp range. I’m right about there with my pump-gas 524, and I was a little over 100 runs since I rebuilt the car and had around 250 passes on the transmission. After tearing it down, I found an unfortunate mess of broken components that were mostly self-inflected. Yes, the planetary gearset had lost two teeth off the sun gear, but I also found that the Torrington thrust washer that lives in the middle of the planetary had lost sections of its hardened race. This was from excessive endplay that hammered the thrust every time you lifted and got back on the throttle; this is nothing you would notice while driving the car. These hardened steel pieces had been running through the planetary gearset and made the teeth fail. If the endplay had been correct I would probably still be running today. Not only did the endplay kill the planets, it destroyed the front pump in the trans and the sealing rings, which transfer the fluid pressure to apply high gear. The endplay was allowing the direct drum to move back and forth, loading these rings and wearing out the sealing ring grooves in the front pump. Finally, the input shaft has a small spud that engages with a bushing in the output shaft. Because of the excessive endplay, the input and output shaft were being loaded and wore the spud of my 300M hardened input shaft. The bottom line to all of this is a ton of money for parts. Luckily, my good friend and racer Jim Galente is helping me out with my rebuild. He owns RaceTrans here in SoCal at www.racetrans.com.

Something as simple as proper setting the endplay killed a ton of good parts. The trans had over 350 runs on it, and everything else looked great. The clutches, bands, and bushings were in perfect shape. I guess what I’m getting at is that it’s all in the details. Keep an eye on everything when you’re assembling your toys to prevent chain reactions.

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