overdrive Posted April 13, 2014 Share Posted April 13, 2014 I'm restoring my '70 SS and I've had the motor on a run stand for the last year. I'm to the point of trying to find what caused the thrust bearing failure after only about 500 miles. Some of you may remember when this happened. Since then, I had the crankshaft repaired and after tearing the motor compeletly down for cleaning and inspection, I put it back together. It runs great on the stand again. Now the trans is my focus after the machine shop verified again everything in the motor is within specs and then rebalanced the rotating assembly. Last weekend, I temporarily installed the 454, TH400, and radiator onto a spare frame that I'll end up putting under the SS. The torque converter is the original and its outer appearance doesn't give any clues to a high pressure problem. I ran the motor and did a pressure test with a 200 psi gauge teed into the line supplying the transmission cooler in the radiator, but so far, I've only learned that the pressure to the radiator cooler is about 40 psi at idle. That's well within the normal range. I got the rear end out from under the car last night and installed it under the spare frame. (I'll start taking the body off the original frame soon.) Today, I cleaned up the driveshaft and found the original orange paint stripe on it. Both u joints were the originals and in good shape, but I removed them a couple weeks ago. I need to find the correct u joints now and finish restoring the driveshaft so I can install it. I need to be able to run the motor and put the trans in gear with a 300 psi gauge mounted in the test port on the side of the TH400. Maybe next weekend I can do the remaining tests. Dan Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted April 13, 2014 Share Posted April 13, 2014 there's not much with the trans that could be the cause of your bearing failure I've seen torque converters not seated correctly by not making sure it was pushed to the flexplate before tightening to the flexplate but you would have a serious vibration, same would be if the converter was out of balance or the converter wasn't seated correctly putting forward pressure on the crankshaft would be the only thing I could think of what side of the thrust bearing was damaged? fore or aft? Quote Link to comment Share on other sites More sharing options...
overdrive Posted April 13, 2014 Author Share Posted April 13, 2014 Aft. Torque converter was seated correctly. I pulled it forward maybe 1/4" to bolt it to the flex plate. I had used B&M parts to rebuild the trans and also for the shift kit. I've since had 2 very knowledgeable full time mechanics tell me to get the B&M parts out of there. They said B&M only makes good shifters. I'd like to identify a trans problem before I tear it down again. I've been doing alot of reading and found a youtube video showing a torque converter being shoved forward as the rpms increased. It was caused by a blockage in the trans, supposedly Dan Quote Link to comment Share on other sites More sharing options...
Mr. Hipster Posted April 14, 2014 Share Posted April 14, 2014 I question your knowledgeable trans guys, B&M makes nothing, only packages parts. Normally brown paper in fwd and intermediate clutch positions and green waffle in the direct for most applications. If the rubber seal is left off the direct drum, a 'trick' to maximize hold power, application might be a little too abrupt. Regarding the thrust issue; it's pretty easy to screw that up if you don't do it every day. After diameter clearance has been verified torque mains 1-4 and check thrust with rear main loose. Should have .008 to.010, snug rear main bolts and tap crank fore and aft with dead blow, using a large screw driver wedge the crank forward and torque rear main, should have with in .002 of untorqued clearance. Some may find fault with my specs but they are the product of trouble free thrust bearing life for many years. Blocked trans cooler is about the only thing that can cause thrust problems when converter/trans clearances are correct. Quote Link to comment Share on other sites More sharing options...
overdrive Posted April 14, 2014 Author Share Posted April 14, 2014 Thank you for taking the time to reply. I appreciate your input. I feel the need to post a little of my background, just so those reading this have a good feel for where I'm at on this project. I'm far from knowing all there is to know about automatics, or engines, for that matter. I've had formal auto mechanics training and I've built a number of motors through the years. I do all my own work and always have. Have I made any mistakes? Of course. I'll be 54 the end of this month and respectfully value opinions of anyone that will offer their knowledge. I have the books on engines (and the trans) and study continuously. (I started reassembly of a 351W today.) I've only rebuilt one automatic, though. That was not too many miles before the motor lost 2 cam lobes and the rear thrust surface had signs of heating and abnormal wear. The first time the motor was rebuilt was before I got it and it was done by a professional machine shop in Kansas City. That's across the state from me. After the lobes were wiped out was the first time I rebuilt it. I had a local professional machine shop in Quincy, Il. clean the block, check everything out and balance it. We believed the problems started when a cam lobe went flat. I showed them the thrust ring discoloring on the crank and they cleaned up the ring and said it was within specs. I had them go ahead and install the crank, while all the parts were there. They're a very busy and popular shop and I'm 99% positive they put it together right. All they do is engines. I bought all the parts from them, including a roller cam/lifters, and finished the rest of the build. About 500 miles later the oil went from clean to dirty quickly and I had some rocker arm noise. I jerked it out and found the thrust bearing ruined and this time I needed to have the thrust ring welded and the crank remachined/rebalanced. I hadn't bolted the trans back to it until last week. Here is a good read. I found the Youtube again. This is what the guy that posted the video said: Quote: The front pump had a restriction behind the stator support (reaction shaft) tube causing a pressure build-up and a forward push. This will and did destroy the initial thrust bearing and crankshaft.... Dan Quote Link to comment Share on other sites More sharing options...
overdrive Posted April 20, 2014 Author Share Posted April 20, 2014 I put my drive shaft back together today and installed it. I raised the rear tires off the ground with my engine hoist and then chained the frame to the trailer hitch of my truck, as a safety measure. I made a video of the flex plate and torque converter as I revved the motor a few times, both in neutral and in drive. Just as I suspected, the converter and flex plate were moving forward, just like the one in the Youtube video I posted the link for, above. I'm relieved to know exactly why the rear thrust surface was ruined, but not sure yet if I'll replace the trans or fix this one. The machine shop and my engine rebuilding book both call for 5 to 7 thousandths of crank shaft end play. I checked it again after the test and it's still at .006. No more testing until the trans changes are done. Dan Quote Link to comment Share on other sites More sharing options...
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