Broken tailshaft on 727

[toolman]

I have a 69 Coronet 500. I bought a Pro-street trans/converter combo from GER. It has a 3500 stall 9" converter. It's hooked up to my modestly built 383(balanced). Newly balanced driveshaft, new u-joints ,3.91 rear, new motor and trans mounts, SS springs. Basically everything new. I put about 200 miles on it around town before I went to the drags. I trailored it, got 5 runs at low 13's and on the 6th run at 13.0 and 103mph I let off and simultaneously the tailshaft broke off 2" behind where it mounts to the front section. Fluid everywhere. the tailshaft then slid back onto the yoke and twirled around it making a huge vibration while I tried not to crash. I drove it 200 ft. off the track and had a look before I knew what happened. Can anyone tell me why it happened or how it could have happened on a newely built trans?

[Comp Chassis]

Check your trans mount, driveshaft length and driveshaft balance. Usually when the tail stock breaks it is because of one of these. I would pull the trans apart and check the sprag, governor support and internals. Im sure it probably didnt do them any good.

[AZMOPAR]

Any sign that one of the u-joint cups moved - allowing the driveshaft to run out of true? I have only seen this type of damage when the driveshaft was running out of round due to the loss of one u-joint retainer - this occurred in a few seconds and destroyed the extension housing, trans case, and output shaft. It does not take too much out of round at the front yoke to create a high level of vibration - especially at speed. I also replaced the front yoke on the driveshaft. In any case the trans case (especially around the bolt holes that retain the extension housing) needs to be checked for cracks. The output shaft, and rear sprag needs to be inspected for damage. From experience I can say that this creates an exciting ride for a few moments. CompChassis also has a good point that a damaged or loose rear trans mount can cause a similar problem.

The term GER also is a worry - I would not use any of their products in my vehicles!!!! Just my 2CNTS.

[This message has been edited by AZMOPAR (edited May 23, 2000).]

[toolman]

I inspected the car today and found one cup and bearings missing on the rear u-joints. the driveshaft flops around about 1/4 inch or so and slides fore and aft also. From what you say, it sounds like you guessed it right. Could it possibly have happened in the reverse, in other words, tailshaft broke first then the cup come out? the u-joint retainer on the missing one is still there and is bolted tight. What do you think?

[Comp Chassis]

Its possible, but I would guess that the U joint flew apart first and then took out the tail stock. If everything is spinning straignt, there is no reason it should break.

I broke a bell housing once by using the wrong U joint clips. I used the thin and should have used the thick. It let the rear joint get off to one side, then it got the drive shaft to vibrate which then warped .150" and then it vibrated so hard it broke off the bell housing. It is not a fun ride at 118 mph when the car is shaking so bad that you cant see where you are going.

[toolman]

Ya, tell me about it. I was only going 103, but it was totally unexpected and I thought the car was going to explode! Thanks for the strap tip. I'll have to have a look. The driveshaft was just ballanced, but it might be too short. It has that large disc ballancer at the front, I think it's from year 1967. my car is a '69. I'm thinking of having a new aluminum one custom built. Also, the pinion angle is just about zero degrees. I plan on adding another 6 degrees. Thanks guys for your help.

[Leigh]

I put together a 904 for a e/sa 71 Duster a few years ago. The output shaft broke off behind where the extension housing bushing is. I felt like the guy was blaming me even if he didn't say anything. I now magnaflux all unknown shafts. Made me really leary of building units for anyone else but close friends for quite awhile. Food for thought.

[sixpackguy]

Key words here: GER.
Check EVERYTHING you get from them. Did some work for a guy here who insisted on buying from them. Three convertors, and much BS later finally got one that would work. The first one was so bad you couldn't even get an input shaft to go in it. Check your tailshaft bushing as well. Good luck.