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#1
02-01-2009, 06:40 PM
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Diveshaft is too long? M-20 explosion
I think I FINALLY figured out why I exploded my M-20 transmission last month. I originally posted that the front bearing retainer bolts had loosened up. BUT, I think they backed out AFTER the explosion. The case was split at every bolt hole.
Today I mocked up the driveshaft and I only have 1/2 inch of yoke slip with the tires on the ground. I believe this is way too tight..? When the trans exploded the car hooked up really well and squatted leaving a patch of rubber. What do you think? How much slip should a driveshaft have? 1 inch?1.5? Thanks, Trent |
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#2
02-01-2009, 07:28 PM
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Hummm... 1/2" maybe a little tight..... 3/4" sounds about right.
__________________
1965 GTO, 408 tri-power, 4 speed, Currie 12 bolt w/3:42's, Hurst wheels |
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#3
02-01-2009, 09:48 PM
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You actually need 1 1/2" slip especially with a 4 speed. It will wrap up and get into a bind quickly. The pinion can move 3-4 degrees very easily with worn springs and isolators....sound like what happened.
By the way the 1 1/2" figure came from my driveshaft guy.
__________________
  Nothing is impossible if you break it down into possibilities. It's all a matter of "Want to". |
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#4
02-01-2009, 09:59 PM
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1 1/2" sounds like a lot to me...
__________________
1965 GTO, 408 tri-power, 4 speed, Currie 12 bolt w/3:42's, Hurst wheels |
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#5
02-01-2009, 10:05 PM
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Have to agree with 1qikta. With wheels on the ground it needs to be able to go in 3/4-1" when rear suspension is lifted up and when suspension lowers 3/4-1" out for a total of 1-1/2" or more. Saw it in an article about drive shaft lengths and measurements.
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#6
02-01-2009, 10:10 PM
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since when do we take any kind of suspension measurements with the weight off the suspension???
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1965 GTO, 408 tri-power, 4 speed, Currie 12 bolt w/3:42's, Hurst wheels |
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#7
02-01-2009, 10:17 PM
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Compressing suspension will reduce clearance. If you want to find out for sure just take the rear springs out and jack the rearend up until it is against the stops. I set both 4-speed and auto driveshafts with 7/8" travel available (slide driveshaft in the tailshaft until it stops and pull out 7/8" and mark).
__________________
Mick Batson 1967 original owner Tyro Blue/black top 4-speed HO GTO with all the original parts stored safely away -- 1965 2+2 survivor AC auto -- 1965 Catalina Safari Wagon in progress. |
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#8
02-01-2009, 11:31 PM
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My driveshaft is 49.5 inches to u-joint centers and I have 1/2 inch slip.So I need a 48.5 inch shaft....I think...?
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#9
02-02-2009, 02:38 PM
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Ymen,
I had a front bearing retainer get loose on an old Vette with Muncie in it. It did not grenade the transmission although I suppose it could. My threads were stripped out and the input shaft damn near rubbled a hole in the retainer. Needless to say oil leaked out the front retainer and soaked the clutch. Seems like you would have that warning sign before the thing blew up. So your other failure mode seems more likely to me. Doug |
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#10
02-02-2009, 05:09 PM
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I found this place online and spoke with them. They have some good deals on used nascar shafts. http://www.musclemotorsports.com/dri...eel--used.html
and according to cirle track magazine....."The correct length driveshaft should have about 1.25-1.40 inches of possible forward movement before the slip-yoke contacts the tailshaft internally or its housing seal externally. Add or subtract from the known center-to-center length of the measuring shaft to determine the measurement that will best achieve this desired clearance. A typical stock car trailing arm suspension will cause the shaft to move forward 1/4-1/2 inch in normal use, yielding an actual running clearance of about one inch." http://www.circletrack.com/drivetrai...fts/index.html Trent |
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