stress cracks? and tranny question

[Joe T.]

i have a 66 convertible, just had stainless steel brake calipers put on rear, a week later noted a big paint chip middle of rear deck just behind the gas cap, when repairing noted small crack in the fiberglass, is this from excessive frame flexibility while on the lift or is this just an odd occurence, also the car is an early 66, has tranny with correct casting number for 66, tranny buile date is p1202 so probably a replacement tranny, it has a magnetic drain plug, can this help tell whether this is a m20 or m21 trans, thanks joe

[Jerry Clark]

Re: stress cracks? and tranny question

Joe
Very doubtful if the crack is attributable to the lifting of the car. While under some circumstances cracks could be produced by lifting, it probably would not occur in this area.
No Corvette transmission had a magnetic drain plug to the best of my knowledge
Good luck

jer

[Steven A.]

Re: stress cracks? and tranny question

Joe: I don't know about the crack, but there are a number of good posts in the archieves regarding transmission ID. The drain plug would have nothing to do with it. As I recall, there are only two ways to know: (i) the are a different number of circular grooves on the input shaft (M20 has two, M21 has one and M22 had none) or (ii) take off the side panel and count the number of teeth on the input gear. Neither one is too practical for novice mechanics like me. However, if your car has a base 327/300 engine, then it should have the M20. Also, I think there is some website out there (see posts) that lets you figure the gear ratios in your transmission (assuming you know which rear end ratio you have).

[Joe L.]

Re: stress cracks? and tranny question

Jery and Joe-----

Early, and possibly later, M-22s may have had a magnetic drain plug on the lower, right side boss. However, if original, the drain plug will have the brand name "Lisle" embossed on the head of the square-headed plug.

Drain plugs could easily be added to any Muncie main case and all 71-74 "661" maincases had them. The "661" main case was also sold for many years in SERVICE as a replacement for any 66-74 Muncie. Consequently, their presence says very little about "what"s inside".

[David Bodily]

Re: stress cracks? and tranny question

Check this site. It has a good amount of info on what you are looking for

[David Bodily]

Re: stress cracks? and tranny question

oops I had a senior moment http://www.dandltransmission.com/muncieratio.html

[Joe T.]

Re: stress cracks? and tranny question

thanks, it is a 327/300hp, interms of the stress crack i just installed a new convertible top, it was very tight until it stretched, do you think it was possible that the pressure from the convertible top pulling on the rear deck lid could have resulted in the crack?

[Bob R.]

Re: stress cracks? and tranny question

The convertable top fastens to a seperate panel. I don't see how it could stress the area below the gas filler. I would think this part of a corvette body would have very little reason to form a stress crack. I' never seen one there before. It might be possible that someone dropped something on the rear deck and didn't repair the damage properly. Then painted the car. Now the damage is showing.