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Drive line quandry big block 1971 (1/2)
 12/13/18 10:36am
70big4speed
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chesterfield, MI - USA

Vette(s):
1979 L48 Auto red on red 1971 Coupe 350 auto 1970 454 4-speed Coupe sold 1977 350 auto sold


Joined: 2/16/2015
Posts: 34

Converting my project 1971 Coupe was a factory base 350 auto(TH400) got it missing engine/trans..  Got myself a short block 454(468) bored over .60 and desided I'd like a 4-speed Muncie in her. Got a 27 spline M21 and now in a quandry about drive shafts and yokes, etc.  I have my original differential 3:55 with standard yokes and I have the 1/2 shafts 2 1/2"  But I bought a pair of 3" half shafts for it a year that need restoring. Been seeing all sorts of parts out there original and after market. I have a slip yoke for the M21 output that has press in u-joint caps but it seems small to me, came out of another Vette with a Muncie M21 not sure of year though. Should I upgrade my diff side yokes to heavy duty with the big caps and bolts? Standards use u-bolt style. Half shafts look as though they'd fit into the standard side yokes. Maybe go with 3" half shafts and standard u-bolt style yoke already in the diff?  Use what I have for the trans driveshaft and slip yoke, just go heavy duty u-joints all around and be done?  I don't think I'll be going beyond 2 steps up at best from a stock 1970 454 power and torque wise.

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Re: Drive line quandry big block 1971 (2/2)
 12/13/18 10:39pm
Adams' AppleLifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


Joined: 11/8/2003
Posts: 19627

70big4speed said:  I have a slip yoke for the M21 output that has press in u-joint caps but it seems small to me, came out of another Vette with a Muncie M21 


Our cars cannot use a trans yoke like that. The trans yoke must be of the bolt/strap type for the u-joints. There's NO way to install the driveshaft into the car with a regular, pressed cap yoke...just can't be done, unless you want to remove the engine & trans every time you need to service the u-joints, driveshaft, or even change the rear seal of the trans.

As far as the half-shafts & u-joints, unless you are building the engine to make gobs of torque, and plan on drag racing, or otherwise hammering on the driveline, the stock stuff will work fine, if you don't abuse the car.


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Joel Adams
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