Editing Driveshafts: Swap solutions

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==Introduction==
This "Swap Solutions" series of Wiki articles is intended to help the customizer, swapper, shade-tree mechanic, or junkyard crawler.

Often an engine or transmission swap requires the driveshaft to be modified. One important part of this is correctly measuring the driveshaft for the correct length.

[http://www.dennysdriveshaft.com/how_to_measure.html Dennys Driveshafts - How to Measure Correctly]

==GM 7.5" out 8.5" in==
A shorter driveshaft is used when the 8.5" rearend is installed in place of the 7.5". The difference is 1 inch. The TH200C, TH250(C), TH350(C) and the TH2004R all used the same length driveshaft.

==Measure, measure, measure!==
The idea is  this: when you pull an axle, engine, tranny, driveshaft, bearing, or ANYTHING from your car, measure the heck out of it. 

Countless times I've found myself wishing I had a source to know if this axle will fit that car, how much that ISB Cummins engine weighs, or if a driveshaft already exists that fits my custom install instead of paying to have one fabricated.

This article is for driveshafts. An often overlooked item, there are a wide variety of driveshafts available that might make short easy work for your swap. While you have yours out, grab a tape measure and let the world know.

#Driveshaft length, from center of the front U-joint to center of the rear U-joint.
#Tubing diameter
#Tubing material. Most will be steel, but some are aluminum or composite/fiber these days.
#U-joint size, front/rear; 1330? 1350?
#Tranny yoke style. 
##Is it a slip yoke or fixed? 
##What diameter and spline count? 
##What tranny does it fit?
#Notes for additional information.

==Making two driveshafts into one==
When doing an engine swap, we often find ourselves needing a special driveshaft length. I usually retain the original driveshaft from the car getting the swap because it will have the proper u-joint on it to fit the pinion at the rear differential. I get the driveshaft from the transmission I'm using in the swap because it has the proper yoke/u-joint on it that fits the trans I'm using. I whack off the tubes a couple of inches past the joints, retaining the front joint/yoke that matches the trans I'm using and the rear joint from the other shaft that mates with the pinion. 

With the car positioned at ride height, rotate the rear axle so that you have an up-bubble on the pinion of 2 to 3 degrees for most rear suspensions on a street machine. Drag cars will want more of a difference between the trans output shaft and the differential pinion because the pinion will be hit harder with engine torque than a street car will and may even be installed with the pinion pointing down a number of degrees due to the tendency of the pinion gear to "climb" the ring gear under hard acceleration. In some cases, a pinion snubber can help to limit this. 

It all depends on the rear suspension system being used. If using leaf springs, there are special angled wedges made for the purpose of changing the rotational position of the housing. The motor/trans will have been installed at about a 3 degree down-bubble, so this will make the crankshaft/transmission shaft parallel with the rear pinion. Notice I said PARALLEL, not necessarily (and often NOT) pointing directly at each other. 

Bolt the rear joint onto the pinion. Slide the front yoke onto the transmission output shaft until it bottoms and will go no further. Now, pull the yoke out 5/8" to 3/4". Measure between the centerlines of the bearing cups on the front and rear joints. This will be the measurement you will give your shop to make your new driveshaft. Give them the front and rear joints and the measurement and they'll make and balance a shaft for you. If you want it to be bulletproof, specify that you want it built with 0.093" tubing. Should you opt for a larger diameter driveshaft, be sure it will clear the floorboards, etc. at full rear end compression.

[[Category:Transmission]]
[[Category:Rearend]]