Driveshaft length tolerances +/-?

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Righty Tighty

Righty Tighty

Blame it on the dog
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Hello all, I have a question about driveshaft length and the tolerances relating to such. The question is pretty simple - how much tolerance is acceptable in regards to proper length of the driveshaft? In other words, say the specs for a particular year/body/trans/rear call for a 49" driveshaft, what are the acceptable tolerances for said dimension? Is 49.50 unacceptable? 49.30? 49.10? Etc., etc.

Obviously, we would want the length to be as close to perfect as possible, but HOW close is close? Are we talking thousandths of an inch? Fractions of an inch? And why? I understand the yoke needs some room to move in and out, but how much room does it need? Is too short better than too long?
 
Go to Dr Diff web site and read his method. I'm too lazy to type it today. But the spec is 1 inch.
 
not knowing how that 49" DS is being measured makes it tough to answer. is that total with the yoke? no yoke? the corrected length accounting for slipping the yoke back after it bottoms? and if so how much? i've had driveshaft builders say anywhere from 1/4" to 3/4" slip. i've had one that was off just over a 1/4" from what i wanted, and it turned out to be fine.
always ask your DS shop how they like it measured
 
The 49" length was an arbitrary I threw out there. Basically I'm wondering how exact the length of the driveshaft has to be as compared to the specs recommended. Let's say the DS length I need is 49", but I found one that's 49.25". These are both being measured center to center of the U-joints. What are the acceptable tolerances for driveshaft lengths?
 
Righty Tighty said:
The 49" length was an arbitrary I threw out there. Basically I'm wondering how exact the length of the driveshaft has to be as compared to the specs recommended. Let's say the DS length I need is 49", but I found one that's 49.25". These are both being measured center to center of the U-joints. What are the acceptable tolerances for driveshaft lengths?
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that's why you should ask the place making it how they like it measured. everyone i've ever talked to want's the yoke bottomed out and then pulled back a certain amount
 
kursplat said:
that's why you should ask the place making it how they like it measured. everyone i've ever talked to want's the yoke bottomed out and then pulled back a certain amount
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Well, I haven't made it to a shop just yet to fab a DS for me. I was just thinking of shopping around for the correct length to avoid having anything cut down. I know the length that is specified for my build, I'm just wondering how close I need to be to that number for it to be acceptable. Thousandths of an inch? 32nds of an inch? 1/4 inch?
 
Righty Tighty said:
Well, I haven't made it to a shop just yet to fab a DS for me. I was just thinking of shopping around for the correct length to avoid having anything cut down. I know the length that is specified for my build, I'm just wondering how close I need to be to that number for it to be acceptable. Thousandths of an inch? 32nds of an inch? 1/4 inch?
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check. call a couple and ask. off hand i'd go with install yoke all the way, pull back 1/2" and measure
 
The point is. There is no one correct answer. If your running a leaf spring set-up you really want to make sure you have minimum clearance right. If you running a 4-link or maybe cal-tracks you could probably fudge the maximum length a bit. You really want to make sure you have the vehicle at build weight and at ride height.
 
I hope all you stuff is "dead stock", because if anyone has changed out the trans or the rear end the length may not be correct???
 
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Blind Squirrel said:
The point is. There is no one correct answer. If your running a leaf spring set-up you really want to make sure you have minimum clearance right. If you running a 4-link or maybe cal-tracks you could probably fudge the maximum length a bit. You really want to make sure you have the vehicle at build weight and at ride height.
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Check. I have looked up some charts that had the correct length, so I assumed that would be THE length. I wasn't sure how rock solid that number was.
 
Personally, i would worry more about one too long much more than too short. Too long will be difficult to get in place (getting the rear u-joint in place) and risk bottoming out on the trans. To specifically answer, 1/2" short wouldnt bother me at all, 1/4" long would.
 
A few things to keep in mind. If you have a "monster" and whether motor plate or rubber mounts, that engine / trans can MOVE some. So allow "some extra" for bottoming. And under accel, the engine will move back and the torque will force the rear axle forward. So you need some clearance "fudge."

On the other hand you don't want it so far back that it's leveraging on the splines or part way out of the bushing.
 
Righty Tighty said:
Check. I have looked up some charts that had the correct length, so I assumed that would be THE length. I wasn't sure how rock solid that number was.
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Charts like these are created for a broad range for fitment. You wanted to know how much fudge factor you have from that base line. I believe you have been provided enough information to think about and make an educated decision.
 
To answer your question: the driveshaft (from stock length) can vary from 1/4" long to about 3/8" short from stock length. If you have any old D/S that you can cut up (like I have done) you can install the yoke (with u-joint) and then install the u-joint on the rear end and get a real good idea measuring from the center of one u-joint to the center of the other. If you don't have a junk D/S then you'll have to depend on a chart (they are out there) to find you correct length. Or you can ask for an FABO member, who has the same body and engine/trans/rear end set-up as yours?
 
You need enough play to be able to clear the rear yoke when installing/removing the driveshaft (with the car at normal ride height). And that's roughly about an inch.

Too short of a driveshaft can cause vibrations easier as the transmission yoke is a little bit further out of the bearing in the transmission tailshaft.
 
I got lost reading that crap online. I asked the shop making the 'shaft and they said "Just measure X from center of rear joint to center of front joint with the front yoke shoved in all the way"

They did all the math after that.
 
Thanks everyone. According to the charts I’ve looked up, I need a 49.27” shaft. That seemed very specific, so I was just wondering if I needed to hit that number exactly, or if there was some play. I appreciate all the input as always.
 
Id say just short of bottoming out at minimum position (rear end squatting to the snubber)/ I have one that sticks out about 1.125 inch at rest but the 904 yoke is like 7" long so I feel this is OK.
 
kursplat said:
so 49 1/4", but just a guess until you measure :D
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Haha, I’m not exactly a mathematical whiz, but yes I’d say you’re pretty darn close!

BUT...this proves my point. Twenty thousandths can be like a mile, or twenty thou could not matter at all. See what I mean?
 
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