Bolts for drive shaft

[Tony Radford]

Guys, what is the bolt size needed for the drive shaft connection to the differential? I went through this years ago - I bought a long bolt with sufficient shank to line everything up and had them cut down so as not to interfere with the diff housing. The last time I had my car worked on - standard 5/15" all thread bolts end up in those four holes. I want to put the right stuff in when I re-install my drive shaft.

[spd4me]

I made up a set with long enough shank and cut off ends. I've got one on my bench and I'll check when I get home. Also used a metal self locking nut. I remember it's a fine thread. I did the same thing with my rear caliper bolts.
Bob

[spd4me]

Tony - bolts are 3/8" x 2" x 24 threads. Shank measures 13/16". Not sure how long I cut off but you can use one of your old ones. I remember it's a bear to try to get a box end wrench on to untighten and tighten.
Bob

[scott h]

i seem to remember that the bolts go in better from one direction than the other

[Tony Radford]

Thanks Bob. I'm hitting Ace on the way to work. I'm going for grade 8. I should be able to hack saw through by Thanksgiving.

[spd4me]

They go in with the nut end facing the rear end. You have to turn the shaft to get each one in. Saw them off and twist them on a grinding wheel. I put a nut on first, then saw and grind and twist nut off. If helps to clean the threads.
bob

[Tony Radford]

Thanks. Picked up the bolts and had them cut down when I picked up the drive shaft. I'll have her nailed back together this weekend.

[spd4me]

Tony - double check that the bolts will fit through holes.

[Tony Radford]

I will (haven't yet). They were 5/16" bolts that I removed, but they were a little sloppy.

[weaver]

You should have 3/8" bolts! We use a 1 1/2" long fine thread bolt with no shank.

[Aggressor]

The question is why you would want to use cut-offs or go through the bother when grade 8 full threads work just fine. If there is a difference it is nominal and probably not worth the effort. Aggressor's starting her second 30,000 miles while running fine on shankless.

- Geary

[Glenview289]

Hey guys, a retired engineer here. There is a difference in the shear strengths of a grade 8 bolt at the body diameter and the minor thread diameter, but I personally think we have reached the point of trying to pick fly$hit out of pepper! For those who really want to know, the shear strength of grade 8 bolt material is 91,000 pounds per square inch (lbs/in2). So a 3/8" bolt (.1098 square inches) that has the body diameter going through the shear plane will fail at 9992 pounds. A 3/8" diameter fine thread bolt with a minor thread diameter of .323" (.0814 square inches) with the threads going through the shear plane will fail at 7410 pounds. Don't forget that there are 4 bolts in the drive shaft rear end connection so that would be 39,968 pounds or 29,640 pounds respectively for a total failure. I don't think a failure would occur with either bolt configuration, and certainly if Geary hasn't done it, nobody will. File this info away, you may win a bet at the bar with it! Happy motoring....

Bill

[arrowdriver]

Well Bill, I'm a retired engineer too and when I was replacing the bolts on mine I did cut down some grade 8 ones to keep the shank in the joint. I didn't bother to calculate the shear strength etc but noted that the ones I removed were fully threaded and showed some deformation in the joint area so considering the small cost in money and time I figured it was worthwhile to do what I did. I've seen what happens to cars when the U joints fail and it can be ugly. BTW, I was removing my tranny to get to the clutch as the relief arms or whatever they are called were coming loose causing it to drag when it shouldn't have! Sure shifts well now.