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Broken JCI driveshaft?


RebekahsZ

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Took car to local hotrod shop to get a driveshaft loop made.  Put car up on jackstands to talk about options and fabrictor noticed cracked paint on the driveshaft tube right where the yolks weld on.  Cracked paint is on both ends.  Any advice?  I did about 40-something passes on slicks this past summer and the car doesn't spin.  Is it time for a new driveshaft?  We have one driveshaft shop in town and I'm not real impressed with how filthy and disorganized the shop is, just doesn't inspire confidence.  What do you guys think? Anybody destroyed a JCI driveshaft?

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Edited by RebekahsZ
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I put the black paint on over JCI's silver paint-I usually wipe everything down with acetone before I paint.  The paint is one coat of Walmart rattle can primer follwed by 2 coats of Walmart rattle can gloss black.  I'm actually thinking of getting a second driveshaft from JCI that is 1/2" shorter (shouldn't I be able to move the driveshaft some axially when I disconnect the driveshaft from the diff)?  I barely have enough slack to install it.  After I strip the paint, can a driveshaft be "magnafluxed" or something to be sure it is OK?

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 (shouldn't I be able to move the driveshaft some axially when I disconnect the driveshaft from the diff)? 

 

After I strip the paint, can a driveshaft be "magnafluxed" or something to be sure it is OK?

 

Yes, there should be some play.  The drive shaft shop should know how long to make the it if you give them the distance from the yoke flange to the tip of the output shaft.

 

You could have it magnafluxed, but only if you can't see the crack yourself.  First try using a magnifying glass and good lighting. You could also try dye/liquid penetrant.

Edited by rossman
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Just got off the phone with Mike at JCI. He wants me to box driveshaft and send it to him. They want to look at it and see if they need a design change or anything. He said they went with a 2" driveshaft due to space limitations in tunnel but we discussed going larger or thicker wall. I'm to measure well to see how much larger I think I can stand. He's gonna shorten driveshaft 1/2" too. There was no hassling or objecting to my issue. We are lucky to have both JCI and JTR.

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Wow, there seem to be a number of variations on this product and I am starting to question what I got now. My JCI driveshaft is 3.5" on one end and 2.75" at the other. Haven't installed it yet so I don't know how it will perform but I also haven't seen anything like this one as it is two tubes, one inside the other. Did I get someone's leftovers?

 

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Get your loop installed #1 priority. #2 Go Moly or AL to lighten that pig up. Nothing like being robbed power from an overweight driveshaft. AL with help on harmonics and allow some flex. Moly will be lighter and stronger than steel since you can go smaller. But without a loop your just asking for a driveshaft to visit you.

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It was when I was having a driveshaft loop made that the cracked paint was found. The driveshaft went in the mail back to JCI on Wednesday.  I'll call on Monday and see if they received it and what they think.  Honestly the construction on that driveshaft look like good quality-I have no complaints.  In the letter I enclosed, I welcomed them to go up to 3", thicker wall tubing or aluminum.  Because the engine sits to one side a good bit, the front yoke is very close to the passenger side of the tranny tunnel, plus, the way my fabricator welded in my driveshaft loop makes things even more crowded.  I think I need to keep my u-joints and yoke the same size as they were, but just find a tougher tube.  It is pretty tight in there-and I still don't even have it filled up with exhaust!

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It was when I was having a driveshaft loop made that the cracked paint was found. The driveshaft went in the mail back to JCI on Wednesday.  I'll call on Monday and see if they received it and what they think.  Honestly the construction on that driveshaft look like good quality-I have no complaints.  In the letter I enclosed, I welcomed them to go up to 3", thicker wall tubing or aluminum.  Because the engine sits to one side a good bit, the front yoke is very close to the passenger side of the tranny tunnel, plus, the way my fabricator welded in my driveshaft loop makes things even more crowded.  I think I need to keep my u-joints and yoke the same size as they were, but just find a tougher tube.  It is pretty tight in there-and I still don't even have it filled up with exhaust!

The 1st post you said you took the car to get one made. I didnt see anywhere you actually had it done after finding the DS was cracked. Just wanted to make sure you went through with the plan.. :icon53:

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  • 2 weeks later...

Got driveshaft back from JCI in less than a week.  John offered me a 3" driveshaft, but I opted for 2.5" due to close clearances in the tunnel-the first one was 2".  It has the same wall-thickness as my old one.  I stripped John's quick paint job off and noticed some welding flux on the welds.  I wire brushed that to remove it (perhaps there was some flux on the welds on my old driveshaft making the paint crack (?) and perhaps it wasn't cracked after all) and wiped everything down with mineral spirits, then acetone.  Anyway, the front yoke looks good, but the rear yoke looks a litte light duty (a lot more u-joint cap is exposed).  I'll ask John about that this week.  It is all painted now and ready to install early this week. I talked to John about the funny driveshaft shown above by boyracer.  He said he has to do Jaguar driveshafts that way, but he didn't think he had ever supplied a Datsun driveshaft that way.  Weird.  I'd contact him if you still haven't installed it.  He's really cool and I don't think he would mind. 

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Got driveshaft back from JCI in less than a week.  John offered me a 3" driveshaft, but I opted for 2.5" due to close clearances in the tunnel-the first one was 2".  It has the same wall-thickness as my old one.  I stripped John's quick paint job off and noticed some welding flux on the welds.  I wire brushed that to remove it (perhaps there was some flux on the welds on my old driveshaft making the paint crack (?) and perhaps it wasn't cracked after all) and wiped everything down with mineral spirits, then acetone.  Anyway, the front yoke looks good, but the rear yoke looks a litte light duty (a lot more u-joint cap is exposed).  I'll ask John about that this week.  It is all painted now and ready to install early this week. I talked to John about the funny driveshaft shown above by boyracer.  He said he has to do Jaguar driveshafts that way, but he didn't think he had ever supplied a Datsun driveshaft that way.  Weird.  I'd contact him if you still haven't installed it.  He's really cool and I don't think he would mind. 

 

Spoke with John and am sending back the two-piece DS for a one-piece, no problem. I like dealing with vendors like that, wish more were like JCI. After checking, the 3.5" end would have greatly reduced any room for an exhaust and was concerned about strength if I put 400-450HP through it. Likely not going to be any more than that, so 2.5" should be ok from what I gather, especially if you are running that in your beast, Keith.

Edited by boyracer
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If you haven't added anything in your tunnel, you could safely go to 3" no problem. I have added some brake lines, some mounting bolts for some things inside the car and I could have done a better plan with my driveshaft loop, so I went 2.5" but I might still have had room to go to 3" but it would have been tight. Also, ask him to use the strongest yokes he can, my rear yoke looks kind of puny.

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Edited by RebekahsZ
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