1974hellarust Posted January 19, 2016 Report Share Posted January 19, 2016 My rear u-joint just went out for the second time and I am looking to put an all new straight shaft in. I don't know exactly how low my grow is but the rear is nearly as low as possible without c notch. I had the truck jacked up from one side and used a large piece of pipe and it looked like it would fit but the suspension was not fully compressed. 1 Quote Link to comment
Draker Posted January 19, 2016 Report Share Posted January 19, 2016 I think you'd find that if you put in a one piece drive line, your U-joints would still go bad. Check the pinion angle on the diff. The truck is lowered.. so drive shaft angles are probably all out of wack. 1 Quote Link to comment
1974hellarust Posted January 19, 2016 Author Report Share Posted January 19, 2016 Yes I was thinking the same thing but since it is lowered wouldn't that make diff to trams shaft straighter? Oh and any suggestions on how to fix the angles? 1 Quote Link to comment
datsunaholic Posted January 19, 2016 Report Share Posted January 19, 2016 Wedge blocks. You want the ANGLE of the transmission output to equal the angle of the diff input. They don't have to be pointed right at each other (and in fact should not, as that causes even more U-joint wear). 1 Quote Link to comment
G-Duax Posted January 19, 2016 Report Share Posted January 19, 2016 It may not be the angle. If you had the shaft apart in the center, and you not get the 3 u-joints indexed properly, the shaft will kill u-joints very quickly. They have to go back together exactly like they came apart, or the rear shaft speeds up, and slows down every half turn. Always mark the center flanges so they are indexed correctly. 1 Quote Link to comment
Rick-rat Posted January 19, 2016 Report Share Posted January 19, 2016 Was the carrier bearing raised when the rear of the truck was lowerered? 1 Quote Link to comment
distributorguy Posted January 19, 2016 Report Share Posted January 19, 2016 The carrier bearing will knock out U-joints as fast as not having the driveshaft assembled properly - ALL u-joints cups at 90 degree increments, not one tooth off. 1 Quote Link to comment
1974hellarust Posted January 20, 2016 Author Report Share Posted January 20, 2016 You guys have brought up a couple good points I didn't know about. Yes I did have the drive shaft apart before and no i don't know about indexing the drive shaft. Never heard of it. I'm not 100% on the whole angle thing neither. If any could help with the angles and things that would be great! 1 Quote Link to comment
Draker Posted January 20, 2016 Report Share Posted January 20, 2016 Start researching these two things. If that doesn't fix it.. get your shaft balanced. Was the carrier bearing lowered when the rear of the truck was lowerered? Wedge blocks. You want the ANGLE of the transmission output to equal the angle of the diff input. They don't have to be pointed right at each other (and in fact should not, as that causes even more U-joint wear). 1 Quote Link to comment
Pacific coast Datsun Posted January 20, 2016 Report Share Posted January 20, 2016 Raise the carrier bearing assembly & that will help a great deal. Did it on my 74 620 years ago when i bagged the rear & it was a pretty basic mod. I raised mine 1 1/2 inches using a piece of square tubing & longer bolts. 1 Quote Link to comment
kelowg Posted January 20, 2016 Report Share Posted January 20, 2016 One piece works fine. As long as u r at ur final ride height(low as u plan goin). But angles r most important thing. Shim u trans if need b and angle blocks on the rear. My 521 has been running one for 5-7 yrs with no issues. 2 Quote Link to comment
1974hellarust Posted January 20, 2016 Author Report Share Posted January 20, 2016 One piece works fine. As long as u r at ur final ride height(low as u plan goin). But angles r most important thing. Shim u trans if need b and angle blocks on the rear. My 521 has been running one for 5-7 yrs with no issues. Perfect! This is exactly what I needed to know! What's an ideal angle for a car with a straight shaft would be my next question? And what's the best way to adjust the rear block angle and measure the angles? 1 Quote Link to comment
datzenmike Posted January 20, 2016 Report Share Posted January 20, 2016 The carrier bearing will knock out U-joints as fast as not having the driveshaft assembled properly - ALL u-joints cups at 90 degree increments, not one tooth off. The carrier bearing only supports the rubber isolator, but the yoke and flange in the end of the front driveshaft is splined and held on with a nut. This needs to be marked carefully so it goes back in exactly. The 521 has a slip shaft that you must be careful to keep the front and back U joints lined up. Otherwise you can't assemble it wrong. All flanges are a rectangular bolt pattern so no way you can get the U joints 90 degrees to each other. You could have the front and rear drive shafts 180 to each other but the U joints are still in alignment.... but IF you were to notice a vibration just unbolt the front from the back just behind the carrier support and rotate 180 and bolt it back up. 1 Quote Link to comment
1974hellarust Posted January 20, 2016 Author Report Share Posted January 20, 2016 The carrier bearing only supports the rubber isolator, but the yoke and flange in the end of the front driveshaft is splined and held on with a nut. This needs to be marked carefully so it goes back in exactly. The 521 has a slip shaft that you must be careful to keep the front and back U joints lined up. Otherwise you can't assemble it wrong. All flanges are a rectangular bolt pattern so no way you can get the U joints 90 degrees to each other. You could have the front and rear drive shafts 180 to each other but the U joints are still in alignment.... but IF you were to notice a vibration just unbolt the front from the back just behind the carrier support and rotate 180 and bolt it back up. Oh crap! I didn't mark the splines that go into my transmission... What do I do now? 1 Quote Link to comment
kelowg Posted January 20, 2016 Report Share Posted January 20, 2016 http://m.summitracing.com/parts/upi-3007?seid=srese1&gclid=CjwKEAiA2ve0BRDCgqDtmYXlyjkSJACEPmdwk_o3tTb-1fRqhr1LS-6oERccXOgLj3eV5wf_etNwlhoC0cvw_wcB 3 Quote Link to comment
Pacific coast Datsun Posted January 20, 2016 Report Share Posted January 20, 2016 Heres how mine came out..keep in mind i made a new crossmember that sits above the frame [truck is bagged] but feel free to copy this setup. Cost about $10 & a few hours under the truck... 1 Quote Link to comment
datzenmike Posted January 20, 2016 Report Share Posted January 20, 2016 Oh crap! I didn't mark the splines that go into my transmission... What do I do now? You don't have to do anything. The splines into the transmission do not apply. Only if you disassembled the front driveshaft to replace the carrier bearing would you have to worry about any splines. Quote Link to comment
distributorguy Posted January 20, 2016 Report Share Posted January 20, 2016 There are splines at the carrier bearing you need to worry about. Quote Link to comment
1974hellarust Posted January 20, 2016 Author Report Share Posted January 20, 2016 You don't have to do anything. The splines into the transmission do not apply. Only if you disassembled the front driveshaft to replace the carrier bearing would you have to worry about any splines. There are splines at the carrier bearing you need to worry about. Ok then I didn't see any splines when I took it apart but thanks! Quote Link to comment
distributorguy Posted January 20, 2016 Report Share Posted January 20, 2016 I only know because I assembled mine off a tooth. :crying: Quote Link to comment
1974hellarust Posted January 21, 2016 Author Report Share Posted January 21, 2016 Just to let everyone know I put the straight shaft in and everything looks great! If I have any problems I will update. Quote Link to comment
G-Duax Posted January 22, 2016 Report Share Posted January 22, 2016 This is interesting. Does the driveshaft contact the hole in the crossmember when you jack it up ? Quote Link to comment
Draker Posted January 22, 2016 Report Share Posted January 22, 2016 More importantly.. how long until the u joints fail. If the angle is off, the issue will re-emerge over time. If that was the issue the first time. Quote Link to comment
G-Duax Posted February 11, 2016 Report Share Posted February 11, 2016 Hellarust, any updates? Any sign of the driveshaft hitting the crossmember? Quote Link to comment
red13 Posted February 11, 2016 Report Share Posted February 11, 2016 I seen a 620 at the junkyard with a straight shaft Quote Link to comment
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