cut and re weld center cv shaft section safe?

[briann510]

I have shortened driveshafts before on 1000hp race cars but how bout a cv shaft center section? Is it wise to cut and re-weld the center shaft portion of a cv shaft?

[zcarnut]

I’ll warn you in advance. The CV axles are extremely hard. Even cutting them apart will be difficult. Welding such material is not for an amateur. Hardened steel is more likely to lose its strength (and hardness) during welding and you risk introducing cracks in the axle due to the heat of welding. Driveshafts are made from a different material, and are far easier to modify.

 

I decided to drill only ¼ inch into a set of CV axles for a roll pin to secure the tripod bearing. I did not trust the “swegged†method used in the 280ZX turbo CV axles. (The Z31 axles went to a much better “snap ring in a grooveâ€.) I got it done, but I ended up breaking two $75 hardened drill bits in the process.

 

The CV axle inner joints can be re-built. I have done several sets. The inner boot metal band must be cut off to remove the inner boot. Tip: The FSM tells you to cut it in the wrong location!

 

You need to cut the band just over the top of the o-ring groove. This will cause less damage to the tripod housing (which must be re-used). You get a new o-ring in the rebuild kits (I use Beck-Arnley) so you can cut into the old o-ring without worry.

 

To install the new boot I make four pairs of saw cuts (about an inch apart) around the perimeter of the top of the band. These “tabs†are then pressed (or hammered) down, securing the inner boot. The exposed groove is then filled with RTV. It helps to have a hydraulic press to clamp the assembly down while you are bending the tabs.

 

If I ever re-build any more CV axles I will first make a collar on my lathe with a tapered inner surface that fit over the band. Then with a press I hopefully will better able to duplicate the factory method and its appearance.

[VinhZXT]

Brian,

Why not just take the center section to a machine shop and let them cut the 1 end and remachine it? Sound like a safer solution.

[briann510]

It looks like the cv axles are runined now from attempts to seperate the inner ends from the shafts and Im not buying 2 more cv axles, im throwing the halfshafts back in and chalking it up to a bad week.

 

Thanks for the explanation on where NOT to cut the metal band. So im curuous though, once the band is off how does the inner end shaft seperate from the actual diff stub section? Is it pressed? peened?

[zcarnut]

Why not just take the center section to a machine shop and let them cut the one end and remachine it? Sound like a safer solution.

 

Good idea, but it won't work. The splined sections have a slightly larger OD than the shafts and make a gradual taper into the axle shaft. This reduces stress where the splined section meets the smooth axle. Standard "good engineering" practice.

[zcarnut]

... So im curious though, once the band is off how does the inner end shaft seperate from the actual diff stub section? Is it pressed? peened?

 

Actually it is the boot band itself which holds everything together! The boot band has an inner lip that prevents the tripod bearing from leaving the inner housing. Since the boot is made with the band, you can't change one without changing the other.

 

Definitely not designed for easy disassembly. BTW, the 1981 and 1982 280ZX FSM says that CV axle disassembly is not possible and that the entire shafts must be changed. However, the 1983 280ZX (and Maxima) FSM does have the CV axle re-building instructions.

[VinhZXT]

Zcarnut,

How long is the spline at the outter end of the center shaft? If the spline section is long enough then I can cut it 3/4" and machine the end to put the C-clip back on to hold the tripod. Is that how it is designed for the 280ZX CVs?

[zcarnut]

...I can cut it 3/4" and machine the end to put the C-clip back on to hold the tripod...

 

No, it’s not that easy. The tripod bearing is secured by the splines. If you remove 3/4 inch of the splines on the shaft you would need to remove the same amount from the inside of the tripod bearing piece. The spline length is just over one inch long. That would give you only 1/4 of splines to hold the tripod bearing piece.

 

I think you need to examine an actual 280ZX CV shaft in detail before you consider modifying it.

[briann510]

Thanks, not going to be doing that as the cv conversion using zxt shafts has been canned.

[VinhZXT]

Zcarnut,

Yep thanks for the info. I opened up the outter CV and checked and realized I can't just cut it short. Seem like the best way is to cut the metal ring on both CV and swap the shorter center section and weld the ring back on. I just played with my setup the past 3 days and fortunately I don't have a problem. I removed the springs behind the metal cups of the CV and installed the CVs on the car. Then I checked to see how much movement of the center shafts (sliding it back and forth) and I got about 1/2 inch. I ended up cutting those springs a little shorter and that helps putting the metal cups and springs back on a lot easier.

 

Brian,

Sorry to hear that you have to go back to the Ujoint axles. Don't throw the CV out just yet.

[blueovalz]

As best as I can recall, I pressed the inner race off with a press. I recall that the ends of the splines were peened. Pressing the inner race off straightens out the peened splines, and once I re-installed the inner race, I simply re-peened the ends of the shaft (near the splines) with a centerpunch.

 

And to answer the original question, no. I've only seen two attempts at welding the axles to shorten them. Both were on very light cars (Formula v and ford) and both failed, the on that lasted longest, lasted about 1 1/2 seasons and it's short success was owed to a 1/4" thick sleeve welded over the butt weld, which helped a lot.

[briann510]

Oh I could easily mod the cv shafts now that I have them apart but I just dont feel like messing with them anymore plus I already have the halfshafts being rebuilt and have no problem using those and I seriously doubt they will ever break or give me problems.

 

It was an interesting learning experience thats for sure and if I had to do it all over again I wouldnt..LOL.

[zcarnut]

Don’t give up on the 280ZX CV axles completely, Brian.

 

I think the easiest solution to the shaft length issue may be in the CV-axle-to-companion-flange adapter design. The reason that the adapter has to be so thick (at least an inch) is because of the protrusion of the spring holder on the sheet metal grease shield cover.

 

If you use the Z31 grease cover you can make the adapter shorter (maybe three-quarters of an inch) or if you have a flat cover the adapter can be even shorter. A flat cover could be easily constructed by hand and glued to the outer CV axle housing.

 

Speaking of the pre-load spring, I recall someone on another forum who removed the springs altogether. Apparently without problems(?). He concluded that since the free-play range (on his axles) was so small the spring did not serve any useful function.

[VinhZXT]

Zcarnut,

"Speaking of the pre-load spring, I recall someone on another forum who removed the springs altogether. Apparently without problems(?). He concluded that since the free-play range (on his axles) was so small the spring did not serve any useful function."

 

I don't think this is a good idea. If the spring is not there the center shaft can slam to the grease cover when the car goes over bumps. Eventually it will hit the nut on the stub axle. I actually did removed the springs on my car and then I thought about it I cut them shorter and put them back.

Vinh