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300zxt cv conversion problem (on a 72 240z)


getZ

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I'm still thinking that a good relatively easy solution for this might be to switch the mustache bar around and move the diff forward a couple inches. The CV's should handle the misalignment just fine. I'm hoping this is fairly easy to do with a Ron Tyler diff mount, and then the only real mod necessary is shortening the driveshaft.

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Jon - that's not a bad idea to keep in mind. At this point now I have a plan C.

 

I did get the driver side in tonight and I think it's going to work. I moved the swing arm up through its range and was always able to move the axle away from wheel side at least a mm at every point, but oddly enough the amount I can pull it away from the wheel never changes either, no matter how high or low the swing arm is.

 

The weird part is my Rock Auto CV which measured out on the short side does not work. It's too long. I guess I need to remeasure the shaft length and not include the splined end. Then again, I can probably do what I did on the driver side. Take the end cap off and grind down the stub axle an 1/8 of an inch. The dremel tool works great. It never put enough heat into the axle to where I couldn't touch it. Of course it took a half hour to grind down an 1/8, but it didn't bother me.

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I was able to find the 300zxt Shaft info.

 

cvspec.jpg

 

from my measurements if I add the 3/32nds of the boss on the outer mating flange to it , the short shaft is the same within a 1/32nd , but the long shaft is an 1/8th longer.

 

 

 

getz , Are you testing with the endcaps on or off now?

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78zlt1 - I was measuring with the end caps on. I wish I bothered to look at this last night or I would have measured the way Nissan has them speced out.

 

I put it all back togther last night and I realized the only way to check if you are going to have pressure from the cv on the pumkin is to simply wiggle the cv in and out. You can't check for any real movement because the shafts click into the pumpkin and the only play you feel is the snap ring on the spline going into the pumpkin. In any case both ends now fit with "wiggle."

 

It did not take much to create the gap I was looking for. A quarter inch of clearance at the axle translates into almost two inches at the strut tower.

 

Just for the archives, this is my setup: 280z control arms, mms axles and companion flanges, 88 300zxt cv on driver side with bearing cage flipped, 88 300zxt cv (rock auto) on passeger side with bearing cage flipped, no end caps on the cv (gains you an 1/8 inch of clearance) and 1/8 inch of the threaded end of the axle grinded off. There are still a 2-3 threads left on the axle, so it shouldn't be an issue. One more thing, I also have 240z spacers between the rear wheel bearings. Fill the axle end up with grease and put the whole thing back together. I was going to put a little gasket sealer around the axle to the cv connection, but I forgot.

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  • 3 weeks later...

After replacing my remand CVs with a set of OEM units I have had no problems at all and the gear oil is free of any metal bits. I will try and have the remand set redone to the same size as the OEM units once I put my Z up for the winter.

 

Do Not use a left side remand CV without checking the length!!! It could cost you a ring set and some bearings.

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After reading this thread and checking clearences on my little project (R200 3.90 w/Quaife, MM billet z31 CF adapters and z31t cv axles with cages reversed). I'm not comfortable with the possibility of binding on the passenger side either so I'm thinking about springing for another rebuilt drivers side shaft. Am I correct in my understanding that I will be able to pull the boot off the inner cv, secure the shaft in a vise and give it a few knocks with a bfh to pop it off a circlip? Do the same with the passenger side and swap the inner cv inputs around?

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  • 9 months later...

I too am undergoing the same dilemma. I have a pn of 6083 for the driver side shaft and 6084 for the pass. side shaft. The 6083 fits great in both sides. Locks in and all. The 6084 fits on neither side. Just about 1/8" too long. Not sure, and I need to physically measure, but I could swear both sides on my 73 are the same length from diff to MM companion flange. In reading this post however, BOTH my shafts have the same input shaft size. They both look like the "long" 3.875" shafts. Could be the place I got them from gave me two of the same side shafts. I don't believe they go to the detail that we do to measure cores and know what side is which. My shafts ARE two different lengths with the cages flipped. The 6084 is about 1/4" longer. I will have to measure the input shaft length tonight. Anyone have any more solutions? I'm trying to find some OEM shafts (the CV rebuilder I got mine from swears they're reman OEM parts and not the Chinese units) and am having no luck. They say I got their last pair.

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OK - I found a set of OEM units on an 87 Turbo. They are indeed the stock shafts. I pulled them both myself and labeled them. Measured up to the reman shafts I have and they're the same. I got the driver side in no problem. I took the advice of an earlier post and jacked up the passenger side rear suspension. The shaft did finally drop in place. I did not jack it up to put the full weight of the car on it, just enough to get the shaft in place, so I DO have a little more upward travel in the rear susp. that will occur with the car on the ground and on its' own weight.

 

I too, am a little concerned about the lack of free play in the side to side motion of the shaft. I sent e-mail to Modern Motorsports asking what the trick was to get the pass. shaft it. NO reply after 4 days. I said "surely you didn't have fitment problems when you did this conversion yourselves and started manufacturing the companion flanges?" Nobody can seem to get this one right! Has anyone spoken with anybody at MM about this issue? Sure - they tell you how to flip the cages, but they don't say anything about the shaft install. Curious if anyone's gotten advice directly from them about this. After all - it IS their conversion that they sell.

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Perhaps the best way to insure that there is enough free play in the CVs at full suspension is to trim an 1/8-inch off the MMS companion flanges. They are beefy enough to allow for a slight trim.

 

Once I put my 240 up for the winter I will be doing just that.

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Yeah - I hear ya. But the one thing that ticks me off is they tout this as a "bolt in" conversion, and I've seen nothing but folks having problems with it and having to modify this or that to get it to fit. Bothers me even more that they won't reply to a simple question (e-mail) that should have been answered BEFORE they started marketing this product. Gnosez - so, you're saying that with the OEM shafts - the correct driver and pass. side ones - you've not encountered any further issues? I still don't have a motor in mine yet, so I'm curious if you - or anyone - has run this setup (now that you have OEM shafts) and encountered any long-term problems. How many miles have you put on the new setup with the OEM shafts? Like I said, my pass. side shaft was a bear to get in there - had to compress the suspension to get it in, and I'm worried about the lack of play at full compression and worried that it might damage my diff.

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Yeah - I hear ya. But the one thing that ticks me off is they tout this as a "bolt in" conversion, and I've seen nothing but folks having problems with it and having to modify this or that to get it to fit. Bothers me even more that they won't reply to a simple question (e-mail) that should have been answered BEFORE they started marketing this product.

 

Not everybody has problems. I never got a big enough response to this thread to make an exact call on what combination did not work, but some combinations seem to be fine.

 

I modified my axles by grinding off the the very ends with just enough material for snap ring to still have enough to grab. The snap ring will come off before the end breaks away. I could have gone one step further and machined a grove to move the end stop ring on the opposite side of the bearing cage from the snap ring and that would have gained me another quarter inch.

 

I would be very cautious about having to force the axle onto the stub. I can get mines on without having to compress the suspension. I don't know this for a fact, but I would guess that to tight a fit will put pressure on the ring and pinion. My car really does not see enough road time to tell if there is a problem, but what I had intended to do was get a temperature reading off the diff cold and after running the hard in turns for a while. I have an infrared temperture gun with a laser pointer to test it out. Well...its on my "to do" list anyway.

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  • 4 weeks later...

Hey, I did this on the weekend. I had to move the control arms out to get the half shafts into place, this is after flipping both races. The driver's side was much closer than the passengers side.

 

I rolled the car backwards and forwards after they were installed, then put some people in the boot and did the same, no hopping or skipping or scraping sounds. I drove it around the block and I'll pull them back out this weekend to see that it hasn't punched the covers out.

 

All in all, this is a very half-arsed solution in my humble opinion. I wish I'd known that I was going to need custom axles before the job would be done properly. I will hopefully keep a very careful watch on this as I'm not convinced at all its not going to break something. If I hadn't read this thread I would be sending them back and saying they're broken. (This was with std green axles I redid the boots/grease on myself).

 

Oh, and there is less than half-a-bees-dick between the outer axle boot at the `big-side' and the sway bar mount. Anyone else has issues with this?

 

Dave

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I don't get why so many people are having problems. My shafts go in with no problems. In addition to flipping the outer cage, I too ground a bit of the end of the shaft leaving about 1/8" before the snap ring groove. But even without grinding the shaft, I think they'd still go in. And I am using the dust caps on the end of the joint. Mind you, my adapters were custom made by a friend of mine, who machined off the old flange and pressed, welded and pinned a new CNC'd flange on. But I can't imagine that the overall dimensions of the MM adapters are that much different. Strange...

 

Nigel

'73 240ZT

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Nigel,

 

That is interesting, you don't perchance have specs for the adaptors do you?

Also, you were dealing with the green Z31 half shafts?

 

Dave

 

Black shaft with green cv housings. I'll e-mail my friend and see if he still has the cad drawings...

 

Nigel

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I don't get why so many people are having problems. My shafts go in with no problems. In addition to flipping the outer cage, I too ground a bit of the end of the shaft leaving about 1/8" before the snap ring groove. But even without grinding the shaft, I think they'd still go in. And I am using the dust caps on the end of the joint. Mind you, my adapters were custom made by a friend of mine, who machined off the old flange and pressed, welded and pinned a new CNC'd flange on. But I can't imagine that the overall dimensions of the MM adapters are that much different. Strange...

 

Nigel

'73 240ZT

 

What kind of differential are you running? I used a powerbrute in a 72 and had fitment problems.

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