I swapped out an aftermarket driveshaft from my parts 85 SE into my DD 85 SE. I also changed the diff fluid w/ royal purple while I was under there. I took it for a spin but before I got the the end of the driveway I had to go back because of the vibration noise. It sounds like its from the rear and seems worse in 1st than reverse. I drained my fluid last night from my lsd but didnt fill it for # 12 hours until I could make it to the store. The fsm said to mark how your old driveshaft was orienteed so it would be balanced when put back in. But I put in a NEW one??!? I oriented it the same as the old one (mark I made corresponds to 1 of the 2 nuckles on that side. Should I flip it to the other one? Take it to have it ballanced? Any ideas? This sucks! It sounds worse than my orig one which was almost ready to pop!
thanks--
--Erik

 

What oil rating does the royal purple carry.

It sounds like the parts car driveshaft has a bad universal joint.

 

If the U-joints of that aftermarket driveshaft are good then next step would be to get it balanced.

 

I'll check on the oil weight but it was gear oil with lsd additive. since it was the first fluid change in prob 100k I dont think that would kill it!!?! The drive shaft was a nearly new aftermarket one from mardatrix (still had stickers on it) and the joints moved nicely with no slop (my old one was BADDDDD). Im leaning towards balance and will try moving 90 or 180 degrees from where it bolts to the diff to see if that helps. Otherwise I'll prob have to tow it to be balanced since I dont think its safe to drive over 10 mph!!

 

Take the drive shaft out to take it to be balanced, they'll need it out anyway.

Fluid change shouldn't break it but it could highlight a issue covered by the old crap,

Before you do take the shaft out try jacking the rear and running it in gear whilst on stands, it may reveal the problem.

 

The oil I used in my lsd was 75w90 weight. I'll see if I can figure out anything more with the rear jacked up and spinning (in the AM). It'll suck if I have to pull it out again but at least its a quick job. Its a whole chapter in the FSM but its only 2 pages!!

thanks --Erik

 

NP GL let me know I'm curious now....lol

 

I have a friend that works at a driveshaft shop. I asked him about replacing the supposedly "non-replaceable" u-joints. He said they had done several Rx-7, and in each case the owner was never really satisfied due to varying degrees of vibration. It didn't matter how, or how many times they rebalanced the driveshaft it was never quite right. He advised me to bite the bullet and buy only an original driveshaft and said he would prefer not to do mine.

I have no personal experience with the mazdatrix shaft, but far as I know they replace the "non-replaceable" u- joints.

 

Morning turned into 9:30 at night (I have a 3yr old and a pregnant wife) but I fnally got it jacked up and assured myself it wasnt gonna come flying off the jack stands (4) when I rev it. I undid the heat shielding since it was hitting pretty bad near the trans. one the suspension unloaded. I reved it up in gear to about 6,500 and the most obvious noise is a grating that seemed to get a bit better as I ran it but never went away. I'm gonna check my diff fluid level (I added ~ 1.7 quarts per FSM) and take it for a gentle spin to see if it gets any better. Should I put any grease on the u joints?

"I have no personal experience with the mazdatrix shaft, but far as I know they replace the "non-replaceable" u- joints."

Are you saying the mazdatrix ones are a refurbished part? I didnt buy it so I cant complain but if true thats interesting. My replacement driveshaft lacked the part that looks like a protective collar where it meets up with the tranmission (circumsized!?!?). I do know the joints are replaceable on the one I have.

thanks alot!
--Erik

 

BTW as a scientist I should know by now to only change 1 thing at a time so I know what caused my problem!!!

 

If you were just backing out of the driveway and had a vibration, it may not be a balance issue. That rarely, if ever shows up at low speed. Recheck the mounting of the shaft at the diff, it may not be seated correctly. Also check the torque of the mounting bolts.

 

I just got back from a short drive and I think my noise was a combination of a rubbing heat shield and my diff being toast and needing a rebuild. The grating sound lessed now to the point where it sounds like a slightly stuck brake pad (which I checked!). If anything the sound disapears at high speed (or at least engine noise drowns it out).

I'm going to reattach my heat shield tommorow and start saving for a diff rebuild which looks pricey from what i've seen of the clutch prices it looks to be about 450$ in parts!! Am I looking to be left on the side of the road if I continue to drive w/ a bad lsd? I have a 2nd vehicle but I prefer the 7...

 

If it's the clutch packs that are worn, you won't get left stranded, you simply join the rest of the one wheel wonders out there. On the other hand, if it's a brearing, that needs to be addressed asap.

 

No idea if Mazdatrix are refurbished. Their website does says the joints are changed over to a replaceable type. All I was trying to bring to your attention was what my friend said about them not really having success swaping out non-replaceable units for replaceable ones.