Anyone else run into this ? Blew up the rear diff in the rx8 ... ok fine , got one from a wrecker for $400 . As im taking the old one out I do the normal checks and find that the u-joints in the d-shaft r gritty as hell and in some spots just simply dead . So i call mazda and they say no u-joints , have to buy whole d-shaft ($1500) ... not happening . So I get on the phones and call some wreckers and went to look at about 6 different d-shafts because I didnt trust the mechanics word that they r good ...... EVERY single one I looked at were all gritty and had dead spots in them and one of the cars only had 53,000M on it . The uni-joints look unreplacable and now I have to put a gritty uni-joint back in and bolt it up to my diff which we all know isnt the best idea as it will strain the gear at every dead spot when its turning which will decrease the life of the diff I just put in there .. Just curious if anyone took theirs to a driveline shop and they replaced them ? to me they dont look replacable . Not everyone is gonna know about this as not everyone drives like I do and work on their own stuff and notice this kind of thing .

 

another foot note , My pinion bearing was TOASTED . I hope it was the clutch drops that took that out and not the gritty d-shaft or it will happen again . gritty U-joint takes out pinion ? which in turn obv takes out the gears

 

I don't know if they're replacable, but you can get whole new aftermarket driveshafts for far less than Mazda's. For example: http://www.mazdatrix.com/getprice.asp?partnum=3191-708A

I think the above price is pretty typical for driveline shops. You probably have one in your area.

 

Yup, I've had one made for an engine swap, they drove out, crawled under my car to measure, and dropped off a new driveshaft after a few days.

Used these guys, but it is worth looking in your area. http://www.drivelinesinc.com/

 

joints are irreplaceable. it happens to almost all Mazda cars.

either go aftermarket or get another new one.

just a note, stock shaft is carbon fiber already so i dont think u will save any weight by going aluminum

 

Probably just a cheaper alternative?

 

That is true.

Mazdatrix has been selling these aluminum shafts with replaceable joints for a long time(not just rx8). It should be ok, I guess.

 

Mazdatrix claims their Al driveshaft is lighter, which made me wonder why the stocker is CF.

Turns out aluminum is rather marginal at 9000rpm in 6th.

http://www.pstds.com/driveshaft_crit...peed_chart.htm

Something called "critical speed." Don't ask me, but I don't like the sound of, "may bend or whip."

 

Good luck pulling 9k in 6th gear ..... the weight of the CF driveshaft as reported in the Tech Forum thread on Stock part weights is lower than the aluminum driveshaft weight shown on the Mazdatrix website. One good scratch or nick in the CF surface and it will come apart too ....

 

Ahh, I was going by Mazdatrix site. So you think the reason Mazda used CF was weight, or just to add a selling point to a spec sheet?

 

Obviously they used a carbon fiber drive shaft to remove weight through the drive train, the RX8 needs everything it can get.

 

I think perhaps Mazdatrix is counting the weight of the shield as well.

Anyhow, I guess for aftermarket it makes much more sense to get an Al driveshaft and spend (a fraction of) the difference on a lighter flywheel.

 

CF is much less prone to bending/whipping and is rated for much higher rpm use. You could hit or exceed a 9000 rpm driveshaft speed in 4th gear with a strong engine (maybe 5th with a really strong engine or rear gear ratio change like the 5.12 Motorsport rear gear), but the Mazdatrix website doesn't state what dia x wall thickness they are using

https://www.rx8club.com/showpost.php...&postcount=155


.

 

That makes no sense. Engine speed / transmission ratio = [exercise left to the reader]

 

Id rather stick with an oem carbon fiber ds instead of an aftermarket one , I just couldnt believe when I seen that the joints wernt replacable . Thats just crazy talk .... its a servicable item and is going to need to be replaced 100% at one point I looked at those AL ones and am not a big fan myself . My car is running good and smooth but the fact that I know there is dead spots in my driveshaft isnt sitting well with me . Gonna try to find a really low km one until I get some with decent u-joints . at 9500rpm id rather not be worried about "aftermarket" design and just have something thats engineered by mazda .

 

as far as I remember all Mazda's RWD cars never had replaceable u-joints, they always want/ask you to replace it.

is it because of a marketing thing (wants you to buy new parts everytime) or safety or whatever? no idea.

There are places that can "Replace" them. but I don't know, if they leave a deep scratch/nick on the shaft its pretty much over.

 

From about 1996

 

Ash try older than that. 2nd gen FC's had to replace the whole drive shaft to replace u-joints.

 

Mazda 929 HBSHE (1995-1997 Production) had replaceable U Joints 0604-89-251A ( from a B- Series truck)...

Much Depends on Model...

AS I said ABOUT!

 

yea ... no replaceable joint for FC, you have to buy a new one, at least that's what Mazda wants.

 

A new joint will go along way unless you continue to beat it and drop the clutch to Rev it at 9,0000RPM

 

Reading this thread I was having the exact same thought.

On the other hand, torque after the transmission transmission ratio...

 

edited: senile retardation moment deleted

 

Once again, you are mistaken. 5th is 1:1, and regarding your backpedaling regarding the involvement of the final drive ratio: LOL.

 

no backpedaling, just senile confusion, you are correct, my (fading) memory was wrong; lol