Riggs

I recently had a vibration in the rear of my NA 91. It definitely felt as though it was the passenger side halfshaft, so I replaced it. Now there is still a vibration, but different.

If feels like it may be the driveshaft or a Ujoint. At least thats what im hoping it is. starting around 3k RPM, the vibration starts while in gear and moving, and gets worse from there. As soon as I let off the gas and coast, its GONE. back on the throttle, and there it is again. It also gets worse the faster I am going. There is also a clunk on upshifts, especially into 3rd, 4th, and 5th. I will be letting the clutch engage, and as soon as it does there is a thunk, almost sounds like the trans is hitting the tunnel, but I checked and there is no excessive play in the motor or tranny mounts. The driveline has been taken out (clutch swap when i bought the car), however it was removed before I had the chance to mark its position. Also, is there a specific orientation for the halfshafts? How would I go about determining how these (driveshaft and halfies) should be situated?

Also, there is a bolt coming straight down from the bottom of the gearbox that goes through the transmission crossmember. There is no nut on it (nor was there when I did the clutch swap), but there is some kind of bushing that doesnt look quite the right size... am I missing something important there??
Thanks in advance

RotaryRocket88

iTrader: (7)

You're missing the nut and washer that hold the tail housing to the crossmember. Your clunk and vibration are probably coming from the transmission bouncing around & banging the y-bracket on the crossmember. If that nut isn't there, the rear of the transmission will be free to move aorund. Also the bushing in the crossmember will likely be blown out. Your front diff mount could also be taking a beating from the added stress caused on the drivetrain.

http://www.mazdatrix.com/g3.htm

Riggs

Oh wow... thanks for your help! Looks like I will have to purchase the entire trans crossmember plus the Y blocks and the appropriatewasher and nut (purchased elsewhere), correct?

RotaryRocket88

iTrader: (7)

I would replace the crossmember and the 2 rubber y-blocks. Figure out the size/thread pitch of the stud, and pick up a replacement nut/washer from Home Depot, McMasterCarr, etc...

Riggs

OK. Bushings mentioned were swapped out. the two y-blocks and a new crossmember, and i found a fitting nut.

This has tightened up things tremendously, however there is still the clunk when upshifting and on acceleration from being off throttle, and the vibration starts at 40mph and just gets worse the faster i go. I am wondering if this is a universal joint issue, or a driveshaft positioning issue since it wasnt marked when I took it off to swap the clutch. help!

RotaryRocket88

iTrader: (7)

Considering the transmission was allowed to bounce around, the front diff mount is probably sheared (clunks on harsh throttle input). Vibration with increasing speed suggests the rear u-joint is bad. It's probably been taking a beating as well.

Diff mount replacement: https://www.rx7club.com/2nd-generation-specific-1986-1992-17/pinion-snubber-diff-mount-replacement-convertible-876959/

Troubshooting: http://www.mazdatrix.com/g2.htm

Riggs

awesome info. thanks!!

How much importance does the driveshaft being reinstalled in the same orientation have in this situation? I would hate to replace all this rubber simply to have the driveshaft out of whack and start eating up rubber again.

Already sourced a new shaft and diff with front mount on it.

RotaryRocket88

iTrader: (7)

I think the driveshaft will only bolt onto the pinion flange one way. The driveshaft will be balance anyhow.

Riggs

I will take your word for it and not worry. It would seem logical to me that the driveshaft itself would be ballanced independently of the diff and trans, however I have read in more than one place that it is very important to mark the shaft's relation to the trans output shaft and pinion flange.

Riggs

In case this may help anyone, the issue has been fixed. Turns out the rear U-joint was toasted. I was able to twist the flange that bolts to the diff several degrees in either direction from center, which explains my clunk and on-throttle vibration. car is sillllky smooth now, minus the delrin diff bushing noises, which I have no real issue with at all. If i wanted quiet, I wouldnt have a 7! Interestingly enough, the front diff mount looked to be only slightly worse for wear, seems the U-joint and trans bushings took nearly all the abuse.


As soon as I get all the tools and old open diff out of the back of my car, I will start road testing in ernest.

MeyerMotorsports

Just to check the obvious, have you checked for a bent wheel?

Jcre8te

Riggs did u ever get this fixed?

Riggs

Yeah dude been fixed!! See my last post.

TII_Arekusu

nice

Jcre8te

Thanks I don't even know how I missed that!