Hi,
I picked up an 88 rx7 from my neighbour last year and i love it, except for the fact that there's this crazy loud vibrating noise coming from somewhere in the back. The neighbour said he just turned the radio up louder and ignored it :p but its finally starting to get on my nerves! Unfortunately I can't figure out what it is; we swapped out the driver's CV shaft on the weekend thinking that was it and the noise didn't change, so we replaced the passenger one with the one newly removed and the noise *still* didn't change, so we're running out of ideas here
Here's what I know:
- noise is not related to engine speed
- kinda like a low growling when slow, and really loud when going above 75km/h
- can't distinguish what side its coming from, kinda echoes in the cabin n:
- not the tires (put some winter ones on last year) but kidna has that 'bad tire' sound to it
- noise diminishes significantly when turning right at high speed , increases slightly when turning left at high speed (?????)
- unlikely to be the CV shafts (as per experiment described above, but i guess they both could have been bad? i figured I would have noticed after replacing one with a new one?)
- don't think its the driver side bearing... turned the hub when the caliper/rotor & shaft were out and didnt have any play at all, and didn't sound like it was grinding or anything. definitely not the front bearings since I replaced those last year (could hear the drivers side one scraping when the hub was turned)

my dad suggested the U-joints on the drive shaft but wouldn't that be the same regardless of whether I was turning left or right?
The only thing I can think of is the passenger bearing, will be checking that one this week. Is there anything else that fits the given description? Is there any other information that would be usefull in diagnosing the problem??

Thanks a bunch,
Dan

 

I'm with your dad on this one. Check the U-joints before you're stranded on a hill.


Good post.

 

While driving, changes in bearing noise can be evident with slight left or right steering pressure as weight transfers. This shift in weight from one side or the other can be an indicator as to which bearing is bad. When the weight is increased on the bearing, the noise increases.

Sounds like your drivers' side wheel bearing is bad. Don't be afraid to check front wheel bearings too. Noises can transfer around in cars and make you hear weird things.


It *could* be a bad U-joint, but not likely. They do seem to go bad quite often in Rx7's, but I'd think that the noise would not change while cornering if it were a bad U-joint. Nevertheless, you should check it out just to make sure. The driveshaft is easily removed, and checking the U-joints is as easy as verifying they move freely without excessive play.

If they're bad, check out Rockford Driveline for replacements. I did mine Friday night and am very pleased with the outcome. I'll warn you that grinding the staked metal takes some time and patience.

 

but the noise will change if he goes around a corner at a certain speed. If he slows down for the turn then the joints won't make the same sound as if he were going straight. Either way, he should look at all these things before buying anything else.

 

Dad was right; we got the car up yesterday and sure enough the front joint was noticeably loose. Got the shaft out last night (without taking the exhaust off even tho the shop/haynes manuals say to!) and ordered the bearings. I found the instructions on how to replace them yourself, but initial attempts at smashing the bearing out didn't amount to much... Just to make sure, the idea is to support the joint itself (not the bearing cap) on the 7/8" socket, and get the push the bearing "through" the socket by beating on the top of the bearing?

I'm still totally baffled by the fact that the sound became a lot quieter when turning right... i was convinced it was going to be something on either side of the car, not right smack in the middle!


heh, thnx. I hate reading moronic posts so i figured i'd at least do *some* homework before I write one


DD

 

Just replace it. You can find NA Driveshafts easily. Are you trying to rebuild the bad Ujoint?

 

Yeah, that was the plan... Not a good plan? Figured i'd do both joints since they are both original, the other is probably a few weeks away from death!
I didn't really think to look around for the entire shaft, but i guess that's an idea. I'll chk a few places, since I haven't payed for the bearings yet Most of the wreckers around here don't have an aweful lot of Mazda tho, and I'm certainly not going to a pick-your-own place in the middle of winter

 

well check the FS sections and your local sub-forum. Look for anyone in your area selling/parting out a 7. Inspect it to make sure it's in good shape and just replace it.

You actually have to modify it DS in order to replace the U-joints and it's better left for a shop to do since they are not supposed to be rebuildable.

so your options are:

Buy the Mazdatrix.com one that comes with rebuildable U-joints for future repairs.
Buy another used one
Buy a new stock one
Have a shop modify your DS and change the U-joints.

 

I had neither time nor patience so I dropped the shaft & X-bearings off at the machine shop yesterday!
It'll be nice to finally put that problem to rest for sure!!

Thanks for everyone's input
Cheers,
Dan

 

Well, f**k me... it wasn't the U-joints after all!!??! Although the front x-bearing was definitely bad (and I ended up just replacing both anyways since the chances of the rear one going soon were probably pretty good), the sound is *still* there, and hasn't changed a bit
My dad was nice enough to take the rear passenger hub off last night, but the bearing doesn't seem bad to him or me... It's not loose or grinding or anything. It's not absolutely quiet tho, kinda sounds like 2 sheets of paper rubbing together. Does that mean it's bad enough to warrant replacement anyways? Am I missing somthing? What do you guys do to check for bad bearings?

Either way, I'm running out of moving parts to replace... so far i've done:
- all 4 tires (last year)
- all front bearings (last year)
- driver's side CV shaft (it seemed fine, so we...)
- put old driver's CV shaft into passenger side (it had a loose bearing, but just barely)
- both x-bearings in the drive shaft

So I guess I should have the rear passenger bearing done, but I'm **** out of ideas after that tho (other than driver's bearing i guess)... I'm not going to call myself a car expert by any means, but doesn't my list pretty much cover every moving part in the car except for the tranny and diff? (*gulp* and *gulp* ) It's ground speed related, so i'm tempted to rule out the tranny for now (not that I would replace/rebuild anyways... i'd just live with it till it died!), and i don't imagine a diff would "growl" like that... If the sound had changed sides when I swapped the driver's CV to the passenger side i'd for sure would have replaced that shaft too, but it didn't, so I didn't.

So, bearings are the likely culprits i guess?


Thanks again,
Dan

 

check and see if u have any fluid in your diff if its running dry its will deffinately grind

 

Checked, and she's right up full...

 

I have a friend with exactly this trouble, he has replaced everything but the differential. After replacing the axle shafts, hubs/wheel bearing, driveshaft and tires, the car still makes the noise. we are afraid it is the diff, especially after we went for some hard accelerations and it was worse (1990 TII).

 

Well, after all that, it turned out to be the passenger side bearing after all.... Once I brought the hub into the machine shop and the guy cleaned it all up it was obviously fucked.
Not that those other things didn't need to be replaced at some point *anyways*, but i probably could have held off a bit and spread out the spending! Oh well... It's done now At least when it comes time to sell I can say that all this work's been done and maybe get an inkling of the $$ back!
Moral of the story: No play != good bearing :p I wonder if one of those mechanic's stethoscopes would have helped pinpoint the problem?

Thanks for all the tips,

Dan

 

hey, at least now you know you can spend $$ on "Go-Fast" mods and won't have to worry about thhese things breaking on you while moving.

 

"crazy loud vibrating noise from rear" .... hmmm after the noise, does it smell like gas? If so, I'm going to have to say someone has gas? Also known as someone farting. Not sure if thats in the FAQ or not though. Normally a quick change in diet will fix it, but I think mazdatrix has some plugs for cheap also.


hahah sorry couldn't resist.

 

I've been having the same vibrations as you, thinking that it could be the bearings, but spending money else where. When I have my car on jack stands this weekend, I will definitely check out those bearings.

Glad you figured it out.

 

Yea i also have been having a vibration at about 25-35mph. It clunks though when you let the clutch out so im pretty sure its the mount. I will also be checking my bearings though. Glad you figured it out.

 

lol i have the exact same problem and i have replaced literally every moving part other than the engine itself and the differential. swapped the trans, new clutch and related bearings, new front wheel bearings, new u joints on the (now modified) driveshaft, 3 sets of wheels and tires, new rear axle on the side that vibrates (i only just found out that the axle is actually whats vibrating) and it STILL vibrates after the new axle so the only possible thing left is to do that wheel bearing, and if that doesn't work then it has to be the diff....i have one sitting in the garage all cleaned up and ready to go in but thats a pain in the *** to do on your daily driver in the back alley because you have no garage. this has been driving me crazy for like a year now

 

clunk from rear after shifting is definitely the front diff mount.