Hi guys.

Here we are with a zinger of a question.

As of now, my car drives great but I have a vibration. Let me explain it.

It happens intermittently about 20 mph or so. it is a rotational vibration meaning it's tied to my vehicle speed. It used to only happen around 60mph but it has crept into the slower speeds. Also, at slower speeds the vibration is not as pronounced but at 60mph for example with the top down it will shake the frame of the windshield and the passenger seat bounces back and forth. No sound at any time from the suspension other than the occasional creak if i hit a dip to quickly.

Remember, it's not constant. It comes and it goes. But it's there. Very much so. I had the wheels balanced and it's still there.

My mechanic, who is extremely good at troubleshooting has noticed the bushing on a rear strut is bad. Also, he has seen front wheel drive cars have a bad axle and behave this way but being a rear wheel drive rotary, we are only using theories right now.

I have googled and googled and seen axles, u joints, bad tires and a host of other ideas. All that googling left us with still just theories.

So here I am, polling the collective knowledge of rx7 club for ideas. If I can, I'll find a back road and take a quick little video of the shake as well.

 

Just a bit more background.

The right rear bushing for the strut is bad. Don't know if that adds to this.

Also, tapping the brakes doesnt help and letting the clutch out so it's just coasting doesnt either.

 

Probably driveshaft needs checking and replacing

 

I had a similar vibration at 30mph and up, this was a nagging problem turned out to be a bad rear strut. Solved by elimination, the driveshaft was rebuilt and balanced when I put a new motor in a few years ago, and last year I put new tires, I was ready to remove the driveshaft and check for bad u-joint and or driveshaft balance when I decided to replace the original struts. The RR strut had no resistance, never really noticed the ride being terribly bad. Once new struts were installed vibration was gone.

 

So a bad strut in the rear (where the vibration seems to come from) could cause this? I know the bushing is bad but I'm not sure what that does.

305k miles and counting

 

most likely a ad u-joint in the driveshaft. remove it and see if it is stiff to pivot, binds or is extremely sloppy.

 

I agree, if the tires/rims are balanced then I would next check the condition of the u-joints, if that proves to be ok then I would look at your rear shocks, mine were original from 1990 so it was long over due....

 

As an added piece - if i fill the gas tank the vibration is pretty much gone (even though it was sporadic before)

 

So I have determined its the rear suspension.

Is the bushing part of the strut? Can I change the struts myself meaning is it an impossible to get to and swap part?

 

On page 13-14 of the service manual suspension section, it looks fairly simple to remove the rear shock absorber... But I noticed it called it a shock absorber instead of a strut. Am I looking at the right thing?

I a bushing a part of it?

Wife and kids are out of town this week so I'm hoping to tackle this.

 

yeah strut/shock/damper are all the same thing in this case. the bottom bushing comes with the new part.

 

Is it as non intimidating as it looks in the service manual? Follow steps to remove,m follow steps to install?

 

yep! you'll need a spring compressor for the springs, and some kind of impact gun for the strut nut, but other wise its very easy

 

Thank you! I'll order some Napa struts for the weekend. They are only around $35 which is nice.

 

I use "shock" and "damper" interchangeably but always thought a "strut" also had to be capable of rotating, while shocks do not.
Could be very wrong though.

And zoomy...yes, they are as easy to replace as they appear.

 

you're right, a strut, and a shock are two different kinds of dampers, but since we're just talking about a replacement part, and not a redesign of the suspension, all three pretty much work.

 

Wait. So I can get either one? For the rear?

 

No.

 

I had the same issue in my vert and it ended up just being a tire out of balance

 

just really quick, springs oscillate, and this needs to be controlled. early cars use something that looks like a clutch, except its lined with leather, so one side is hooked to the body, the other is hooked to the suspension, and the friction of the leather on leather damps the spring. its pretty neat, they are easily adjustable, and sometimes from the cockpit. http://en.wikipedia.org/wiki/Friction_disk_shock_absorber
the hydraulic damper was adopted pretty early on, there are many different types, and basically they all function the same except for the way they look/mount.

for instance a strut, refers to the type of damper the FC has in the front, where the shock is also part of the suspension, in effect its a control arm.

a shock is more like what we'd think of in the back of a truck, where the shock is like an add on piece to the suspension, and isn't structural.

the FC rear damper, is a shock, but it looks like a strut and since you're just buying a replacement part, you can walk up to the parts counter and say shock, or strut and get the same thing.

as an aside, you'll read the words coil overs a lot, and this technically refers to when, like the Rx7, they put the COIL spring OVER the shock.

 

Hi again.

So which is the right one? I was well on my way till this little variable confused the heck out of me.

NAPA AUTO PARTS

OR

NAPA AUTO PARTS

 

so how did you come to the conclusion it was a strut? did someone see the wheel bouncing while driving or does a particular tire have a "feathered" pattern on it?

i ask because failed driveshaft joints are quite common in the verts versus the coupe due to the additional load/weight and body flex amplifies it. of course i usually start with tire balancing/rotation unless you have noticed one of the above.

 

i don't see what variable you're talking about but KYB > monroe

 

Just mean that I don't want to buy the wrong thing and these two items seem very different.

 

Noone has seen it shaking, no.

But we have taken the wheel off and there is fluid from the shock leaking out and the bushing is completely gone. Also, as time has gone on it has gotten worse. It's not as pronounced with a full tank of gas (which I assume means its compressed down).

I rotated and balanced tires hoping it would help but no sir.

It's been a huge mystery for a while and I'm aching to fix it.