Hey guys,
I have a 1985 GS with a 12A and it has been having some issues for awhile that me and my dad can't seem to figure out. As I said in the title, the whole car shakes. My dad said that he was driving the car when all of a sudden he heard/felt a bang somewhere in the car then it started vibrating/shaking violently. It's A LOT better now though (flywheel nut was torqued to all of 10ft lbs). The engine still has good compression. I have replaced the dizzy cap and rotors, and spark plug wires trying to solve the problem but have had no success. I know the tranny is starting to go out so that could possibly be part of the problem but the car still shakes even in neutral and when the clutch is pushed in.

My dad and I are thinking that it could possibly be a vacuum leak somewhere, and so I was also wondering is it better to get new vacuum lines for the rats nest (if so what size and how much) or just do a rats nest delete. And one last question is whenever I do decide to do a rats nest delete (want to get a Weber or Dellorto at some point) how do I time/tune the engine considering the engine has a vacuum advance system that runs through the rats nest?

Thanks for reading/helping me with this, can't wait to hear what you guys have to say.

P.S. If you have any experience with/ideas what my problem could be please let me know and thanks again.

 

Does it shake when you aren't moving or while you are going down the road?

 

Wow, lots of new posters here in the SA/FB forum - which is GREAT to see! Welcome aboard!

Qingdao is asking if the shaking occurs idling in your driveway as well as driving on the road to figure out if it's driveline related or engine related.

If it happens when you're driving it, and the shake increases with speed - it's your universal joints (U-joints) on the driveshaft. Driveshaft U-joints aren't replaceable, so you'll need to buy a new driveshaft or find one at a Pick-A-Part. Mazdatrix offers rebuilt driveshafts complete with replaceable U-joints which are affordable and a long term solution, as they are a wear component.

If the shaking occurs at speed and sitting still, then it could be something else with the engine that will have to be tracked down based on your explanation of the symptoms. Post back and there's some great expertise here who can help you out.

 

Could be a knot in a tire.

 

It happens both when driving and sitting still. The higher the rpms get, the shaking/vibrations get more and more violent (even with clutch engaged).

 

great isnt it!? the "1st gen rx7" page on fb has been growing rapidly within the past few months

i second the driveshaft, U joint issue. i would check that

 

He already said in the first post it happens when the clutch is pushed in (disengaged) so its not
a driveshaft issue or a driveline issue. Its something to do with the engine. Could be a misfiring
or a vacuum leak.

Lets ask some questions first:

1. History on the car, when did you get it? Whats been done to it? Any pertinent info to share
would good background to help you solve this.
2. How long was it running fine before this started? What changed right before it started?

 

Possibly a broken motor mount?

 

possible that it is a bad water pump or alternator, i've had bearings fail on both. the water pump was funny, it had like 1/2 of play, but didn't leak a drop

 

Ok thanks, I'll take a look at them.

 

I don't think they're bad/going bad because I'm not able to shake it by hand.

 

1. My dad got the car in 2003 from my uncle (all it needed was a new clutch), swapped in a new engine in 2005, and put in a poor mans direct fire system shortly after.
2. It was running fine up until 2 years ago, my dad was driving and when he was shifting from 1st to 2nd the car made a clunk noise, wouldn't go into gear (until he pushed the clutch in again) then started shaking ever since.

 

Broken tranny mount maybe? A broken tranny mount will let the
engine and tranny dance all over the place.

 

How do I check? I've dropped the tranny 4 times in the last 3 months and I didn't see any cracks or anything.

 

The "clunk" and not being able to put it into gear is familiar, but not the shaking. Turned out I damaged the pilot bearing (high rpm from stop on a sharp left-turn). Had it replaced along with the clutch and the issue was resolved.

(I don't know enough to know if the above is relevant to your issue.)

 

My dad says that when he checked it, it seemed fine. Should I replace it anyways?

Is there something in the rats nest that would possible cause this?

 

Since pushing in the clutch disengages the transmission and stops the rotation of all transmission components, I'd say the problem is from the clutch forward. Sounds like an out of balance, rotational issue. The "bang" sounds like something broke. I'd suspect something it the clutch itself. Have you given it a good look? Maybe part(s) of the friction material fractured off and was thrown out, creating the out of balance issue while the clutch still actually functions.

 

i'm surprised no one went further into this. so i will.

did you take the flywheel off and check the woodruff key? i have had a flywheel turn 170 degrees after shearing off the key. the cause was the nut being too lose. this was a motor 7k miles after a rebuild. to it was tight for enough for break-in and some spirited driving after that, but not tight enough for hard shifts.

It sounds like you have had the flywheel off and woulda check this, but its better to ask then assume. other things have been said.. trans mount, pilot bearing/ input shaft bearing

 

if the flywheel isn't on straight, it would be a big vibration, as the flywheel has a counterweight in it to balance the rest of the engine....

no. its just 4 solenoids and 8 vacuum lines.

 

how big of a vibration? like enough to... shake the whole car?

 

the one i saw with the wrong flywheel on it, did this

 

I'm not sure just what the problem is then.....

 

Yes. It shakes so bad that it's hard to see out of the side mirrors and it made the starter almost completely fall out, then ~2-3 weeks after that, the shaking completely broke off one of the mounting brackets on the starter.

 

I still say its a motor or tranny mount. You may not see it unless you actually take the mount
off and hold it in your hand. Could be the rubber no longer is bound to the mount. Looks fine
until you pull it and it falls apart in your hands. If you had the tranny out you would have noticed
I think, so my vote is its a motor mount.

If its not a mount then its an issue on the rotating assembly. Like lastphase mentioned, make
sure the flywheel is actually in the right position because its a balance wieght and a flywheel.

 

Motor mounts are cheap enough it would be prudent to just buy a new set (30 yo rubber needs replacement).

But if you wanna check them yank the E brake. Drop the car in first and slowly come off the clutch (keep your foot on the hydraulic brakes as well). If the engine shifts upward; one of the mounts is bad. Try again in reverse to check the other side.



I don't think its a motor mount issue. I had bad (completely separated mounts) in my gold car. It didn't shake unless I reved the engine and let off. Even still it was just the engine jumping around in the engine bay. Not a violent shaking.


It is possible to have the key way shear off of the flywheel. If you spun the flywheel on the e-shaft it will make it shake. I've seen an outboard motor shear a keyway and the flywheel spun on the shaft. The key way basically welded the flywheel to the shaft, but the engine was only out of time by a hair so we still used it till we sold it.