Help! 95 Miata shakes when launching

"Abject_Penitent" (nosek) 09/17/2014 at 12:57 • Filed to: miata

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Hey guys, my miata has developed a problem of shaking whenever the car starts moving. I can't figure it out and any information would be greatly appreciated. I'm not driving it hard or anything, this is normal daily driving. It also gets worse once the car is warmed up.

I now have to be super careful in reverse or it feels like it's going to tear the car apart. I read on one forum that it may be hot spots and I could burn them off by slowly letting the clutch out at high rpms in third but I figured I would ask about the problem here first. I have only had it since February and I foolishly forgot to ask if he knew how old the clutch and tranny and all that stuff is.

Anyone know what might be going on?

crowmolly > Abject_Penitent 09/17/2014 at 12:59

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Basics:

1.) Any codes?

2.) Does it do it when you are not in gear and free-rev?

3.) Is it RPM specific?

Twingo Tamer - About to descend into project car hell. > Abject_Penitent 09/17/2014 at 13:01

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Heavily worn transmission or motor mounts?

IDROVEAPICKUPTRUCK > Abject_Penitent 09/17/2014 at 13:01

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If it's only while you are launching I would expect it to be something with the clutch.

FriskyDingo > Twingo Tamer - About to descend into project car hell. 09/17/2014 at 13:11

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Seems like a trans mount

Abject_Penitent > crowmolly 09/17/2014 at 13:23

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There's no CEL on so I didn't think to try for codes

No shaking when out of gear or when I free-rev.

It just gets worse as rpms go up. If I do a super slow start and basically let it roll to 3 miles an hour it is pretty much fine.

Abject_Penitent > FriskyDingo 09/17/2014 at 13:25

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how might I check that? I got under there but just saw where it was bolted to the frame but couldn't really diagnose anything

Abject_Penitent > IDROVEAPICKUPTRUCK 09/17/2014 at 13:25

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That's what I fear

jariten1781 > Abject_Penitent 09/17/2014 at 13:29

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If there are bad enough hot spots that you're noticing them, you probably would have caused them. Lots of dumps or drag launches can do that. Done anything like that? They're not something that the previous owner would have caused if the symptoms just developed recently. They can be caused by stuff like an improperly torqued flywheel, but again not something that I would expect to have pop up randomly. If that does turn out to be the issue I'd have the mating surface machined, just doing slips is going to wear off material with questionable gains. If you haven't been rough on the clutch I'd find problematic hot-spots to just be some pretty bad luck.

It could also be things like cracking of the clutch disk, bad u-joints, bad TPS, bad mounts, etc. Lots of stuff can go wrong on an old car: start simple and move down the line.

evil2win > Abject_Penitent 09/17/2014 at 13:39

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It sounds like a clutch problem to me. The first time I replaced a clutch on a car I didn't torque everything down properly and it started doing the exact same thing. I ended up replacing the clutch again, but I think all I really needed to do was tighten everything up properly. Has the clutch been replaced recently? it might have been a botched job. Have a look and see if you can see any missing, loose, or broken bolts between the bellhousing and the engine block. Hopefully the pressure plate isn't coming loose. Look for broken motor mounts, and transmission mounts as well, it won't hurt.

Abject_Penitent > jariten1781 09/17/2014 at 13:49

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No racing for me. I do a little spirited driving here and there but nothing serious and I haven't dumped the clutch once. Time to start moving through that list of possible problems. Thanks for the info

Abject_Penitent > evil2win 09/17/2014 at 13:54

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It definitely hasn't been replaced anytime recently or I think the guy I bought it from would have told me. I was going to start checking all the bolts today or tomorrow but one thing I don't know is how to tell if the transmission mounts are bad. Any tips? This is all new for me

FriskyDingo > Abject_Penitent 09/17/2014 at 14:01

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grab the transmission by the tailshaft and try to shake it, does it seem to have excessive movement? It shouldnt move very much if the mount is good.

Abject_Penitent > FriskyDingo 09/17/2014 at 14:19

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It certainly had some wiggle to it but nothing seemed loose. Thanks for the info.

FriskyDingo > Abject_Penitent 09/17/2014 at 14:21

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Sounds like it may be bad.

evil2win > Abject_Penitent 09/17/2014 at 14:22

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first thing you'll need a set of jack stands so you can get under the car. The transmission mounts are usually towards the back of the transmission. Uaually about 2/3 the way back. You'll need to get under there and have a look. A broken mount should be obvious. I've never worked on a miata, but it shouldn't be that much different from other cars.

Abject_Penitent > FriskyDingo 09/17/2014 at 15:33

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In that case it looks like that is my starting point. Thanks for the help

Abject_Penitent > evil2win 09/17/2014 at 15:36

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I have a sloped curb so I got under it that way. I didn't see any cracks but the transmission wiggles a bit. I won't have my Jack until Sunday so I will have to wait until then to really get under there. Thanks for help