ok so i have a 95 camaro 3.4L SFI
and when in the overdrive gear, between 45 and 55 the engine shakes very badly, just put on a pcv valve so that wasnt it, and ive put in new spark plugs and wire, so that couldnt be it. what do you guys think it could be from?

A crappy mid-90's American built car with a crappy, underpowered engine? That could be it I think!

Seriously though, if it also vibrates badly in neutral, then check your engine mounts.

check your engine mounts.

between 45 and 55 the engine shakes very badly

it starts shaking at 45 and gets worse up to 55, not in neutral

and it cant be the mounts, it only shakes at 45 to 55, at like 60 itll stop, which if it was the mounts itd get progressively worse as the mounts got looser.

plus it only happens in overdrive, when in drive or second it does fine.

Check engine mounts, transmission mounts, and I would also check the wheel bearings. Check tire balance as well if you can. It is most likely something in the drivetrain. It is probably not an engine problem, if it only does it at those speeds, because the engine should be hitting that rev range through other gears. Could be a transmission problem, but it is probably some other drivetrain problem.

it starts shaking at 45 and gets worse up to 55, not in neutral

and it cant be the mounts, it only shakes at 45 to 55, at like 60 itll stop, which if it was the mounts itd get progressively worse as the mounts got looser.

plus it only happens in overdrive, when in drive or second it does fine.

So when you are driving down the road in [D] and it starts shaking, you can shift into D or 2 and it will immediately stop?

The mounts themselves offer resistance to an angular displacement. As they age that resistance decreases allowing them to resonate with a particular back-and-forth frequency. It is entirely possible that they are in bad enough condition to resonate at the RPM at 45 to 55 and not at 60.

So when you are driving down the road in [D] and it starts shaking, you can shift into D or 2 and it will immediately stop?

The mounts themselves offer resistance to an angular displacement. As they age that resistance decreases allowing them to resonate with a particular back-and-forth frequency. It is entirely possible that they are in bad enough condition to resonate at the RPM at 45 to 55 and not at 60.

this. My motor mounts were out, and from 0-35ish my car would shake like crazy. I replaced the mounts and all was well. Might not think it's the motor mounts, but Check them anyway. Also check the tranny mount. usually goes bad, fast, when the motor mounts are out.

^^^ABnSW, so, it'd only do it when driving but not if you'd rev the engine through the same RPM range while in neutral?

^^^ABnSW, so, it'd only do it when driving but not if you'd rev the engine through the same RPM range while in neutral?

f it's in neutral it's not loading the mounts at all, so there is no doubt that it wouldn't shake.

So when you are driving down the road in [D] and it starts shaking, you can shift into D or 2 and it will immediately stop?



The mounts themselves offer resistance to an angular displacement. As they age that resistance decreases allowing them to resonate with a particular back-and-forth frequency. It is entirely possible that they are in bad enough condition to resonate at the RPM at 45 to 55 and not at 60.

yes, that is what happens. and i doubt its any of the mounts since i've went over them and the rest of the engine before i bought it, always check shit like that.

Just because the mounts are not broken does not mean that the bushings in them are in good conditions. Oil can quickly degrade rubber, so if they ever had oil leak on them, there is a chance the rubber has significantly softened.

my dad seems to think it's the transmission shifting between drive and overdrive.

my dad seems to think it's the transmission shifting between drive and overdrive.

if its not the trans, and mounts are fine, if it does it at the same speed, regardless of gear, it could be that your tires are out of balance. i know on the miata's they have this thing called a 55 mph shimmy, where the factory specs for balance make it feel a very very slight shake at 55 mph, this was remedied by using aftermarket wheels and proper balance. have your tires been balanced in a while? you could check and see if the wheel weights are there as well.

my dad seems to think it's the transmission shifting between drive and overdrive.
That could be the problem.
When I worked for ford we had a problem with the transmissions in the crown vics.
It was called a 4th to 5th gear SHUDDER.
what was happening was that the the clutch packs got a glaze on them and would shudder when they applied.The fix was to do a complete fluid flush and it would go away after about 100 miles.
I don't know if GM has had the same problems but it sounds the same:)
Try a fluid change and see what happens

The Camaro and Firebird of that era had a skip shift feature where if you didn't mash the throttle it would shift out of first and directly into 4rth, saving fuel. I think it entirely plausible to suppose that the fluid pressure required to grip in 4rth at such a low speed would be higher than what it can get. Like when you tow a heavy load and you need higher RPM so your clutch packs don't wear out from slipping.

check out this on how to eliminate skip-shift.
http://forums.corvetteforum.com/showthread.php?t=2118944