Pun intended in the posting title. but I'm dually rattled by this one.

So, I'm losing it here. My van is running like a champ. I recently replaced all the vacuum lines, fuel pump, plugs and wires and distributor, and cleaned the whole carb. Why? Well I was driving one day and she just started shaking above 25 MPH around 2500 RPM. Just like that. All those things were in need of general MX so I went and did all that in hopes of it remedying the problem. I was thinking misfire or something with the fuel and the engine mounts are 5 years old. It has new tires and they are balanced and its aligned. It still shakes like crazy at any speed above a slow idle. Starts fine and runs strong. Any have any idea what I could be looking for. I'm thinking misfire or harmonic balancer? I put the plugs back in correct order and have gone through most of the bonehead mistakes ....I think.

As always, any insight is much appreciated. I put her back in the garage as she's so annoying to drive. Hoping have her up and running for spring summer and fall camping, surfing and tailgates!

-dave

 

When I bought my van, the torque converter was bad (I knew it was too)
It felt the same as you are describing. But, you are right it could be your balancer.

 

I was really hoping torque converter was not going to be mentioned as I am super hopeful its not that. I also thought clutch fan.

 

Are you sure the vibration is not suspension related? Doubt it could be wheel/tire @ 25MPH also wheel/ tire vibration usually goes away if you increase/decrease speed.


If you are sure it is engine related, one of the weights on the torque converter may have come loose. Also possible the tranny, drive shaft or even the rear end could have issues easier to have a look at the tranny/ rear end first.

 

Im fairly certain its not the suspension and the u joints were replaced less than two years ago. I showed my mechanic bud this thread and he took it to get it on a lift etc. He is a molar guy I am hoping for harmonic balancer. thanks for your updates. Ill report back after I get it back from him.

 

Now I am just recalling only the 360 has external weights so if you have a 3.9/318 hope that your flex plate or torque converter is damaged. I do not believe a harmonic balancer would give you major vibration at normal RPM (under 3500rpm).


I say that because if your driveshaft is balanced your suspension and rear end ok locating the source of your vibration becomes much more difficult.


Best of luck.

 

You can rule out both the harmonic balancer and the torque converter. If either of these were the problem you would have the shaking at any RPM in neutral, park, or drive. To me it sounds like something within the tranny broke, such as 3rd gear or O/D if equipped.

What happens if you keep the tranny in 2 instead of D, does it still start shaking at 25 mph/2500rpms?

 

good question

 

As Alloro said the tranny could be the problem and the more I think about it the more I believe it's the cause. If your engine had a internal balance issue your main bearings would likely be toast by now and there would be vibration before 25mph so that is not likely.

 

I will investigate that next week. Been driving from NJ to California in a 2001 Subaru....I'll be reunited with something not powered by rubber bands mid next week and run said diagnostic.