My 69 GS400 has a vibration at higher speeds, usually above 55 or so. I always figured it was the usual suspects - unbalanced wheels. But I discovered putting it in neutral at speed and coasting at idle makes the vibration go away. The vibration has gotten worse in the 5 years I've owned it. Haven't done any driveline work at all since I've owned it. My first thought was a u-joint or the drive shaft, but they haven't been off the car. Not really sure where to start as I've never had this issue before. Any idears?
Does te vibration change on ad off the throttle? Have you jacked it up and felt the I joints to be tight yet.
For the sake of $40 get the drive shaft balanced. Cheapest thing to do first I did mine and it would not balance. Had a new tube made with new joints and it made a huge difference!!
That would eliminate a driveline problem. I'd start looking for an engine vibration. This might sound a little odd but I did this on a GTO years ago and it worked. You have 3 bolts that hold the torque converter to the flexplate. Mark them 1-2 3, then put a mark next to #1 on the converter. Unbolt it and rotate it to hole #2 and take it for a drive. In the case of the GTO the vibration got a little worse. If so, then unbolt it again and rotate it to #3. In my case the vibration went away completely. Not saying it will work for you but it's free so it's gotta be worth a try.
OK, now that you have said that, the drive shaft is still spinning when it's in neutral. I knew that Looks like a thorough check is in order, since the vibration has been getting worse. Thanks your your assistance, fellers
For that, of course, we'll need a little more information like when does it most occur, under part throttle cruise, WOT, letting off, etc.
being an old car if you have the abilities and cash. i would have the driveline redone at a driveshaft shop and put all new rear end bearings in it and make sure everythings right just for peace of mind even if it doesnt turn out to be the concern.
Seems to be speed related only and not dependent on throttle position. The faster the car goes, the more it vibrates, and I really only notice it at highway speeds. Of course, that could be because that's when I'm driving at a constant engine speed the longest. Step on it at 55 and the vibration increases with the speed of the car to match the acceleration rate. Accelerate gradually from 55 to 75 and the vibration increases with the speed of the car to match the acceleration rate. I have not noticed that it does it, say, in 2nd gear at a lower speed but the same engine speed as highway travel in 3rd gear. I don't think it does, but then I don't spend extended time at 3000 RPM in 2nd gear. That will be something to test to see for sure, which I'll do if I can get out this evening. The engine has always seemed not terribly smooth at higher RPM when accelerating, or revving it, something I would not expect from a Buick. That might be my answer as to where I should look first - torque converter, maybe the HB. I can't imagine the internals are not balanced although the PO did say he had the engine out and apart to replace leaking seals, so maybe something got put back differently.
Something else to note. I replaced the front power drums with the discs from the Chevelle (they were original, but I felt they were not safe), and at the same time swapped in the a-arms with poly bushings and the HD Chevelle convertible springs that I got from NPD in 1998 when I redid the Chevelle's suspension. They are small block springs, and as such it sits lower in the front by an inch or so. This may have changed the angle of the trans/drive shaft/rear end slightly. I don't recall a noting a change in the way the car drove after that, aside from the fact that it no longer slid sideways when I hit the brakes
I've gotten a little confused here. Does it stop if you slip it into neutral at, say, 65mph or does the vibration continue the same as when it was in gear?
Sounds like the dartboard method.... First you need to determine if it is speed related, or engine related. If its speed related it can only be duplicated when driving on the road. Engine related can be duplicated on the road but also in park in your garage. If it is speed related, you still don't need to leave the garage. What you do need to do is start eliminating components as possible culprits. Here is what I would recommend: Get a sirometer. Its a simple tool but I have been able to track down the frequency of a vibration and it matches some of the "pricier" electronic vibration analyzers out there. (MTS 4100). Once you know the frequency of the vibration, the rest falls into place. For example, a low frequency such as 10-15 Hz will be wheels and tires. But not just wheels and tires. Multiple components within your vehicle operate at wheel and tire speed. I.E. Wheels, tires, drums, axles, carrier. The drive shaft will spin faster than the wheels, approximately 3 times faster depending on your axle ratio. Example: Your case its 3.23 times per tire revolution. I mentioned wheel and tire but it could also be driveline or engine speed related. I would raise the rear of the vehicle up in the garage and slowly get to 60 mph and see if you can duplicate it. Remember to chock the front wheels and securely raise the rear of the vehicle. If you can duplicate the vibration inside your garage, remove the wheels and tires, install tapered washers below the lugnuts and torque them down. Repeat, does the vibration still occur? If so, remove the drums and run the car up to 60mph while keeping in mind that you should not touch the brake pedal. This is an example of how I would eliminate components for the equation so I can definitively rule them out. No guessing. Ultimately it would be much easier if we determined what the frequency of the vibration is. From there we would know where to focus our efforts, wheel and tire if its a low frequency, slightly higher would be drive shaft, higher than drive shaft would be engine or engine accessory. Do you have a sirometer? Did you change the control arm bushings in the front or rear? Does your drive shaft have a double cardan joint at the pinion or two individual sets of u-joints, one at the output shaft and one at the pinion? How were your wheel and tires balanced? RFV? Did you get a sheet with the readout? How much weight did each assembly (wheel + tire) take? Have the brakes drums ever been cut? Are they true? What is your tire pressure at? How old are the tires, abnormal wear, bulges? What engine speed is the engine rotating at at 60mph?
no, it stops completely. ---------- Post added at 11:17 PM ---------- Previous post was at 11:14 PM ---------- Good info Rob, thanks. It might take me a while to track it all down but I'll be sure to post when I do.
You said it goes away in nuetral when on the highway, which eliminates any driveline issues (driveshaft, wheels, axle and diff. bearings) So That makes me think its engine related, since the vibration goes away when in nuetral and the engine drops to near idle speed at freeway speeds. If you have a flex fan, double check it!!! DONT CHECK IT WITH YOUR HEAD UNDER THE HOOD AND REVVING THE ENGINE!!!! Broken flex fans have injured or killed quite a few people:eek2:
In that case, I'll revert back to my first post about the torque converter. Also motor mounts, transmission mount, harmonic balancer, the list goes on but don't discount what may seem like simple things, like the fan as Mark suggested. Since it's engine, or at least RPM related, some of this stuff can be tested in your garage. A bad fan clutch can cause it so take a look at that. I would also start the engine in the garage and try to get a feel for the vibration, then remove the fan belt/belts one at a time and see if it changes or goes away. Sometimes these things have to be dealt with by the process of elimination.
I've never thought long and hard about a problem like this, looks like it goes well beyond just a few simple things to look at. The engine also has a groaning sound or a low growling sound coming from the front of the engine in the water pump area, I figured it was the water pump going bad but perhaps it's related. The fan is original to the car or at least stock type. I've never really had cause to look at it closely, is it a clutch type similar to what was on the SS396? I'm trying to get some work done on my convertible before I have to leave for work again (hope to have the new door skins on, if I can get a day when I can spray some primer), but I'll try to get a look at it sometime this week or the weekend and report back on what I find.
That still does not eliminate driveline, rear end , etc......... Not to say its not torque converter or engine related but he will be ready to pull his hair out if he thinks that eliminates the driveline, rear end, etc... If its not te engine, converter... Need more information...
You're thinking that it still could be something in the driveline that only shows up when power is applied, correct? CMIIW but if it were something like that the vibration should stop when you let off on the gas and coast with it in gear. I believe it still vibrates but I'm not 100%, so it's something else to check. Perhaps it will stop raining today and I can get out for a test drive and check a few things.
