low rumble & vibration at highway speeds
#1
Hey Guys,

When I take my 1969 mach 1 on the highway or do about 60MPH and higher, I get a low rumble & vibration that sounds like its coming from underneath the car from rear end. I'm not 100% sure though. It almost feels like I'm riding over the shoulder where the road indents are but just not as extreme of a vibration. Its a consistent 1 second vibration then goes away for 2 - 3 seconds then back on and consistently does this until i slow the speed to under 50MPH and lower. I though it might be tire balance so i waited until i bought the bfgood TA tires and had a wheel alignment and balance done. I was hoping it would be this but vibration is still there. So I can rule out tiring balancing. Anyone ever had this problem before?
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#2
Several things can cause this. First I would think of a driveline out of balance or bad universal joints. Bad motor mounts or bad transmission mounts also cause strange vibrations. I've seen a bent axle or wheel cause vibrations. But those are usually at all speeds. I guess a severely worn tail shaft bushing in the trans could allow the driveline to vibrate around but I haven't seen it.

If it were mine, I would pull the driveline, replace the U-joints and have the driveline balanced. If you find an obvious bad U-joint you then maybe try it without balancing it.

Spicer brand U-joints are about the best you can get. Napa's more expensive U-joints are Spicer brand. I've also seen Spicer U-joints on Summit Racing's website. If you cannot find Spicer, most parts stores offer different quality U-joints so at least opt for a higher end part. Cheap U-joints simply don't last very long and often have looser press fits into the yokes of the driveline.

Regards,
Mike
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#3
Ok I will look into this
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#4
U-joints are indeed a possibility and more than likely your culprit.

I would not rule out a rear wheel bearing either.
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#5
Good point on a wheel bearing. Those definitely make a rumble but not much of a vibration. Anyway, one simple test for wheel bearings is make left and right turns when the noise occurs. Not sharp turns but enough so the car leans some to transfer some weight to one side. With a bad wheel bearing the noise will increase as the car leans because of the added load on the bearing. I've had found one and both bad wheel bearings doing this.

Regards,
Mike
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#6
I put the car on a lift and both front and back u joints are tight. I did notice about 1/8th of play on slip yolk inside fmx transmission. I should also point out the car here's when I put in reverse or drive in addition to floor vibration at 50mph. Should there be any slack on slip yolk?
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#7
I am not sure I understand the second part of your question about putting the car in drive and reverse. Maybe you could clarify.
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#8
The car jolts too much when I move it from park to drive. Or ftom parK to reverse. I'm wondering if it's a worn slip yoke.
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#9
I'm trying to figure out the cause of the car's vibration at 40mp + speeds. The higher I go, the more it vibrates. I have new tires and they are balanced. The u-joints are tight with no play. The only part with some slack is the slip yoke (the one with the splines) that connects to FMX trans. Theres about 1/8th of play. I'm debating whether to buy the slip yoke or if some play is normal.
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#10
(11-16-2015, 09:29 AM)rindel Wrote: I'm trying to figure out the cause of the car's vibration at 40mp + speeds. The higher I go, the more it vibrates. I have new tires and they are balanced. The u-joints are tight with no play. The only part with some slack is the slip yoke (the one with the splines) that connects to FMX trans. Theres about 1/8th of play. I'm debating whether to buy the slip yoke or if some play is normal.

Vibrations can be annoying and the most common reasons for them have been covered above. I am not sure there is supposed to be vertical/horizontal play in the yoke. You can try and replace the yoke but it may be possible there is a worn bushing in the tail housing.

Out of curiosity, did the vibration start after you put new tires on?
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