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Driveline vibration

TDitty

TDitty

New Member
Hey guys,
I know I havent posted in a while but, I have been busy finishing my T will post pics later. I have some questions. I am getting a vibration in my T during test runs from 20-30 mph. I am using a SBF 302, FMX AT and a 9in uncut. I did find the rear had to much back lash and growled no biggy got another chunk and no more growl. I still get the vibration though I am thinking rear tires or driveshaft possibly a combo of the two. is there any thing I may be overlooking. Also I wanted to ask do these things have a natural vibration to them something i will chase and never get rid of being they are light all the way around. Thanks guys,
Russ
 
Put on jack stands and see where vibration seem to be from. If you don't have posi you can have one wheel up and spin it up one side at a time to get vibration.Just be careful that somebody is inside ready to stop if it falls for some reason. DON"T CRAWL UNDER IT DURING THIS TEST. You should be able to see the vibrating parts.
 
putz said:
Put on jack stands and see where vibration seem to be from. If you don't have posi you can have one wheel up and spin it up one side at a time to get vibration.Just be careful that somebody is inside ready to stop if it falls for some reason. DON"T CRAWL UNDER IT DURING THIS TEST. You should be able to see the vibrating parts.
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Thanks putz
 
RPM said:
Have you had the rear tires balanced and checked for run out?
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Ron,
That is next I was asking to see it there was anything I was missing on these cars being that this is my first one.
Russ
 
Does it come on suddenly or does it work it's way up? What I'm saying is these cars are cars. They behave the same as big cars. Or heavy cars.
If it seems that the vibration is coming from the rear, then most likely it's the rear tire balance. I mean aint much else back there. Especially if the tars are those big ol' tars. Do you have them aired up correctly? At this point better to be a little over inflated than under-inflated. Were the tires balanced on the car? If you are test driving, is everything screwed down and tight? Are your angles on the driveshaft within proper limits? Is this a frequency vibration? Has the drive shaft been shortened and balanced properly? Was the driveshaft phased properly? Coil overs new? Or do you have springs and separate shocks? Are the shocks new and working? Is the tailshaft bushing tight?

Just throwing this stuff out there. John

P. S. Congrats on getting it running.

P.P.S. No offense Putz, but I am not a big fan of leaving one tire on the ground. Put the stands under the rear axle, with 'bout three or foue inches clearance, and only run it up to a low rpm on the drive shaft speed. Be careful.
 
A couple of thoughts...

Could you have the drive shaft u-joints out of phase?

A loose transmission mount?

Everything has natural frequency and there can interferences of natural frequencies, though not very common. Take a look at the rear end of a Ford Explorer. They have a five pound weight hung on the rear end which I see as a cheap fix for what might have been frequency intersection.
 
one finger john said:
Does it come on suddenly or does it work it's way up? What I'm saying is these cars are cars. They behave the same as big cars. Or heavy cars.
If it seems that the vibration is coming from the rear, then most likely it's the rear tire balance. I mean aint much else back there. Especially if the tars are those big ol' tars. Do you have them aired up correctly? At this point better to be a little over inflated than under-inflated. Were the tires balanced on the car? If you are test driving, is everything screwed down and tight? Are your angles on the driveshaft within proper limits? Is this a frequency vibration? Has the drive shaft been shortened and balanced properly? Was the driveshaft phased properly? Coil overs new? Or do you have springs and separate shocks? Are the shocks new and working? Is the tailshaft bushing tight?

Just throwing this stuff out there. John

P. S. Congrats on getting it running.

P.P.S. No offense Putz, but I am not a big fan of leaving one tire on the ground. Put the stands under the rear axle, with 'bout three or foue inches clearance, and only run it up to a low rpm on the drive shaft speed. Be careful.
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Guys we have done the jack stand view and we did find that we had lower the trans and that took alot of vibration out (first run testing). So after refab of the trans mount we got rid of alot of vibration except between 20-25 MPH. I guess with the 2in offset in the 9in I am worried that it is causing the vibration even though we have checked, checked and rechecked the front and rear for square. I am going to take the driveshaft to get balanced out and my cousin is going to take the tires with him to work to double check them for balance.
 
TDitty said:
Guys we have done the jack stand view and we did find that we had lower the trans and that took alot of vibration out (first run testing). So after refab of the trans mount we got rid of alot of vibration except between 20-25 MPH. I guess with the 2in offset in the 9in I am worried that it is causing the vibration even though we have checked, checked and rechecked the front and rear for square. I am going to take the driveshaft to get balanced out and my cousin is going to take the tires with him to work to double check them for balance.
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i have an off set 9 inch and has no vibration jacking it up will help diagnose but will also change your drive shaft angle also could get worse or better and maybe no change. we also built our own drive shaft and did not balance it but at 17inchs shouldn't realy need it anyway. did have a violent shake at 65 and it was my rear tire ot of balance
 
A couple of things about the previous posts come to mind. First, if you raise the vehicle's rear axle and set it on jack stands, nothing will be in a different alignment than it was sitting on the tires. Since the weight is still on the springs, no angles change at all. Second, having the rear pumpkin offset a couple of inches won't cause the vibration by itself. Now it the engine / trans were to be angled to point more toward the pumpkin, that WILL cause a vibration, but I assume you have them in line. Remember, the driving shaft (trans output) and the driven shaft (pinion) should be operating on the exact same plane, horizontally and vertically. Also, When it comes to ujoints, a little bit of angle and movement of the joint in normal operation will keep it from wearing out at one specific spot, so the offset pumpkin can be a GOOD thing.


Chances are very good that you are looking at tire issues. You could try jacking it onto jack stands, then remove the rear tires/wheels, and run it up to the vibration speed and see what happens. If you do this, be sure to account for the fact that the brake drums will fly off unless secured or removed, so either put ALL nuts back on to retain balance and secure the drums, or remove the brake drums all together. This will isolate the tires from the drive line. You COULD even be looking at an out of balance flex plate or torque converter, or a wrong harmonic balancer, or even something belt driven. To check for that, run her up in nutral, and if that's OK, just remove the driveshaft and run her up in case the issue is inside the trans (not very likely). Lot's of possibilities with vibrations.

JMHO, Corley
 
Corley said:
A couple of things about the previous posts come to mind. First, if you raise the vehicle's rear axle and set it on jack stands, nothing will be in a different alignment than it was sitting on the tires. Since the weight is still on the springs, no angles change at all. Second, having the rear pumpkin offset a couple of inches won't cause the vibration by itself. Now it the engine / trans were to be angled to point more toward the pumpkin, that WILL cause a vibration, but I assume you have them in line. Remember, the driving shaft (trans output) and the driven shaft (pinion) should be operating on the exact same plane, horizontally and vertically. Also, When it comes to ujoints, a little bit of angle and movement of the joint in normal operation will keep it from wearing out at one specific spot, so the offset pumpkin can be a GOOD thing.


Chances are very good that you are looking at tire issues. You could try jacking it onto jack stands, then remove the rear tires/wheels, and run it up to the vibration speed and see what happens. If you do this, be sure to account for the fact that the brake drums will fly off unless secured or removed, so either put ALL nuts back on to retain balance and secure the drums, or remove the brake drums all together. This will isolate the tires from the drive line. You COULD even be looking at an out of balance flex plate or torque converter, or a wrong harmonic balancer, or even something belt driven. To check for that, run her up in nutral, and if that's OK, just remove the driveshaft and run her up in case the issue is inside the trans (not very likely). Lot's of possibilities with vibrations.

JMHO, Corley
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"just remove the driveshaft and run her up in case the issue is inside the trans" Corley, ya gonna need some floor dry for that one, but the point of the test is taken....ruggs
 
Do the simple things first before going wild:
1. Check and make sure your motor mounts and trans. mount are tight.
2. Make sure your u-joints are tight and seated, and that the driveshaft isn't gyrating. Make sure your driveshaft is balanced. Some really short ones come out fine unbalanced.
3. Grab your pinion and shake it....is it tight? Wheelbearing?
4 Are your wheels balanced? Are the rims running true?
--While your bucket is up on those jackstands letting it run, look at your pinion angle and make sure theres no 'crabbing' going on.--
5. Look at the tires themselves, make sure they're not wobbling on the tread or side walls.

If you 'feel' the vibration, it'll kinda tell ya where its at. If it feels like its in a wheel, it'll be slower in rythum but heavier. If its in the driveshaft and rear pinion area, its gonna be faster.
If it goes along with engine speed, could be the converter or flexplate.
Does it go away when you get on the breaks? Does it go away when you throw the power to it? Did it just start all of a sudden?
 
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Chances are very good that you are looking at tire issues. You could try jacking it onto jack stands, then remove the rear tires/wheels, and run it up to the vibration speed and see what happens. If you do this, be sure to account for the fact that the brake drums will fly off unless secured or removed, so either put ALL nuts back on to retain balance and secure the drums, or remove the brake drums all together.


Leave your tires off, put on 3 flatwashers on each lug, then run down your lug-nuts snug against the flat-washers.....and try it as he suggested.
 
Ruggs: Yeah, I should have mentioned using a trans shaft plug.

SM: Probably better to use 5 washers/nuts than 3 and keep things in balance.

Lot's of ways to skin a cat here, and while vibrations can be a bitch to find, they can also usually be found pretty quickly by isolating the components.

Little story: When I was a teen, my older brother had a '41 Chevy with a vibration at about 45 mph. He tried everything he could think of, no luck. It seemed to come from the rear of the car, so when tire balance and wheels didn't fix it, he got drastic and swapped the rear end. Still no luck on fixing that rear end vibration. Finally, days later, he found a bad front wheel bearing. Vibrations can really act and feel weird. Back when they always used a motor to spin your wheels on the car to balance them, some cars would shake like crazy, and I've seen a rear bumper shake violently when they were spinning a front wheel, while the front bumper seemed rock solid.

Have you noticed those huge hunks of metal that Ford and GM hang off the most odd places? Those are to help fix a vibration problem. Weird, I say, ...weird...

The point is, you can't always tell by "feel" or listening where a vibration is actually located, but sometimes you can, so as SM says, pay attention to the speed of the vibration too. In fact, all the above ideas are good at isolating a vibration, but the one that finds it is the best, so keep trying different ideas until you isolate and fix it. Be methodical, don't just swag it... You will get there eventually... Now if it ONLY manifests itself while driving, and is fine on the stand, you are definetely looking at a tire / wheel issue, or something up front. (I'm still betting on tires.)


JMHO, Corley
 
Corley said:
SM: Probably better to use 5 washers/nuts than 3 and keep things in balance.
Click to expand...

That is actually what he said -

Screaming Metal said:
Leave your tires off, put on 3 flatwashers on each lug, then run down your lug-nuts snug against the flat-washers.....and try it as he suggested.
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I had to read it twice to see it, too. Too much code dancing around in front of my eyes. :zingy:
 
Mike, SM, et al,

You are right, I was wrong, missread it, look stupid, etc., and now I'm not only depressed, but ...

Oh well, ... Seriously, you are correct, I missread SM's post. See what old age can do to a person? Don't do it! (get old that is...) Good catch Mike... My appologies SM! Anyway, the point was to keep it in balance, and SM's point was to take into account the shoulder on the wheel stud when bolting down the drum.

Corley
 
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