At about what speed would a drive shaft out of phase start to show up? I have a 31 model A that the car starts shaking at about 57 MPH and mostly goes away at 65 MPH. Could a drive shaft act like that or would it just get worse as speed goes up? The car has a 2.3, T5 and 9 inch ford rear. The shaft is a little less than 36 " in length. The shaft was balanced but it is offset 1 1/2 inch to the side. It not a new problem has been like this since I built it.
could be the driveshaft. If it's offset but parallel, that should not make it shake. Is the angle at the front and rear U joint, in the vertical plane, the same?
as stated - check angles at trans & rearend - post some side pics of your ride & if possible drive shaft
An out of phase drive shaft vibration should always be present, and should get worse as the driveshaft rpm increases, I've never experienced a driveshaft balance issue that got better with speed. Out of balance tires tend to vibrate the most at the speeds you want to drive at, and can go away at a higher or lower speeds. An out of balance tire vibration coming up through the seat is usually rear tires, vibrations coming through the steering wheel are usually front tires. Gene
Switch the tires around, front to back. Also see how much they run out, place a jack stand next to each one and rotate the tires. The last bad shaft I had the vibration came in at 2500 RPMs and got worse with more revs.
A one piece driveshaft cannot be " out of phase " unless it was built that way. It can be out of balance, bent, welded wrong, but very unlikely out of phase. It takes a slip joint to be installed wrong to truly be out of phase. Read here, vibrational-issues
If the car in question is the one in your avatar I feel the "skinny" wheels and tires would behave in that fashion.......I own stock Model A's and at 45-55 mph they are happy and will run all day but at higher speeds the tires, wheels, must be in perfect alignment, balance and the suspension perfect.........at that "GO" I would be more concerned with the "WO" [stoping power] .......imho bobbycoke
The offset is parallel. The pinion and yoke are at the same angle. Less then 3 degree if I remember correctly. The consensus seems to be the vibration would get worse with more speed. Which is good that eliminates a critical error on my part. I have always suspected tires. My first shake down run on the build was a set of used 600/16 bias on Ford rims. I was to scared to drive through the shake and just kept it below 55 that year. During the winter I put new 15 inch firestone radials on used Ford 15" rims and used 185-85-16R on the old Ford 16s and had them all balanced. It handled better but still had some vibration but I could drive through it. Next I bought new 15" rims for the front but no change. I'm thinking maybe now a bad tire or too much rim run out in the back. I would just switch tires and rims from one of my other cars but the model A is using a 5x51/2 bolt pattern. Thanks for the replies.
Sorry, the same car but not those rims. Brakes are 55 F100 fronts and 82 E150 van rears. That pic was after mockup was complete but no rims or tires yet. At that point I still had to take it all apart to paint frame and suspension.
I would bet that one of your tires is out of dynamic balance. The static balance could be perfect, but if the dynamic balance is out, the wheel will normally behave just like you are describing. If the wheel is mounted on the front, and there is a loose frontend component, such as a loose wheel bearing, a small imbalance will be considerably magnified. It is remotely possible that it could be the beginning of a tread separation in a tire, but with this problem, you will normally feel a wiggle at a lower speed as well. Bob
If it has an open rear end that will let you stick a jack under one side of the axle and raise the tire a couple of inches off the floor so you can run it up and see if you have a vibration I'd do that. That will tell you real quick if one side shakes more than the other. Over the years I found out that a lot of drums are out of balance from the factory and will cause a shake that regular off the car balancing won't fix. I had one new out of the box drum so far out that there was no way to balance it. While you are at it set something by the tread and rotate the tire by hand and see if it appears to be out of round. Tire stores have a gauge for that but a Jack stand or anything else that can set up so it is about half way up the height of the tire will let you see if the tire is round or not. At the same time check the side runout the same way. On the driveshaft angles 4x4 trucks run more angle on the driveshafts all the time without excess vibration they just go though more ujoints than a lot of us do. Get over to the hot rod side and a lot of us tend to panic if a driveshaft isn't almost perfectly straight from the trans to the rear with only a slight angle deflection. As someone mentioned not having enough of the yoke in the trans will cause a vibration. That will usually knock out the rear seal and bushing in the trans though.
j-jock; All radial tires (2 new ones in the front & used in rear) were road force balanced. When the new front rims came in the fronts where dynamic balanced. Mr48chev; Yoke is up close & bushing is good. Is it safe to spin one axle at high speed for a short time (maybe 4-5 minutes) while the other one is stationary ? I tried this once but I had both sides off the ground and on jack stands. I didn't notice anything but I though maybe the stands dampened the vibration. My next step is to find a shop that has the old balancer that spins the tire while on the car. I have checked for run out and out of round. There is some but what is acceptable tolerance? It's the car in my avatar but with different tires now.
If you are spinning one rear tire, and the other is on the ground, the spinning tire is spinning at 2X what the speedo says. If your vibration is at 60, the spinning tire should read 30 on the speedo. Gene
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