Looking for some ideas for a problem I am having. I have a 302/C-4/9 inch set up in a 52 Panel. Under full power, no vibration. When cruising or decellerating above 60 mph, pretty noticable vibration. I change U-joints, no joy. I have measured the angles on the tranny and rear end at 4.5 degrees up (engine pointing up) and 6 degrees up for the pinion input. I think the pinion misalignment may be my problem. Any suggestions?

 

Check to see if the driveshaft is balanced. Sometimes the weights come off. They should also be able to help you with the pinion angles. The U-joints could also be worn. Look for a local driveline shop (custom driveshafts) to help you.

 

Thanks for the input. I examined the driveshaft an all the weights are there, no evidence of anythin missing. I have replaced both U-joints since the problem arose. It has been a gradual thing, getting worse as I put miles on it.

 

If you have 6 up on one and 4.5 up on the other... your center lines are not parallel... the center line of the transmission and the centerline of the pinion need to be parallel... no matter what the angle... isn't that right ??

John

 

Here's a nice little article about how to set pinion angle

http://www.carcraft.com/howto/91758/

 

We need the driveshaft angle to correctly calculate your angles. As just comparing the transmission to the pinion won't give you the true story. Both could be parallel but the joint angles could be too much.

This shows the basic angles.

This is just an example to show you how to calculate the U-joint angle.

 

What kind of motor mounts are you using (rigid or some type of anti-vibration mount), and is this new or has it always been like this?

 

you are correct john,the line's need to be paralle.then when you find that angle you push the pinion down 2 or 3 degree's to compensate for when it is under tourqe from the engine.under that tourqe the line's will come back to the parelle line.this is what i have done over the year's and it has worked ok for me.

 

Do I understand right that your engine is tilts up front-to-back? That the tailshaft of the tranny is higher than the crank snout? Like this / \ ?

Normally the tranny output shaft points down 3-6 deg. You want your pinion to point up an equal amount. Like this: \ \ That aligns the centerline of both the engine crank and the pinionshaft.

They can be offset from one another up/down or sideways as long as the centerline parallel. You do want some offset, otherwise the u-joints will fail from lack of lubrication. Don't make it like this: _ _

Practical ramblings fwiw:
On a fullhouse dragster dumping total torque over a quarter there is a benefit to dropping the pinion to allow for axle wrap. No so on our drivers as you'll get momentary wrap up, but it drops back to the rest position as you drive. Take the box off your truck and watch what happens.

2. If the pinion and crank centerline are parallel it doesn't matter what the driveshaft angle is - it will be equal and that's all that matters. Studies I've seen indicate that 13 deg is about the limit a u-joint can operate and failure rate is high at that point. Try to keep the offset less than 6 deg.

 

Thanks for the reponse. No, the engine and tranny tilt 4.5 degrees down when looking from front to back, like this \. The pinion shaft is tilted up 6 degrees like this \. So, they are fairly closely aligned \\, just 1.5 degress out of parallel at rest. I ordered a 2 deree shim from Summitt Racing last night which should put me at 4.5 in the front, 4 at the rear at rest. Any torque should keep it within reasonable limit. What puzzels me is the vibration is in a cruise mode or decel mode, not under hard accel.

I will let you know what happens with the shim in place.

 

Thanks for the link. It looks like there are as many opinions as there are angles. I guess it depends on the use of the vehicle. Mine is a daily driver that I occasionally get on to mess with some Camero driver. I am going to try the 2 degree shim which will take me to 1/2 degree out of parallel. After I get that shim in place I will measure the angle between the tranny and drive shaft and the drive shaft and pinion. That is my plan of attack.

 

The engine mounts are anti-vibration Ford truck mounts. I can not remember the year or type. The truck had the 302 conversion in it when I bought it. I replaced the mounts when we rebuilt the engine and suspension. The vibration was not there before the engine rebuild. The engine was moved back 3/4 inch to allow more room for the Thunderbird power rack. That would have change the geometry some. Shortly after getting back on the street, I broke the welds on both spring perches. A fabricator rewelded them for me (I don't have the equipment or expertise for that one). After he was done, there was a small vibration that has continued to get worse, like a bad u-joint. The u-joint was new when I put the truck back together 1,500 mile ago.

 

I'll offer up my experiences to date, in possibilities it's not pinion angle related. I have a '51 F1, Flat V8, stock 3 speed, 9 inch rear out of a '68 Ford. I had to shim the axle a bit more than most I've read, rather than cutting the perches and rewelding, but my measurement was verified by two other people as matching the trans and pinion perfectly. Still had vibration between about 55 to 63 mph. Had a new driveshaft made and balanced, still had the vibration. Took truck to a tire shop that did a "road-force" balance on the tires, where they don't just spin it and hammer on a weight, but they actually dismount the tire and rotate on the rim to match as perfect balance as they can, then balance it with weights. They found each tire was out some (bought them originally and installed at Walmart), and found one tire had a broken belt in it and was not able to be balanced. Walmart replaced it for free, it only had about 500 miles on it. After all the balancing, I think it knocked out a good 80% of the vibration. Now, I still have a mild one and am thinking possibly one of the brake drums are warped. It's the only other thing spinning in the drivetrain that hasn't been replaced, and sometimes pulling up to a stop with the brake lightly applied, the truck seems to bounce up and down with a rythm that in my head at least feels like it's very quickly braking and letting off, like a drum is warped and dragging a little each turn of the wheel. All the drums are brand new, but who knows if someone didn't drop one of them at the factory or parts shop.

Anyway, thought I'd offer everything I've worked on to eliminate vibrations, just so you don't get stuck focused on the pinion angle.

 

Thanks for you input. I'm glad I'm not the only one with vibration challenges. My life has been hectic this week so haven't had the chance to get back under the truck. I found some 2 degree shims at Summit which should be here today or tomorrow. My plan is to go over the mounts with a fine tooth comb to make sure everything is straight and tight, drop the rear end and shim it with the 2 degree shim and test drive to see if it changes. I also have a set of 4 degree and might try them and adjust the tranny higher. If that isn't the problem, will start looking at brakes, etc. Thanks again for everyones input.

 

Scott123- Does your brake pedal pulsate on application of brakes? I should think a drum out of round would cause same.