Bad vibrations (part 3)

[Dave145]

I still can't get rid of this vibration in my '64 Polara. Here's hoping this thread won't need a part 4...

Here's the scenario. It vibrates from 65mph on up. Currently it starts with what feels like a bad u joint kind of vibration in the rear, then by 70-75mph it starts a pounding kind of vibration under the front seat. Steering wheel is steady and doesn't vibrate. Coasting and decelerating has no effect on the vibration. Putting the car in neutral doesn't affect it either.

The car is a '64 four door hardtop Polara. It's got a bone stock Poly 318/727 in it, along with it's its original 741 case 8.75 rear end (2.76 ratio).

To date, here's what's new/replaced, for those who are just tuning in PR don't want to read the other threads on this (they're really long and hard to weed through).

New rubber motor mounts
New polyurethane transmission mount
Motor verified level when mounts were installed
Full tune up (NGK plugs, O'Reilly wires)
Pro-form electronic ignition kit (orange box)
New cap and rotor with distributor
Accel super stock coil
Rebuilt Motorcraft 2100 carb (originally was a very worn out Stromberg)
New Monroe shocks in the front
New Gabriel air shocks in the rear
Front end rebuilt with Moog bushings
Tie rods, ball joints, pitman and idler arms replaced with Moog components
Stock torsion bars
New timken wheel bearings up front (inner and outer)
Front brake drums have been turned
Rebuilt original ball and trunnion driveshaft and replaced ujoint
Later replaced driveshaft entirely and had one made with two ujoints and a slip yoke *this shaft is currently in the car*
Replaced rear brake drums and converted to 65-up "slip on" drums
Replaced rear wheel flanges (part with wheel studs in it)
Replaced leaf springs with new ones from ESPO. Stock 5 leaf springs.
New gas tank, sending unit, fuel pump, fuel filter
New rear outer wheel bearings
Tried two sets of steel stock wheels
Tried three different sets of tires (current tires are MasterCraft Avengers 215/70r14 size)
Aligned at a local shop in town
Rebuilt all brakes and verified ebrake isn't hanging up or sticking.

At this point we are still questioning pinion angle. Here are the measurements I took last night usuing my phone's inclinometer.
Trans: 3-4 degrees down
Driveshaft: 2.1 degrees down
Pinion: 4 degrees up

I have tried adding 2 degree shims under the rear end to give me 2 degrees up. This didn't change the vibration at all.

I have 70lbs of air in my rear shocks to give the car a forward take a bit. Vibration is the same with shocks aired up or down.

Tires have 32lbs of air in each tire.

The car does not vibrate idling at any rpm. Car vibrates regardless of if it's warm or cold outside.

That's all I can think of for now.

 

[PurpleBeeper]

Man...that sure "sounds" like you've got a bad rear bearing/bushing in your transmission. If you grab ahold of the front yoke, can you wiggle it up & down or side-to-side at all? It should be pretty darn tight. I've had the symptoms you describe with this problem before.

I've also gotten your same symptoms when I had a driveshaft about 2"-3" too short. The front yoke wouldn't fully locate onto the transmission tailshaft splines....I mean it "looked good", but wasn't....if there's much more than about 1" of the splined sleeve part of the front yoke showing, you might have this problem. Hope this helps

 

[Fran Blacker]

I still think your rear trans bearing/bushing could be the problem. I had a bad vibration as you describe. Mine was a bushing, not sure what's in a trunion trans. The new bushing had 2/3 thousands clearance, no vibration after changing it. Old bushing had .010 to .014 clearance. If you can any play in your trunion flange that where I'd look. Don't think you need to pull trans to change bearing/bushing.

 

[Dave145]

I have grabbed the flange and attempted to wiggle it, but it doesn't move. However would I feel the .01 or so of clearance just by wiggling it? A agree that it sure "seems" like a likely candidate. It has recently begun dripping (maybe seeping is a better word for it) fluid out of the tailshaft as well.

 

[Glenwood]

Pinion angle is wrong. It looks perfect right now until you drive it. If your transmission is down 3 degrees your pinion needs to be down also as it will come up when you are driving. If your measurements are accurate you should point the pinion down by 1-2 degrees. It travels up 3-4 under acceleration loads and higher under heavy load like launching. You can get some 5-6 degree shims to point it down to try. I went through the same thing on my 64 polara. Check my thread in the last few pages where I install new perches to correct the angle. I used a proper angle finder though. I don't trust apps for this.
Mine is perfect now with the old drive shaft and the new conversion like you have.

 

[Dave145]

I thought my numbers looked pretty off. I've read about pinion angles all last night. I can't tell though, do I want my angles "equal but opposite" at rest or while driving? Seems like I'd want them like that while driving correct? A friend of mine has a better tool for checking pinion angles, so I will try to get a hold of him to get more exact numbers.

 

[Glenwood]

The angle finders are cheap, about $20 or less usually. It can be tough to measure without a wheel type lift as all four wheels have to be on the same plane.
The goal is to end up with equal angles opposite each other when under load. So you allow for a pinion shift upwards of approx 4 degrees from rest to get there.
Transmission down 3 degrees = pinion down 1 degree so when it shifs up 4 degrees under load it will be approx 3 degrees up and equal but opposite of the trans.
According to your measurements, your pinion will be up approx 8 degrees under load or 4 deg higher than it should be.
I think racers will point the pinion down as much as 7 degrees to compensate for hard launches and reduce stress on ujoints.

 

[Glenwood]

Try installing your shims the other way to bring it down and see if you notice a difference. They may not be enough but you should see a change if your measurements are correct.

 

[747mopar]

Could be a few things, the POUNDING you describe really doesn't sound like an angle issue but I wouldn't rule it out. I've dealt with them with mine and it was just a bad vibration but no pounding. I think the driveshaft length is something worth looking into as well. Are you the same guy that's been all through this on other threads? If so you might bring everyone up to speed on what you've already done.

Bad thing about tuning driveshaft angles is it's hard to know what's going on under there in driving conditions without throwing a go pro under it. You might set it up perfect but a weak set of springs will allow movement under load throwing it back off. This is where being extremely observant comes in, if it's an angle problem you can generally get a handle on what's going on by bringing it up to the speed where it vibrates then lay into it hard then repeat only letting it go into coast. If either lessons it you know which way to move the angle. If it gets better under hard acceleration try moving the pinion up, if it gets better in coast then move it down. Check your leafs out too, missing spring straps (the thingies that bind the stack together) will allow more pinion movement as well.

I think your best bet is to reach out to someone to give you a second set of eyes and ideas, easy to overlook something not to mention it gets aggravating quickly.

 

[Glenwood]

The thing is if your measurements are wrong, the axle is original and unaltered and the trans angle is in the stock position, it should be correct. the issue could be in the transmission, tail bearing and or the differential as mentioned by others.

 

[brian6pac]

pinion angle?

 

[Jcharger]

Long shot, but check the side to side angles too. I didn't see what gear you are running. I had issues and they were pinion angle, but they changed with deceleration and acceleration, and I ultimately had to have very low angles. Also had to have the driveshaft balanced 2 times (a truck shop ultimately did the trick). It sounds like you have thought about all of these things so just tossing out ideas to see if they happen to stick or help.

 

[MoparLeo]

Just more info:
http://www.moparts.org/Tech/Archive/axle/8.html

 

[Dave145]

Alright everyone I'm back. Took the weekend to spend some more quality bonding time with the car. Here's what I got.

I decided to get rid of the air shocks. I purchased a shackle kit to give the car the stance I want. I also installed new rear gas shocks. Then...

I finally was able to borrow my friends pinion angle gauge. I will post a photo of it so everyone knows what it looks like. As the car sat at the time of the first test, it tunrs out I had:
1° positive (downward) off the tailshaft
1.5° negative (upward) off the pinion

Seems like the kind of angle I would want while cruising under load...not sitting still statically. My friend advised me to set the pinion down 4° to accommodate any wind up the pinion may have. Fortunately, I had some 4° shims laying around, so I slid them under the axle. After remeasuring my angles, I currently have:
1° positive (downward) off the tailshaft
3.5° positive (downward) off the pinion

Numbers look good to me. Took it for a drive. No more shudders during Accel or decel. No more grinding feeling at the rear u joint. However, under seat vibration remains the same. Starts at 65-70 and gets worse going up.

I am next going to check the side to side angles of the driveshaft at the tranny and pinion to make sure they are equal.

I may throw a tailshaft bushing in for shits and giggles...provided I can find one. Seems most places online don't even show a bushing for a '64 727...just the later 67+ 727s. Anybody have any insight here?

I have a feeling when I had my new driveshaft made, that it was not balanced with the slip yoke/front u joint assembly attached to it. I am considering buying a trunnion rebuild kit for my old shaft, rebuilding the trunnion joint, and then taking my original driveshaft to a different shop to have it balanced. Only reason for this consideration is that the b+t joint shaft was used forever...up to '70 in A100 vans...so there must be a reason why they favored it over a conventional slip yoje and ujoint up front. Right?

 

[Dave145]

I will try to upload the pictures tonight. My phone is being stupid again.

 

[5.7 hemi]

I could have swore that a few members on here told you to check pinion angle months ago. But nonetheless, you’ve finally got “most” the problem figured out.

 

[khryslerkid]

Alright everyone I'm back. Took the weekend to spend some more quality bonding time with the car. Here's what I got.

I decided to get rid of the air shocks. I purchased a shackle kit to give the car the stance I want. I also installed new rear gas shocks. Then...

I finally was able to borrow my friends pinion angle gauge. I will post a photo of it so everyone knows what it looks like. As the car sat at the time of the first test, it tunrs out I had:
1° positive (downward) off the tailshaft
1.5° negative (upward) off the pinion

Seems like the kind of angle I would want while cruising under load...not sitting still statically. My friend advised me to set the pinion down 4° to accommodate any wind up the pinion may have. Fortunately, I had some 4° shims laying around, so I slid them under the axle. After remeasuring my angles, I currently have:
1° positive (downward) off the tailshaft
3.5° positive (downward) off the pinion

Numbers look good to me. Took it for a drive. No more shudders during Accel or decel. No more grinding feeling at the rear u joint. However, under seat vibration remains the same. Starts at 65-70 and gets worse going up.

I am next going to check the side to side angles of the driveshaft at the tranny and pinion to make sure they are equal.

I may throw a tailshaft bushing in for shits and giggles...provided I can find one. Seems most places online don't even show a bushing for a '64 727...just the later 67+ 727s. Anybody have any insight here?

I have a feeling when I had my new driveshaft made, that it was not balanced with the slip yoke/front u joint assembly attached to it. I am considering buying a trunnion rebuild kit for my old shaft, rebuilding the trunnion joint, and then taking my original driveshaft to a different shop to have it balanced. Only reason for this consideration is that the b+t joint shaft was used forever...up to '70 in A100 vans...so there must be a reason why they favored it over a conventional slip yoje and ujoint up front. Right?

What I'm reading is that you have the trunion converted to a slip yoke? Like in this picture.

If you do, make sure the yokes are orientated the same, front and back. Also make sure there is plenty of shaft inside of the front yoke. Push up and down in this area for play. Check with the weight of the car on the axel. Your driveshaft shop needs to balance the shaft with the yoke attached and check for trueness. I've heard that some shops don't have an adapter for the front flange. Find a shop with one or your shop needs to have one made.

 

[khryslerkid]

Let me clarify the yoke orientation with a pic...

 

[Dave145]

Yes that is exactly howy driveshaft is built. Your point about shops not balancing the yoke with the shaft is my main concern. They originally told me they couldn't balance a bolt on driveshaft like mine. Then the called me telling me it was done. I assumed they found a way to.balance the bolt on shaft...something tells me they balanced the shaft with the yoke off which is why I'm having an issue.

 

[Glenwood]

Can you try the old one now that the pinion is at a better angle?