Bad vibrations (Part 2!)

[Dave145]

The leaf springs are brand new.

Brake drums are brand new raybestos drums.

The pinion angle is fine. -1 degree between tailshaft and driveshaft, +1 degree driveshaft to pinion.

Pinion bearing I would think would make noise. I've had it on stands and run it up to speed and haven't heard anything from the rear end, plus I can crawl under it with the driveshaft off and I can't wiggle the pinion at all.

Front and rear wheel bearings are all new, greased, and properly torqued as well.

Vibration is in the floor and seat.

Tach says it's somewhere between 2100-2300 rpms. Don't remember the exact number off hand.

90% of the time the car vibrates as soon as I hit 70. 10% of the time it doesn't vibrate at all. There's no predicting when it will or won't vibrate, but when it does vibrate it does it exactly at 70 and is felt only in the floor.

 

[Sixpactogo]

I think your pinion needs to go down a few degrees. I know that Spicer and a few others say the pinion and drive train should be parallel but my car didn't like that scenario either. I found another on-line site that recommended the pinion be nosed down 5-7 degrees for axle windup on leaf spring cars. I nosed mine down 3.5 degrees and it still has a little noticeable tremble when I let off on it but at least my rear view mirror is no longer distorted at 70 mph. It seems like our cars are like us. Don't all like the same thing.

 

[5.7 hemi]

I set my Dana 60 at 4* nose down cause it’s a leaf spring car. On the other hand, I set my buddy’s Dana 60 at 0* on his 4 link. Both cars are vibration free.

 

[bearman]

Talk with glenwood he is doing his car for different reason but might have insight. Sorry if I missed it but did you have the rims checked. I know its out there but it sounds like you have done a lot already. If you have done the check then I with trans mount or angle of the dangle.good luck.

 

[747mopar]

The leaf springs are brand new.

Brake drums are brand new raybestos drums.

The pinion angle is fine. -1 degree between tailshaft and driveshaft, +1 degree driveshaft to pinion.

Pinion bearing I would think would make noise. I've had it on stands and run it up to speed and haven't heard anything from the rear end, plus I can crawl under it with the driveshaft off and I can't wiggle the pinion at all.

Front and rear wheel bearings are all new, greased, and properly torqued as well.

Vibration is in the floor and seat.

Tach says it's somewhere between 2100-2300 rpms. Don't remember the exact number off hand.

90% of the time the car vibrates as soon as I hit 70. 10% of the time it doesn't vibrate at all. There's no predicting when it will or won't vibrate, but when it does vibrate it does it exactly at 70 and is felt only in the floor.

Okey doky, not saying it is a pinion angle problem (sounds like it) but if you simply say it's fine because it's -1 and +1 you'll never quit chasing your tail if it ends up being the angle. Once the car is being driven down the road what you measured all changes, how much it changes is the unknown which is why it takes some tuning. Wish it was that easy.

 

[Dave145]

Well then short of tossing money to the wind playing test 'n tune with shims, how am I supposed to know what and where this angle is supposed to be?

This car is bone stock. It hadn't been touched in a long time until the previous owners found it. They monkeyed with it and got it to run, then sold it to me. The anemic poly 318 still lives under the hood, mated to the 727. Everything from the starter to the carb is original and has never been removed. The rear end is the god awful 8 3/4 that's likewise never been apart.

I guess the only reason why I'm not on the same page is because of that. The car is untouched. How could the angle have changed so drastically from the time it was new to now? Assuming worn parts would/could cause this difference, everything underneath this thing has been replaced with new quality components that have been set up to factory specs.

Knowing all this, how could the pinion angle be anything other than what it left the factory with??

 

[Ski 61701]

Did you check your trans mount? Make sure its not torn?

 

[Dave145]

Yeah I crawled around under it today. The mount looks fine. I didn't see any tears or cracks in either motor mount or the trans mount at all. I even poked em with a screwdriver and they're still soft (not mushy soft, but they don't feel like bricks either).

 

[miller]

-New driveshaft with trunnion delete

Any chance the new driveshaft had the balance checked?

 

[Ski 61701]

Yeah I crawled around under it today. The mount looks fine. I didn't see any tears or cracks in either motor mount or the trans mount at all. I even poked em with a screwdriver and they're still soft (not mushy soft, but they don't feel like bricks either).

What you need to do is jack the car up and once its level put a 2x4 on the jack pad and gently jack just the trans up paying attention to trans mount. Even though you poked at it with a screw driver, I personally dont do this because you can take a questionable mount and push it over the edge.
By jacking it up ever so slightly you take the load off and you'll see if you have any tears. You can check motor mounts by putting the car in gear and having a friend gently brake torque it while you look at motor mounts to see if you have any excessive movement.

 

[Dave145]

I've done that with the motor mounts and they are fine. I just checked the trans mount again and it's definitely still solid!

 

[Paul_G]

What you may find is a combination of small problems that together create a bigger one. How old are the trans and engine mounts. They will sag over time, that will change the angles of the drive line.

There are two things to consider with pinion angle, the up/down angle, and the left/right angle. The tail of the trans should be about 1 1/2" off center to the passenger side. It's a Mopar thing. Make sure it is.

 

[Dave145]

The motor and trans mounts are original. I haven't replaced them yet because they appear just fine. The motor doesn't try to jump out of the car when I gun the gas, and the trans isn't rolling around back there either.

Yes the driveshaft was balanced when it was built.

The motor and trans are offset to the passenger side by roughly 1/2". I don't really get why Dodge did this, but oh well.

 

[747mopar]

What you may find is a combination of small problems that together create a bigger one. How old are the trans and engine mounts. They will sag over time, that will change the angles of the drive line.

There are two things to consider with pinion angle, the up/down angle, and the left/right angle. The tail of the trans should be about 1 1/2" off center to the passenger side. It's a Mopar thing. Make sure it is.

This is more often the case then not... many little things.

Well then short of tossing money to the wind playing test 'n tune with shims, how am I supposed to know what and where this angle is supposed to be?

This car is bone stock. It hadn't been touched in a long time until the previous owners found it. They monkeyed with it and got it to run, then sold it to me. The anemic poly 318 still lives under the hood, mated to the 727. Everything from the starter to the carb is original and has never been removed. The rear end is the god awful 8 3/4 that's likewise never been apart.

I guess the only reason why I'm not on the same page is because of that. The car is untouched. How could the angle have changed so drastically from the time it was new to now? Assuming worn parts would/could cause this difference, everything underneath this thing has been replaced with new quality components that have been set up to factory specs.

Knowing all this, how could the pinion angle be anything other than what it left the factory with??

First thing is eliminate everything else like your doing, having the driveshaft checked, checking mounts, tires, leafs, bushings, etc.. when everything else is eliminated then start looking at the pinion angle. If it is speed sensitive and not rpm sensitive then you can bet it's rear of the tranny which narrows it quickly. I've spent many hours diagnosing mine and can tell what needs done just by driving the car but it took a lot of playing around and research.

If you narrow it down to a pinion angle issue simply take it out on the freeway and do some testing, when it starts to vibrate see what lessons it.... letting off and coasting or nailing it and loading the springs. Doing this will tell you if it needs to go up or down. It's not like your throwing money at it either, shims aren't too expensive and are quickly installed.

As for why it started, who knows? Weak springs, Missing leaf clamps allowing more movement, Incorrect shackles, etc? In my case I believe it was my new leafs that threw it off because that's all that changed other than ride height. Again.. not saying it is the problem but don't look at it as a major expense or headache because it's not.

Something I'm going to do this summer is put a go pro camera under my car just for ****'s and giggles to see how much its moving, I bet it will be surprising.

 

[747mopar]

The motor and trans mounts are original. I haven't replaced them yet because they appear just fine. The motor doesn't try to jump out of the car when I gun the gas, and the trans isn't rolling around back there either.

Yes the driveshaft was balanced when it was built.

The motor and trans are offset to the passenger side by roughly 1/2". I don't really get why Dodge did this, but oh well.

It's called driveshaft phasing, you never want driveshafts perfectly straight, they need movement at the universals to keep the bearings moving and the universals need to cancel each other out. Chevies typically offset the pinion and center the engine instead.

 

[Glenwood]

Had a similar problem when I first swapped the 64 rear end with a 70. The pinon was pointing down 7* and the tail was also pointing down 2.5*. Vibrated like a cheap motel bed when I was on the highway. Shimming it by 4* helped but wasn't quite right. I found this explanation helpful.

Found this in a post from Dr Diff regarding setting the pinion angle:

"Pinion angle is the relationship between the pinion centerline and the transmission centerline. It is not relative to the ground nor to the angle of the driveshaft.
Ideally, you want the pinion to become parallel to the transmission under a load, so you point the pinion downward a few degrees when the vehicle is resting on its suspension to compensate for pinion wind-up.
In other words, make the pinion parallel to the transmission as a base line, then roll the pinion downward 2-4 degrees and weld the perches. This is how a 2 joint driveshaft is designed to work." Cass

 

[oldmanmopar]

One thing I did not see mentioned here that I had just found to be causing a vibration of a car that was just here.

The saddles that the drive u-joint sits into on the rear diff on a car that was here did not center the universal joint. Before tightening the straps you could move the joint side to side. Some of these yokes demand the c-clips to hold them centered. Others have a boss built into the out side of the saddle. Check this.

One more thing make sure the shaft is clocked correctly. U-joints should be square front to back. also there is a front and back to a shaft. Weights to the front. Just some suggestions you could try. Steve

 

[Ski 61701]

This happened to me once, I had a driveshaft made for a car new everything, I take it out and I had a slight vibration. Not bad but drove me nuts, chased my tail and I took it out and found another drive shaft shop, sure enough my "new" driveshaft was out of balance, the 2nd shop instead of only spinning it like 900 rpm spun it up to 2,800 rpm. I can't remember at what rpm is started to vibrate, but after I got it back smooth as silk.
Maybe this is your problem, another thing to try if you haven't already is take pinion straps off and rotate the shaft 180 and reinstall, or unbolt from trans flange and shift it that way.

 

[oldmanmopar]

Once had a 4spd car here the vibration was so bad it kept cracking aluminum bell housings. Had the drive shaft made and took it back three times to the same place. We had it on my lift and the shaft would start shaking at 55 to 70.

We put an original rusty shaft in with old u-joints i had laying here. He begged me to sell him the shaft the car never vibrated again. He took the made shaft back to the company that made it and told him the results of what we found. they argued with him until they bolted theirs back in the car and saw for themselves

He got his $346 back and is still driving the car with the $50 rusty shaft from me.

So what I am telling you is never trust one part you replace. Try some tried and true parts from other cars. And it is better to put your parts on cars that work . So test your parts on other cars if guys won't lone you their parts.

 

[Dave145]

I will try flipping the driveshaft and reinstalling it, along with checking the U-joint straps. I sure thought it was centered, but everything is worth a check.

The shop that made my driveshaft has been in business practically since the car was new. It's been recommended to me by several people, but if all else fails it's certainly worth having the shaft checked out again. I have run the car on stands with the rear end supported to match my ride height and watched everything spinning up to 70mph. I have not seen the shaft shake or wobble at all, as well as everything else under there.

While driving the car the vibration starts at 70 and gets worse as you pick up speed. 80 will shake your brain out. It's done this pretty much since I purchased it last year. Most it'll vibrate like no other. Other times it dossn't at all. In other words, 99% of the time it shakes. It feels like the rear tires become ovals or eggs and lope down the highway. It's a vertical feeling vibration. We've tried to pin down where it's coming from while driving the car, but to no avail. I measured everything tonight again under the car. Let me know what you guys think.

Tranny yoke: 3.5° downward
Driveshaft: 2.4° downward
Pinion yoke: 3.5° upward

The trans yoke angle I got by placing my inclinometer on a cast flange that's just behind the bolt area for my driveshaft.

The driveshaft was taken in the middle.

The pinion yoke was taken straight off the yoke.

My tires are currently Cooper cobra GT Radials sized 225/75r15, running on stock 15"x6" stock steel rims. I had the tires and rims checked for runout separately on a Hunter roadforce machine and had them balanced then too. I have tried balancing beads in the tires and the steel weights. No change with either setup.

My second set of tires was a used set of Goodyear Viva 2s mounted on 15"x6" stock steel wheels and balanced using steel weights. The runout for both the tores and the rims was fine when we installed them. We soon found out that one of the tires has a bad belt in it. I guess that's why they were used takeoffs from behind the shop!

The RPMs this begins at is ~2800. Verified with my tach in the car.

My timing is set to 10° BTDC, champion plugs, and oreilly wires. Pro-form dirstributor. Stromberg WW carb that I fully overhauled this winter. She pulls 19" of vacuum at idle as well.

My springs were made by ESPO Springs and Things. I had them make me a pair of stock 5 leafs springs and press in the front bushings for me. I installed the rear bushings and stock shackles myself when I installed the springs.

The wheel bearings have all been replaced, packed, and torqued.

The front end has been fully gone through and all bushings have been reaced with Moog parts. Ball joints and tie rods replaced with Moog parts as well.

I'm not sure if any of this info will help clear anything up, and I'm sure I'm forgetting something or a bunch, but I figured it was worth putting out there what I could come up with at 11:00 at night.

Personally I'm thinking it may be the tires, though I'm not ready to shell out $500 on a hunch...