This is a little long sorry.

Short version - Ryan's Dart 72 Swinger has a vibration. Feels like driveline to me

Long version.

Vibration has been there for a long time. He drives it but doesn't worry much about. I don't drive it but would like it fixed. He went away this week and I again stole his car and thought I'd try and figure this out while he was gone. On drive home it has a serious vibration now. Worse than last I drove it.

The car has a new driveline and it has about 3 1/2 inches spline engagement into the transmission. Transmission was a rebuilt overdrive unit and there is no play at the tailshaft bushing. Rear transmission mount was a brand new poly unit and both u-joints are new. New SS springs. 4.30 rear with cone posi. Street slicks for drag racing, but usually just street tires.


Tonight I found a series of things wrong and I want your help with what to do. I think these are all related and together are the cause of the vibration. I don't want to miss something. Thanks in advance


#1 - Poly tranny bushing mount was broke off. Not the Poly, the steel right beside where it bolts on.

#2 - Driveline has marks on the rear u-joint area where it has been hitting the yoke on the rear end. The car has no traction bars or snubber, so it looks as though the rear was rotating enough on launch that the angle got so bad that the yoke and the area on the driveline where the u-joint caps push into are making contact. ( Yes we need a adjustable snubber, there is no room for traction bars)

#3 -Once the driveline was out you could obviously see the area at the outside of the U-joint cap is pushed down some.

#4 - I noticed that the backlash in the rear seemed to have way to much play.


Plan of action.

Rear goes to shop tomorrow to have it checked. The backlash seemed a lot less once I got it out on the floor. We'll see.

Buy a new adjustable snubber to prevent wind-up

Questions:
1 - Is there any way to tell if the yoke on the rear end is bent? I know it wouldn't take much back there to cause a vibration. Should I just replace it?

2- If I take the driveshaft to a balance shop will they be able to pick up whether or not it is bent clear out at the end where the caps press in? Or should I just have a new end welded on?

3 - I suspect that the damage caused to the tranny mount could have been caused by the hard launches and these 2 items hitting together when they shouldn't? Opinions"

Anything I'm missing? I need to get this done for Mason Dixon for sure!

Thanks Rick

I have found poly trans mounts to transmit way too much vibration. I use poly motor mounts but stock trans mounts.

If the yoke is mashed I would check the shaft for round and install a new yoke.

It would require a lot of spring windup to mash the yoke if your driveshaft angle is correct. Is the angle correct? Is it equal on both ends?
(You can shim the axle to spring to get the correct angle)

See you at Mason Dixon!......

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Sandy, Not sure about the angle. It was a stock rear end out of a 70 Swinger that I bolted into Ryans Dart. I never checked the angle. The yoke on the rear doesn't look damaged, but the end on the driveline where the caps press in has definitely been hitting it.

He was tearing the stock mounts pretty regularly, so he wanted to try the poly mount.

THanks

You really need to cure why it was tearing up stock mounts. I have never broken one, even launching on spray with a trans brake.

Is the motor tied down good?

Is the car jacked way up or real low in the rear?

What kind of shape are the rear springs and shocks in?

I would try a pair of the cheap Lakewood clamp on slapper bars. Make some shims so that the snubber is just off the front spring eye at rest.

Have the driveshaft checked for true and balance when putting the new joints in. If it's bent it will just kill the new joints sooner.

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Official Cookie and Mater Tormentor.

That sounds really serious if the pinion yoke was hitting something (floor?). Could be pinion bearing is really munched? Maybe I am misunderstanding...

Lou

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Home of Slant6-powered fun machines since 1988

I'd venture to guess that if the yoke is hitting the floor the rear springs are worn out.

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Official Cookie and Mater Tormentor.

Yep, could be springs really bad too, and no snubber is not a good idea. At least get a stock snubber on there.

Lou

_________________
Home of Slant6-powered fun machines since 1988

Ok, I may be explaining poorly. Please forgive me.

The engine has new stock mounts and is bolted down with a turnbuckle to hold it in place when at the strip and running the street slicks.

There is a stock snubber on the car, not an adjustable one though.

There is not room for bolt on traction bars, with his slicks. The Lakewoods he had on before hit the inside on the tires. If we space out the wheels they would hit the fenders.

The springs are new(last year) Super stock A-body springs and the car does not set very high. A little bit higher than stock. Lou has seen it a few times.

The Shocks are new new Gas-A-just I believe


The pinion yoke is not hitting the floor. The yoke on the rear is making contact with the end of the driveline. I try and explain.
With the car at rest and driveline in place, say you have 3/4" between the end of the driveshaft (Where the caps are pressed into) and the yoke on the rear. On launch as nose of the rear goes up that 3/4" on the bottom side of the yoke(closest to the ground) gets closer & closer as the nose goes higher. Obviously the top side of the yoke gets a correspondingly wider distance. Anyway, the axle windup appears to have been bad enough that the 2 pieces (rear end yoke & the end of the driveline) came into contact. Boy that is harder to explain than you think. Does anyone understand what I am saying? Hopefully.

I got the rear back and the backlash is fine. He also said that it would be awful hard (not impossible) to bend the yoke, but put everything back together and check the runout on the driveline right in front of the rear U-joint and see what the runout is. That is my plan right now.

So what could be breaking the rear tranny mounts?

I will try and check the pinion angle as well.

Thanks for the help.

Rick

OK, I think I get it. Sounds like the pinion angle is too large (nose of diff up). Hard to believe that is happening with that car setup.

Lou

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Home of Slant6-powered fun machines since 1988

Yes Lou, I just took a quick peak at the rear end this morning before I left for work and it most definitely is pointiing up. I bought a Magnetic protractor today and will check the angle when I get home. I looked in my(65 Plymouth) FSM to see a procedure and it is no help that I can see. I don't even see recommended angles listed in there unless I missed it. It talks about special tools...etc. So is there a simple step by step somewhere.

Thanks,

Rick

Stick car you want the pinion 3-4* nose down relative to the angle of the trans/motor. Also make sure the motor/trans are in line with the diff.

I had to trim my Lakewoods to get them to clear the rim, but it is doable.

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Official Cookie and Mater Tormentor.

Ok, I have read 27 different ways to Sunday on how to measure this and I am still and not sure what I'm reading. So please help.

Engine and transmission 1 degree down
driveline angle - 2 1/2 degree down
rear yoke angle 5 1/2 degree up

Dennis, are you saying this is 4 1/2 degrees up? And don't worry about the driveshaft angle? If this is the case I need to go 7 or 8 degrees to get to 3 or 4 nose down.

Also the stock pinion snubber is 4" from where it would touch the floor pan. It has never touched the floor.

I put a dial indicator on the driveline and placed it right at the rear end of the shaft . As I rotate the shaft and it passes the area where the driveline has hit the yoke it has about .012-.015 blip on the dial indicator then comes back close to zero until it gets to the other side where it has hit and it has about the same reading.

I move the indicator to the center of driveshaft and it has close to .030 runout. Is it time for a new shaft? Time for a new end that was damaged and rebalance? Or should I correct this angle problem and drive it first and see if the vibration is gone?

Thanks, Rick

If I have to go that far am I better off to just cut off the perches and weld on a new set where they need to be? I see most of the shims come in 2-4 degrees? HAve to search to see if they make an 8*

Thanks, Rick

Rick,

The angles you measure to determine nose-up or nose-down is the difference between the driveshaft and pinion angles. Having the pinion pointed straight at the driveshaft would be 0°. The pinion needs to be 5-7° down toward the ground relative to the driveshaft. The angle to the ground doesn't really matter. It appears someone welded the spring perches on backward in regards to pinion angle so they got is 5° up instead of 5° down. I think you have a cut and weld project at this point.

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Joshua

Josh,

Thanks for the response, and I figure that it would probably be just as well to cut them off and weld new ones on. However I still don't understand.

Dennis says 3-4 down relative to the engine/tranny (I understand this)
Your saying 5-7 down relative to the driveline? (Not sure I understand this)

It doesn't seem that those 2 ideas are the same.

Please help. If I cut these things off I want to weld them on correctly the first time.


Rick Covalt