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1995 Roadmaster Sedan
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Discussion Starter · #1 ·
Just finished installing a new 3.5” 1350 driveshaft I had built because of a vibration in the stock DS. Took it for a spin and above 60mph there is a significant vibration. Worse than the stock DS. Got it up on jack stands, put it in drive got it up to 40mph and can see a visible wobble. Took some video but am unable to post it. I take it there’s not supposed be a visible wobble?
 

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No there should not be.
In a perfect world it would be perfect.
In the real world .010 -.015 indicator ?
You need to make many checks to see what is going on before you approach the builder.
Front run out
Center run out
Rear run out
Next you need to determine if your front or rear yoke is a cause or contributor.
Rear is easy , mark and record the rear runout.
Disconnect and reconnect 180 ° out.
The new numbers will tell you if it is shaft , yoke , or both.
If it is worst in the middle then no amount of playing - fudging is going to solve the issue.

Various people have had good and bad results from many vendors.
My go to is Mark Williams for a 1350 driveshaft and 1350 yokes
 

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I had the vibes around 67 MPH ... then I took off the drive shaft and then the U joint next to the rear diff. rusted binding..
I put the marks on the shaft and the yokes .. replaced the U joints ... then the drive shaft has no vibs ,, works great when I did my job...some drive shafts had the fall off the weights in the old decades ..
 

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Discussion Starter · #4 · (Edited)
No there should not be.
In a perfect world it would be perfect.
In the real world .010 -.015 indicator ?
You need to make many checks to see what is going on before you approach the builder.
Front run out
Center run out
Rear run out
Next you need to determine if your front or rear yoke is a cause or contributor.
Rear is easy , mark and record the rear runout.
Disconnect and reconnect 180 ° out.
The new numbers will tell you if it is shaft , yoke , or both.
If it is worst in the middle then no amount of playing - fudging is going to solve the issue.

Various people have had good and bad results from many vendors.
My go to is Mark Williams for a 1350 driveshaft and 1350 yokes
It was a local guy that came highly recommended by a few people I know that drag race and road race.
Check the run out by putting it in neutral and spin it by hand with a dial indicator?
Front yoke is brand new. Came with the driveshaft. Rear yoke is a fairly new GM 3r less than 2k on it and about 6 months old.
Waiting to purchase a 1350 8.5 pinion yoke and really don’t feel like opening the rear again until spring.
After paying $720 for this one. I should’ve just bit the bullet and went with a MW unit. But hindsight is always 20/20.
Thanks!
 

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Yes exactly , dial it by hand .

Once you figure out the where and way and how much , you can approach the builder with solid info.
While not often , new yokes can be out.
If it is the shaft and you are stuck with it , there are things you can do if it is out on the ends.
There are hard to locate selective thickness clips. You can also grind- shim 1350 clips .
Yeah you should never have to to that but sometimes " the cards you are dealt "
Problem is if it was balanced with run out , that goes for a crap.
" should of "
I had a 5" Silverado SS shaft shortened locally for my wagon. They made a right mess out of it.
Another shop had lots to say about the first shop but when they got completely different run out numbers than me I took it home and pulled the weights + fudged the clips.

Worked fine to 110 mph with 4.56
It was shelved for a MW carbon and billet yokes when I did the drivetrain swap.

A word on yokes , you will find many of the driveshaft company's high end option is MH.
Says something when someone is selling a competitors product.
 

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Discussion Starter · #6 ·
Yes exactly , dial it by hand .

Once you figure out the where and way and how much , you can approach the builder with solid info.
While not often , new yokes can be out.
If it is the shaft and you are stuck with it , there are things you can do if it is out on the ends.
There are hard to locate selective thickness clips. You can also grind- shim 1350 clips .
Yeah you should never have to to that but sometimes " the cards you are dealt "
Problem is if it was balanced with run out , that goes for a crap.
" should of "
I had a 5" Silverado SS shaft shortened locally for my wagon. They made a right mess out of it.
Another shop had lots to say about the first shop but when they got completely different run out numbers than me I took it home and pulled the weights + fudged the clips.

Worked fine to 110 mph with 4.56
It was shelved for a MW carbon and billet yokes when I did the drivetrain swap.

A word on yokes , you will find many of the driveshaft company's high end option is MH.
Says something when someone is selling a competitors product.
Yes exactly , dial it by hand .

Once you figure out the where and way and how much , you can approach the builder with solid info.
While not often , new yokes can be out.
If it is the shaft and you are stuck with it , there are things you can do if it is out on the ends.
There are hard to locate selective thickness clips. You can also grind- shim 1350 clips .
Yeah you should never have to to that but sometimes " the cards you are dealt "
Problem is if it was balanced with run out , that goes for a crap.
" should of "
I had a 5" Silverado SS shaft shortened locally for my wagon. They made a right mess out of it.
Another shop had lots to say about the first shop but when they got completely different run out numbers than me I took it home and pulled the weights + fudged the clips.

Worked fine to 110 mph with 4.56
It was shelved for a MW carbon and billet yokes when I did the drivetrain swap.

A word on yokes , you will find many of the driveshaft company's high end option is MH.
Says something when someone is selling a competitors product.
Awesome! Thank you for the advice. I won’t be adding shims or messing with the DS. That’s on the guy who made it. $720 is a good chunk of money and I honestly don’t have a clue what material he used. It’s not aluminum and is about a third heavier than the stock one. Be it mild steel or chrome moly? A little pissed at myself for not going the MW way.
 

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Well as noted...the ship has sailed relative to where to get a DS.

MW is arguably top shelf. Alternate would be Denny's. I have his 1350 3.5 AL in the Impala. Have his 1330 yoke 3.5 in my 67 Camaro

Both are smooth as silk and the Imp has 4:10 gears
 

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Discussion Starter · #9 ·
UPDATE
I took the DS to a shop that looked it over. Both ends were out by 20 thousandths and the yokes were out of phase. Cost was $60 to cut the ends off and re weld/rebalance. So hopefully tomorrow when it stops raining I’ll throw it back in and be cruising.
I’m definitely calling the guy who built and let him know. Not sure if he got in a rush or if his equipment is out of calibration. I’m hoping that he’ll at least pay for the fix.
 

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Discussion Starter · #10 · (Edited)
UPDATE 2.0
Well, I got the DS back from the other shop that repaired shop #1’s crappy DS and installed it today. Just got back from test driving it. The only change is it vibrates at 50 mph now. I’m racking my brain trying to figure out what it could possibly be. With the stock DS it vibrates 65mph and up, but is bearable.
Any ideas are welcome. Trying not to eat $780 for a crappy DS if I can. $720 to have it built and $60 to have it fixed not counting the diesel to make a 2 hour round trip. I feel I already have too much money in now.
 

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Anything ideas are welcome.
Sorry I have questions not answers.
Has your axle been moved back?
Are you at stock ride height?
Are your pinion angles equal?
Are the two yokes going the same distance into the tail?
Do the two yokes have the same amount of spline contacting the tail shaft?
What diameter is the new shaft?

Question for the forum. Can the tail shaft bushing be worn or damaged without showing fluid leakage?

I seem to be the lucky one with the hotchkiss arms AND 3.73 but no shake up to red line with what looks like a OEM driveshaft.

I honestly don’t have a clue what material he used. It’s not aluminum and is about a third heavier than the stock one.
I would have expected with 3.73s any drive shaft company would have suggested aluminum.
 

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I bought an old aluminum Crown Vic police DS for $35 at the local junkyard, and it cost me $125 to have it shortened, and balanced. It runs flawlessly.
 

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Discussion Starter · #13 ·
They are the same length just bigger joints.
Stock control arms, pretty much stock height. Might be a 1/2” lower.
New shaft is 3.5”
 

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Discussion Starter · #14 ·
I bought an old aluminum Crown Vic police DS for $35 at the local junkyard, and it cost me $125 to have it shortened, and balanced. It runs flawlessly.
I doubt I’d be able to find one around here. But appreciate the advice.
 

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They are the same length just bigger joints.
Stock control arms, pretty much stock height. Might be a 1/2” lower.
New shaft is 3.5”
What are the same length? It was shortened by about 2" to match the stock DS. Yes it has larger universal joints, so, I used an adapter joint.
 

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Discussion Starter · #16 ·
What are the same length? It was shortened by about 2" to match the stock DS. Yes it has larger universal joints, so, I used an adapter joint.
Sorry for the confusion. I was answering the question prior to your post.1
 

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UPDATE 2.0
Well, I got the DS back from the other shop that repaired shop #1’s crappy DS and installed it today. Just got back from test driving it. The only change is it vibrates at 50 mph now. I’m racking my brain trying to figure out what it could possibly be. With the stock DS it vibrates 65mph and up, but is bearable.
Any ideas are welcome.
Answers to ?'s from post 11 would help as they all affect DL vibrations

Unless the #2 shop, and the original one, has the high $ high RPM balance machine (few do) than DS vibrations often result of aftermarket DS ESPRCIALLY if you have one or more of the ?'s post 11 asks (lower than stock gears, lowered car, rear axle moved back)

IIRC Dennys DS can balance to 8k RPM. I have two of their 3.5 aluminum shafts and both are smooth as butter even on my 4:10 gear Impala SS (stock height and rear axle position)

At this point you need to confirm your DL angles are in spec especially if the answer to the ?'s asked from #11 regarding lowering or extended control arm exist

You could 180 the DS at rear yoke to see if that helps...likely not as the pinon was not included in the balance (stock DS was) process but costs no $ and takes little time

Did the 2nd shop mention anything about runout? (read did either shop confirm it has none)
 

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Discussion Starter · #18 ·
Answers to ?'s from post 11 would help as they all affect DL vibrations

Unless the #2 shop, and the original one, has the high $ high RPM balance machine (few do) than DS vibrations often result of aftermarket DS ESPRCIALLY if you have one or more of the ?'s post 11 asks (lower than stock gears, lowered car, rear axle moved back)

IIRC Dennys DS can balance to 8k RPM. I have two of their 3.5 aluminum shafts and both are smooth as butter even on my 4:10 gear Impala SS (stock height and rear axle position)

At this point you need to confirm your DL angles are in spec especially if the answer to the ?'s asked from #11 regarding lowering or extended control arm exist

You could 180 the DS at rear yoke to see if that helps...likely not as the pinon was not included in the balance (stock DS was) process but costs no $ and takes little time

Did the 2nd shop mention anything about runout? (read did either shop confirm it has none)
Questions were answered in post 13 and my signature.
Axle is in the same spot and stock upper and lower rear control arms
The car is 1/2” lower tops.
Gear is 3.73. Stock driveshaft had a noticeable but bearable vibration. Even with a new pinion yoke which was changed when the gears and a new posi were installed.
I don’t see how a larger diameter driveshaft would change the pinion angles if nothing was changed but the diameter of the tube and the size of the joints. Both driveshafts are within 1/8”-1/4” of each other in length. I’ll check the pinion angles when it gets warmer.
I did turn the shaft 180 degrees and it helped just a little, but it’ll still rattle the mirrors where you can’t see anything in them.
As far as high speed balancing is concerned, I’m sure it’s great, but there’s enough evidence I’ve found, that supports it not being needed.
Shop #2 found the yokes were out of phase and the shaft had .002 runout on both ends which would explain the initial vibration.
I’ve done a little more research and I’ve found people having vibrations at half critical speeds. This is where I’m leaning towards.
I’m re doing the tailshaft bearing/seal and buying a new 1350 pinion yoke with new u joints. It has a new 3R yoke on it now.
 

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Gear is 3.73.

I don’t see how a larger diameter driveshaft would change the pinion angles if nothing was changed but the diameter of the tube and the size of the joints.
.
As far as high speed balancing is concerned, I’m sure it’s great, but there’s enough evidence I’ve found, that supports it not being needed.
A larger diameter DS will not affect DLA...it will however move the critical speed balance up the RPM range (good)

Don't know what evidence you found that says high speed (RPM) balance is of no benefit...its everything

Most Stock B bodys had 1-2 shims between trans & rear mount. If trans has been out for service these are often not re-installed....check if yours are there. If just 1, add a second one to see if that resolves your problem. This would show up by checking DL angles...which is something you should do before spending any more time & dollar on other than a quick look if shims are there.

IMHO don't use the Tremec phone app to measure DL angles, get a cheap magnetic angle finder
 
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