Drivetrain vibrations while accelerating - Ideas?

[LS3Z]

Just picked up a well built beast of a 280Z.  New to Zs, new to LS engines so I am learning a lot.  I have been scouring this forum for weeks now.  The car I got is well built using quality parts and deep pockets.  One of the first things I noticed while accelerating, other than the insane acceleration, is a vibration equal to the frequency of the driveshaft.  It is not terrible, but it is an easily noticed rumble.  It is only there while accelerating, not deceleration, not cruise at any speed.  Brand new driveshaft shop driveshaft and Hoke engine/trans mounts.  With higher HP/Tq setups, is some vibration normal for these cars?  Any ideas where to start looking?  Thanks and I look forward to learning from you all and eventually becoming a solid contributor to the knowledge base.

Edited June 9, 2017 by LS3Z

[ZHoob2004]

What does your differential mount look like? With the torque that LS is putting out, I wonder if it's moving the nose of the diff enough to misalign your driveshaft and that's where your noise is coming from. I know a lot of people switch to the Ron Tyler style mount to cope with the added torque.

[NewZed]

That's a logical point.  Misalignment only during acceleration.

 

Not a lot else to go on.  Assuming an LS3 due to forum name choice.  And " Brand new driveshaft shop driveshaft and Hoke engine/trans mounts".  Not even really clear what the Hoke parts are.

 

http://hokeperformance.squarespace.com/store/

 

http://hokeperformance.squarespace.com/ls2-engine-mounts/

[LS3Z]

Sorry for the late response, had family in town all weekend so no time for wrenching or researching

That's a logical point.  Misalignment only during acceleration.

 

Not a lot else to go on.  Assuming an LS3 due to forum name choice.  And " Brand new driveshaft shop driveshaft and Hoke engine/trans mounts".  Not even really clear what the Hoke parts are.

 

http://hokeperformance.squarespace.com/store/

 

http://hokeperformance.squarespace.com/ls2-engine-mounts/

Hoke takes your cross member and welds in everything needed for the engine install.  They then powder coat it and send it back to you.  They also provide the engine/trans mounts.  A very robust engine installation solution that is 100% bolt in.  

Car/engine specs are in my signature

 

What does your differential mount look like? With the torque that LS is putting out, I wonder if it's moving the nose of the diff enough to misalign your driveshaft and that's where your noise is coming from. I know a lot of people switch to the Ron Tyler style mount to cope with the added torque.

All of the diff mounts look stock.  I have been thinking the same thing as you with misalignment.  I was curious if this is typical for the application and what the best bang for the buck would be to remedy the situation.  I haven't heard of the Ron Tyler mount.  Thanks for the tip.  I'll start researching it. The front diff mount looks fine, the mustache bar inserts look a bit chewed up.  The flex in the mustache bar mounts become obvious when lifting the car by the diff as shown in the pics.  It would seem logical that firming up the mounts will fix the rumble that we are talking about if the mounts are allowing the nose of the diff to pitch up.  

Edited June 12, 2017 by LS3Z

[NewZed]

Here's a good start - http://forums.hybridz.org/topic/58895-what-is-the-deal-with-solid-diff-mounts/

 

There are other descriptive threads out there, including one by Ron Tyler, explaining why he made the modified diff mount.  His moniker here is RTz.

 

Use Google and "site:hybridz.org" in the search box along with your search words to search the forum, the site's search function is very poor.  It won't even use the three letters RTz so you can't search for Ron's post.   And he's a moderator.

[LS3Z]

Here's a good start - http://forums.hybridz.org/topic/58895-what-is-the-deal-with-solid-diff-mounts/

 

There are other descriptive threads out there, including one by Ron Tyler, explaining why he made the modified diff mount.  His moniker here is RTz.

 

Use Google and "site:hybridz.org" in the search box along with your search words to search the forum, the site's search function is very poor.  It won't even use the three letters RTz so you can't search for Ron's post.   And he's a moderator.

Thanks for the tips.  Lots and lots of reading to do.  The RT mount looks to be exactly what I need and a fair price from technoversions.  Reading about the RT mount, it seems that it lowers the nose of the diff considerably which some say is good for V8 Swaps.

 

My question now is if I have no vibrations when cruising/decel....will lowering the nose of the diff induce vibrations?  How far does the RT mount lower the nose of the diff?  Guess I need to get under the car and measure all my angles.

[Boy from Oz]

I had a somewhat similar issue except that the vibration/knocking occurred when I backed-off after hard acceleration. 

 

I rebuild new CV shafts and replaced the brand new CVs with used units - still had the problem. I swapped the diff for another - still it was there.

 

I did notice there was a pulsing back through the brake pedal at the same time but I couldn't understand how that could relate to the cause of the issue so regarded it as a consequence.

 

Eventually I had the car raised on a hoist and the suspension supported with the wheels removed. I sat in the car while others watched underneath. I tried for about 10 minutes to recreate the vibration/knocking but it became harder and harder to detect. We eventually gave up when the smell of the brakes, from constant application and no air flow, became overpowering.

 

When we refitted the wheels and drove home there was no vibration/knocking and there hasn't been since.

 

We surmised it was the brake pads not being bedded-in sufficiently and that had be achieved, albeit inadvertently, when the car was on the hoist.

 

The fact that the issue was, apparently, the pads but only occurred when the car was accelerated hard (not braking) completely threw me.

 

I don't offer these comments as a solution to your problem but as a suggestion you also consider the brakes as a possible culprit.  

Edited June 13, 2017 by Boy from Oz

[lowrider]

What type of half shafts/axles are you running? What has been done suspension wise? The reason I ask is I had vibration issues with my 260Z during acceleration only for several years on both the stock suspension, lowering springs, and coilovers. I swapped the differential from the stock R180 to a R200 along with shortening the driver half shaft and still had the vibration on accel only. It wasn't until I converted to CV axles that the vibration went away. I blame it on the half shafts being imbalanced/bad u-joint angles. It only was happening during acceleration because the rear of the car was squatting enough to change the halfshaft angles.

 

That might be something worth checking out.

[NewZed]

My question now is if I have no vibrations when cruising/decel....will lowering the nose of the diff induce vibrations?  How far does the RT mount lower the nose of the diff?  Guess I need to get under the car and measure all my angles.

 

The RTz design can be modified if your angles are off.  Holes can be slotted, the GM mount can be ground.  You're right though, if it's good at cruise and decel now and you change the angle, you might create a new problem.  The best way to go is to measure and make it right.

 

Hoke probably considered angles when he designed his mount.  You might send him a message and ask what diff angle he designed for.  Apparently he monitors his Facebook page most closely so that's probably the quickest route.

[LS3Z]

What type of half shafts/axles are you running? What has been done suspension wise? The reason I ask is I had vibration issues with my 260Z during acceleration only for several years on both the stock suspension, lowering springs, and coilovers. I swapped the differential from the stock R180 to a R200 along with shortening the driver half shaft and still had the vibration on accel only. It wasn't until I converted to CV axles that the vibration went away. I blame it on the half shafts being imbalanced/bad u-joint angles. It only was happening during acceleration because the rear of the car was squatting enough to change the halfshaft angles.

 

That might be something worth checking out.

Thank you for this first hand account.  I had also been considering this as a possible cause of the vibration.  The car has Eibach springs and Tokico struts.  The back end does squat notably under hard acceleration and I would say that the magnitude of the rumble is linear with the amount of squat.  I dont really get on it in 1st, but the rumble is most pronounced in 2nd, less in 3rd, less in 4th, etc.  Definitely torque or squat related.  

 

The RTz design can be modified if your angles are off.  Holes can be slotted, the GM mount can be ground.  You're right though, if it's good at cruise and decel now and you change the angle, you might create a new problem.  The best way to go is to measure and make it right.

 

Hoke probably considered angles when he designed his mount.  You might send him a message and ask what diff angle he designed for.  Apparently he monitors his Facebook page most closely so that's probably the quickest route.

Thank you for the, once again, very valuable information.    

 

Before I go throwing parts at this, I'd like to mount a gopro camera under there to measure the actual deflection.  If the diff nose is not pitching up, no point in chasing front diff mounts.

[softopz]

This is probably not your problem but Id start with your mustache bar bushings they look shot from the pics!! Id replace those. But accel vibrations could be allot of issues from transmission all the way to axles. Good luck

Edited June 16, 2017 by softopz

[Miles]

Are you assuming that the driveshaft was cut and balanced correctly?

 

I ask because I had a similar vibration and it turned out that the driveshaft shop welded the driveshaft off axis after they shortened it.

 

Suggestion:  Pull the shaft and take it too a quality driveshaft shop and have it checked out.

[LS3Z]

This is probably not your problem but Id start with your mustache bar bushings they look shot from the pics!! Id replace those. But accel vibrations could be allot of issues from transmission all the way to axles. Good luck

You are right, they look a little chewed.  They look particularly bad with the diff supporting the weight of the car as shown in the pics.  I agree that they should be freshened up.

 

Are you assuming that the driveshaft was cut and balanced correctly?

 

I ask because I had a similar vibration and it turned out that the driveshaft shop welded the driveshaft off axis after they shortened it.

 

Suggestion:  Pull the shaft and take it too a quality driveshaft shop and have it checked out.

Driveshaft is brand new from Driveshaft Shop Specialists.  I would assume that the rumble would always be present if something were welded off axis, but it is always worth taking a look to verify.  I'll check the run out.

[Miles]

You are right, they look a little chewed.  They look particularly bad with the diff supporting the weight of the car as shown in the pics.  I agree that they should be freshened up.

 

Driveshaft is brand new from Driveshaft Shop Specialists.  I would assume that the rumble would always be present if something were welded off axis, but it is always worth taking a look to verify.  I'll check the run out. Check balance too.

[NewZed]

Just a refocusing type comment, but driveline balance and runout problems would be more tied to drivehsaft RPM, not load.  The original comments about angle changing due to diff nose lifting seem most likely.  Based on the stated facts.  Something that changes when load is applied.  Seems like this latest effort might be helpful but off target.

[Boy from Oz]

...  The original comments about angle changing due to diff nose lifting seem most likely.  ..

 

True. Have you seen this video?

http://forums.hybridz.org/topic/125670-yikes-movement-in-moustache-bar-mounts/

[NewZed]

That's a good link and answers a lot of questions.  It's an interesting area, the Z car diff mounting is an odd thing.