Rear end vibration. Driveshaft alignment?

[Darius]

My S14 has had a bad rear-end vibration for a couple of years, but I have no idea where it is coming from because I changed so many things on the suspension at the same time.

I installed aluminum subframe bushings, aluminum differential bushings, Endura-Tech coilovers, 18-inch wheels and low-profile tires, and I filled the RB25 transmission mount with Flexane. Now it vibrates at highway speed.

I never noticed any vibrations with the stock 16-inch wheels and OEM tire size, but they weren't on the car for very long since I broke the driveshaft the first couple of weeks after the rebuild at the drag strip. I had a new driveshaft made up and have only dragged on it once since.

The previous wheels were mustang non-hubcentric wheels and the Work's are not either but I figured they just weren't centered properly. This is still a possibility, but I'm wondering if it is something more.

My main question is how does one go about lining up the driveshaft when the differential is fixed? How far off can the output shaft be from pointing at the diff both horizontally and vertically? Isn't that what the u-joints are for?

Sorry for the newb questions, but my gf is constantly asking for rides in it.

[gawdzilla]

probably an obvious suggestion, but i'd rule out your wheel and tire balance first by mounting a known good set of wheel/tire on it, or getting your setup rebalanced.

[240z4u]

Is it dependent on speed? Gear? RPM?

I suspect your feeling the rear end growling because of your solid mounts in the back.

Evan

[Darius]

Will, I figured that the rears were vibrating because they were old, shot tires and were just out of balance. When I got the new Works and MT DRs, I thought the problem would go away with the new set. Didn't happen like I had hoped. So I've kinda ruled out the wheels/tires unless it is, in fact, due to the wheels not being hub-centric.

Evan, I anticipated some added resonance from the diff gear and VLSD, but this is a definite vibration. To give you an idea, I can't see anything out of my rearview mirror when going down the highway at first. The weird thing is that it seems to smooth out after a while. When I get going fast 80-90+, it vibrates like a massage chair. It is definitely dependent on speed, but not on gear or rpm or anything. If I take it out of gear entirely, there is no change in tone. So this is why I'm thinking it is a mechanical issue behind the transmission output shaft or a driveshaft misalignment thing.

[gawdzilla]

there arent really any adjustments you can make to the rear or the transmission. what trans mount do you have? could it be a driveshaft balancing issue? i had a problem with my weights busting off at some point and had a speed related vibration

[TECHLINE08]

can also be caused by bad u-joints, drive shaft missed alignment. Its hard to measure drive shaft angles since you can only have a difference of 2.5 degrees.

[Darius]

there arent really any adjustments you can make to the rear or the transmission. what trans mount do you have? could it be a driveshaft balancing issue? i had a problem with my weights busting off at some point and had a speed related vibration

I made a new transmission mount based off of the TopHat mount but out of C-channel steel bar. Frickin rigid! I'm still using the RB25 transmission isolator though.

The driveshaft could be out of balance, but I checked it out earlier this spring when I was installing the new transmission mount and it seemed to be intact. The bolts were tight too. Going to take it off this winter or a rainy fall week to have its balance double-checked.

If the driveshaft has to be within 2.5* of the diff, I can 100% guarantee the alignment is within spec. (48" tan 2.5*=2.09" laterally=4.18" diameter range) That is a HUGE margin of error. So I think if it is still in the driveshaft hump, it is AOK.

[240z4u]

If the driveshaft has to be within 2.5* of the diff, I can 100% guarantee the alignment is within spec. (48" tan 2.5*=2.09" laterally=4.18" diameter range) That is a HUGE margin of error. So I think if it is still in the driveshaft hump, it is AOK.

Whoa, crack that math whip.

I also get a bit of rumble from my diff area, not as bad as you though. I attributed it to my billion mile junk J30 differential that I stuck in there.

I know you said you changed a lot, but what exactly did you change when you started noticing the vibration? My rearview vibrates a little bit as it is, I can't imagine solid mounts.

Evan

[Darius]

Thanks again for that alignment spec techline. It is good to know that the driveshaft alignment is probably not the issue.

The J30 diff was in before the RB in so unless it has taken a dump since then, it is probably okay. I think I'm going to throw the stock 5-spokes back on the rear to compare the vibration level.

When I broke the first drive shaft, it was because of wheel hop at the drag strip. Could I have warped some axle shafts in the process? I'm grasping for ideas here because it makes the car feel like it is going to vibrate apart at speed.

[Ramius83]

I installed aluminum subframe bushings, aluminum differential bushings,..... Now it vibrates at highway speed.

I am betting on this. With no "rubber" insulators between the driveline and the body, there is no way to dampen the normal vibrations caused by normal conditions. My rear-view mirror does the same, but with only aluminum sub-frame spacers and no metal diff bushings. Try tightening up the screw located behind the rear-view mirror or install a rubber insulator between the rear-view mirror mount and body. Worked for my brother......

[Sil240]

I would def drop a couple bucks on the Hub centric spacers. I have some kinda plasticky ones. Not quite plastics (ABS) but def not metal.Some kinda composite material, If I find the package i'll let you know.

When I took my car out with the Stock Z32 wheels she was ok, then I decided to look pretty and put the 18's on and up high she had a lil bit of vibration. (I was too lazy to put the spacers on)

[Darius]

This update has been a long time coming, but I finally threw my stock wheels and tires back on the car. The vibration is still there and equally strong. So I can conclude that it isn't the wheels and tires being out of balance nor is it the need for hubcentric rings because the stock wheels are hubcentric and they didn't make any difference.

Now I'm focusing on the driveshaft, diff, and halfshafts. I'm leaning away from driveshaft because if it was out of whack, I would feel it in the shifter.

So between diff and halfshafts, the odds of a diff vibrating are fairly low since it would probably discintigrate quickly after beginning to fail especially with the power I'm putting through it. This leads me to the halfshafts. I'm calling up a local driveshaft shop today to see if they can make me up a set of shafts for less than what driveshaft shop wants for theirs, which shouldn't be too difficult at $1000 a pair...

[xnyc1]

i would really recommend having the driveshaft checked by a different shop. you could also put in a stock d/s and get to vibrating speed to eliminate d/s as a possibility if it still vibrates. it is not uncommon for 1 pc or custom driveshafts to cause this. the sensation is enhanced because of your mods. the shifter shouldnt vibrate because you have flexane trans mount. if anything, the vibration should transfer down the shaft and cause the diff to vibrate.

wheels being misaligned is very unlikely because its still lugcentric even when not hubcentric

[Darius]

That was the first thing I was going to check since it was free but kinda ruled it out since it was balanced when I installed it and it hasn't lost any balancing weights. I can't put a stock driveshaft back in because that wouldn't really work out.

[robbie2883]

if you don't have hubcentric rings then i would get those FIRST!!! i used to run a wheel shop...wheels without centering rings can vibrate like crazy. not always the solution....but even if it's not the problem you are taking a load of cross torsion stress off your studs.

do you feel the vibration in the steering wheel too or just the seat/body of the car ?

[Darius]

I ruled out the hubcentric wheels when the OEM wheels were reinstalled. Still leaning towards axle shafts.

[Darius]

I ruled out the hubcentric wheels when the OEM wheels were reinstalled. Still leaning towards axle shafts.

[HxC_Nismo]

do you have any spare axles lying around, if so swap em out and test drive it and see what it does, but i personally think its the solid mounts.

[S14-NEO]

I had a similar issue with mine when i had mine made..the problem with mine was i went with a cheaper driveshaft shop place and they installed a seamed tube rather than a solid rube..once i change out the seamed driveshaft i with a solid tube shaft my vibrations went away. just a thought...also when i went with the SPL solid subframe bushings it did transmit vibrations and more noises but i just accepted it..at least i didnt have any more wheel hop...lol

[johnny butt]

do you have a sway bar in the rear? if so, does it give enough clearance for your driveshaft at all times?

[silviasgp06]

When my friend had rear end vibration issues we put the rear end of the car on jacks, started the car and put the car in gear and brought the speed up until the vibration started to occur. then (SAFELY) we visually found the source of vibration in the drive train. Turns out he had the driveshaft doughnut bolted upside down on the s13, of course this isn't your issue since you have a after market d/s.

[Darius]

i just heard from the machine shop that the driveshaft fabricator didn't weld the tube on straight so they marked the high and low points on it and I'll bring it back to the driveshaft place to have them fix it.

<edit> The machine shop said the transmission yoke was welded on at a very slight angle from square. And it was also welded approximately 0.040" off center. I asked him if that small of a difference could cause a vibration and he said, "yeah it will only get worse as you go faster too." Another funny thing was that someone else brought a huge truck driveshaft in from that same driveshaft shop because it was vibrating. I may have to mention that if they raise hell about fixing their driveshaft that was dodgy from the date of purchase.

[l0nestar]

As you know, slight variations in 'square' on a rotating assembly can cause major havoc. Glad you got it fixed.

I wouldn't pay a cent. Their fabricator d!ck up.

[Darius]

Oh hells naw. I'm not paying anything. It has been d!ck up from day one.

I got a call back from the original fab shop this morning and they said it was more than 0.040" off on the one end AND the balancing weight was placed at the wrong end of the shaft. How that ever left the shop in the condition it was in baffles me.

Anyways, they said they fixed it and I am picking it up tonight and will reinstall it. I'm hoping to take it for a test spin later to make sure everything is smooth.

[Darius]

It runs as smooth as glass now! Now I can take video that isnt' all blurry and distorted.

[l0nestar]

It runs as smooth as glass now! Now I can take video that isn't' all blurry and distorted.

LOL! Gasp! You don't say!
I am delighted to hear this Matt!
(now where are the dang videos???)

[Darius]

hahaha I just drove it around the block last night but I'll put the camera on the mount tonight and take her for a spin. This will definitely test out the camera's night focusing abilities. I'm curious to see how it performs.