Driveline Vibration?

[GlennC]

I apologize ahead of time for bringing this up again but the confusion continues. I'm getting a vibration I think is coming through the driveline, at least I would like to make the necessary adjustments to eliminate as a possible cause. I've read all the info (on this site and other sources) associated with this subject, which is extensive, until I'm brain dead & I'm not sure I completely understand it. I used a digital angle gauge & the Spicer Driveline Angle Calculator to come up with the specs. According to the specs there is a difference between of 2.5* between the two operating angles which violates the recommended limits (1*). I have a live axel in the car with the FFR 4 link fixed length upper & lower control arms so the angle of the pinion is not adjustable. The flange of the pinion points down (slopes) towards the ground around 2.5* (the Spicer Calculator considers this as "up slope" though when inputting the data). The angle of the eng/trans also slopes in the same direction as the pinion ("up" in Spicer terminology) about .5*. The driveshaft slopes in the opposite direction ("down" in Spicer terminology). If I understand the theory of needing to put the two operating angles in parallel planes within acceptable tolerances (1*) I would need to shim the rear of the transmission up slightly? I guess I could also drop the engine mounts down some too if possible? According to the Spicer Calculator I would have to set the eng/trans at around 1.5*-2* "up" to obtain the proper alignment.

Does it sound like I'm headed in the right direction with this thinking?

Is there any issue running the eng/trans at this direction of slope?

I would appreciate any input you guys might have.

Thanks,

Glenn

[Dgc333]

You want the angle of the pinion to be equal but opposite of the engine/tranny. That is if the pinion is pointing down 2.5 degrees then the engine tranny needs to be pointing up 2.5 degrees.

[cv2065]

I'd be sure to understand where the vibration is coming from. If you can feel it in the wheel, its coming from the front end. If it's coming through the seat, then it's your driveline.

[GoDadGo]

Ditto CV

I'd be sure to understand where the vibration is coming from. If you can feel it in the wheel, its coming from the front end. If it's coming through the seat, then it's your driveline.

If you are running a 4-Link rear and can't get the angle of the dangle right, you may need adjustable upper and lower control arms.
You need to make sure you are at ride height because the 4-link system just doesn't have a lot of wiggle room.
Should you need adjustable uppers and lowers, there are many companies that make them.

Shown below is a possible control arm option that may be of use to you:
https://www.spohn.net/shop/Factory-F...-MK4-Roadster/

This video will show you why things get goofy with the 4-Link:
https://youtu.be/ZHtQwQzY8uM

U-Joint Phasing Video:
https://youtu.be/Idk3BVDVHq4

Hope This Helps & Good Luck!

[Ford & Jeep Fan]

Is it mainly feel it you are on the gas?? do the arms on the rear axle have rubber bushings?? To make the rear pinion angle adjustable you only need adjustable upper OR lower arms BOTH are not needed.

[GoDadGo]

Is it mainly feel it you are on the gas?? do the arms on the rear axle have rubber bushings?? To make the rear pinion angle adjustable you only need adjustable upper OR lower arms BOTH are not needed.

You are correct about only needing Adjustable Uppers or Adjustable Lowers to tackle the pinion angle; however, with the 4-Link adjusting the Thrust Angle is easier to tackle having the full adjustability of having both upper and lowers. Centering the axle is also easier too.

https://youtu.be/tFk9H63QODM

[Ford & Jeep Fan]

You are correct about only needing Adjustable Uppers or Adjustable Lowers to tackle the pinion angle; however, with the 4-Link adjusting the Thrust Angle is easier to tackle having the full adjustability of having both upper and lowers. Centering the axle is also easier too.

https://youtu.be/tFk9H63QODM

I agree with your statement however I was just trying to fix his pinion angle problem first. If he is running rubber bushings I'd make darn sure to run one degree downward on the pinion so that under WOT when the axle torque mashes the bushing it comes up one just where it needs to be.

[GoDadGo]

I agree with your statement however I was just trying to fix his pinion angle problem first. If he is running rubber bushings I'd make darn sure to run one degree downward on the pinion so that under WOT when the axle torque mashes the bushing it comes up one just where it needs to be.

1. We definitely agree that the 4-Link rear suspension, while okay for street cruising, needs all the help it can.
2. Using The Rubber Baby Buggy Bumper Control Arm Bushings Only Makes Things Worse!
3. The Fox Body rear steer issues and wheel hop are also problematic.
4. Stiff springs at least reduce those Fox Body traits.
5. Quad shock may or may not be needed.

[GlennC]

Thanks for the responses. The vibration I'm noticing is mainly in trans (shifter shaking) and feeling it in the seat. I can feel a very slight vibration in the steering but not as much as the trans & seat. I'm just trying to eliminate the misalignment of the driveline to see if this has any affect on the vibration. With my driveline numbers out of spec this is probably a good place to start. As far as the adjustable rear control arms, I've read the info concerning their possible use but I was trying to avoid that for right now if I could to see if the issue could be corrected by adjusting the driveline. I kind of figure if FFR thought adjustable controls were really necessary they would have included them with the kits instead of the fixed length. According to the specs I'm getting on the pinion angle I think they're pretty close to what is recommended for a 4 link setup.

Thanks

[chmhasy]

Is your motor mount broken or did the bolts loosing up?

[Mastertech5]

I installed my engine and trans in mine as suggested by the manual for my combination using the trans mount bushings they sent me. I am using adjustable upper control arms that I initially set the same length as the non adjustable ones and my opinion angle was way off (down). I had to lengthen the upper arms to get the angle right. I used Tremec's phone app on my iPhone to check. It uses the level function of the phone to tell you 3 angles and what's off. Engine at the damper, driveshaft and pinion flange. 3 degrees max is the spec that most go by.

[cv2065]

Thanks for the responses. The vibration I'm noticing is mainly in trans (shifter shaking) and feeling it in the seat. I can feel a very slight vibration in the steering but not as much as the trans & seat. I'm just trying to eliminate the misalignment of the driveline to see if this has any affect on the vibration. With my driveline numbers out of spec this is probably a good place to start. As far as the adjustable rear control arms, I've read the info concerning their possible use but I was trying to avoid that for right now if I could to see if the issue could be corrected by adjusting the driveline. I kind of figure if FFR thought adjustable controls were really necessary they would have included them with the kits instead of the fixed length. According to the specs I'm getting on the pinion angle I think they're pretty close to what is recommended for a 4 link setup.

Thanks

Does the vibration happen just at idle and then smooths out on take off or does it remain while you are driving?

[GlennC]

Vibration is occurring while driving. Motor mounts are tight. From what I've read about 4 Link pinion angle 2*-3* pointing down is fairly standard. I know that there is movement & "wrap up" during hard acceleration but I feel that my current pinion angle of 2.5* (pointing down) is in the ball park. If I find that I can't get the vibration out with the driveline adjustment I'll start exploring other methods of adjustment. At this point I'm starting with putting some shims under the trans mount to get the trans tail shaft & pinion parallel.

[GlennC]

PS - I'm using the Spicer Calculator because the Tremec App is no longer available through the App Store.

[33fromSD]

Could be the engine mounts. I had a old mustang a couple years back with a terrible vibration on acceleration. Previous to that I did a complete chassis upgrade (engine, suspension, engine mounts, trans mounts, rear end, etc.). Once that was done the vibration was terrible so I started with the obvious and looked at the drive line angle since I swapped to a 9" rear. Everything looked good. Next I swapped out the harmonic pulley and even the flex plate thinking I had a mismatch with weights, nothing fixed the vibration. Even ordered a brand new driveshaft professionally balanced.

I was about to pull the tranny and have that gone through thinking it was something internal when I read an article about how poly bushings on engine mounts were too harsh for most vehicles and were really only meant for racing. Well, I upgraded to poly on the engine and tranny mounts when I did my chassis work so I ordered a new pair of rubber engine mounts (rubber, not poly) & tranny mount, swapped those out and magically the vibration was gone (not lessened, but completely gone).

Not saying this is your issue but sounds familiar.

Jim

[Just 1 More]

I went full adjustable upper and lower. Ridetech built these for me with the "R" joints, so much better than a solid heims joint
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