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Unread 06-25-2013, 10:55 AM   #1
TA-YJ
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Finding Vibration Source

I just finished getting my rebuilt engine and new clutch setup into the jeep. I was using brown dog motor mounts but when I got everything back together I decided I couldnt deal with the vibrations. I ordered JKS lift plates and went back to them with stock mounts. Now vibes at idle are almost gone, but when I start moving they get pretty bad around 30mph then disappear until about 55-60mph. The vibrations are resonate loud enough that you have to yell to talk between the two front seats.
For a little history on the setup and problem:
-Lift is same as before, BDS 2" lift, 5/8" Boom shackles, 1" MML
-Motor mounts and trans mounts are all in good shape
-Vibrations are only when engine is under load. I can take the clutch out when at highway speeds and all the vibes go away. I can rev the engine freely with no vibes what so ever.
-Before with the old engine there were decent but tolerable vibes at idle, but as soon as the engine was under load they would go away. Pretty much the exact opposite of whats going on now.
-U bolts are tight at 90ftlbs

It didnt really seem like the typical symptoms of u joints and there doesnt seem to be any play in them. I will post up a pic of drive line angle later today. Any help to figure out the problem is appreciated.

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1992 YJ 2.5L
Engine Mods:4.0L TB, Ford Design III 19lb Injectors, Firepower Ignition System, Ford TBird Electric Fan, Pacesetter Header, Magnaflow Cat, Dynomax Super Turbo Exhaust
Suspension Mods:BDS 2" Lift, M.O.R.E. 5/8" HD Shackles, 1" Brown Dog MML
Other:LED Tails and Herculined
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Unread 06-25-2013, 11:51 AM   #2
superj
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it is not the clutch or something in the trans bell housing?
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Unread 06-25-2013, 12:45 PM   #3
TA-YJ
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Im not sure. The clutch seems to be working perfectly. Im not sure how I should go about diagnosing if its a problem in the bellhousing.
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1992 YJ 2.5L
Engine Mods:4.0L TB, Ford Design III 19lb Injectors, Firepower Ignition System, Ford TBird Electric Fan, Pacesetter Header, Magnaflow Cat, Dynomax Super Turbo Exhaust
Suspension Mods:BDS 2" Lift, M.O.R.E. 5/8" HD Shackles, 1" Brown Dog MML
Other:LED Tails and Herculined
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Unread 06-25-2013, 01:04 PM   #4
TA-YJ
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Could the torque arm/stud be causing these vibrations? It looks pretty worn out, but it seemed fine before.
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1992 YJ 2.5L
Engine Mods:4.0L TB, Ford Design III 19lb Injectors, Firepower Ignition System, Ford TBird Electric Fan, Pacesetter Header, Magnaflow Cat, Dynomax Super Turbo Exhaust
Suspension Mods:BDS 2" Lift, M.O.R.E. 5/8" HD Shackles, 1" Brown Dog MML
Other:LED Tails and Herculined
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Unread 06-25-2013, 05:22 PM   #5
Louie4
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Quote:
Originally Posted by TA-YJ View Post
Could the torque arm/stud be causing these vibrations? It looks pretty worn out, but it seemed fine before.
Possibly. For me, the nut on the torque arm stud was gone so whenever I started in 1st gear from a stop the shifter would shake quite a bit, so much that it popped my wrist bone which did not feel too good. I think you should replace that and see how it acts.
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Unread 06-25-2013, 06:01 PM   #6
idaholtby
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For the motor and tranny mounts, are you running with Poly or rubber?
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Unread 06-25-2013, 06:05 PM   #7
mrdeath2000
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your change in mounts could allow more flex in how the motor sits and thus changing your pinion angle. Worth checking it out, i didnt see anything in there that said SYE.
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Unread 06-25-2013, 08:14 PM   #8
TA-YJ
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Louie4- Already got it ordered today. Hopefully its just a simple fix like that.

Idaholtby- Just stock rubber mounts on all 3. They're all in good shape or new as well.

mrdeath2000- I do not have an SYE or TC drop, just the 1" MML. I was hoping it wasn't going to effect pinion angle that much just switching from brown dog to stock mounts. I did feel quite a bit of vibration with the BD mounts after swapping the new engine in though. Here is a pic of my drive line angle for reference. I didn't think it looked bad enough to cause vibes like this.

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1992 YJ 2.5L
Engine Mods:4.0L TB, Ford Design III 19lb Injectors, Firepower Ignition System, Ford TBird Electric Fan, Pacesetter Header, Magnaflow Cat, Dynomax Super Turbo Exhaust
Suspension Mods:BDS 2" Lift, M.O.R.E. 5/8" HD Shackles, 1" Brown Dog MML
Other:LED Tails and Herculined
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Unread 06-27-2013, 12:24 PM   #9
idaholtby
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Your pinion angle looks to be too low. With the mild lift (2") and 5/8 booms, there typically is not an issue with driveline angle. No t-case drop, but this should be offset with the motor lift. Do you have rear shims installed? If so, are they possibly reversed? I had a similar lift in the past and my drive-line angle was nearly perfect.
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Unread 06-27-2013, 06:28 PM   #10
TA-YJ
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Nope. No shims on the springs. The BDS kit didn't come with any so I didn't put any on. Here is a pic of it right after the lift was installed. Like I said there were no vibes like this before swapping the engine/motor mounts.
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1992 YJ 2.5L
Engine Mods:4.0L TB, Ford Design III 19lb Injectors, Firepower Ignition System, Ford TBird Electric Fan, Pacesetter Header, Magnaflow Cat, Dynomax Super Turbo Exhaust
Suspension Mods:BDS 2" Lift, M.O.R.E. 5/8" HD Shackles, 1" Brown Dog MML
Other:LED Tails and Herculined
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Unread 06-27-2013, 07:10 PM   #11
idaholtby
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Quote:
Originally Posted by TA-YJ View Post
Nope. No shims on the springs. The BDS kit didn't come with any so I didn't put any on. Here is a pic of it right after the lift was installed. Like I said there were no vibes like this before swapping the engine/motor mounts.
Well, your pinion angle is definitely too low. I would suggest installing shims that most kits come with and or the least favorite option.... a t-case lowering kit. The ideal option would be a SYE with a CV rear shaft, but with your size lift, this really should not be necessary. If you are thinking of going to a larger lift soon, then this would be the option to pursue. I'm thinking though that rear axle shims will get you what you need.
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Unread 06-27-2013, 08:12 PM   #12
laybackman
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Since it only vibrates bad under load did you get your flywheel 'refaced' when you installed the new clutch and TO bearing? Clutch chatter can be caused by a un-surfaced flywheel not mating properly with a new clutch disc.
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Unread 06-27-2013, 11:38 PM   #13
TA-YJ
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Laybackman- Actually I picked up a new flywheel to put on the engine. The old one was passable, but I decided not to cut corners and put a new one on.

idaholtby- I do have a Tcase drop kit that came with the lift so I will try that and see if it goes away. I thought the MML would have compensated for the change in angle though. My only question is why this would have manifested into such a significant issue after having the lift for over a year? Would the change from BD motor mounts to stock with lift plates really do that much?
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1992 YJ 2.5L
Engine Mods:4.0L TB, Ford Design III 19lb Injectors, Firepower Ignition System, Ford TBird Electric Fan, Pacesetter Header, Magnaflow Cat, Dynomax Super Turbo Exhaust
Suspension Mods:BDS 2" Lift, M.O.R.E. 5/8" HD Shackles, 1" Brown Dog MML
Other:LED Tails and Herculined
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Unread 06-28-2013, 11:39 AM   #14
laybackman
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Quote:
Originally Posted by TA-YJ View Post
Laybackman- Actually I picked up a new flywheel to put on the engine. The old one was passable, but I decided not to cut corners and put a new one on.

idaholtby- I do have a Tcase drop kit that came with the lift so I will try that and see if it goes away. I thought the MML would have compensated for the change in angle though. My only question is why this would have manifested into such a significant issue after having the lift for over a year? Would the change from BD motor mounts to stock with lift plates really do that much?
Maybe your U joint(s) are worn....... That could cause all kinds of vibrations at certain speeds.
Check the easy stuff first!

Also check your rear brakes. Some time back My buddy developed a vibration in his Blazer about a month after he did a rear brake job. He checked everything except the brakes because his logic said heck they are new!

I said pull the rear wheels since it was the last thing he touched. Eventually he did and found a spring holding the brake shoe in place had popped off and the shoe caused the vibration!
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Unread 06-28-2013, 02:47 PM   #15
TA-YJ
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They looked good when I pulled the rear shaft, but Ill pick up another set at work tonight as they could probably use replacement anyway.
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1992 YJ 2.5L
Engine Mods:4.0L TB, Ford Design III 19lb Injectors, Firepower Ignition System, Ford TBird Electric Fan, Pacesetter Header, Magnaflow Cat, Dynomax Super Turbo Exhaust
Suspension Mods:BDS 2" Lift, M.O.R.E. 5/8" HD Shackles, 1" Brown Dog MML
Other:LED Tails and Herculined
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