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Discussion Starter · #1 ·
I just finished my 8.2 swap along with a Re-gear to 4.88 Yukon gears and I installed a Metaltech Long Travel kit. I have an 09 AT with 170k on the clock. I took it out for a drive last week for the first time to check any problems that I might have had, and I have this very slight low vibration, I can feel it in my butt. It happens at low speeds, and I have not taken it over 45mph yet. It has a very consistent vibration I can't really feel it getting faster or slower. I can here a low hum as well, I know the gear company told me that I might hear a humming noise until the gears seat themselves.

I talked to the local company that did the regear and he told me that I should get my driveshaft balanced. So I talked to another local place that said they could but it turns out his machine is not accurate enough to balance Toyota driveshafts (are they really that good?) anyways there are no more "local" places to take my driveshaft to balance, short of driving 2 hours.

I was wondering if anyone had any insight on what else I could check or how to diagnose the vibration. I was first thinking of having my buddy tow me behind his truck to see if the vibrations was there. Also maybe driving it with the front Shaft in only then doing again with the rear shaft in only. Then I got to thinking about transmission shudder, I have no idea what it feels like or sounds like, I did have the FJ sitting for 4 months while I worked on it. Maybe the transmission fluid sat unmoved for too long, now I have a shudder? Would a badly adjusted parking brake make a vibration? (I know I didn;t do a good job on those)
 

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I really doubt it’s the transmission. Alignment, tire pressure/wear are also simple things to check. If it is the driveshaft you could also look at it as a chance to upgrade and get a rebuilt Toyota shaft (yes they really are that good) with an HD case - I got one for a really reasonable price from South Bay Driveline and have subsequently landed on it - hard - with no ill effects. BTW when my original driveshaft was dying it would shudder lightly, and only at certain speeds - problem diagnosed as a U joint, but I wanted the beefy HD casing for rockcrawling 😁
 

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Discussion Starter · #4 ·
Clock the shaft and see if anything changes. It will give you more information


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By "clock the shaft" you mean remove it, right? Sorry I'm bad at lingo🤪

problem diagnosed as a U joint
My dad had also suggested this. But if I was to replace U joints I would probably replace the whole shaft.
 

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Replacing U joints requires the specialized skill of balancing, so per my own research at the time, cost came out fairly similarly. Is the vibration at all speeds, just while throtttling or coasting, uphill or downhill etc. What are your specific symptoms?
 

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Discussion Starter · #7 ·
Replacing U joints requires the specialized skill of balancing, so per my own research at the time, cost came out fairly similarly. Is the vibration at all speeds, just while throtttling or coasting, uphill or downhill etc. What are your specific symptoms?
I did it all on level ground and it's mostly at low speeds (anything under 45mph as I have not driven it any faster than that) with light throttle, but it is still there while coasting, maybe not as much but it's still there.

I'll try to re-install rear driveshaft tonight and check if it's still there I'll rotate and try again. It's raining today and tomorrow so hopefully I can get to it.
 

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Did any part of the recent work include any suspension changes that might affect the driveshaft angle?

With 170K miles on the driveline, have the U-joints on the rear driveshaft every been replaced?

How about the service history for U-joint lubrication? Lubed at every oil change since the vehicle was new?

There will be no value in trying to balance the driveshaft if there is any detectable wear in the U-joints, and driveshaft vibration caused by worn U-joints can create the low-frequency shake you describe.
 

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Discussion Starter · #9 ·
@FJtest
Before the swap I had stock Coils with a 1.5" (I believe) spacer, I went to a Metaltech HD long travel coil so it would have raised another 1.5"-2" roughly. I don't have the alignment done yet but it is scheduled soon.

I have had the FJ since 130k and per the available service records the driveshaft or U-joints have not been replaced. Also as far as the records go there is no specific info on greasing the drivelines. Although I started greasing them 2 years ago when I learned about them.

I rotated the U-joints when I ad it out and I could not identify any detectable wear or "play", they move very freely in all directions.

Also I took it for another drive last night to really track the vibration. It seems to only happen between 15mph and 30 mph, while on the accelerator lightly, if I coast there is a lot less vibration. It also happens in any gear.
 

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If you are saying that your suspension mods lifted the chassis at front and rear another 1.5 - 2 inches, then your driveshaft angle definitely increased (this affects the range of angular travel that the U-joint needle bearings swing through for each revolution of the driveshaft).

The shop that did your re-gearing ... they are experts at assembling differentials and setting up differential bearing preloads, and have done scores or hundreds of diff rebuilds?

The new "humming" noise and the new vibration could possibly be linked; neither are normal after a diff overhaul.
 

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Discussion Starter · #11 ·
The shop that did your re-gearing ... they are experts at assembling differentials and setting up differential bearing preloads, and have done scores or hundreds of diff rebuilds?
Yes, they are more of a race shop (I'm in Iowa) but yes they said in 2019 they did a couple thousand regears/assembling differentials (I actually think he said 20k axles went through there shop but that seems like a ridiculous amount). I was limited on options and I didn't want to send my gears half way across the country. They were extremely helpful and came highly recommended from other off roaders around the area. They also told me that a slight humming noise is normal for the first 500 miles, along with a weird smell. Also from my own research it does seem that Yukon gears are fairly noisy at first. The vibration is definitely more pronounce than the humming noise

Could I change the orientation of the axle by adjusting the upper links (I have Metaltech upper links) to relax the angle of the U-joints. So I would make the upper links longer to rotate the top of the axle housing towards the rear of the vehicle. I know that I wouldn't be able to get much angle "out" of it, but it was a thought that I had.

Also someone had mentioned that I should check that the front and rear U-joints on the driveshaft were in phase or aligned with each other. I haven't done that yet, hopefully tonight I can get to it.
 

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If you've got adjustable rear links, you can 'roll' the entire axle a few degrees to get back closer to the previous driveshaft angle and see if that makes any detectable change in the vibration. Even if there is some level of wear/clearance in the U-joints (and there has to be after 170K miles) reducing the driveshaft angle should make some small change in vibration, IF the vibration is U-joint related.
 

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Discussion Starter · #13 ·
The vibration is gone! I lined up my U joints and the vibration went away, I can't feel any vibration up to 55mph.
I haven't slid that yoke off for at least a year (well before my re-gear) apparently the increased rpm of the driveshaft or angle of the driveshaft increased the vibration. Either way I appreciate all of your help, lessons learned for the future!
 
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