diff bushing

[digglesworth]

So out wheeling and I feel what feels like a little binding. Checked the underside and the diff bushing is nasty. Got about an hour and a half drive home. Can I make it?

 

[rsm688]

Yes just take it easy on the starting and stopping, bumps and turns. There is a bolt through there and two side diff mounts as well.

 

[rwbagnato]

Big washer on the bottom side of the cross member should stiffen things up enough to get home.

 

[Bigunit]

I didn't and ended up shearing off the diff bolt. Got it off the trail just in time to call AAA to tow it home before I could trash my front diff. Time for a PCF Scorpworks cross member - last one you will ever have to buy. I would guess that once you remove your cross member you will discover that the cross member itself has cracked. A known problem that the other cross member fixes/options do not address or fix.

 

[digglesworth]

Driving ok so far.

 

[digglesworth]

I parked it as soon as I saw it. Hopped in with my buddy after that. Thanks for that last tidbit Luis. I'll be sure to inspect the crossmember now....

 

[digglesworth]

 

[derian06]

May be a dumb question, but seems like a good time to ask. What exactly does the diff bushing do, and how does it work?

 

[digglesworth]

Your front diff is mounted to the truck in 3 spots. This on the crossmember and one on each side where your cv shafts plug in. This one is notorious for going out. It then allows the diff to flex from the torque of the front driveshaft. It'll bounce up and down on the bolt. Baaaad! Like bigunit said. He snapped his bolt from the movement. Flex in the diff is bad. You want that sucker held in there tight.

 

[digglesworth]

Ok.... Looked at it again when I got home.... going off the pic above, in that pic the bottom washer is tight against the bottom of the crossmember and there's a space of about an inch from the top of the crossmember to the bottom of the hole in the diff. Now, looking at it, the diff has seated back down on top of the crossmember and the bottom washer is about an inch below the bottom of the crossmember... I'll get a pic in a second. But could it be that the nut on top has backed off somehow about an inch allowing the diff to slide up and down on the bolt?

 

[digglesworth]

The diff has seated back down on the crossmember...

 

[cgalpha08]

That gap is always there on the oem one. Look how it moves in the video I took of it. It moves down every time you step on the gas. The aftermarket bushings don't let it do that so when you step on the gas, your going to get more vibration because there is direct contact.

Hummer H3 crossmember movement: http://youtu.be/jY2z2_EB_ws

Hummer H3 crossmember movement: http://youtu.be/jY2z2_EB_ws

 

[Bigunit]

cgalpha, I get zero vibration with the PCF cross member when I step on the gas, so I have not experienced what you have described. You must not be running the same one I have or that vibration might also be from a broken/cracked crossmember.

 

[cgalpha08]

Hmm, I'll have to look into it. I didn't see any cracks when I took out the cross member.

 

[PreferredChassisFab]

That gap is always there on the oem one. Look how it moves in the video I took of it. It moves down every time you step on the gas. The aftermarket bushings don't let it do that so when you step on the gas, your going to get more vibration because there is direct contact.

Hummer H3 crossmember movement: http://youtu.be/jY2z2_EB_ws

Hummer H3 crossmember movement: http://youtu.be/jY2z2_EB_ws

The vertical movement that is allowed on the OEM design is the cause of the differential mount bushing, mounting bolt and cross member failure, The "barrel" bushing that is used in the OEM mounting, is designed to support loads on a 90 degree axis to the center sleeve length-not on a inline loading to the center sleeve as is the case on the OEM design. Also using a hard durometer mounting bushing on any active component will cause harmonic noise transfer and undue mounting stresses. A "caged" bushing design made with a compound that allows flexing will control harmonic noise and mounting shock. Addressing the the failure without looking at the problem is not the solution.


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[digglesworth]

So what can be done to address the outboard bushing ? If one gets replaced, why not all 3...? Looking at the outer bushings last night and there appears to be a gap in those also between the head of the bolt and the bottom of the bushing.

 

[freeze]

You should definitely replace all three at the same time.

 

[digglesworth]

That was my question...... Without getting into the same argument as the steering rack bracket....

Scorpworks has a really good design for the crossmember but nothing for the outer bushings. It's a complete unit that is easily swapped out with 4 bolts plus the diff bolt. Compared to other kits, it's expensive... $200+ for one bushing fix. Now there's talk of potential cracks in the crossmember... That's new info to me...

The outfitter design kit is a replacement for all 3 bushings. It's diy so the work has to be done by the individual. It's the same price for all 3 bushings vs just one. You don't get a crossmember with the kit so inspection and verification of no cracks is a must. The harder material transfers noise and vibration.

There's definitely pros and cons for either kit. I may be potentially throwin in a slightly used Rancho Kit which will void whatever method is used to fix this bushing.

So look people, seeing this is a very similar issue like the steering rack bracket, can we keep things civil and unbiased. I'm sure Duane is a hell of a guy and very knowledgeable. I'm sure the people at OD are nice people too... The fact is, I don't know either sides personally... I do know that I run the OD steering kit and it has worked very well. I'd just like to know peoples opinions who have used either product. If I install the Scorpworks, will that take all the stress off the outer mounts and just throwing new oem bushings in the outers will be ok.... What I've figured out so far is that gm uses crap bushing in the entire truck. Any time an upgrade is available over stock rubber, it gets my vote.

 

[Bigunit]

You are right diggs. OEM ones are crap and no need for arguments or drama. I know the PCF products and I know they work really well. BTW, PCF does make the side diff mount bushings, they come already pressed into the mount brackets (core exchange, like the cross members) - someone on the forum bought the first set. Alrock has been running one of the prototype mount brackets for over 2 years without any issues. I'll be putting a set on my rig as soon as Dwaine gets some free time in the next month.

 

[Bigunit]

Additionally, the cracked crossmember issue is a real issue with the original style first generation cross members. Now that PCF has taken in and inspected a few hundred of them, the issue is very real, factually and statistically documented and very common. The second generation crossmembers do not have the same issue and are actually more robust and stronger than the first generation CMs. Just my guess, but probably why GM went with the second generation design in the first place.

 

[PreferredChassisFab]

The differential side/end mounts are placed just forward of the axle centerline. This placement exerts limited stresses on the end mounts, since the mount only supports and locates the differential. When the differential bushing fails, the differential "torque rotates" which can cause front axle component failures which we all have discussed. The end mount bushings are the same "barrel" bushing design as the cross member bushing, and are used in the same vertical loading but also are smaller due to the limited stresses subjected on them. The OEM end bushings are made to have a taper to the top and bottom of the bushing so a small gap between the torque surfaces and the end bracket bore is normal. If the differential is allowed to run loose on the cross member for an extended time it will damage the end bushings most commonly the right side. Of all the end bushings that I have replaced I have only seen a few that have had more than normal wear and failed.


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[digglesworth]

thanks luis and dwaine!!! i just pulled all 4 tires to clean out all the mud from my undercarriage and suspension. i looked at the outer bushings and the passenger side is definitely more worn than my drivers side. this leads me to believe that my crossmember bushing has been deteriorating for some time now. i have the first gen crossmember on my 06. is it possible to swap to a second gen style? also, what would the total cost be for all 3 pieces if i was to go that route? dwaine, you can pm me that info if youd like. again, thank you both.

 

[jamesrhodes2053]

2006 H3 front diff bushing.... looks like you guys have some solutions. Can someone throw up a link for some replacement bushings, thanks.

 

[LS12FAST4U]

I need to replace all of my bushings as well. I have an 06 but not sure which generation I have of mount. Any links to the bushings would be great.

 

[digglesworth]

guys... go to the sponsor section and look and the scorpworks section. Read through the thread on the front diff crossmember bushing replacements. It goes over how to tell which crossmember you have. I'm not gonna post links as a courtesy to dwaine. His thread tells you what you need to know about the bushings. Buying the bushings you want is up to ya'll...