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kkheitman

Torque arm problems

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Posted (edited)

I have 1994 Mack RB 688 dump truck, the torque rod continuously breaks the mount bolts on the rear axle, we've had it in 3 different chassis shops and no one can figure out why. Any Ideas?

IMG_22541(2).jpg

Edited by kkheitman
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Same driver ???

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32 minutes ago, david wild said:

Same driver ???

Different drivers

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Recent problem? How long have you had the truck? Give us some history so we know if this is a new to you problem truck.

Miles? 

Are your axle stops ALL in place? All 4 of them? 

Are the bolts being overtorqued on install? If so that stretches the bolt, which makes it thinner, thus weaker.

How long are you getting out of the bolt before it breaks?

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Joe, we've had the for 4 years problem started 3 years ago and keeps getting worse. Axle stops are all in place. We've even welded the bracket to the axle and it breaks it off.

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Posted (edited)

How are your trunnion bushings, U bolts are tight?

In my opinion judging by that pic, if you were to lift that diff out the banjo housing will be cracked LH side!

Edited by fjh
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I believe the studs that screw into the banjo that hold the bracket go all the way through, that probably explains the gear oil running down the back.    terry:MackLogo:

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Drive the truck around in a circle  without the torsion arm.if the wheels walk off while turning then ur trunnion or bushing might be extremely worn.therefore while turning loaded that single bracket is taking all the stress of keeping the bogie straight which causes the bolts to break.

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also What kind of suspension rating do you have ? Bronze bushings or rubber ones?

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2 hours ago, R.E.D said:

also What kind of suspension rating do you have ? Bronze bushings or rubber ones?

Bronze bushings less than a year old

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2 hours ago, R.E.D said:

Drive the truck around in a circle  without the torsion arm.if the wheels walk off while turning then ur trunnion or bushing might be extremely worn.therefore while turning loaded that single bracket is taking all the stress of keeping the bogie straight which causes the bolts to break.

I tried that and get no movement at all 

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3 hours ago, fjh said:

How are your trunnion bushings, U bolts are tight?

In my opinion judging by that pic, if you were to lift that diff out the banjo housing will be cracked LH side!

What makes you think it would be cracked? 

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Posted (edited)
25 minutes ago, kkheitman said:

What makes you think it would be cracked? 

I Highly doubt all the oil slobber is from just the loose studs Could be wrong However Seen it before!

Does the front diff have a bracket as well?

Edited by fjh

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59 minutes ago, kkheitman said:

I tried that and get no movement at all 

Did you try it with a load on ? Some components must be worn enough to be putting stress on those bolts.

Also does the truck have the thick washer between bracket and banjo housing?

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Good explanation buddy! My bet is the bolts are loose inside the cover . Your on the money for the repair as well !it also held to have the torque rod on the front diff as well spread the load around!

Edited by fjh

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Get a set of rebuilt pumpkins and call it a day.

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Thanks Mack Technician a wealth of information there. I'm headed to a different mechanic this morning with the info you've provided. Spoke with him last night and he's pretty much on the same page you're on, he also couldn't believe they welded it to the cover. I'll let ya know what the outcome is. 

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13 hours ago, R.E.D said:

Did you try it with a load on ? Some components must be worn enough to be putting stress on those bolts.

Also does the truck have the thick washer between bracket and banjo housing?

No there is no washer between the bracket and the housing.

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I think you might have nailed the problem

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The washer allows the bracket to square up with the diff housing.no washer allows up and down movement which loosen or stresses those four bolts while truck is turning.

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5 hours ago, R.E.D said:

The washer allows the bracket to square up with the diff housing.no washer allows up and down movement which loosen or stresses those four bolts while truck is turning.

Good call, no washer (and an impact torqued bolt) adds thousands of pounds of additional internal stress to an already severe application. 

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On 9/1/2019 at 8:24 PM, Mack Technician said:

Good call, no washer (and an impact torqued bolt) adds thousands of pounds of additional internal stress to an already severe application. 

Was at the mack dealer today and they don't show a washer in there

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