kkheitman Posted August 31, 2019 Share Posted August 31, 2019 (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? Edited August 31, 2019 by kkheitman Missing information Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/ Share on other sites More sharing options...
david wild Posted August 31, 2019 Share Posted August 31, 2019 Same driver ??? Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431197 Share on other sites More sharing options...
kkheitman Posted August 31, 2019 Author Share Posted August 31, 2019 32 minutes ago, david wild said: Same driver ??? Different drivers Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431199 Share on other sites More sharing options...
JoeH Posted August 31, 2019 Share Posted August 31, 2019 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? 1 Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431202 Share on other sites More sharing options...
kkheitman Posted August 31, 2019 Author Share Posted August 31, 2019 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. Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431205 Share on other sites More sharing options...
fjh Posted August 31, 2019 Share Posted August 31, 2019 (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 August 31, 2019 by fjh 1 Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431207 Share on other sites More sharing options...
terry Posted August 31, 2019 Share Posted August 31, 2019 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 Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431209 Share on other sites More sharing options...
R.E.D Posted August 31, 2019 Share Posted August 31, 2019 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. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431210 Share on other sites More sharing options...
R.E.D Posted August 31, 2019 Share Posted August 31, 2019 also What kind of suspension rating do you have ? Bronze bushings or rubber ones? Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431211 Share on other sites More sharing options...
kkheitman Posted August 31, 2019 Author Share Posted August 31, 2019 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 Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431215 Share on other sites More sharing options...
kkheitman Posted August 31, 2019 Author Share Posted August 31, 2019 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 Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431216 Share on other sites More sharing options...
kkheitman Posted August 31, 2019 Author Share Posted August 31, 2019 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? Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431217 Share on other sites More sharing options...
fjh Posted August 31, 2019 Share Posted August 31, 2019 (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 August 31, 2019 by fjh Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431219 Share on other sites More sharing options...
R.E.D Posted August 31, 2019 Share Posted August 31, 2019 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? 1 Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431220 Share on other sites More sharing options...
Mack Technician Posted September 1, 2019 Share Posted September 1, 2019 (edited) 1 hour ago, kkheitman said: What makes you think it would be cracked? There are two bolts inside the gear window which are trying to do the work of 6 bolts. They loosen, leak out to exterior space below the window, cause a stress crack to the rim of the banjo and require a weld repair to banjo mouth. When things really go south the crack will span through the threaded holes for the hold-down bolt and now you can't repair weld it properly. Wouldn't explain your problem, but adds another visible issue to your list. Sounds like you have real head scratcher. Stop welding it, shouldn't need it, plus, sorry dude, your welds are horrible. You welded it to the 1/8" thick output cover? Change all the studs, nuts and the Diff mount bolt. When installing run the four stud nuts up slight snug then torque the carrier bolt to banjo. Loosen the four studs, retorque banjo bolt again, run all 4 stud nuts up tight and torque each to grade 8 spec. Everything has been checked, your running hard. If it keeps doing it after that convert the centers to Neoprene Severe Duty bushings. You have fresh brass on a hogged out center stub, Neoprene will resurrect the center for the span of another service life. Edited September 1, 2019 by Mack Technician 2 Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431224 Share on other sites More sharing options...
fjh Posted September 1, 2019 Share Posted September 1, 2019 (edited) 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 September 1, 2019 by fjh Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431238 Share on other sites More sharing options...
JoeH Posted September 1, 2019 Share Posted September 1, 2019 Get a set of rebuilt pumpkins and call it a day. Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431243 Share on other sites More sharing options...
kkheitman Posted September 1, 2019 Author Share Posted September 1, 2019 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. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431244 Share on other sites More sharing options...
kkheitman Posted September 1, 2019 Author Share Posted September 1, 2019 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. Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431245 Share on other sites More sharing options...
Popular Post fjh Posted September 1, 2019 Popular Post Share Posted September 1, 2019 16 minutes ago, kkheitman said: No there is no washer between the bracket and the housing. There needs to be washers or a thick washer between the bracket and the housing on the bolt that goes into the bango housing or it will not stay tight! The difff casting has milled flat cut outs for flat washers to fit there all the way around the diff if you don't put the thick washer there or at least several flat washers there for the bracket to seat to the bracket will never stay tight! 3 Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431251 Share on other sites More sharing options...
kkheitman Posted September 1, 2019 Author Share Posted September 1, 2019 I think you might have nailed the problem Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431255 Share on other sites More sharing options...
R.E.D Posted September 1, 2019 Share Posted September 1, 2019 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. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431268 Share on other sites More sharing options...
Mack Technician Posted September 2, 2019 Share Posted September 2, 2019 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. Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431296 Share on other sites More sharing options...
Popular Post Mack Technician Posted September 2, 2019 Popular Post Share Posted September 2, 2019 (edited) I looked up the clamp force produced by A single fine thread 5/8” grade 8 bolt. If you run it to 170 ftlbs with oiled threads it produces 20, 350 pounds of clamping force. That’s crazy. Gotta be what’s killing the studs. Get the specific OEM thickness washer from Mack. Who cares if it’s $10. Edited September 2, 2019 by Mack Technician 3 2 Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431297 Share on other sites More sharing options...
kkheitman Posted September 3, 2019 Author Share Posted September 3, 2019 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 Quote Link to comment https://www.bigmacktrucks.com/topic/58843-torque-arm-problems/#findComment-431380 Share on other sites More sharing options...
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