BucketTrucker688 Posted November 14, 2017 Share Posted November 14, 2017 I have a clunk almost as if a torque arm was bad on my 1991 rd688s with 44k Camelback. Spring shop says suspention looks good possibly in the driveline. It's a identical feel to a bad torque arm...I changed 1 torque arm that had play in it but the thud I get from the back of the truck when I dump the clutch at say a stop light and when I brake hard at low speed is still there...any ideas on a diagnosis? I put a reman forward rear in about 50,000 and run same tread depth tires on all 8 drives all the time as to not tear up rears. I am the only driver the truck has seen since I bought it in 2009. Quote Link to comment https://www.bigmacktrucks.com/topic/51676-clunk-coming-from-the-back-of-the-truck-when-starting-to-accelerate-and-brake/ Share on other sites More sharing options...
tjc transport Posted November 14, 2017 Share Posted November 14, 2017 check the rubber blocks between the springs and the spring caps. if the alignment dowel breaks off in the spring, the rears will shift about 2 inches on takeoff and stop causing the spring to move in the caps until the "T" on the end of the spring hits the cap. easy way to check is to have someone stand along side the truck and watch the wheels as you take off hard and brake. you will easily see the rears move. we bought a 05 Granite one that was bad for so long the springs actually wore a groove into the caps. Quote when you are up to your armpits in alligators, it is hard to remember you only came in to drain the swamp.. Link to comment https://www.bigmacktrucks.com/topic/51676-clunk-coming-from-the-back-of-the-truck-when-starting-to-accelerate-and-brake/#findComment-384921 Share on other sites More sharing options...
Lucky dogg Posted November 16, 2017 Share Posted November 16, 2017 I agree with TJC, I have two 1998 Mack Rd 688s and have fought problems like what your describing in the past. It's most likely a torque arm or dog bone as my mechanic calls them. I have found over the years only changing one at a time ends up causing me hardship down the road bc the other will need changed. When one wears out I change the other also to ensure the rears are not moving any direction they shouldnt. I'd stick with the torque are deal. If a mechance says there fine then you have a spring issue with pads or trunnion bushings ect. Keep in mind if the torque arm had movement previous this could cause other things to work also. Good luck Quote Link to comment https://www.bigmacktrucks.com/topic/51676-clunk-coming-from-the-back-of-the-truck-when-starting-to-accelerate-and-brake/#findComment-385052 Share on other sites More sharing options...
Jamkar Posted January 3, 2018 Share Posted January 3, 2018 Maybe turntable bushes or jaw issues. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/51676-clunk-coming-from-the-back-of-the-truck-when-starting-to-accelerate-and-brake/#findComment-388926 Share on other sites More sharing options...
turckster Posted February 17, 2018 Share Posted February 17, 2018 Excessive play in the 5th wheel or a power divider going out, my money is on the power divider. Quote Link to comment https://www.bigmacktrucks.com/topic/51676-clunk-coming-from-the-back-of-the-truck-when-starting-to-accelerate-and-brake/#findComment-392234 Share on other sites More sharing options...
Glensts Posted February 18, 2018 Share Posted February 18, 2018 Had the peanuts in the power divider giving us grief and clunking. If we engaged the power divider it wouldn't do it anymore. 46000 mack rears airride 1 Quote Link to comment https://www.bigmacktrucks.com/topic/51676-clunk-coming-from-the-back-of-the-truck-when-starting-to-accelerate-and-brake/#findComment-392330 Share on other sites More sharing options...
blackdog2 Posted February 18, 2018 Share Posted February 18, 2018 Pull fill plug they magnets on them . . Quote Ed Link to comment https://www.bigmacktrucks.com/topic/51676-clunk-coming-from-the-back-of-the-truck-when-starting-to-accelerate-and-brake/#findComment-392340 Share on other sites More sharing options...
OldRedMack Posted May 7, 2018 Share Posted May 7, 2018 We have a 94rd with 44k camelbacks that had a lot of play like your describing, but no real loud clunk. Ended up being the axles, we never broke an axle but after 20 years of use the axle splines were almost wore off. Put new axles in it and the play was gone. Also on the same truck, which thinking now probably more mirrors your situation. Was the power divider, if the tires on the drive axles ever got more than 3/8 of an inch out of size from the front drive to the rear drive it would clunk. Had the power divider rebuilt and it took care of that problem. Quote Link to comment https://www.bigmacktrucks.com/topic/51676-clunk-coming-from-the-back-of-the-truck-when-starting-to-accelerate-and-brake/#findComment-398441 Share on other sites More sharing options...
Ricci randanella Posted January 28, 2019 Share Posted January 28, 2019 Was wondering what was outcome of your truck. My 1998 rd is doing exact samething . Both rears are moving a little bit front and back. Making noise only once in a while when pulling out and stoping. Quote Link to comment https://www.bigmacktrucks.com/topic/51676-clunk-coming-from-the-back-of-the-truck-when-starting-to-accelerate-and-brake/#findComment-414311 Share on other sites More sharing options...
JoeH Posted January 28, 2019 Share Posted January 28, 2019 Good info here, my 95 rd688s does this same thing once in a while on takeoff, only as clutch is being let out. Will have to check for wear on spring T's. My truck does NOT have the auto power divider. Could my issue still be with power divider? Quote Link to comment https://www.bigmacktrucks.com/topic/51676-clunk-coming-from-the-back-of-the-truck-when-starting-to-accelerate-and-brake/#findComment-414328 Share on other sites More sharing options...
fjh Posted January 29, 2019 Share Posted January 29, 2019 (edited) 42 minutes ago, JoeH said: Good info here, my 95 rd688s does this same thing once in a while on takeoff, only as clutch is being let out. Will have to check for wear on spring T's. My truck does NOT have the auto power divider. Could my issue still be with power divider? yes, are your tires evenly worn? Edited January 29, 2019 by fjh Quote Link to comment https://www.bigmacktrucks.com/topic/51676-clunk-coming-from-the-back-of-the-truck-when-starting-to-accelerate-and-brake/#findComment-414331 Share on other sites More sharing options...
Rob Posted January 29, 2019 Share Posted January 29, 2019 I purchased a 72 R-685 once that clunked terrible upon both acceleration, and deceleration which turned out to be the elephant pads and locating pins basically gone. The bottom castings, (aluminum) were almost paper thin where the "T" of the leaf springs had been rubbing against them. Both axles really moved a lot when going through shallow turns. Prior owner replaced the castings and pads when the truck was finally put out of service. Still have the rears as they were sound, but the truck was cut up after parts usage for many years. Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/51676-clunk-coming-from-the-back-of-the-truck-when-starting-to-accelerate-and-brake/#findComment-414333 Share on other sites More sharing options...
JoeH Posted January 29, 2019 Share Posted January 29, 2019 47 minutes ago, fjh said: yes, are your tires evenly worn? Not particularly, we never change all 8 drive tires all at once. Only ever do one set of 2 at a time. We've been doing it this way for 30 or 40 years. Quote Link to comment https://www.bigmacktrucks.com/topic/51676-clunk-coming-from-the-back-of-the-truck-when-starting-to-accelerate-and-brake/#findComment-414334 Share on other sites More sharing options...
fjh Posted January 29, 2019 Share Posted January 29, 2019 13 hours ago, JoeH said: Not particularly, we never change all 8 drive tires all at once. Only ever do one set of 2 at a time. We've been doing it this way for 30 or 40 years. So with out a power divider ( lock out ) which people get mixed up on alot, you wouldn't be able to nail down if it is a power divider or not with out taking the unit apart ! if the tires are un even it makes the power divider work harder and has it constantly Turning and adjusting position if it has a worn spot on the cams inside or a broken wedge these can all cause clunks and noises !with the power divider lock out you can lock the power divider out and join both diffs together as a test ! and the unit is out of the picture ! with out it your guessing! Something I would look for Is Broken or slipping wheels ! Spoke wheels can slip and if your running STEEL buds the inner wheel can be cracked an you won't see it! Quote Link to comment https://www.bigmacktrucks.com/topic/51676-clunk-coming-from-the-back-of-the-truck-when-starting-to-accelerate-and-brake/#findComment-414364 Share on other sites More sharing options...
JoeH Posted January 30, 2019 Share Posted January 30, 2019 10 hours ago, fjh said: So with out a power divider ( lock out ) which people get mixed up on alot, you wouldn't be able to nail down if it is a power divider or not with out taking the unit apart ! if the tires are un even it makes the power divider work harder and has it constantly Turning and adjusting position if it has a worn spot on the cams inside or a broken wedge these can all cause clunks and noises !with the power divider lock out you can lock the power divider out and join both diffs together as a test ! and the unit is out of the picture ! with out it your guessing! Something I would look for Is Broken or slipping wheels ! Spoke wheels can slip and if your running STEEL buds the inner wheel can be cracked an you won't see it! I've never worked on one, I'll have to get the books out to see how they're constructed. I've had problems with wheels spinning in the past, (spoke hubs) but I have them tightened well right now. We've replaced a couple hubs on this truck with broken spokes. Elephant pads look pretty worn out IIRC, so broken dowels as a potential cause caught my attention. It got new torque arms put on when we bought the truck, so I expect it's not them. Plus it doesn't do it all the time. Quote Link to comment https://www.bigmacktrucks.com/topic/51676-clunk-coming-from-the-back-of-the-truck-when-starting-to-accelerate-and-brake/#findComment-414419 Share on other sites More sharing options...
JoeH Posted January 30, 2019 Share Posted January 30, 2019 Crawled under the truck, shows signs of right intermediate axle sliding on the spring. Looks like the truck is getting elephant pads this spring when the cash flow starts up again! Quote Link to comment https://www.bigmacktrucks.com/topic/51676-clunk-coming-from-the-back-of-the-truck-when-starting-to-accelerate-and-brake/#findComment-414484 Share on other sites More sharing options...
JoeH Posted January 31, 2019 Share Posted January 31, 2019 It's a 44k bronze bushing. It'll just get cribbed up and the rears lifted off the springs enough to pop the new ones in. I don't expect to be touching the U bolts or bushings. Is that website the Atro pads? Quote Link to comment https://www.bigmacktrucks.com/topic/51676-clunk-coming-from-the-back-of-the-truck-when-starting-to-accelerate-and-brake/#findComment-414532 Share on other sites More sharing options...
Rob Posted January 31, 2019 Share Posted January 31, 2019 54 minutes ago, JoeH said: It's a 44k bronze bushing. It'll just get cribbed up and the rears lifted off the springs enough to pop the new ones in. I don't expect to be touching the U bolts or bushings. Is that website the Atro pads? Atro is one brand of urethane pads and there are several out there. Atro seems to be of first rate quality and what I've used on my own. Don't rule out looking over the balance of the suspension. If it's been let go far enough the rears are clunking and walking, there may be more to be found. I don't like doing something twice myself but no longer need job security..... 1 Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/51676-clunk-coming-from-the-back-of-the-truck-when-starting-to-accelerate-and-brake/#findComment-414537 Share on other sites More sharing options...
JoeH Posted January 31, 2019 Share Posted January 31, 2019 Noted; we operate a 15-20 mile radius from our yard, truck only occasionally sees 60mph. It's a '95 with about 245k miles on it. Pads look dry rotted more than anything, but I'll see that we check things over. Quote Link to comment https://www.bigmacktrucks.com/topic/51676-clunk-coming-from-the-back-of-the-truck-when-starting-to-accelerate-and-brake/#findComment-414538 Share on other sites More sharing options...
Rob Posted January 31, 2019 Share Posted January 31, 2019 Get the weight off the suspension, and use a forklift or skid steer to apply some "easy" side force to the axle hubs while watching the trunion area for deflection. I do it by chaining a forklift of skid steer to the tire with a fork on the hub. On the bronze bushed variety remove the cap so you can see the innards. If there is movement between the tube and arm, the bushings are loose. I always found it too hard to do with a pry on the floor with everything still bolted up but I'm weak in stature. Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/51676-clunk-coming-from-the-back-of-the-truck-when-starting-to-accelerate-and-brake/#findComment-414541 Share on other sites More sharing options...
terry Posted January 31, 2019 Share Posted January 31, 2019 As rob said be sure to carefully check out the trunnion bushing, might be looser than you think. terry Quote Link to comment https://www.bigmacktrucks.com/topic/51676-clunk-coming-from-the-back-of-the-truck-when-starting-to-accelerate-and-brake/#findComment-414557 Share on other sites More sharing options...
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