Doffer Posted July 4, 2013 Share Posted July 4, 2013 I've attached a video from yesterday, but its really bad since had my 4-ways on the whole hill so all you can really hear is BEEP BEEP BEEP... had about 45 cars behind me at the bottom of the hill ...Anyways, whats going on is when i'm in the 1400-1700RPM range when using the engine brake the truck starts to bounce almost like its driving overtop of small bumps in the road. Im just wondering if the transmission may be going bad? Any tips on what you might think the problem is?Thanks guys, your the bestBrandon Quote Link to comment https://www.bigmacktrucks.com/topic/31810-99-mack-weird-noise-and-bouncing-when-going-down-hill/ Share on other sites More sharing options...
rsb502 Posted July 4, 2013 Share Posted July 4, 2013 I doubt its the trans, sounded like you could hear the bounce in the exhaust, any chance that hill was slick and you were slipping a wheel causing some hop in your camelback suspension ? Quote "Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin"If your gonna be STUPID, you gotta be TOUGH" "You cant always get what you want, but if you try sometimes you get what you need" Link to comment https://www.bigmacktrucks.com/topic/31810-99-mack-weird-noise-and-bouncing-when-going-down-hill/#findComment-192506 Share on other sites More sharing options...
Doffer Posted July 6, 2013 Author Share Posted July 6, 2013 I doubt its the trans, sounded like you could hear the bounce in the exhaust, any chance that hill was slick and you were slipping a wheel causing some hop in your camelback suspension ?yeah at the end its definitely audible .. the hill i was going down was completely dry as well.Just for reference, this is the same truck that backfires out the exhaust when the engine first starts to warm up while using the engine brake Quote Link to comment https://www.bigmacktrucks.com/topic/31810-99-mack-weird-noise-and-bouncing-when-going-down-hill/#findComment-192971 Share on other sites More sharing options...
staxx Posted July 6, 2013 Share Posted July 6, 2013 How is the condition of the turbo? Quote Link to comment https://www.bigmacktrucks.com/topic/31810-99-mack-weird-noise-and-bouncing-when-going-down-hill/#findComment-192990 Share on other sites More sharing options...
Doffer Posted July 7, 2013 Author Share Posted July 7, 2013 im not sure, i'll have to pull the piping off and inspect for shaft play. It looks to me like it's a relatively new turbo housing, so im guessing it was replaced at one time ... but looks can be deceiving. i'll let you know what i find Quote Link to comment https://www.bigmacktrucks.com/topic/31810-99-mack-weird-noise-and-bouncing-when-going-down-hill/#findComment-193084 Share on other sites More sharing options...
rsb502 Posted July 7, 2013 Share Posted July 7, 2013 "Backfires out the exhaust while warming up using the engine brake", well it actually makes me think the valves need to be adjusted or it may be slightly out of time somehow. An engine brake works by opening the exhaust valves at the top of the compression stroke before combustion and the power stroke basically turning the engine into an air compressor. By the sound of a "backfire" it would seem to me that the combustion was taking place before the valve opened making it louder thru the exhaust. As for the hop it just seemed like Camelback hop to me does it do it on flat ground or just on steep grades? Quote "Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin"If your gonna be STUPID, you gotta be TOUGH" "You cant always get what you want, but if you try sometimes you get what you need" Link to comment https://www.bigmacktrucks.com/topic/31810-99-mack-weird-noise-and-bouncing-when-going-down-hill/#findComment-193114 Share on other sites More sharing options...
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