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mp8 vibration


cxn613

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2008 mp8 485 has around 475,000 on it, has vibration under load. Rpm's fluctuate when its acting up. This is not a consistent problem. Has the same feel as an injector being cut out but power is not effected when it does this. Truck has had all new cups and injectors and cam in the last 100,000 miles. Riding the jake down a hill seems to vibrate the worst. 

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Its Possible the engine brake slaves are coming apart they are screwed together and some times they work loose!

The only way to tell is to  remove the vCover and check  the valve set  if the brake adjustment has tightened up then you got to lift the rocker shaft and check the slaves.

Edited by fjh
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15 hours ago, Mackpro said:

FJH, did you see the new bulletin that came out today  on the engine brake pistons? We ordered the tools, they were not to bad on the price, I was shocked. We have been seeing alot of these come apart here lately causing lots of problems. 

Exhaust Rocker Compression Brake repair.pdf

Thanxz for the post MP

No MP I hadn't seen that . All I got to say is what took them so long we've been having issues with this for three years or more All models ! As for the price this may be a record as well  we have been repairing them with out the tools for so long they better make it worth while !Ya got to do what ya got to do!

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thanks for input. truck is doing a regen about once a week now compared to the once a month like it usually does, so may be onto something with the jake slaves. also the truck just has a slight choppyness while cruising down the road. almost like your on a light rumble strip all the time. truck runs in normal road conditions and not any off road use. has virgin bridgestone tires on. shocks all are new, cab mounts and engine mounts seem good. 

 

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2 hours ago, cxn613 said:

thanks for input. truck is doing a regen about once a week now compared to the once a month like it usually does, so may be onto something with the jake slaves. also the truck just has a slight choppyness while cruising down the road. almost like your on a light rumble strip all the time. truck runs in normal road conditions and not any off road use. has virgin bridgestone tires on. shocks all are new, cab mounts and engine mounts seem good. 

 

Don t wait to long to have it looked into! Keep us up to date so others can benefit from your findings!

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Usually noticed in the higher rpms! Know engine codes  but anything is possible like MPro said lots of different symptoms! You may have injector or injector harness  issues  If its coding / hard to tell till you look!

Edited by fjh
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I will say, this is one of the best pulling trucks I have ever road in or drove. The owner picked me up and we took a load of corn to the grainery last friday.  Grossed out at almost 98,000 pounds and bad injectors we had no problems in the hills or in heavy traffic.  I thought it was awesome but he said it was no where as good as it usually is. Truck is a CHU daycab  with a 505 PLUS MP-8, T-310 trans , Meritor rears with 3.21 gears and disc brakes all the way around. Running super singles  on the back 445/50 R22.5 .  No speed limiting and he dont baby it at all and still getting 6.1 MPG on his trips.   I have pulled up some of his other longer and lighter trips and they were in the very high 7's . 

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Wouldn't it be nice if this fixes his problem for good! 

Yup If your an O/O these days You Don"t dare NOT Buy A super Warrenty And hopfully you earn enough to be down while its being repaired Don't matter whos truck you own! Cummins is everybit as bad for not giving the rats ass if your unit is down . unless you happen to have a fleet! then THEY MITE  kiss ass a little!

Edited by fjh
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Got to drive the  truck today with a load. I do believe it is in the engine. Pulling a hard grade with rpms up it seems fine, but cruising over a knoll or just interstate cruising the engine will flutter. Really notice it if the cruise is on and you hit your target speed and the engine backs off then when it starts to come back it will flutter and tach needle will bounce. Coming home empty it runs perfect. Did get rid of the "hope" in the ride fixed by using those centering pins to center the wheels and drums.

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  • 5 months later...

Thanks for this Thread, this last week, noticed vibration under load with full jake, loud clunk when I throttle out of Jake. Also a load noise(sounds like air rush to clunk) when downshifting on hill quickly, if I throttle down a little and then shift no noise... Half Jake no symptoms. Trying get home, be ok if I drive no exhaust brake? I just bought this truck with 461k and have put $15k into parts and repairs so far...this exhaust problem is a 8 hr fix?

Edited by Sharkbiteray
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  • 4 weeks later...

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