macattack

so your saying it was your insulator pads in the front rear axle. did you replace all the rubber pads? thanks

i have been fighting a similar problem. replaced and retorqued a bunch of things. let us know what you find out. i think there are a few out there with similar problems. good luck.

thanks. just want to make sure.

i got a e7 300 mack mr688s with a allison 740rs transmisson. how many mounts are there for the engine alone. i noticed there is on the front of the engine and a mount on each side of the tranny. should there not be mounts on each side of the engine?? thanks

ok. i understand. i will see what i can do. thanks

thanks again. i will put more air in the rears and see what happens. i may be able to get the rear end lifted up this weekend. i am gonna try to run it at the issue speed with the rears up to see what the heck is going on. being in a smaller town a guy does not always have quick access to the right equipment. thanks

thanks 84superdog. this wobble thing has got me. i will explain it a little better. accelerating up to 35 mph everything is fine. between 35-40 a wobble begins and lasts for only a very short time. it does seem to be worse rite before the final shift from 3rd to 4th. once in 4th everything is fine. almost feels like the driveshaft is whipping. if that makes sense. driving the truck my steering wheel does not shake or vibrate. you can steer like its new. when i go downhill in gear and let the truck coast the wobble shows up and then dissappears once i get to 35mph. wobble lasts for about 5mph. it actually feels like someone is rocking the cab between 35-40mph. if i stay hard on the throttle wobble is still there but not as bad. i thought it may be my transverse rod (one from the rear axle to the frame), but it seems fine. i had much the same wobble issue on my other truck (international) and my transverse rod was shot, but this one seems to be fine. the truck has the large 425 in front and 12r22.5 in the rears. i have only 90lbs in the rears maybe i should up them to 110 or so?? i should also mention that this truck is equipped with air throttle. found this out when my modulator valve screwed up. the throttle is controlled by a small motor connected to the linkage on the pump. also since it is air operated, the mod valve is a pneumatic type. anyway may have something to do with the way it shifts?? just a thought. thanks for your expertise.

more air = stiffer ride??

thanks guys. yah still trying to isolate that wobble. happens at around 35-40 and after that fine. the truck has an ht740rs allison trans. it seems that just before it shifts into 4th is where the wobble begins. after it shifts everything seems fine. i checked the trans filters for debris and found nothing. oil looks brand new. the wobble also shows up when coasting back from hiway speeds. if i let it coast downhill with no acceleration it begins to wobble from 35-40?? once its passed it rides great. changed and checked alot of things still hunting.

thanks david.

just wanting to know if these lug nuts look correct. should they not be nuts with washers? thanks

i believe the sidewall says 120 psi. i think my tireman put in 100.

got some balance beads put in my front 425 65r 22.5 steers. definately helped out my bounce wobble, but its still there. the fellow at the tire shop said they put in 12oz in each, i think maybe the4y need more. i read should be around 16 to even as hi as 20. anybody with the same tires run the cbb beads. also what do you think the tire pressure should be on this big tires? thanks

had this happen on my old cummins 240. oil cooler was shot. suck all my antifreeze into the motor oil. replaced the oil cooler and about 6 months later BANG. spun a bearing.

no i wish there was. i guess i could jack up both rears and take it up to the speed and see from there. just a little chicken shit to try you know. anyways if i remember the wobble still seemed to be there when i put the truck in neutral and coasted. if that says anything. thanks for your help.

if the brake drum is out of round would i not see it when the tire is turning? do you mean front drive axle?

checked my tires today. they all seem pretty good. jacked up the back and rotated each by hand. no issues there. yah this has been keeping me busy. dont really know what to check next. my wobble happens at around 35- 40 mph and after that fine. when i slow back down to 35-40 its there again. the steering wheel does not shake, its like the whole truck rocks side to side between 35-40. now at times its seems if i creep up to 35-40 and hold it for a while just before the wobble it does not seems as bad. weight doesnt seem to make any difference. i also noticed that it seems to happen just before the last shift on my trans. its an allison 740rs automatic. it feels like maybe my driveshaft may be whipping or something. all new u joints and the center bearing seems fine. some movement in the rubber but no more than my other units. i also installed a set of timbrens on the back camelback suspension. it helps for road shock, but did nothing for the wobble? what now? i guess i will keep checking. does anybody think this may be a power divider issue? i also checked my tranny and motor mounts. they seem good. any info on what i can check next would be appreciated. thanks

thanks. my front steers are 425 65 22.5 . the front and all my drives are balanced. but i will take a closer look. i was under the truck yesterday going over it with a fine tooth comb. be damned if i didnt find the driver side front spring shackle (rear of the front shackle. slipper style) the two bolts that hold the spring in the shackle were loose. i retorqued both bolts and one of the bolts threads were stripped. purchased a couple new bolts, washers, nuts all grade 8. let you know how it goes. thanks again

i have been fighting a wobble/sway issue i have with my truck. i changed pads , bushings, torque rods,tie rods, tire balance etc etc etc...... at around 40 mph my truck begins to wobble, sometimes worse than other times. at 40 wobble begins and at 45 it ends. when i deaccelerate the wobble shows again at around 40 mph then goes away. i only operate the truck once a week so trying to diagnose can be a pain. i have been messing with the idea about front shocks. my wobble feels like someone is shaking it from side to side. so thinking maybe some shocks would help. anybody have pics of their mr s with front shocks? any other info about my problem would be greatly appreciated. would power divider cause this? thanks

do you know where a guy may find a kit or hardware to mount a set of shocks to the front of my mr688s. my avatar is the truck in question. thanks

did mack ever have front shocks on their mr 688s trucks?

changed mine out a few weeks ago. didnt really notice any change.. easy to do though. what handling issue do you have? there is also a transvers torque rod that goes from your rear drive axle to the frame. the toruqe rods keep your axles from hopping under torque and the transvers torque rod keeps things aligned. hope this helps.

thanks. i have a wobble/wiggle that happens around 35-40mph. been fighting it for a while . i replaced bushings.pads,tie rods, springs,torque rods tires balanced etc... i just did my torque rods the old ones rubbers were squished. gonna give it a try in a few days see if i solved anything.

checked out the center bearing today. i laid down underneath the driveshaft and pushed up on the shaft. the rubber squished about a 1/4 inch maybe a little less. does this mean its bad or just weak rubber? i was told they all move in the rubber just as long as the bearing is tight your good. ????? also if i replace it can i leave the one driveshaft hooked to the trans and just rest it on some jack stands to replace the center bearing? what is the best way to replace the center bearing? thanks

ok. just found out the torque rod to the last axle is 4 inches shorter than the front rear axle. had to exchange one rod. now that i have the proper rods, i was wanting to know if i should jack up the rear before i retorque everything back down. just for alignment reasons? i was thinking of placing a jack under each trunnion saddle and raiseing the rear. what you think thanks