macattack

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

i believe 44 rears. the cost was 230.00 per rod plus 40 bucks for the bolts, nuts washers. no problems in replacing both rods. was a simple procedure. only had to cut one bolt out. so just under 500.00 total. this is in canada.

thanks gang. gonna replace both rods while i am there. the rubbers are definatly squishied out. replacing all bolts,nuts and washers. did not realize that where the 2 rods meet at the crossmember 2 longer bolts hold the 2 rods togeather. so to change just one did not really make sense so i am doing them both. let you know how the road test goes when my parts arrive.

what would be the best way in holding the housing still?

would it be advisable to jack up the rears to do this? could i jack under the saddles. LOL. serious though??

thanks. its the saddle type. got to grab the thesaurus and a 6 pack. think i may need some help, better get 12. thanks again

any tips on replacing the torque rod on my mack. its the one that goes between the rear axles. not the transverse. thanks

thanks. i just thought maybe there was a measurement that would kind of tell me.

just wanting to know if my mr688s should have one or two wedges? i believe the original owner replaced the pass side front spring and may have not replaced the spring wedge on that side. either forgot or never realized there may be a wedge. unfortunately the original owner is deceased. the driver side has a wedge, but not on the pass side. my question is can i take a measurement anywhere to see if there should be one on the other side. thanks gang.

i think its time for a rebuild. mine did the same thing until the rebuild. easy to remove.

thanks guys. i am gonna check it this weekend. 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. ?????

thanks. mine is mounted in rubber also. so are you saying that there should be no movement at all.

what is the proper procedure to check for play in a center bearing? how much play is allowed? could a bad center bearing cause a wobble/shimmy. my problem is at 35-40 mph. then wobble goes away. any tips on replacing it. does not look like to big of a job. thanks happy summer!!

my fronts are 425 65r 22 and about a year old, but i will check that. thanks

thanks for the info. can a guy remove a plate to inspect or clean these things?

been slowly tracking down a wobble issue i have with my mack. another member mentioned the peanuts in my rears. this is what i began to notice. at around 35-40 mph i get a wobble that feels like a flat tire or a bulge in a tire. if i hold it for a few seconds during the first sign of the wobble and then increase my speed the wobble is not as noticeable, but if i try to fly thru the wobble at a fast speed the wobble gets worse. now does my next statement make any sense. feels like maybe the those peanut thingys or whatever are try to balance themselves or catch up to speed. the truck is a mr688s with an allison 740rs auto trans and mack rears. one note i am getting my front springs replaced early next week. i will post my results. thanks

to test gauge. remove wire from sending unit and ground it out. if gauge is good the needle will move over to max. if it does not go to max gauge is faulty. also what temp is your thermostat? should be around 180 or 190.