R686St Banging Noise And Jerking

[RyanL]

Hi, well i have a 78' R686st mechanic's special truck that i bought and put a 14' dump bed on and done alot of fixin up. anyway it makes this banging noise and jerks. it don't do it all the time, i can make it start doing it with heavy acceleration, etc. it has tandem 38k axles wit 4.50 gears it says. i have put all new caps on trk. I have replaced and checked almost everything i can think of, have changed trans, replaced wedges and cams, spider gears,axle gears, bull gears,axles,etc I have counted all teeth on one gear carrier, but forgot to count on frnt carrier before i stuck in back down in housing. What are the odds of having different ratio's? What is acceptable size/wear difference between rear tires?

[HK Trucking]

Hi, well i have a 78' R686st mechanic's special truck that i bought and put a 14' dump bed on and done alot of fixin up. anyway it makes this banging noise and jerks. it don't do it all the time, i can make it start doing it with heavy acceleration, etc. it has tandem 38k axles wit 4.50 gears it says. i have put all new caps on trk. I have replaced and checked almost everything i can think of, have changed trans, replaced wedges and cams, spider gears,axle gears, bull gears,axles,etc I have counted all teeth on one gear carrier, but forgot to count on frnt carrier before i stuck in back down in housing. What are the odds of having different ratio's? What is acceptable size/wear difference between rear tires?

http://www.bigmacktrucks.com/index.php?showtopic=12971

http://www.bigmacktrucks.com/index.php?showtopic=12973

[other dog]

hmmmm...sounds like Double L's upstairs neighbors.

[RyanL]

well i checked all rear tires and all seem to be same hieght. So i took the trk for a drive and got on a backroad and started up the grade, and it was popping/banging so i mashed throttle down and it became qiuet? and as soon as i let off it again it started popping. i checked rearends and nothing seems to be warmer than normal other than maybe power divder(which is where id say im getting the popping from). So i stopped and backed up and pulled ahead a few times and drove another 2 miles or so back home while jus taking it easy and shiftin at low RPM and stuff and it never maid a noise SO??? i don't know but im goin to go with very close but mismatced gear ratio's, and bite the bullet and pull the front carrier back out and count teeth, which i forgot to do when i just changed spider gears the other nite at about midnite,lol

Edited March 13, 2010 by RyanL

[Packer]

I'm going to stick my neck out a mile and say that unless

the power divider is locked in, gear ratios won't be the issue!

IH at one time had a system that had two, 2 speed axles.

The first up-shift was in one axle and the next shift was the second axle.

Meaning the truck was running with two differant axle ratios at the same time.

May not sound right - - - just how it was!!

This is a good time for someone to stomp me into a mud hole - - - Have at it Guys!!!!

I'm just pitching a differant train of thought and someone may, or may not, find fault!!

This in maybe the reason an alias comes in handy on the forum!!!!!

LMAO

Packer

[HK Trucking]

I'm going to stick my neck out a mile and say that unless

the power divider is locked in, gear ratios won't be the issue!

IH at one time had a system that had two, 2 speed axles.

The first up-shift was in one axle and the next shift was the second axle.

Meaning the truck was running with two differant axle ratios at the same time.

May not sound right - - - just how it was!!

This is a good time for someone to stomp me into a mud hole - - - Have at it Guys!!!!

I'm just pitching a differant train of thought and someone may, or may not, find fault!!

This in maybe the reason an alias comes in handy on the forum!!!!!

LMAO

Packer

That was the Eaton 3 speed tandem axle setup you're referring to.

1 was both axles in low, 2 was 1 axle in low and 1 axle in hi, and 3 was both axles in high.

Those used a conventional spider gear type inter axle power divider though, and not the cam & wedge type power divider like the Mack tandems.

A spider gear type power divider will not clunk or bang if there is a difference in axle ratios or tire sizes the way a cam & wedge type power divider will.

That's why with "brand X" tandem setups you can match the tires the same across each drive axle without concern for any discrepancy in diameter from front drive axle to rear drive axle, whereas on a Mack tandem, you must match tires the same front and back on one side and then do the same on the other side so there is not a great difference in average tire diameter from front drive axle to rear drive axle(keeping the larger 4 on the curb side to compensate for road crown).

[Packer]

I stand corrected!!!!

Didn't factor in Mack vers 'Other' diff's.

Knew it wouldn't last long but I did have to toss it out!

Been too long since I worked in a truck shop and still

have OLD views on things and my mind being what it is - - -!!

LOL

That Herb guy is sharp!!

Packer

[cgallamore]

i was driving for someone a 97 ch 613 the truck had lo pro 22.5 the owner put standard 22.5 on front drive had the popping bowed up feeling going down grade. took about a month, 5 or 6,000 miles to tear rear end out. it felt fine in a pull. don't know if this helps.

[HK Trucking]

i was driving for someone a 97 ch 613 the truck had lo pro 22.5 the owner put standard 22.5 on front drive

That would definitely put the kibosh to a Mack power divider in short order if it had lo pro on one drive axle and standard 11R22.5 on the other drive axle.

.

[RyanL]

thanks for all the replys. Im just at a loss on what to do or where to look. i guess im young and this is my first mack so im kinda learnin as i go. But when i traded for this truck it had 10 and 11R tires mixed up on rear. which is probaly why the spider gears was busted out. I drove the truck around a lil bit just as a tractor and never noticed and popping or anything. I then took trk to unkle's welding shop and we doubled frame and stuck a 14' steel dump with subframe on the truck. and at this same time i put all new 11R22.5 recaps on rear and virgin 11R22.5 on front, and drove trk home and this is when the popping first started, but this was before in knew bout broken spiders. I have put prob close to 200-300 miles on trk like that, it jus embarrassing and noisey and jerky somtimes. then jus the other day i replaces trans with a used one, and rebuilt spiders in front and rear, and put new inner cam and wedge in power divider. So i dn't know if any of this helps.

[HK Trucking]

I drove the truck around a lil bit just as a tractor and never noticed and popping or anything. I then took trk to unkle's welding shop and we doubled frame and stuck a 14' steel dump with subframe on the truck. and at this same time i put all new 11R22.5 recaps on rear and virgin 11R22.5 on front, and drove trk home and this is when the popping first started,

I'm gonna take a shot in the dark here, and I'm sure you guys knew better than to do this, but:

Is there a chance that when you were welding that the ground clamp was put somewhere that it allowed current to flow through the wheel bearings or diff bearings?

That could cause rollers and races to be welded together or at the very least severely pitted which would cause some bad noises.

Just a thought, as it seems you have already addressed the usual causes.

Also, measure all those new 11R22.5 recaps and make sure they are installed as described in my earlier post.

.

[RyanL]

well, i took trk for another ride to gather some more info, this time as a passenger. The noise resembles the noise a hammer makes when hitting driveshaft tube (kinda hollow, tin can soundin, kinda noise) but it makes the truck do some fierce jerking. it don't do it goin doin hill in gear with or without jake on, and it dn't do it coasting in neutral. it only does it when in gear (any gear) while appling throttle or load and it seems to be worst when (as far as jerking more so than noise) while just maintaining speed. and it sometimes will be fine and not make noise or anthing at all. i can't pin point source of noise even standing out on fuel tank. I checked all tires and all seems well. i also don't thnk any bearings are bad. i checked all u-joints driveshafts and all are in phase and what not. I was told the other day that sometimes torque arms being to long or short will throw driveline angles out enuff to cause problems?? We did replace torque arms with other new ones we found and cut on and welded it back together with a heavy sleeve over it, but i wasn't there when this was done so i dn't know how close in length these new ones was. Sorry bout long post

[HK Trucking]

Is there a hanger bearing on the driveshaft?

If so, is it in good shape?

.

[RyanL]

yeah there is and yeah it seemed to be ok to me when i changed trans

[fjh]

yeah there is and yeah it seemed to be ok to me when i changed trans

Ryan I bin following this post and the input has been all valid here!I would how ever check the top gear sets on both diffs for peices if you havent already,pull the side covers and look at em.your ratio mis match is highly likly at this point wouldn't take very much with this style of interaxle drive to cause a problem like this! I beleive this was mentioned But again, If one of the diffs has a Mack limited slip in it, this will bang and pop.

Bud or spoke Wheels?

spoke Are they Tight?

Simple but valid questions

Cracked bud wheels make one heck of a noise!

[RyanL]

i checked top gear sets when i pulled carriers out cuz ya have to remove covers to get two of the bolts. I'm stumped, i thnk the next step is to pull frnt carrier back out and count all teeth. it has dayton whls all around. and i will go double check and make sure all are tight.

[fjh]

i checked top gear sets when i pulled carriers out cuz ya have to remove covers to get two of the bolts. I'm stumped, i thnk the next step is to pull frnt carrier back out and count all teeth. it has dayton whls all around. and i will go double check and make sure all are tight.

I agree its time to count!

[Chuck C]

With Dayton wheels look at the lip that the lugs tighten up against. If you have the wrong combination of lugs and spacers even though the lug nuts are tight the rim may still be slipping on the spokes If this is happening the lip will show signs of the slippage. Check both inside and outsid rims. The torque rods must be the correct lenght or it will do that also. When I first started driving the ten wheel dump kept blowing the interaxle drive shakt. The owner finally found the right torque rods and the problem was solved. I would contact Mack and make sure the torque rods are the right ones for the axles.

Chuck

[Timothy B Demarco]

Hi, well i have a 78' R686st mechanic's special truck that i bought and put a 14' dump bed on and done alot of fixin up. anyway it makes this banging noise and jerks. it don't do it all the time, i can make it start doing it with heavy acceleration, etc. it has tandem 38k axles wit 4.50 gears it says. i have put all new caps on trk. I have replaced and checked almost everything i can think of, have changed trans, replaced wedges and cams, spider gears,axle gears, bull gears,axles,etc I have counted all teeth on one gear carrier, but forgot to count on frnt carrier before i stuck in back down in housing. What are the odds of having different ratio's? What is acceptable size/wear difference between rear tires?

Well if you ask me it sounds like a power divider. I just had a truck that did the exact same thing as yours and the cam inside was bad. It only popped every now and then.

[RyanL]

Well im going to count teeth here in next day or two when i get a chance to pull it back out. i didn't see any signs of wheel slippage. As far a power divder, its just got new wedges and inner cams and what not, that was first thing i changed. im goin to do sum checkin on torque rods, sinse these was just replaced and modified to fit. I heard just the slighest difference from factory will cause problems.

[cgallamore]

Well im going to count teeth here in next day or two when i get a chance to pull it back out. i didn't see any signs of wheel slippage. As far a power divder, its just got new wedges and inner cams and what not, that was first thing i changed. im goin to do sum checkin on torque rods, sinse these was just replaced and modified to fit. I heard just the slighest difference from factory will cause problems.

i had a trackhoe push me out, stuck the dipper in the load of dirt he just loaded, and bent a tork rod, had a viberation imediately,

if it sounds like it's in the transmission, the smallest chip in a bull gear will sound and feel like tranny.

i would count teeth and closly inspect bull gears.

just my opinion.....

[RyanL]

hey, sorry guys bout not gettin back to ya. We been workin 7 days a wk which is 66hrs at my day job, and then i been comin home and runnin trackhoe til 10pm tryin to get a new building site done and old barn cleaned up and what not, so i haven't had chance to lk at ol mack, and tryed to do it 2nite but had company and didn't get nothin done but B.S.ing But the plan is check ratio's. Sorry bout the wait and ill try to figure sumthin out in next day or two. Thanks to everybody who has offered suggestions, and help thus far.

[RyanL]

well i just went out and took side cover off and counted teeth on ring and pinion to start with. The rear axle has 17 on ring and 13 on pinion. ( i counted these a few wks ago when i had it out) Now for the front it has 17 on ring and 14 on pinion. Now this sounds like its the problem cuz it acted like at ratio problem all along, and got worse when i put new guts in power divider. But i want to take rear cover back off and recount teeth jus to make sure, but key got left on and batterys r dead so i can't get bed high enuff yet to check them, but will in a few hopefully. So are the ring and pinion gears sumthing they change ratio's with these trucks or just the bull gears? dumb question i know, sorry im young and learnin.

[MACKS]

Ryan,I had the ratio changed in my 83 RD a while back and I'm pretty sure all that was changed was the ring and pinion gears,they said it was the cheapest way to go and would give me what I was looking for.

[RyanL]

well guys i just confirmed my findings there is one tooth difference between front and rear pinion gears. i didn't pull carriers out and check bull gears, would they be different too? the way the truck acts, i don't think there is much more than a tooth difference. I also found a similar story like this on web somewhere.