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I agree with driveshaft out of balance

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Congratulations,  you found your problem. I'm a little put out. I said it was most likely a driveshaft problem before jmech but he gets the credit! You Yankees are discriminating against us

Did the hoping stop now that Easter is over?

The problem is in fact that you have been using Hy-Tran inside the driveshaft when you should have been using Official Yellow Wonder Bucket Fluid!!!

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2 hours ago, bitty said:

I agree with driveshaft out of balance

could be more that one thing, but hard to say with out puttin a set of eyes on it

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Just seeing the drive shaft pictures posted behind video (still pictures just now appearing).

From all of my experiences:

The yokes from the hangar bearing going into differential are out of phase. 

Simple way to look at it:   (one end of stick----should match other end of same stick)

Also-----the yoke needs to slide freely on the splines shaft.  

 

I had lots of experience with out of phase U-Jts back in my Howard Rotavator days-------saw tractors traded; only to have same problem when Rotavaor hitched to new tractor.

Good luck-----keep us posted.

 

DD

 

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So I set out to try changing the phasing of the driveshaft and broke the tab on the U joint cap. 🤬no updates tonight. I should be able to get a replacement tomorrow. 

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I agree the rear shaft is out of phase.   Don’t worry about the tin tab.   Put some lock tite on it and call it good.   You do not worry about trans output and diff yoke being the same.   The yoke ends of shaft have to be the same like someone posted.   

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So, you're going to turn the rear shaft in the slip joint to get the rear phasing correct, right?  I think someone else asked about the travel in the slip joint. I don't see the splines sticking out so I'm wondering if that has enough extra slip travel in it. But, it might just be made that way internally.

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All the ones that I have seen are timed by a different spline and the guy welding it together has to keep it in phase. This is apparently different than the Mack's we have . It might be possible to get it 180° out of balance also then . We have only done one without worrying about balence and we are not going above 45 mph in 70's-80's Mack's

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As others have said , Pull slip-joint apart and turn it 90-degrees and reassemble

shafts will be properly phased

 

1726246748_sethphasepaint.jpg.d683f42306e41f56fac9be58689d162b.jpg

 

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11 hours ago, vtfireman85 said:

Did not balance shaft

Have it checked before you drive your self nuts

Low speed off road stuff doesn't need it but on road the drive shaft speeds get fast enough to cause big vibrations if not balanced properly   

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We started out with the shaft in the suggested rotation, i am going to give it a shot, but i don't have much faith, gotta get the joint at least cleaned up. 

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Suggestion:

Saying you have tried it in our recommended position-----

Might be worth your while to engage transmission and observe front shaft to hangar bearing for vibrations while disconnected???

At least get a point of direction as to where the problem is coming from.  You may have more than one cause.

Would take some cobbling up of a power source to turn the rear axle at speed without driveshaft input------but that may be needed????

Don't disregard the suggestions of "balancing of the shafts"-------plus make sure there is no slack in the hangar bearing.

But no doubt-------short rear shaft is out of phase (as discussed earlier).  Eliminate one problem at a time------somewhere you will find the magic trick needed to cure the problem.

Too nice of a truck to give up on.👍

 

DD

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I can't believe how many comments this rang up in short order...

Problem is obvious and twofold:

1.) Driveshaft phase is incorrect. 

2.) Driveshafts must be balanced.  Even the best welder can't build it perfect.  There is a reason there are shops that specialize in building driveshafts.  Not just any hon-yock with a welder and a lathe can build them.  Take it out and find a driveshaft shop that can balance it.  They'll likely find it not welded together correctly as well.  

First section does not need a slip-shaft either. 

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Since I haven't noticed this question posted . How are the valve stems on wheels aligned? Should be 180 from each other, not in the same opening. Have you tried removing all rear wheels and running in gear?

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7 hours ago, J-Mech said:

I can't believe how many comments this rang up in short order...

Problem is obvious and twofold:

1.) Driveshaft phase is incorrect. 

2.) Driveshafts must be balanced.  Even the best welder can't build it perfect.  There is a reason there are shops that specialize in building driveshafts.  Not just any hon-yock with a welder and a lathe can build them.  Take it out and find a driveshaft shop that can balance it.  They'll likely find it not welded together correctly as well.  

First section does not need a slip-shaft either. 

thing is the driveshaft is in the position it is in in an effort to try something different, and it did not make a difference. I will of course give it another try in a different position. around here the shop that built it is/was the go to for engines and drivelines, many race cars rolled out of there and lots of trucks and equipment are still on the road and at work because of their expertise, while the guy that took over when the owner died may have not gotten this shaft perfectly balanced, I would not go so far as to say he's just some Hon-Yock with a welder. perhaps where you live specialty driveshaft shops are popping up like dandelions, around here not so much, so you either take to google and hope you find someone qualified 3 hours away or you go to the person you have trusted for years or that someone else has had good luck with. 

as to the slip section where the **** would you put it? apparently GM felt it needed to be there because that is where it was when the truck left the factory. 

I value your input, more people would value it if you weren't such a snotty prick with it. 

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On 3/29/2021 at 6:14 PM, vtfireman85 said:

tried u joints both ways, I would say the hop is in the seat, though some does transmit through the steering wheel it shakes everything in the cab, drive it for an hour and your nipples are sore. driveshafts are also in alignment, that is to say there is no bend in the middle. 

Back to square one.

Did you drive this with the fire truck pump on it and if so, was the hop there at that time?

Trying to determine if the issue was there before the truck was shortened?

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I also agree the last section of drive shaft is out of time.  Slip the spline out of the yoke, turn 90 degrees oor untill the crosses line up, then re assemble.

 if spline has a 'dead' land, (extra wide land) to match a corresponding key  in the slip section , shaft needs to be cut apart and assembled correctly.

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On 3/30/2021 at 6:15 AM, bitty said:

I believe that the front and back one are supposed to be in phase 

The crosses on each end of a section of tubing need to be in the same plane

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Need slip on front chunk since it allows flexing of frame from all that power...

 

Anyway.....

Rephase, but it may not help

GET IT BALANCED...with low gears that baby is spinning fast.  New guys idea is actually not a terrible one for testing.  My KW has a dime sized wt on a part of the driveline to get balance

Is that carrier bearing from the wreak of the Titanic? 

You'll get it

😁 

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On 3/29/2021 at 5:55 PM, vtfireman85 said:

as I have posted on here we recently put a 1989 GMC TopKick 7000 on the road with a dump body on it, retired firetruck, moved the axle forward, new springs and hangers, took out the pump in the center and had a custom driveshaft section made to replace it. has 1 carrier bearing in the middle. total of 3 U joints in the shaft. had a hop when driving before the dump body went on, more under load than not, but some still while coasting, and even going down hill, hops while braking, hops in neutral, but it is worse under load. figured it was rear tires, so we replaced them with new, and new rims, no change, had them balanced, no change. put new fronts on, with new rims, no change. tried taking the driveshaft apart and aligning the joints, no change, tried opposing the joints, no change. it is possible it is in drums I suppose but they look fine and it has no unusual behavior while braking. any suggestions would be appreciated, we are kind of at a loss here. 

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If phasing the back joints doesn’t help. I wouldn’t get all that worried about balance yet. It will just shake a bunch at speed if not balanced. You describe a intermittent hop or noise and shake correct? This is almost always from something loose or binding. If it was rear end I would suspect it would be making lots of noise. I am still leaning to something loose up on your rear motor mounts, bell housing bolts or motor Mount attaching bolts.

first try and phase joints

inspect drive train for any thing loose

i wouldn’t get all excited about balance yet that just produces a shake corresponding with drive shaft speed.

being it is automatic I would inspect flex plate bolts and flex plate’.

what you describe isn’t common but back in the day I used to work on tons of medium duty trucks. It usually was something in the rear mounts that produced what you describe. But I have found busted pinion end bearings and if manual trans some problems in trans causing it. I am going to leave you with a bit of advice that was in a transmission repair flier with a kit I got once. They had found 95 % of complaints of spicer aux 4 speed trans problems were not trans related. Most common problem of trans complaint was water pump , fan idler or any front bearing going out. Second was clutch related. Another thing that just popped in my head is check front wheel bearings and wheels they can do crazy things good luck.

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23 minutes ago, dale560 said:

I would inspect flex plate bolts and flex plate’.

Perhaps coasting with engine off would isolate a flex plate issue.

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1 hour ago, vtfireman85 said:

thing is the driveshaft is in the position it is in in an effort to try something different, and it did not make a difference.

I don't care what you have tried.  There is only one correct way to phase a shaft, and in the pictures it is out of phase.  

1 hour ago, vtfireman85 said:

around here the shop that built it is/was the go to for engines and drivelines, many race cars rolled out of there and lots of trucks and equipment are still on the road and at work because of their expertise,

Then why was the shaft not balanced or correctly phased?

1 hour ago, vtfireman85 said:

perhaps where you live specialty driveshaft shops are popping up like dandelions,

No, they are few and far between.  Two within 50 miles of me in opposite directions.  Commonly near truck shops.

1 hour ago, vtfireman85 said:

as to the slip section where the **** would you put it? apparently GM felt it needed to be there because that is where it was when the truck left the factory. 

I assure you it didn't leave the factory with two slip shafts on it.  Someone has changed this truck. 

1 hour ago, vtfireman85 said:

I value your input, more people would value it if you weren't such a snotty prick with it. 

You are the one who is having trouble with a truck.  You come to get free advice.  You have 100+ answers here, but 98% of them are guesses and pure bs.  I've built a lot of drivelines and I can see, plain as day, the issues with yours, yet you want to b!tch about how I tell you what's wrong just to earn some brownie points with your buddies????  Good luck with it then.

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At the risk of antagonizing another poster I'll offer my experience.

As a kid I "jacked up" one of my '64 Chevy Impala SS. It changed the pinion angle enough to cause a similar problem. I was "told" it was a driveshaft balance problem and had it balanced - no help. Further investigation and the help of a wiser man pointed out the incorrect angle - something you're familiar with a lifted Jeep. That was my drive line issue.

As for balance issues, I had some, especially running 5.38 gears in my '40 Ford. It wasn't a hop from phasing or angle issued but rather a buzz, as that shaft was really turning.

I ran dual AFBs on a cross ram on a 327 .60 over. Had a cruising range of about 45 miles with those gears. I'd blown up my rears and borrowed the 5.38s. They were  fun but axle snappers.

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Driveshaft shops are gone round here but some truck shops still build, repair and balance Driveshafts. 

The driveline is the most likely source but it can be other problems.

Check the carrier bearing, rubber and mount carefully. All engine and transmission mounts.

I've never had a medium duty truck with an automatic but when a flex plate/flywheel cracks it can knock. A torque converter can do strange things as well.

Thx-Ace 

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well i see it as plain as day, you have 2 problems. the drive shaft is not timed correctly at the rear to diff, 90 degree's out, and the slip joint is backwards. the outside of slip joint should be on the rear shaft.

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