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Vibration after regear

C

COKE

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Vitoria(Spain)
I removed my 3.07 ratio 10 bolts rear axle and put a 12 bolts with a new set of 4.11 gear and a Eaton posiperformance unit.

After solving my brakes issues,i have gone out for the gears break in procedure.
I have noticed a horrible vibration from the rear,mostly under acceleration and at high speed when the OD was engaged and i pressed the pedal.

I have backed home and i have lost the wheels nuts and torque them again.
Also i have removed the pinion yoke four bolts and i have turned the diveshaft positon 180º.The shaft is the one wich came from the factory.I put a 10 bolts yoke on the 12 bolts to fit it.

Now it goes better,but still vibes a bit.

The yoke side u joint was replaced few miles ago,so it is almost new .The T Case side one doesn,t seem to be bad.

The new gear set manufacturer specs (Motive gear)are 2.750" pinon to ring centerline distance and 0.08" backlash

I finished setting up with 2.756" and 0.10" Backlash.Could these small differences cause the vibes or would i need any kind of balancing?

The wheels are 33s the same that i had before the gears swap.

Thanks
 
did you change the entire axle or just the gears...?
 
its probably your driveshaft...its now spinning an extra rotation then it was previous to the gear swap, this will enhance vibes unless everything is completly perfect, angles and joints.
 
I've been hearing noise after gear swap too. I went from 3.08 to 4.56 on 10 bolts.

It sounds to me like the T-case is not used to spinning so fast. According to my speedometer it thinks it's going 90 mph when I am really going 65mph. That makes a lot of noise.


I don't know how to fix it, I just wanted to chime in just in case someone else does.
 
not that this has anything to do with the vibe but .010 is a really open for backlash. I dont know exactly what spec is but if thats inside it its probably on the upper end. I like backlash around .007.
 
I vote for d-shaft issues. It's spinning waaay faster now so any slack (like in the slip shaft, u-joints) will totally cause that.

D-shaft angles will cause that too!

Is the yoke you swapped the right size for the u-joint?

All this first before you tear into the gears again....
 
-Like i said before,i changed the whole axle.
I used to have a 10 bolts and mounted a 12 bolts with brand new gears.

-The suggested backlash stamped in the ring is 0.008, i suppouse that 0.010 would be into specs? :dunno:. In fact ,the suggested BL for my front axle gear set was 0.010".

-The yoke is from a 10 bolts.I just mounted it for using the existing driveshaft cause i don,t have one for the 12 bolts yoke, wich uses a smaller u-joint.

-Can a 10 to 12 bolts swap causes changes on the DS angle ?


Thanks a lot for all the inputs
 
COKE said:
-Like i said before,i changed the whole axle.
I used to have a 10 bolts and mounted a 12 bolts with brand new gears.

-The suggested backlash stamped in the ring is 0.008, i suppouse that 0.010 would be into specs? :dunno:. In fact ,the suggested BL for my front axle gear set was 0.010".

-The yoke is from a 10 bolts.I just mounted it for using the existing driveshaft cause i don,t have one for the 12 bolts yoke, wich uses a smaller u-joint.

-Can a 10 to 12 bolts swap causes changes on the DS angle ?


Thanks a lot for all the inputs
Click to expand...


For the record .010 is not in spec if its calling for .008. In fact backlash is a range like .004 - .008. I believe 14bolts have a huge range like .005-.012 or something ridiculous like that not that it really applies but Im just saying its not 1 set number. The back lash has nothing to do with your vibe though.

Lemme ask you this. When you put your 10 bolt yoke on, had you already had the 12 bolt yoke on and switched them? Cause if thats the case your crush collar is definitely all out of whack and if you crushed it too far when you put the new yoke on I bet the pinion will slap in and out of the case.
 
Depending on how you swapped yokes you may have changed the pinion bearing preload, which should be corrected before driving anymore. I have also heard of situations where the U-joint and yoke looked like a match but had some slop. It's also possible that the two axles were set up with different angles for the spring pads so you have changed the pinion angle. You should measure the U-joint angles, anyway. It's also possible (as was said before) that this problem was always there, the driveline is just spinning a lot faster now.
 
New crush collar,new barings,new seals...I bought the whole master kit for the installation

I also bought a torsion wrench for adjusting the correct bearing preload.
Anyway,i will follow you suggestion and i will adjust the backlash again.Just in case.

The springs and the axle came from a parted out 79 jimmy.I installed the jimmy springs years ago, cause they had an extra leaf and the original ones were a little sagged,so they have been mounted with the 10 bolts since them.But they came from the factory with the 12 b axle that i have installed now.


How can i meassure or correct the angles?


However there is a thing that i don,t understand:

Until now i have been running the 3.08 stock axles and 33,s but the truck came from factory with 3.08 ratio and 275/75 r15 tires.
I don,t know wich is the difference with 4.11 and 33s" but i think that the relationship should be very close to the original one.


Thanks again
 
The factory size being about 31", the 33"/4.10 combo will have 25% higher driveline speed speed than the 31"/3.08 combo. Running the 33's with 3.08s would have been about 7% slower than stock. But your speedometer has already confirmed all of this if you've never changed the speedo gears.

You can find a way to make this work. 3.08 was a poor gear for the stock tires, but GM loved sticking them in all kinds of trucks. With 33's it's almost silly and pretty hard on the transmission. 4.10 with 33's is a great driving combo.

They sell little angle finders at Sears, home depot, etc. You want to find the angle in each U-joint, which means finding the difference between two measurements. T-case to driveshaft and axle pinion to driveshaft. You want the two angles to be within 2 degrees of each other.
 
Blue85 said:
The factory size being about 31", the 33"/4.10 combo will have 25% higher driveline speed speed than the 31"/3.08 combo. Running the 33's with 3.08s would have been about 7% slower than stock. But your speedometer has already confirmed all of this if you've never changed the speedo gears.

You can find a way to make this work. 3.08 was a poor gear for the stock tires, but GM loved sticking them in all kinds of trucks. With 33's it's almost silly and pretty hard on the transmission. 4.10 with 33's is a great driving combo.

They sell little angle finders at Sears, home depot, etc. You want to find the angle in each U-joint, which means finding the difference between two measurements. T-case to driveshaft and axle pinion to driveshaft. You want the two angles to be within 2 degrees of each other.
Click to expand...


I woul like to comment,that due i still haven,t homologated the 33´s :doah:i need to mount the original set up for passing the Vehicle Technical Inspection twice a year.
With 3.08 and those 235/75 R15 "Vespa" tires,the truck runs like the devil in comparison with the 33s.
Now with 4.11 gears i don,t feel that difference.I suppouse the weight will has a lot to see too(Those wagon wheels are pretty heavy)


Thanks for the angle info.That is what i needed to know.
Do they sell shims or something for correcting this?


Thanks a lot for your invaluable help.
 
COKE said:
I woul like to comment,that due i still haven,t homologated the 33´s
Click to expand...
What?

The 4.10s with 33's should pull stronger than the stock setup. If it indeed "ran like the devil" stock, then maybe they weren't really 3.08s?

Yes, they make angle shims that go between the axle and the spring. Ideally you put the spring center bolt through the shim and the whole spring pack together. You should be able to get that stuff from DIY4x4, but the first step is to know what your angles are now.
 
I need to mount the original tires for every inspection cause i haven,t legalized the 33s yet.Here in Europe is mandatory.Once i have passed the inspection i install the 33s again.:waytogo:
Off course the gears i removed are 3.08s.What i mean is that the truck seemed to accelerate faster with the original set up .Maybe because now i,m paying too much attention to the vibes.
However 235 75 r15 are not 31" diameter tires,i guess they are smaller.

Thanks again for the angle correction info.
I,ll try to get the angle tool soon.
 
I was working off the 275/75/15 you posted further up. 235/75/15 is the smaller factory tire size - only about 29". Still, the gear change is more significant (33%) than the tire size change (14%). But 4.10 with the little tires must be pretty fun!

So can you get the larger tires approved or something or will you have to swap them out periodically for inspections? What if you get pulled over or have an accident with the 33's?
 
On Thursday i went to pass the technical inspection with the 235s and the 4.11s and i can guarantee you that it not was fun at all.
I went the 30 km that i have to drive to the inspection facilities ,grabbing the center console with my right hand due the noise it was making.The vibrattion is horrible running the small tires. I did belive that i was going to break and U-joint.Not driveable with this set up.

Yes, i can get the 33s aproved paying a good amount of money ,like everything in this country.In the rest of Europe the things are not so difficult.
If i have an accident, i suppouse the insurance company would find a pretty nice excuse for playing dumb.

I know that this can sound a little careless,but with all these stupid laws and bureucracy, you always finish cheating.However i,ll try to homologate them for the next inspection.

Definetively,you are very lucky in that side of the pond.I wish we would have the same freedom for everything related to the cars hobby .
 
Just a thought and an easy oops. done this my self. Is the u-joint seated properly in the yoke. Had a bunch of grease and mud in mine after a change and I didn't notice it was not seated properly. Shook the truck like a mother f#%&^*.
 
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