Slight vibration at high speeds

[snampro]

I just installed 3.73 gears (had my diff rebuilt by a highly recommended shop), Unitrax half shafts, and replaced the u-joints on my drive shaft.

driving the car yesterday I thought I felt a very slight vibration around 80 to 85 mph. I shifted from 6th to 5th and it didn't seem to change, which makes me think it is behind the trans. It didn't get worse with increasing speed (accelerated to approximately 100 mph).

I know the half shafts come balanced, so I think that eliminates them. I checked all the bolts and everything is seated well (u-joints seated in the yokes) and snug. I am considering unbolting the drive shaft and rotating it 180 degrees on the pinion yoke.

should I be worried about this? should I have the drive shaft balanced?

I'm going to drive the car again and make sure it really is a vibration and not just the car (hadn't driven it for a few weeks).

 

[Joseph Dell]

since you haven't driven it in a while, check your tire pressures. GA has been up-and-down with temp. i wouldn't be surprised if the tires are different pressures.

how are you enjoying the 3.73's?

JD

 

[SNKEBIT]

Did you replace the straps for the u-joints? Had a similar problem with a car here, replaced the used straps and problem was gone.

 

[snampro]

oh yeah, replaced the half shaft straps and bolts with the ones Unitrax provided and replaced the drive shaft straps and bolts with OEM parts.

I think you posted in another thread I had on the subject and I made sure to do it.

checked the tire pressures, everything was at 30psi when I made the run. this could be a tire balance issue.

the 3.73's are awesome. its more like a 3.55 now since I have the 345/30-19 rears, but its great.

Joe: I was thinking to having an alignment done at that shop you suggested, I guess they could balance the wheels for me?

 

[Camfab]

since you haven't driven it in a while, check your tire pressures. GA has been up-and-down with temp. i wouldn't be surprised if the tires are different pressures.

how are you enjoying the 3.73's?

JD

I agree Joe, it sounds odd but the same thing happened to me when I went with 3:55 gears. In the end, it was fresh tires that cured the problem. In my case I had marked the exact relative positioning of the yokes to the diff and the diff to the driveshaft with marking paint. A bad u-joint could also be the culprit, as the 3:73 gears are yielding much higher driveshaft speeds at any given speed. A bad u-joint at the half shaft would also be a potential problem since youv'e described your vibration at speed vs. rpm.

 

[snampro]

hmm, that bothers me because the half shafts (and their u-joints) are brand new, and the u-joints in the drive shaft are new.

 

[Camfab]

Try this, jack the back end of the car up. Put the car in neutral with the e-brake off. Spin the rear tires by hand and watch carefully for run out. You can even put a dial indicator on the inside lip of the rim to check for wheel run out. Make sure the wheel hub and the wheel are free of rust and are seating perfectly. While your at it take those rear tires to a tire shop and have them checked for balance.

 

[snampro]

jacked the car up, I installed the half shafts correctly (they have appropriate sides according to Unitrax), wheels spin fine, no obvious issues and the wheel weights are still on the wheels. I did notice one of the fronts has none and I don't remember it not having any when I installed them.

I'm going to make an appointment for an alignment and have the wheels balanced at the same time.

 

[Jeff Torrey]

Be carefull of a bent rim. I know you have aftermarket rims so they are probably better than stock. But with the deep rear rims any oversized *** hole can throw a rim out of round. Over time the wobble can wear on the lug holes and the wheel centers exaggerating the condition.

I just put new tires on my car, had to throw out a set of stock rims for these very reasons...they were junk, to dangerous to save.

 

[snampro]

thanks for the tip, but I haven't hit anything. I'm betting the driveshaft just needs to be balanced since I put the new u-joints on it. the wheels were fine when I started this mod and there's no reason they would be bent. I'm careful with tightening the lug nuts. I'll make sure the shop checks the rims when they aligned and balance the car on Friday.

 

[RTED]

This could be a long shot, but if you have not driven the car all winter, you may have flat spots on the tires from sitting. Just a guess, but worth checking. Good luck!

 

[snampro]

not bad thinking, but the car is driven a minimum of once a week, with the only exception being when it is down for mods, which it was for about two weeks, but it was on jackstands the entire time, so there was no weight on the tires.

Update: removed both rear wheels and carefully seated them on the hub and torqued the lugs nuts. also removed the drive shaft and will have it balanced tomorrow.

 

[Camfab]

Unsure why the driveshaft would need rebalancing with u-joint replacement. It is possible that you may have thrown a weight off the driveshaft. As I remember the weight on my driveshaft was just tacked on one side. It sounds like youv'e done everything right with no skimping, very commendable.

 

[99 R/T 10]

As small as our driveshafts are, it would have to be dented or damaged badly to cause a vibration, then it would have increase as speed increases. I would look at the newly installed half-shafts.

 

[snampro]

If its the half shafts I have no idea what to do. Should I send them back to Unitrax or Roe? They were drop shipped directly from Unitrax.

The only thing that I noticed about the half shafts when installing them is the left one was a little tighter, like it was compressed more than the right when installed on the car. However, both went on fine and the u-joints seated properly in the yokes.

 

[Camfab]

So what was the culprit, tires? The half shaft upgrade was my next venture, really curious if they are problematic.

 

[snampro]

I have my appointment for the alignment and balance today. I just put the driveshaft back on after having the driveshaft shop balance it. They used only a small amount of weight. In addition, I used another new set of u-joint straps. I noticed these seemed to seat better on the u-joints than the set I ordered through MOPAR. Both sets were spicer sets, but the ones from MOPAR did not have the exact same number on them as the ones Unitrax sent. After driving the car for about 5 miles I don't feel the vibration anymore. It now just feels like a GenI VIPER with a rough suspension and engine.

I did talk to Devin at Unitrax and he advised me to replace the NAPA heavy duty u-joints I insalled on the driveshaft with spicer life u-joints. I have ordered a set of these u-joints and will have them installed when I get them.

So, the vibration is not there anymore, and I think the true culprit might have been the new straps I ordered through MOPAR, they just didn't clamp right.

I have a 30 mile freeway trip to get to the alignment shop today, so that will give me a significant amount of time above 80mph to make sure everything is fine.

 

[EllowViper]

Alignment and balance did it for me. Shook like crazy right at 80-82. After the alignment/balance, perfect. Now that I'm up to around 14K since the last balance, its doing it again, so it appears a consistant balance is the key with these wide asymetric tires.

 

[snampro]

had the car aligned and balanced at Gran Turismo East today, car is great. I think the straps had something to do with it, but the balance and alignment took everything out.

thanks for everyone's help!

 

[Camfab]

Now that you mention it, I remember that I bought extra straps because some of the new ones did not have the necessary preload(gap). Some of the straps fit flush against the mating surface before any torque was applied. Youv'e really got to watch all the details on these cars. I remember that I was chastized by the parts guy because he said I was being too critical.