What's the deal with it, how many RPM's, machine, techniques etc... I'm not 100% confident in the balance job my rear shaft has. I don't know how he balanced it if the Grease fitting wasn't even on it... Figured out that vibe I get from 65+ is 99& sure the Rear Dshaft. I've had the tires shaved, removed the wheel spacers, checked for runout, everything passes with flying colors. IIRC I called a few local jobs a while back to have it done and they only balanced it to 3K/4K rpm's.. that's not a whole lot. Figure 4th gear is 1:1 ratio. 5th gear is overdrive. so at 70mph in 5th i'm doing 3K. so that shaft is going faster than 3K rpm. Hence why i have a slight vibe. Does anyone do HIgh speed shaft balancing?

I think 3500 or so is tops for most machines. Here is a search list with some "high speed" balancing shops listed, maybe one of them might be able to do higher speeds. I recall Jesse at High Angle Driveline mentioning once that the Toyota CV joints are not terribly smooth at high angles and speeds. I think some of the domestic brand joints have smoother operation.

This doesn't make sense to me. If the driveshaft is downstream from the transmission wouldn't it be spinning slower in overdrive? <img src="/forums/images/graemlins/confused.gif" alt="" />

The driveshaft speed is strictly dependent on the wheel speed and the axle gear ratio.

exactly. the input is slower than the output in OD. Hence "over drive". it's over driving. When below 4th gear input speed is greater than output speed.

1-3>output
4th=output
5th<output

the Driveshaft is on a 1:1 (constant/fixed) ratio with the rear axle and speed depends on R&P ratio and tire diamter and speed of vehicle. Well I guess being able to do 65 smooth as glass isn't that bad of a thing for what the truck is. I've been in people's stock-ish 4x4's and they vibrate worse at 35mph than mine at 65 or 70. so i'm deffinately ahead of most people with a 4x4 that's mod'd.

did some math. man things clear right up... heres what I got. 5.29 R&P, 35's that measure 32.5" roughly OD, the trans has a O.D. Ratio of .838 from what I saw. SO...

-3k rpm; 65mph; 3,486 Dshaft RPM

-3.5K rpm; 76mph; 4,067 Dshaft RPM

As you can see the shaft RPM's are WAY up there when traveling in 5th gear over 3K engine rpm. hence why I have vibes I couldnt find. So either I should of done 4.88's, OR the Tires need to get taller, which I was planning on anyway. Now if you work backwards... let's say I can do 60mph w/out vibes to be on the safe side. that gives me a Dshaft rpm of.. 3,225 for a safe working vibration free limit. so with it in 5th gear, engine at 2,775rpm, having the Dshaft spin at 3,225rpm and be at the legal 70mph speed limit i'd need a 38" tall tire. WOW. that puts things in perspective. So either I have to put 37's on it, or throw 4.88's in it.

4.88's, 5th gear, 2,775 engine rpm, 3,225 Dshaft RPM and 35" tall tires would do 70MPH. And vibration free technically.

this is probly why most trucks (V8 trucks) have 4.56's, 4.11's etc and run 35's and haul ARSE 80mph down the interstate w/out problems. Another thing to think about is Joint angle. the higher the angle the slower the Shaft RPM can be w/out vibes. Phycics and math... they always come back to bite you in the but after it's all said and done. <img src="/forums/images/graemlins/drunk.gif" alt="" />

i have the same exact problem. i get a vibe from 65 to around 80. i even had my driveshaft balanced by a shop that also balances for racecars.

well looks like we need to run 40" tires on the street or throw 4.88's in it... or somin. lol. Guess I just gotta live with it. Oh well, live and learn. but what are you supposed to do? 4.56's were stock. that gear with 35's and a 3.0... you're underpowered like all heck off-road. Oh well, at least we know now and theres no need to spend money on race car shaft balancing... won't help. at 4,500 driveshaft RPM and a nice large operating angle.. it's gonna vibe. Another reason why the Longer wheel base trucks are better IMO. 110" is to short. 128"+ within reason. that'll reduce the operating angle of the CV. Oh well...

NOW YOU KNOW!!!! Like bill nye the science guy used to say. <img src="/forums/images/graemlins/mrt.gif" alt="" />