Driveshaft length causing vibrations
Driveshaft length causing vibrations Talking about shafts and length, let's save the " that's what she said" jokes.
Okay, I have a pic's The first picture is when my car ate a tailshaft housing. I have since installed Adjustable LCA's, Adj panhard bar, and Relocated the Torque arm to the body. Now since doing this the car ran fine after and even went to the track a few times but I have always had a vibration issue. 2nd pic is a video where the length is now.. Finally got to this point.
http://www.youtube.com/watch?v=4PuDY...ature=youtu.be
My good friend who builds transmissions for a Chevy dealership came by and had a look. Driveshaft is too short. it has way too much play in the front and he was surprised it hadn't ate at the tailshaft seal. LCA's are adjusted to stock, the wheels are centered and the 275 40 18's are at the limit to the wheel well. I had to add very little length 1/4 an inch because the tires rubbed when I hit bumps.
So, What are my options? Is adding length a bad thing with my steel driveshaft? how much will it cost? would it be cheaper to buy new? and no I am 99% sure that I can not adjust the LCA's any further with out ruining tires.
any ideas or thoughts would be appreciated.
Okay, I have a pic's The first picture is when my car ate a tailshaft housing. I have since installed Adjustable LCA's, Adj panhard bar, and Relocated the Torque arm to the body. Now since doing this the car ran fine after and even went to the track a few times but I have always had a vibration issue. 2nd pic is a video where the length is now.. Finally got to this point.
http://www.youtube.com/watch?v=4PuDY...ature=youtu.be
My good friend who builds transmissions for a Chevy dealership came by and had a look. Driveshaft is too short. it has way too much play in the front and he was surprised it hadn't ate at the tailshaft seal. LCA's are adjusted to stock, the wheels are centered and the 275 40 18's are at the limit to the wheel well. I had to add very little length 1/4 an inch because the tires rubbed when I hit bumps.
So, What are my options? Is adding length a bad thing with my steel driveshaft? how much will it cost? would it be cheaper to buy new? and no I am 99% sure that I can not adjust the LCA's any further with out ruining tires.
any ideas or thoughts would be appreciated.
Adj lca's are for making your rear straight, not for pushing your whole rear end forward to compensate for wrong driveshaft length..
Sounds like you need a custom length DS since you changed a lot of key components..
It depends on your power level but i would not lengthen a DS, pst has some good deals on driveshafts.. Check brute speed out for that, free shipping!!
Good luck
Sounds like you need a custom length DS since you changed a lot of key components..
It depends on your power level but i would not lengthen a DS, pst has some good deals on driveshafts.. Check brute speed out for that, free shipping!!
Good luck
Last edited by Burken01; Sep 30, 2013 at 04:01 AM.
While shortening a DS is a fairly common thing, I wouldn't lengthen one. The cost for putting in a new tube and balancing it would be as high if not higher that buying a new custom shaft. Do a price comparison. Look at the places burken01 suggested. My new 3.5 inch aluminum shaft from action machine in south bend was just shy of 400 delivered, balanced to 10K RPM with new U-joints and slip yoke for a T56.
would 500 horse and or 170 mph be okay with an extended driveshaft? or should I invest Into some wheels with a better off set then the C5 thin spokes to push the rear forward by a bit? I understand the purpose of lca's
The added length shouldn't impact things at all - you're only talking about half an inch tops. The more I think about your situaation, however, the more I'm wondering if there is something else causing your vibration. A quarter inch change in distance between the rear end and the trans might cause a vibration, but you did do a fair amount of modification to the rear suspension.
Have you checked to see if the angle that the driveshaft connects to the rear end changed at all? Looking at the rear axle from the direction of one of the brake plates, is the pinion in the same clock position, in relation to the ring gear, as it was before your mods? I'm guess that to make the LCAs work with the revised track length, you had to roll the pinion up or down a little to make the bolts line up.
There are certainly more informed builders out there, but my understanding is that the angle of connection at the trans end should be equal and opposite of the angle at the axle end. If you were to draw lines through the pinion and the trans yoke, those lines should be parallel, and not intersect or spread.
I'm guessing that one end is off alignment, most likely your rear end.
Have you checked to see if the angle that the driveshaft connects to the rear end changed at all? Looking at the rear axle from the direction of one of the brake plates, is the pinion in the same clock position, in relation to the ring gear, as it was before your mods? I'm guess that to make the LCAs work with the revised track length, you had to roll the pinion up or down a little to make the bolts line up.
There are certainly more informed builders out there, but my understanding is that the angle of connection at the trans end should be equal and opposite of the angle at the axle end. If you were to draw lines through the pinion and the trans yoke, those lines should be parallel, and not intersect or spread.
I'm guessing that one end is off alignment, most likely your rear end.
Last edited by 1981TA; Sep 30, 2013 at 07:22 PM.
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UPDATE!!! Som I added length to the driveshaft. Had it rebuilt to add 2 inches to the stock length. Cost was 140. Not bad and everything runs perfect again. I do know for a fact there is a very tiny vibration on hard launches and that is because the adjustable torque arm is off by maybe a quarter degree because of the added length. But everything checks out and is good to go. Track soon to test the new 3600 stall.
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I would have opted for the custom driveshaft.
Critical speed is determined by weight of the rotating object, material property, and diameter. You just added more weight while retaining the same diameter.
This will lower the critical speed at which your driveshaft can spin at. So keep that in mind when doing top speed runs OR changing rear gears to 3.73 or numerically higher.
If auto, stock 3.23, 4th gear 170 mph is 5100 rpm, 3rd gear 6900 rpm
If manual, stock 3.42, 6th gear 3700 rpm, 5th is 5400 rpm, and 4th 7100rpm
As you can see, you are around 6900/7200 rpm to hit 170 with stock ratios, step up to the more common mod of 3.73 or 4.10's and you will get dangerously close to the critical speed of the DS. The stock 3 inch aluminum balances out around 5500 rpm for half crit speed and you want to be below 85% of that crit speed.
Critical speed is determined by weight of the rotating object, material property, and diameter. You just added more weight while retaining the same diameter.
This will lower the critical speed at which your driveshaft can spin at. So keep that in mind when doing top speed runs OR changing rear gears to 3.73 or numerically higher.
If auto, stock 3.23, 4th gear 170 mph is 5100 rpm, 3rd gear 6900 rpm
If manual, stock 3.42, 6th gear 3700 rpm, 5th is 5400 rpm, and 4th 7100rpm
As you can see, you are around 6900/7200 rpm to hit 170 with stock ratios, step up to the more common mod of 3.73 or 4.10's and you will get dangerously close to the critical speed of the DS. The stock 3 inch aluminum balances out around 5500 rpm for half crit speed and you want to be below 85% of that crit speed.
Last edited by SladeX; Nov 7, 2013 at 09:02 AM.
The stock driveshafts for these cars are very thin, and it is not uncommon for them to split open for people. I carry the PST line of driveshafts, shown at the link here. http://shop.brutespeed.com/82-02-F-B...afts_c2286.htm
The PST driveshafts are known for top notch quality. Bob
The PST driveshafts are known for top notch quality. Bob
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ATI ProCharger and Moser Sales 260 672-2076
PM's disabled, please e-mail me
E-mail: brutespeed@gmail.comob@brutespeed.com
https://brutespeed.com/ Link to website
