Put on your thinking caps

[Det_Riot]

What would cause a speed related vibration in a rear end? [MENTION=341]1997cobra[/MENTION] and I swapped his rear end into my car. Its factory cobra with a 4.30 and Moser axle brace "professionally" installed by a local shop.

Well first time I hit freeway speeds, I was caught off guard by the vibration that felt like my drivetrain was going to come through the floor. I did the clutch test to see if its motor or drive line and its definitely trans back because its still there when you push in the clutch. I tested rpm by taking fourth over 70 and below 70 @whatever rpm was smooth. Immediately over 70, violent drive line shakes. I'm lost and without an answer to it all.

Help!

[iRoush]

is it shaking the wheel. if so tire balance is off IMO. if it doesn't shake the wheel then the gear lash is not set correctly and it will cause a vibration as the gears are turning faster and faster.

[Det_Riot]

The whole car is shaking. I can feel it on my seat, shifter, wheel. That and violent howling

[PRPVinyl]

Was the axle installed and used in the other car before being installed in yours? Or was it just built and never run? Generally a howling rear end is caused by improperly set back lash. Of course go back and check all of the basics, all mounting points are tight, driveshaft bolts are tight

Matt

[Yeahloh95]

two things pinion angle or drivshaft phasing, try pulling driveshaft and turning it 180 on flange , then take car back out , what control arms are you using ?

[Det_Riot]

Hpm megabytes juniors. Uppers and lowers. Gonna reclock the driveshaft today and see if that helps. Rear end was in Donovan's car previously and he had the same issue.

[Det_Riot]

Hpm megabytes juniors. Uppers and lowers. Gonna reclock the driveshaft today and see if that helps. Rear end was in Donovan's car previously and he had the same issue.

[PRPVinyl]

If he had the same issue then you need to pull the cover off and check the back lash. Checking the back lash is very easy and the and specialty tool you need is a dial indicator with a magnetic base. If I remember from reading a howling rearend is a loose back lash.

matt

[Yeahloh95]

jack car up and make sure its not a bent axle ?

[1997cobra]

back story on the axle: 45k, no issues until i took it to dts for the gear swap. Im on a bone stock cobra motor and street tires, so I doubt the shafts are bent.

Bryan and I will toy with it today. I'm slightly pissed because I've been chasing this vibration thinking it was trans swap related. But I now know for a fact that it is the rear end. Bryans car was smooth before we swapped it into hos car.

thanks for the help guys, one of us will chime back in with our findings

[Rolocut]

I joints/driveshaft balance? A few ounces makes a huge difference, a few times in high school we played jokes and put hose clamps on each other's driveshaft in school parking lot and thing shook violently ha.

On going project, 94 cobra, r block, tfsr225, hp efi, vortech ys

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[NVRL8TE]

Still chasing a similar vibration in my car.

[01yellercobra]

I have a similar issue since going to 3.90s. When I first installed them the vibration would start around 70mph. I reclocked the driveshaft 180 degrees and now it starts at 90mph. I'm going to have the driveshaft rebalanced. The only thing I can figure is the increased rpm is causing the issue.

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[mustangcobratim]

If donovan had the same issue I would say the gear install. Is it on decel or accel?that can point if it is a coast or drive pattern issue. Any other gear than frpp gives the 8. 8 a issue. Usually you give up a good pattern on either tje drive or coast etc. That is strange since dts usually does a goood job of setting up gears. But it cam happen!

[OnyxCobra]

Let me know if turning the driveshaft helps, I have a similar issue minus the howling. I think howling would point me to the gears but that might not be causing the vibration.

[PRPVinyl]

I still say pull the diff cover and check the backlash. If I recall it should be .008-.012. And a couple of thousandths on either side will make a big difference.

matt

[iRoush]

I still say pull the diff cover and check the backlash. If I recall it should be .008-.012. And a couple of thousandths on either side will make a big difference.

matt

THIS THIS THIS. stop overlooking the obvious. if it only happened after the gear swap, clearly the gears are not setup correctly IMO.

[1997cobra]

I joints/driveshaft balance? A few ounces makes a huge difference, a few times in high school we played jokes and put hose clamps on each other's driveshaft in school parking lot and thing shook violently ha.

On going project, 94 cobra, r block, tfsr225, hp efi, vortech ys

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Possible, dts made the driveshaft at the same time as the gear swap

Still chasing a similar vibration in my car.

It's because t56s are garbage, you should swap back to a t45 lol jkjkjk

If donovan had the same issue I would say the gear install. Is it on decel or accel?that can point if it is a coast or drive pattern issue. Any other gear than frpp gives the 8. 8 a issue. Usually you give up a good pattern on either tje drive or coast etc. That is strange since dts usually does a goood job of setting up gears. But it cam happen!

Anywhere over 70 mph, accel and decel. IDK if I told you this, but dts also didnt even tighten my diff cover

Let me know if turning the driveshaft helps, I have a similar issue minus the howling. I think howling would point me to the gears but that might not be causing the vibration.

Didnt help at all

I still say pull the diff cover and check the backlash. If I recall it should be .008-.012. And a couple of thousandths on either side will make a big difference.

matt

THIS THIS THIS. stop overlooking the obvious. if it only happened after the gear swap, clearly the gears are not setup correctly IMO.

Next step is this. Bryan is going to rotate the driveshaft 2 more times. If that doesnt fix it, we will dig into it

also, I should note that 1000 things changed on my car along with the gear swap. This just verified that it is in the rear axle. otherwise id still be blaming the trans

Edited September 22, 2013 by 1997cobra

[Det_Riot]

Didn't have time to pull the diff cover. Rotated the driveshaft 180 and no change. Gonna check the external things before I pull the cover and check the front nut and make sure that's tight.

[MENTION=461]mustangcobratim[/MENTION], the shake is there on all fronts. Accel, decel, and coasting in neutral.

[Pushrod91]

Its gears.

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[iRoush]

Its gears.

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we been there before. lol

[Duff Daddy]

If you feel the whole car shaking, its in the rear so lets start there.

1) rotate tires front to back and see if the vibration is effected at all

2) if its still there and you have access to a lift, drive the car on a lift and run it at 70, look for any axle movement, one could be slightly bent just enough to clearance and still spin but give you a vibration.

3) also, if your saying its speed related not rpm related then you know its not drive shaft forward.

Keep it simple and look at wheel/tire axle(runout) first then go internal.

[Det_Riot]

If you feel the whole car shaking, its in the rear so lets start there.

1) rotate tires front to back and see if the vibration is effected at all

can't with staggered wheels

2) if its still there and you have access to a lift, drive the car on a lift and run it at 70, look for any axle movement, one could be slightly bent just enough to clearance and still spin but give you a vibration.

Will tall jacks stands work?

3) also, if your saying its speed related not rpm related then you know its not drive shaft forward.

Keep it simple and look at wheel/tire axle(runout) first then go internal.

Runout meaning set up the dial on a flange and check to see if there's high/low spots

Edited September 23, 2013 by Det_Riot

[Duff Daddy]

Runout meaning set up the dial on a flange and check to see if there's high/low spots

Yea but you wouldnt even need that if you have someoen drive it on the lift watch the lip of the wheel and look for wobble. up/down movement. The lip of the wheel will move if the axle is bent. or you can take the wheel off, set a dial indicator up on the axle tube and spin the axle shaft. Personally, i like the wheel on option.

[Det_Riot]

Runout meaning set up the dial on a flange and check to see if there's high/low spots

Yea but you wouldnt even need that if you have someoen drive it on the lift watch the lip of the wheel and look for wobble. up/down movement. The lip of the wheel will move if the axle is bent. or you can take the wheel off, set a dial indicator up on the axle tube and spin the axle shaft. Personally, i like the wheel on option.

Got it. Yah that would make life much easier. After watching a video on checking backlash, I remember rolling the diff whenit was in Donovan's car still and thinking how sloppy it was. Will be checking backlash next weekend most likely unless I'm feeling motivated this week.

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[Det_Riot]

I know its not cover off but this is the slop with the car in neutral and tires on the ground

[1997cobra]

dat leaky pinion seal

[OnyxCobra]

so is that not supposed to move at all, or what is normal?

[Det_Riot]

I think that is only supposed to move .008-.012

[OnyxCobra]

hmm, that's like, nothing. God damn it cars piss me off.

[Blackmage]

I wanna say mine moves a little less than that and i have a nice growl out of my rear end, but no vibrations like what you say! No time to pull that diff cover yet?

[Det_Riot]

Not yet. I don't have the tools to do it at my house. I think I found another source of problem. My car with the 3550 now has a crank center line angle of -8*. My pinion flange is rocking an angle of -3* and I think my drive shaft angle is like -2.5*(didn't think I needed that so I didn't really check it) well if your drive line angle is the relationship between crank centerline to pinion angle does that mean I'm currently at -11???

[MENTION=113]F8L GT[/MENTION] [MENTION=6]iRoush[/MENTION] [MENTION=460]Froush[/MENTION] [MENTION=64]The Mk2[/MENTION]

[64bit_Tuning]

http://baselinesuspensions.com/info/pinionangle.htm

[Rolocut]

Not yet. I don't have the tools to do it at my house. I think I found another source of problem. My car with the 3550 now has a crank center line angle of -8*. My pinion flange is rocking an angle of -3* and I think my drive shaft angle is like -2.5*(didn't think I needed that so I didn't really check it) well if your drive line angle is the relationship between crank centerline to pinion angle does that mean I'm currently at -11???

[MENTION=113]F8L GT[/MENTION] [MENTION=6]iRoush[/MENTION] [MENTION=460]Froush[/MENTION] [MENTION=64]The Mk2[/MENTION]

Pinion angle simply refers to the angle of the differential's pinion in relation to the driveshaft.

Use the angle finder on your iphone with the new ios7.

In general, the largest angle for racing applications should be 2 degrees and the centerlines should be parallel within 1/2 degree. If the centerlines are off too far, the u-joints travel at different speeds causing vibration (this is the same problem induced by poorly phased end yokes). This vibration is hard to distinguish from an unbalanced driveshaft.

Using a gravity angle gauge (Available at hardware stores) to measure the angle between the driveshaft and the ground & the pinion flange and the ground.

Hold the gauge on the bottom of the driveshaft. Align the gauge front-to-back under the car in line with the driveshaft and read the number from the gauge (Note if angle is up{+} or down{-}). Write down this number.

Next, hold the side of the gauge against the front of the pinion flange (beside the driveshaft). Write down this number (Note if angle is up{+} or down{-}).

Subtract the first number from the second number. This is your pinion angle. And questions text me. I've done this on all my friends cars. My car and my brothers 2011 gt with cobra jet suspension

On going project, 94 cobra, r block, tfsr225, hp efi, vortech ys

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[Det_Riot]

Alrightie, so I remeasured things today. Numbers make a little more sense as I had the angle gauge in % not degrees.

Pinion flange is -3*

Driveshaft is -1*

Crank Centerline is -3.5*

So according to the baseline site, I should set it mine equal to 2ish since i have a mix of polyurethane and solid bushings. To achieve this, I'd rotate my pinion flange up to 3.5 so that it's parallel with the crank centerline, then knock it down to +1.5 on the pinion. So basically just rotate the pinion angle up 4.5 degrees.

[Rolocut]

Alrightie, so I remeasured things today. Numbers make a little more sense as I had the angle gauge in % not degrees.

Pinion flange is -3*

Driveshaft is -1*

Crank Centerline is -3.5*

So according to the baseline site, I should set it mine equal to 2ish since i have a mix of polyurethane and solid bushings. To achieve this, I'd rotate my pinion flange up to 3.5 so that it's parallel with the crank centerline, then knock it down to +1.5 on the pinion. So basically just rotate the pinion angle up 4.5 degrees.

Did you do the math I just sent you. Your right at 2 degrees. -1 - (-3)=2

On going project, 94 cobra, r block, tfsr225, hp efi, vortech ys

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[Det_Riot]

Did you do the math I just sent you. Your right at 2 degrees. -1 - (-3)=2

On going project, 94 cobra, r block, tfsr225, hp efi, vortech ys

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Apparently not. So crank centerline means nothing? Right now my drive line sits like this \ _ / exaggeratedbut you get the idea. I was under the impression that having your driveshaft in that condition is horrible for your u joints

[Rolocut]

Apparently not. So crank centerline means nothing? Right now my drive line sits like this \ _ / exaggeratedbut you get the idea. I was under the impression that having your driveshaft in that condition is horrible for your u joints

Lol so your driveshaft goes up to the rear and the rear is pointing down?

On going project, 94 cobra, r block, tfsr225, hp efi, vortech ys

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[Rolocut]

You should have your drive at -2 to -3

On going project, 94 cobra, r block, tfsr225, hp efi, vortech ys

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[PRPVinyl]

I still think you need to check the backlash. That axle did not have a vibration issue in the original car with the original gears. Gear ratio was changed and high speed vibration started. Axle was installed in different car and axle vibration moved to new car(and continued at the same point.

Unless the shop did something tho the mounting brackets to cause the pinion angle to significantly change, the only thing to change in the axle was the gears.

Pull the cover and check the backlash

matt