Brake rotor centering
 

Should brake rotors be centered by the studs or the hub register on the axle? Just slowly working on my vibration issue before I decide to set the car on fire.

Thank you

The hub should index the rotor. Same with the wheel.

Yup both

Explain your vibration and mods

Thanks guys. That's what I was expecting you to say.

I found that my rotor bores are at 2.78 inches and the axle hub is 2.68 inches. This cased the rotors to drop down onto the hub when putting everything back together. I thought I was locking the rotors in eccentrically and this might be the cause of my vibration. So I got some shim stock, put it between the rotors and hub register to tighten up the slop, and that did squat to help the issue. I was so fed up I just parked the car. For all I know, the shim stock didn't stay put some how but I doubt it since it felt the exact same. Maybe I'll look at it tomorrow.

Randy, I talk about the issue in the last few pages of my build thread. There are also other threads I've started concerning the issue. If you do a search for threads started by me, I'm sure it'll come up. The simple answer is I start vibrating at 55mph and up. It's at its worst at 55-60. It's speed related not engine or rpm related. It's definitely the rear end area, confirmed via dyno, and the wheels are true, confirmed via Wheel Wizards a rim straightening company here in Atlanta. Literally, nothing I have done has had any affect on it positively or negatively. It's maddening.

Thanks

unfortunately rear end vibrations can be a number of issues. u-joint angles, wheel tire combo, brakes, axle itself.

you said you had the rims checked, was that with tires installed (good balance)?
rotate the wheels front to back if possible?
double check all drive line angles.
if you do believe it is brake related, can you safely put rear on jack stands (weight of vehicle on axle) and accelerate to 55-60mph, see if vibration there. then slowly start removing parts and retesting. remove wheels, install lugnuts, torque to specs and check for vibration. remove rotors (ziptie block of wood in caliper not to blow out pistons), and see if vibration still there.
if still there, vibration maybe within axle, or drive shaft.

also vibration is worse between 55-60mph, does it dissipate or get worse with more mph? if the vibration intensity is matched at 110-120mph you would be looking at u-joint area for binding

I appreciate the response. I've checked all of those components multiple times. That's what is so frustrating, nothing changes with any of my adjustments. It's not on or off throttle dependent either only speed.

I've put the car on jack stands before but the vibrations were minimal compared to on the road. I put the car on a dyno to verify it was the rear area of the car for that reason.

Thank you

Check the following:


PINION ANGLE / Working angle


Driveline slip yoke - or more correctly - the length the slip yoke and it's engagement in the transmission.

This is an area I think could/should be improved. I have a good bit of slip yoke engagement now, but to be more correct, I need maybe 3/4" more engagement. I wasn't wanting to just throw parts at the car, but I'm starting to get there because I'm seriously fed up and starting to look at E34 BMWs, lol.

Thanks Greg.

Did you get your driveshaft shortened?

Call up the driveshaft shop. They will build you a 3 1/2 aluminum driveshaft for around $450. This fixed my vibration issues the same ones you are describing. They are 1 of 3 shops in the US that balance the driveshaft high-speed. I have 1/4" slip yoke sticking out now past the t56 magnum dust boot.

I was getting vibration around 50 and it got alot worse 70 plus. Old steel driveshaft was double checked for balance and I couldn't figure it out. I did what unmentioned above and it fixed it. Also ask for the antivibration dampened option.

Really does sound like the drive line vibration issue I chased...which I finally fixed with a 3.5" steel driveshaft. My car originally came with a 2.5" shaft and the drive shaft shop said they wouldn't build a 54" driveshaft in anything less than 3.5"...said they'll "noodle" at speed if not big enough diameter.

Hope you find it...I hate vibrations...

You're running BMW wheels, yes? The wheels should be mounted "hubcentric" (indexed on the hub), and given the difference in bolt pattern between GM and BMW...

Know anyone with a set of GM wheels you can borrow?

I have hub and wheel centric adapters from Motorsport-Tech/BORA to correct the bolt circle and hub diameter differences. I've also removed the adapters and bolted the wheels directly to the car since the bolt pattern difference is very minor. There was no change in the vibration even though I could only center the wheel using the lugs.

Yes, factory driveshaft was shortened back in 09 when I did the LT1/T56 install. I had a good, local company do the work. I didn't have the vibration issue until 2014. Shaft length was perfect until I put the new suspension on the car. That raised the rear a little which caused the length needed to change. Problem is, I did more than just the suspension at one time. I also can't remember at this point if I had this vibration before I changed to the 3.90 gears which would change shaft speed. I also had other vibrations like tires being old and out of balance and a u-joint not perfectly secured that I found during my searching for a vibration solution. It seemed like I'd fix one thing only to realize it was only part of the issue. This current issue just won't go away.

I appreciate the insight. I was considering them or Denny's. I was also only considering steel since I'm no race car. I've had my drive shaft balance checked by multiple shops and it came back perfect each time. U-joints are good too which is why I say the yoke stick out is the only thing not perfect.


I'm going to measure soon but I think I'm close to 54 inches. Maybe it's 45. I can't remember. It's the factory shaft with 3R u joints whatever it is. Plenty strong enough for the power and I don't run road courses so every thing I've read is it's fine to use. Maybe they disagree and can recommend a solution. I hate this vibration crap too. Love the power curve and drive characteristics but dear lord is this vibration ruinous to the enjoyment of the car.

Thank you all. I appreciate the responses and thoughts.

Get the 3 1/2" aluminum driveshaft, vibration reducer mod, and it will handle anything that you need. With the aluminum the critical speed was more than enough for what i was doing. Again 1 of 3 companys that do high speed balancing. The guy below is who i delt with. My buddy also had the same issue in his 69. Same issues as you and mine. Called the driveshaft shop and had one within 2 weeks as well and fixed his issue. My total length was 48 3/4". If you have a email i can send you a email with all that i delt with, measured etc

Lucas Bartholomew

The Driveshaft Shop
4530 Southmark Dr.
Salisbury, NC 28147
800-564-2244

Thanks Randy. I'll give Lucas a call.

I measured 48 9/16" so 48.5" I'm sure is what they'll cut it to. I confirmed again that I'm about 3/4" short now.

Thanks everyone

Trey, I sure hope that a new shaft fixes the car. I have a relative in the driveshaft business, and maybe I can save you a buck or two if your interested? Send me a pm...

Me too, Scott. I appreciate the offer. I've already started working with Drive Shaft Shop. We'll see what happens.

Thanks

I believe I've goofed on my working angles and I'm way over the 3* limit. I had always taken my measurements with the car sitting at ride height. Well, tonight I took them with only the rear off the ground and it became obvious to me that I think I screwed that math up. I'll see what Lucas at Drive Shaft Shop says in the morning.

Thanks

Easy enough to do ----

Motor should be about 2 to 3* DOWN at the tranny pan --- REAR END should be about 2* UP --- and if the slip yoke is correct (they make all kinds of lengths) -- you should be close.

The other thing I've seen --- a too small diameter drive shaft for the overdrive tranny / rear end gear combo. The shaft has a working RPM and when exceeded can go into harmonic death wobble. LOL

Glad you're on it.

Those values are actually pretty close to what I have for pinion angles now. The issue is my rear end if higher than the rear of the transmission so the drive shaft is down in front. The solution is to raise the trans more. I'm not sure I have the room due to my headers though.

I didn't want to get into it just yet as I'm waiting to see what the Drive Shaft Shop has to say, but I'm getting really concerned with some things about my build compared to what others have had to do with their similar builds. This whole car is a learning experience for me. I'm worried I may have missed or done some critical stuff wrong after all. We'll see what happens. I hope I'm just over reacting.

Thanks

Ah -- yeah that won't work....


Tunnel issues with the new bigger transmissions --- and combine that with our low stances --- yeah --- that's usually a tranny hump mod and driveline tunnel raise....

Those are easy mods even in a done car..... it's a carpet issue --- and back seat tunnel modification...

I've already cut my tunnel once for the trans and don't mind doing it again. I'd like to do an integrated chassis brace and trans mount like DSE does while I'm there. I also don't mind doing the tunnel for the shaft as I have no interior now. It's the fact that many other people are running SBC/T56 combos in 2nd gens and aren't having these issues at all that concern me. Maybe I am just that low compared to them, but I'm concerned I'm doing a lot more than other's have had to do. That makes me questions what I've done wrong.

Thanks Greg. I appreciate the reply.

Ah -- gotcha Trey.

Your motor only need be down 2* - and assume you have a degree / angle indicator.... The car needs to be on it's own 4 -- so jackstands under the axle so the weight in on it.... and place the angle indicator on the face of the pinion... if it's up 1 to 2*....

Then it's a matter of suspension travel.... and that's probably UP 2" and down 2" or in there.... and of course there should be a "bump stop" of some kind to prevent the stuff from hitting...

Trey, my driveshaft is same way, higher at the rear than the front. A lot of guys with lowered vehicles are in the same boat...with no vibrations.
Driveshaft angle is irrelevant. You should see the angle of my brothers rear shaft on his 87’ truck. 17” of lift. It’s steep, and there’s no vibrations with 44” Boggers.
Engine/trans combo should be 2-3 degrees down. Even 4 is ok, I’ve done it. The trick is your rear must be up the same, whatever it is. These angles are also irrelevant of frame/chassis angle. Measure against shop floor, not chassis.
Are you using shims under the rear end to adjust angle? I’ve seen these shims not be exactly the same, and cause binding on the rear end housing when the u-bolts were torqued down tight. Angled lowering blocks can be the same way.
I know you’ve been all over this for too long now. Let’s hope the driveshaft change fixes it. DONT TORCH THE CAR!!!!

The problem with the rear end being higher than the trans output shaft is that the working angles increase when the suspension compresses. So if you start out with a working angle of 3.5, under full compression it may go to 5.5.

This is exactly why you see people on here cutting their tunnel to get the tailshaft of the trans up higher. That will allow for more conventional and smaller working angles. The more severe the working angle, the more they tend to vibrate as speed increases.

This is what I'm thinking will end up happening. I'm just not sure I can raise the engine due to how close I built the headers to the floor.

I know a CV shaft has greater working angle capacity but I'm not sure it would be right for my application. I'll see what the information they come back with. I didn't hear from Lucas today. Maybe tomorrow.

Thanks everyone.

Have you determined your actual working angles? I can't imagine a vibration around 60 mph unless your angles are very severe. Not in the 3-5 range. Normally is would get worse with speed with this scenario. Start to feel it around highway speed and increases as you speed up.

About 5.5 to 6 degrees, Todd. Unless, of course, I'm doing it wrong again.

With the whole car sitting on cribbing, I get 2.5 degrees nose up on the pinion, 3 degrees front down on the driveshaft, and 3 to 3.5 degrees down on the tail shaft.

Vibration doesn't get worse as I speed up, but it's still very obvious. The frequency may increase a little with speed though. Intensity does not.

Thank you

So your rear working angle is 5.5*

Your front working angle is 6 to 6.5*

It looks like this exaggerated drawing of passenger side view

pinion / \ / engine

You need to roll the pinion down.....a lot.

You will find if you set it up like

pinion \ _ / engine

you will be able to get working angles under 3* and then get them to match.

AH --- actual real numbers to work with!! LOL


Donny is correct..... your working angles are a total mess.


I'm glad I got you to look at them. LOL

Donny's numbers are correct. Those are pretty severe working angles for a performance car.

I don't agree that lowering the pinion will get you proper working angles though. From what you are saying, your driveline/pinion angle are within .5 degrees of each other on the same plane. As you lower the pinion, you will move away from parallel angles. It will decrease your working angles, but the variance in working angles from driveline to pinion will increase. Right now you have 5.5 and 6-6.5. Lowering your pinion will spread those numbers which can also cause vibrations. I'm guessing that if you drop your pinion 2 degrees to .5 up, your pinion working angle will go to 2.5 and your driveline to 5. I think your tailshaft still needs to go up to get conventional working angles.

While the angles aren't great, they are parallel and appear to be within .5-1. I think you may have something else going on since the vibration comes in at such low speed and doesn't get worse. You may have two things going on here. A driveshaft issue and then your working angles may cause you vibrations with speed. I'm no expert on this stuff, but I fought the same situation on my car. If I kept that car, I would've cut the tunnel and raised the tailshaft.

The driveshaft is running up from the transmission to the rear end, right?

If you roll the pinion down, the driveshaft also goes down in the rear, resulting in a lower working angle for both the front and rear u joints.

It's pretty hard to diagnose any vibration through a forum but the driveshaft angles are not good the way they are so it seems like a good place to start.

Correct, but as Todd mentioned, the angles are nearly parallel just in different planes now. I've always thought that was the correct way to have the pinion angle and transmission?

Thanks everyone

Forever the equal but opposite theory was the common theory that was regurgitated by magazines, driveshaft manufacturers, etc. and for most street rod swaps it worked. 3 degrees was the magic number, if you set everything there it would work and for the most part it did. But these aren't 40 Fords and the math doesn't work out.

The reality is that the u joint does not care about the angles on your pinion or your tail shaft and it especially does not care if they are parallel to each other.

All the U joint cares about is the angle that you are asking to work at.....and it wants to work at the same angle as the other U Joint. The lower the working angle, the happier the ujoint will be.



Incase embed doesn't work. https://www.youtube.com/watch?v=gmV4qwLfOMY

Thanks Donny. I'll watch the video when I get home. I appreciate the information.

I ended up doing what Donny is saying on my car. Instead of cutting the tunnel I got my working angles as small as possible by lowering the pinion angle. I do think it caused an oscillating vibration over 85 on my car. The harmonics are no longer in sequence. It's certainly worth a shot.

If you have adjustable shocks, you could raise the car up as high as possible. That will effectively reduce your working angles and let you know if you are on the right path.

I agree though, 5-6 degrees of working angles is a problem regardless.

Watching the video Donny posted, they reiterate that the working angles need to be the same between the two u-joints while showing the working angles at each end being fairly extreme. Which is more important? I can rotate the nose of the pinion up more easily than bringing the tail shaft of the transmission up. That would get my angles the same between the two joints but the angles would be more extreme. I'd be simply doing this as a test to see if it effects the vibration at all.

I swear I've done this before and it had no effect on the vibration. Then again, I swore my angles were good, too.

Also, if I were to nose the pinion down 3.5 degrees to match the tail shaft, causing the drive line to look like this \ _ /, wouldn't that cause the drive shaft to become unstable or bind?

Thanks everyone.

Your current working angles per your measurements are within .5-1 of each other. 0-.5 is ideal so you are close.

What you are describing with the pinion pointed down 3.5 is exactly what I just talked about. You are getting your working angles on both ends of the shafts as small as possible. It takes some trial and error. The problem with this strategy is that you may get an oscillating vibration. When the working angles are equal and opposite, you get a consistent hum or vibration, when they are not you will get a stronger vibration followed by none.

Equal and opposite and small working angles gives you the smoothest operation.

OK, I think I'm getting confused. I'm going to do some more reading and get back with you guys. I think I'm getting my terms mixed up or something.

Based on the measurements I have given, what is my pinion angle?

Thank you

Do this All angles are measured on the drivers side of the car.

1. engine/trans is on ____ angle and it heads down in the back. Meaning the crankshaft is higher than the tail shaft

2. The Driveshaft (if not there use a string or a piece of wood to go from the center of the output shaft to the center of the pinion) is at a ___ angle and it heads down in the back. The connection at the transmission & driveshaft is higher or lower than the connection at the rear diff to driveshaft. Does water from from the front driveshaft down to the rear or would it run from the rear to the front towards the engine

3. the pinion is at a ______ angle heads up or down in the back. The driveshaft and pinion create a V or a /\ ?. Would water placed on top of the diff run behind it or onto the driveshaft.

Base on this we will figure out the rest.


To give you an idea my angles were close but still caused a vibration and the aluminum bigger driveshaft fixed this. Mainly because the driveshaft was very level and caused a jump rope effect not to mention the driveshaft shop high speed balanced my new one.