Car is a back-half mustang 25.5 spec. With 4 link rear suspension. I have always set pinion angle referencing driveshaft and rear end pinion flange. Example d/s 1 degree positive (climbing to rear flange) and pinion - 2.5 degrees so under power = -1.5 degrees. Never referenced transmission rear angle, but I believe it goes down a couple degrees negative. I will take driveshaft off and measure rear transmission angle tonight. Have I been doing this wrong? Reason I ask is I have a vibration when car leaves about 30 ft out and 2nd kit comes on hard, also some vibration at top end. Everything is balanced, feels from center rear area.

Yes... you've been doing it wrong.

See this thread from just the past few days...

http://www.yellowbullet.com/forum/showthread.php?t=2279002




Jeff

 

So if my transmission is position down let's say -3 degrees my rear end pinion flange should point up positive 2 degrees so under power would be 3 degrees positve?

 

You want them to line up under power.

You need to determine how much deflection will happen under power. 4 link applications with solid ends typically deflect somewhere in the 1° range.

In your example above you would have 1° negative pinion angle.

-3 at the transmission and +2 at the pinion would be -1° pinion angle. Draw it out on paper if that works better for you. Remember... the pinion will attempt to move UP under acceleration.




Jeff

 

if your tail shaft of your trans is 3 degrees up and your pinion is 5 degrees down then your pinion angle is -2

 

So if trans is pointing down 3 degrees(negative) rear end should point up 2 degrees(positive) so that under power they would like up with the 1 degree of deflection?

 

This ^^^^^is correct...and dont let anyone tell you its wrong. Trans down 3....pinion up 3 is zero pinion angle. Then (as you said) the pinion up only 2 will give you 1 degree down pinion angle.

 

Ok I took driveshaft out and .measured transmission angle at seal next to shaft transmission is pointing down -4 degrees. So it would be correct to point pinion flange to positive 3 degrees to allow for 1 degree positive movement up to make 4 degrees positive?

 

YES

Here is a visual for you. Open your hands and with the palms down and finger tips pointing toward each other. With your left hand tip your fingers down like the trans is... and with your right hand tip your fingers up like your pinion angle is. It will quickly tell you what you need to line up your driveline.


It's not as hard as so many try and make it. lol




Jeff

 

As I have it now transmission is -3 degrees and pinion is -2.5 , so I have like -4.5 under power? I am going to switch it to referencing transmission and rear pinion , not driveshaft to see if it solves the problem

 

Sorry meant trans is -4 degrees and pinion is -2.5, so under power it is -5.5 degrees

 

So if the centerlines of the pinion and crank are parallel , you have zero pinion angle . What happens when the height of the centerlines change ? Expand on this , from 2 inches to 2 feet .

 

Parallel is parallel... no matter the height difference, assuming that the U joint in question can allow the clearance required for the driveshaft required.





Jeff

 

That's a response not an answer and a poor one at that . If you are convinced that your position is correct , you should have no problem backing up your thinking . No cute responses trying to make people think you are superior with LOL's and " it's always been done that way " comebacks . State your position and back it up with facts , not what you heard from your wife's mother's sister's aunt . I , for one , have some questions about the different settings and how they change going down the track . It might be you are correct but as I said show me the facts .

 

That's a response not an answer and a poor one at that . If you are convinced that your position is correct , you should have no problem backing up your thinking . No cute responses trying to make people think you are superior with LOL's and " it's always been done that way " comebacks . State your position and back it up with facts , not what you heard from your wife's mother's sister's aunt . I , for one , have some questions about the different settings and how they change going down the track . It might be you are correct but as I said show me the facts .

Your quote above wasn't taken from anything I posted in this thread.

If you believe that my answer is wrong... post your answer. I have no duty to back up my thinking to you... or to show you the facts.

I only post answers on things that I know are correct. And my answer to this question was based on my racing experiences since 1977, and from talking with other racers over the years. This is my first 4 link application. Before that it was all leaf spring setups.

My data logger allows me to see what a change in pinion angle does to my truck going down the track. If it has too much, or too little pinion angle my driveshaft sensor reading shows it.

If you have questions about "some questions about the different settings and how they change going down the track"... maybe you should start your own thread?





Jeff

 

So what's the correct way?

 

Jeff, curious what do you see on your driveshaft sensor with different pinion angles? I am asking because I see some weird stuff sometimes as far as spikes. Is that what you are seeing from vibrations being caused by incorrect drive angles?

 

Mine will show small spikes going up and down slightly, then back to "normal"... just for fractions of a second. I'm assuming it's showing what what this video shows happens when your drive-line isn't inline.

Mine seems to like slightly different pinion angles depending on where my IC is set at. Probably due to the fact that some IC settings will load the drive-line harder than other settings? I'm talking small changes in the pinion angle... I usually set mine anywhere from -0.5 to -1.5




Jeff

 

I agree with you on that because I see those spikes also and mine is out of whack by this setting as shown in video. Well if all I change is pinion angle set up theory and spikes and vibration go away bingo. Who knows probably losing some power to the 60ft.

 

Give it a try and post up what you find. Even if you don't pickup et in the 60'... you might pick up some consistency? You'll for sure get a smoother ride down the track.




Jeff

 

Definitely, problem is if my 4 link bars will let me move that much. I am going to shorten bottom ones and lengthen top ones but don't want to have rod ends out too far. Maybe will try loosen motor plate , mid plate and try shinning trans up slightly if possible. Or will have to remove 4 link lower bars, remove rod ends and cut tubes shorter? Whatever it takes to get closer than I am now

 

I'm sure someone will correct me if im wrong.
On a 4 link car to change pinion angle you use the top left bar. Unhook the top right bar set pinion angle with top left and then adjust top right to put your preload back in.

 

Yep... you are correct. But, you can also set pinion angle with the right upper bar and preload with the left upper bar. Everyone I've heard of sets pinion angle with the left upper like you said. Just wanted to make sure I'm giving out accurate info.




Jeff

 

Just wanted to follow up results. Changed pinion settings and the vibration I would feel went away. So this way is the best.

 

Thank you Jeff, and Mike.

 

Thanks for the update .

 

Thanks for the update... and you're welcome. :smt023





Jeff