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Diff pinon angles.


heywier427

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Has anyone played with changing the diff pinion angle ever?

 

They are kinda locked at -1 at the stock location.  I need to get it to +1 for my engine setup.

 

I always had a driveshaft vibration due to my rotary engine sitting too high.  Rotorys have to sit very low to get a good angle (crank shaft is directly in the middle of the engine, not down low like a piston engine), but the drag link is the limiting factor (Maddat sells a modified one for this reason).  That and the tunnel, but thats easy to remedy.

 

I have re configured my set up this weekend and brought the engine forward 1.5" and down 1".  This gives me a -1 downward tilt.  Way better than the 4+ I was at!

 

So, unbolting all the diff mounting points, allows the diff to drop without any clearance issues other than more bind on the half shafts.

 

Im thinking just weld a beefy plate to my mustache bar to be able to give it the drop.  About 1.5" is where it needs to go.

 

Any one ever have to do this?  Any ideas on why this shouldnt be done?

 

Thanks.

 


Edit:  Will hopefully be doing my sr20 swap this coming winter, but I want to drive my car now!!! ?  Thanks.

Edited by heywier427
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Just make sure the driveshaft U-joint angle at the trans matches the U-joint angle at the diff.   I am betting that is where most of your vibration came from.  U-joints aren't CV (constant (same) velocity) joints.  U-joints actually speed up and slow down during a rotation (unless the angle is 0) and the farther away from 0 angle, the more the rotational differences.  The different angles from one U-joint to another will cause problems.

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medium.gif

 

Just make sure the angle of the drive shaft to transmission is the same as the drive shaft to the differential. As they bend more and more the driveshaft has to accelerate and decelerate as it turns through an ellipse not a circle. Drive shafts are built with the opposite U joints opposed so that as one accelerates the other decelerates and they cancel. This only works if the two angles are the same.

 

Driveshaft-5.jpg

 

Measure trans and diff angles with the vehicle on all four wheels. If real OCD put someone in the driver's seat and full tank of gas.

 

Driveshaft-6w.jpg

 

 

I lowered my goon and never took this into account and  noticed a sub bass sound when driving. On dips in the road it would lessen and bounce right back. I checked these two angles with a protractor and a string with a washer on the end as a plumb bob. Put a 1/8" shim under one end of the leaf spring mount to tilt the diff down at the front to correct it. The difference was amazing!

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Thanks guys.  This is what I am correcting.  My engine "was" as +4 and my diff was as -1.  Thats a huge no-no.

 

Now I will be +1 on the engine/transmission side, and -1 on the diff end.  This is within the ideal range (0-0 being perfect).

 

 

 

 

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If the differential moves perfectly up and down the angles change but are the same so no vibration going through a dip in the road. Although mine was minor, I could barely feel vibration, mostly I could hear it as a VLF drone.   

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This is on a 510 with irs.  The diff is fixed, and cannot move.

 

I miscalculated.  I do not need to move the diff.  Hurray for no more fab work!  Boo for poor math skills ?

 

Will be up and running tomorrow.  Maybe...

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On 8/6/2018 at 11:03 AM, heywier427 said:

This is within the ideal range (0-0 being perfect).

 

 

Just to clarify, 0-0 is not perfect.  You want some operating angle in the U-Joints so they stay properly lubricated and do not sit in a fixed position.

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This is correct, but laymens/shadetree/internet peoples, it is 0/0.  

 

0/0 is easiest and most normally measured vertically.  It is the wag left and right of the trans snout that you get your +/- degrees off.  If your engine is fully rubber mount isolated, this becomes less important to be "not" perfectly 0/0.

 

I did end up dropping my diff down 1 full inch.  Will snap some pickaroo's tonight.  

 

Thanks.

 

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The idea is to drive it so fast it gets quiet ?

 

That almost valve floating sound!

 

It started!!  Without much hiccup either.  And thats something for a rotary that hasnt started in over a year!

 

Giggity!

Edited by heywier427
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