I figure I'd start a new thread rather than rehashing the old one....

I recently installed helper leafs on my 69 RR and after getting her up on my level lift, I took these readings with my angle meter.


(All readings taken from the driver's side)

Output Shaft -1* (trans point down towards rear of car)
Drive Shaft -1* (drive shaft pointed down towards rear of car)
Pinion +2* (pinion pointed down towards front of car)

Now correct me if I'm wrong, but if I were to zero out trans, I'd subtract that number from the pinion reading, giving me 1* down angle, correct?

From what I've read, the suggested setting for a car with leaf springs is 5* for a street car and 7* or more on a track car.

So I take it that I need 4* shims to give me that 5* setting?

Thing is, I can't wrap my head around how the drive shaft reading comes into play (if it does at all)

 

FORGET the drive shaft. The only things that really matter is this:

"In theory" under hard acceleration, you want the TRANSMISSION shaft and the PINION to be PARALLEL

However, you do not want, ideally, for all three to be "in a straight line." In other words what you really want is for the suspension to be at such a level that one shaft is above or below the other, but PARALLEL (Spicers says each joint should have at least 1 degree at each joint, not in a straight line

Now, forgetting the negatives and positives which you POSTED and assuming what you DESCRIBED is correct, you have the trans 1 degree down at the rear, and the trans 2 degrees down at the front. What this means is, you have a THREE degree difference, because if you brought the pinion up to one degree up in front to match (parallel) the trans, it would be three degrees down to what you started with.

THIS IS within the accepted range "sitting." This however must be measured as the car "sits" properly, on it's tires, fuel, and if possible, "the driver."

This is ALSO affected by the SPRINGS. If you have an Impervious with soft, mushy springs, and you've put a 600hp monster in there, the soft springs will "wrap" more. If you are running SS springs, they are designed to be stiffer under power and will not wrap as much.

ALL of this is obviously a compromise.

 

The readings were taken with a full tank and a trunk full of junk on a flat lift (no driver though)

The springs I'm using are OEM replacement leafs + 1 helper leaf per side to bring it to the proper height with load.

The SS springs I had before were terrible, sitting way too high and they rode like a box truck

What shims would you suggest being that it's typically a street car on G15's, but I still like to play on the weekends with big MTs?

 

Drawing a picture with a center line always helps me, but here I go the way it works for me. Under load Trans and Pinion should be Parallel.

Trans points down 1 degree.

Pinion down 2, bring it up 3 degrees = Parallel with Trans. So I have 3 degrees down now.

If I want 5 down add 2 degrees pinion down.

If I want 7 down add 4 degrees pinion down.

 

Sounds good to me

Should I try 3* shims since it's both street/strip?

 

That is the $64,000 question. If you have the leaves behind the axle all clamped I'd go 5 (add 2 down). if your unclamped and drag racing then 7 to really plant the tires.

Have long shocks or extenders so they don't bind when the rear of the body lifts during hard launch.

 

They're clamped.

Here's a video on MT's (good wrap)


And another on G15's (spin city)

 

From your readings, I'm not sure I'd add ANY

 

If I'm at 3* Down, wouldn't I want to add at least 2* being that it's a street/strip car with leaf springs?

I've read probably a hundred pages on this and it seems everyone has their own opinion on what's correct

This old tech archive has a chart, but some of wording used for describing pinion down angle confuses the hell out of me

http://www.moparts.org/Tech/Archive/axle/8.html

 

You should not be concerned with U-Joint working angle, it is important for smooth operation say in your luxury car or long haul truck where you don't have alot of axle twist and U-Joint service life is important. Hi-Performance cars are always a compromise in these regards.

The three top photos are like any you will search, showing trans centerline and pinion centerline being parallel is most desired. If that is achieved then working angle can be calculated not to exceed the manufacturers recommended maximum. If you do these two things you will have the smoothest, longest lived drive system you can have for your car.

Now take that same car and turn it into a brute like yours mash the pedal and when that axle twists up you run the risk of binding the joint and tearing it right out.

You have yours very close to parallel and almost ideal for long haul cruiser but like shown in the 2nd video (I think) at 4:20 you need to point the nose down some.

 

OK, I'm a bit confused on the whole parallel thing cause this is what I'm working with.....



The trans and drive shaft share the same center line with both measuring -1*

Now, taking the drive shaft out of the equation and just adjusting the pinion angle so that it matches the trans on a parallel plane under load, it would look like this (sorry about the crude diagrams....I suck at photo shop)



This is pretty much the opposite of what I see printed on most pinion angle diagrams because they typically show the axle center line to be below the trans

 

There ya go, you got it. If that 2nd drawing had the axle lower on the page it would look like those other drawings but that's not relevant, parallel is.

What you have shown is your axle rotating up 3 degrees. Yours rotates more under power, so...

Add 2 degree shim = 5

Add 4 degree shim = 7

Your just trying to shim it down back to parallel when under power.

 

OK, so when the pinion is angled up like it is at 4:20 in the first video, it's of no real concern as long as the pinion is parallel with the trans when it does?

I called up my local drive line shop earlier today and they pretty much said the same thing, but I've had a few folks on other forums say it just completely wrong cause it doesn't look like the picture in the angle guides

 

Yes, if it is parallel. It looks to me that it goes a bit past but the camera angle could be deceiving. A run with the camera pointed 90 degrees to the drive shaft would show both angles.

If it were mine I'd add +2 more down. I think some of the confusion comes from some who say 5-7 down means pinion down as it relates to the ground. I've read this on some forums and they swear by it, which would be OK if it all is close to level like yours, but if you want it right it should be done like your doing. Thorough and know for yourself not just based on someones say so.

 

I don't think the pinion angle is your problem.

Go by the transmission shaft/ crank centerline, not the ground.

 

I measured from the output shaft of the trans and the pinion yoke using a socket on the cups of U-Joints (horizontal reading)

Then I measured again on the trans seal and flat against the pinion yoke with the drive shaft removed (vertically)

The readings matched both ways.

Now, I just found this video showing a side view of a pinion angle at the strip.

It looks to be level with or slightly below the drive shaft at rest, then goes nose up under load.

From what I gather, as long as the axle center line is parallel with the center line of the transmission under load, then what he has going on there is good, correct?


It just looks bass ackwards when compared to the diagrams on all the pinion angle guides

 

Maybe these might help...
http://www.carcraft.com/howto/91758/

http://www.iedls.com/asp/admin/getFi...&TID=28&FN=PDF

 

Thanks for the links

In the first link, the parallel diagrams are like the majority of the ones I've seen in guides with the pinion center line below the center line of the trans

In the second link, it shows the pinion center line above the center line of the trans (which is what my car has)

Now, I have an interesting dilemma because I've posted up on numerous forums and not only do I have conflicting opinions from regular members, but I also have two well known drive line shops (actually 3) that deal with this stuff on a daily basis with totally different suggestions

On one hand, I have DoctorDiff who suggests that a true 4* pinion angle is the absolute max on a street car and that I should leave mine as is at 3*, which goes against many of the MOPAR pinion angle guides I've seen.....

On the other hand, I have SuperShafts (as well as my local shop, Advance Driveline) suggesting that I install 3* shims in order to get a 6* pinion angle, which is pretty much on par with most of the MOPAR guides.

 

Doesn't matter, "above" or "below" as long as the two shafts are parallel

Here's why

Regardless of the terminology you use, when you have two parallel shafts, with a one-piece shaft between, what happens is that one joint actually speeds up and slows down every 1/2 turn. the driveshaft is ACTUALLY changing speed!!!! The matching angle at the opposite end cancels this out. When one angle is different, this relationship no longer holds true.

The reason for setting the pinion "down" somewhat in relation to the trans shaft is simply to allow for spring flex under power. This is going to change depending on power, the spring pack stiffness in front of the axle (wind up) and the "up down" stiffness of the spring as well. In other words, anything in the rear suspension which allows the axle to "wind up" is going to change the amount of "pinion down" you want to start with.

What Ma used from the factory was obviously "designed in" for thousands of nearly identical assembly line cars.

So you have to be careful about recommendations. Are they in the context of SS springs? Stock springs?

And be careful when you "quote" that someone is saying "6 degrees down" Is this 6 degrees down from the transmission, or with the car sitting level? Huge difference, there.

 

I'm assuming (I know I shouldn't) that they mean 6* down from the center line of the trans

I gave all 3 shops the same readings I got while on a flat lift and simply asked what shims they recommended for an OEM leaf sprung street/strip car.

2 shops recommended I start with 3* shims and 1 suggested I leave it be

DoctorDiff got back to me last night and here's what he had to say:



What he's saying makes sense, but again, goes against what many others are suggesting.

Now, does braking actually stress out the u-joints as much as accelerating?

I would think the load would be minimal when compared unless you're decelerating hard in gear

Also, if I were to go with say a 1* shim to give me a 4* down angle from the center line of the trans, that means the pinion would have to rotate 4* up under acceleration to reach the parallel line of the trans and still have 4* more travel before it reaches the equal and opposite downward angle at coast.

I guess if I throw my adjustable pinion snubber back in, it should help keep the rear from rotating above the center line of the trans?

 

OK, I decided to go with what my local drive line shop and Super Shafts suggested and went with 3* shims

After a little cruise up to about 60mph, everything seemed fine, so I went down the back road for some WOT runs and it felt great under acceleration and deceleration with no vibes at all

However, when I got her on the highway and let her coast at part throttle, she has an on and off vibe around 75-85mph.

It's still far less than what she had without the shims, so I guess I'm on the right track

Brought her back, put her on my flat lift and checked the angles again.

-1* at the output shaft
-1* on the drive shaft
+5* at the pinion


Thoughts on the high speed vibe?

I've already had the drive shaft balanced twice, but I can't say I've been nice to over the last few months (as you can tell from my videos lol)


U-Joints are new solid Spicer units (no grease fittings)

 

Just a thought could it be not in the drive line and be tire balance??? Im just wondering some times we get so focused on one problem we over look the simple stuff...Bill

 

Tires are balanced and in the past I've tried 3 different sets with the same results.

Gunna slap the Mickey's on later today, but I doubt there will be a change.

 

What do the people doing the shaft balancing have to say? I still say pinion angle is not the problem, and of course by "remote control" this is hard to say.

The thing is "back in the day" I used to see all sorts of sillyness with "hijackers" with extended shackles, and add on traction bars. The cars tolerated all that fairly well.

 

Wow I havent heard that term in along long time...Highjackers by Gabreal...They had the car as high as it would go and everyone painted the Gas tank, trunk bottom,rear diff. etc...White some even had clearence light under the car to light it up at night...LMAO those were the days...Bill

 

I haven't spoken to them since last week when they suggested installing the 3* shims.

The shaft has been balanced twice before and it usually stays quite smooth until I give her the beans, then the vibes just progressively get worse


Well, after the shim install, things have much improved, so I think I'm on the right track.

Without the shims, the vibes were pretty bad during normal driving speeds, but now the vibes are less and have moved beyond normal driving speeds, so it's much more tolerable

That being said, I'd like to get rid of the vibes altogether and SuperShafts seems to think the DS just needs better balancing and probably just got tweaked again.

The last time I had it balanced, the shop suggested having a beefier drive shaft made for the power that I'm running, but that doesn't come cheap

 

In the video you show after the burnout...the pinion does really torque up and changes the angle immensley... and the car grabs good traction with the tires you have...So you might be on to something I would be curious to see if the driveshaft has gotten tweeked by the power/traction causing the vibration...Bill

 

<---- used to have hi jackers and the white painted underside, my grandfather always wanted to know what kind of gas mileage I got because as he said the car is always going down hill! lol