Moparts Tech Archive
pinion angle and leaf spring setting question?pinion angle and leaf spring setting question?
ive got SS springs on my cuda w/ the front mount that has an upper and a lower hole for the spring eye. i have been running it in the lower hole, but recently saw here that someone mentioned the car will hook harder with it set in the upper hole. is this true?
if i set it in the upper hole my pinion angle gets all messed up, goes to 0 degrees. already have 2 degree shims on it. i stacked another 2 degree shim on it but the alignment dowel on the springs hardly sticks above the shims. i dont like this, dont feel like the rearend is located properly.
also, w/ two shims stacked (total of 4 degrees), the angle only goes to -1 degrees. why's that? it was 0 degrees w/ only one shim. remember these are 2 degree shims.
should i just go back to my old setting? is it worth moving the spring eye up to the top mount hole at all? CHIP
Moving the front spring-eye verticle raises the I.C. of the suspension and slightly moves the rear tires forward. I don't know of any SS spring car that hasn't benefitted from this change from a standpoint of traction. Recheck your driveshaft/trans engagement as the distance has shortened. I am not sure you are properly measureing your pinion angle.
Ok heres my opinion on pinion angle !!
It gets really bad when you move something!!!
If it ain't broke don't fix it!!
I hope ya own a welder to do it right!!!
I don't care for the shims, just for the causes you named.
But I have used them, so I'm guilty of takin the easy wau out also. Even a set hangin on the shop wall as I type this. But I try to use them only on street cars.
Me, I'd leave it alone if the angle is correct and it's hookin.
Now if you want to try the new angle with the shims on a trial basis, and then remove and weld new perches on if you like the outcome, go for it.
But in most cases the shims are used to correct the angle not experiment with the chassis set up. As what you're wanting to do is opposite of what they are for.
Which ain't a good thing, it might help the hook but it could also hurt the tranny or rear end it's self.
And when you 'rolled' the snout of the rear end up and raisin the front eye of the spring you decreased the pinion angle and then the 2 degrees you added back wasn't enough to overcome the amount you raised the front eye.
if that makes sense to you or I confused you even more???
any of this help???
I have mine at -3deg. Don't be afraid to use a stock spring with Caltracs at all Racebeeper68. They work great for me best 60ft.1.451..I also rewelded the spring perches at the -3 deg. setting to avoid any shim use....Eric
FYI THIS MONTHS CAR CRAFT HAS AN EXCELLENT ARTICLE ON THIS VERY TOPIC LOTS OF BICKEL AND CURRIE STUFF INFO
My 2 cts.... on pinion angle. Aug 24 '02 I had 4 degrees Nose UP pinion angle..... 1.52 60' and car launched mildly, pulled left front ~4" in air.... Changed to 6 1/2 degrees Nose DOWN.... 10/27/02 1.50 60' car launched ALOT more violently and transferred the weight better... Wheels now up more evenly right front ~14" up left up ~10".... Every one I talk to says with S/S Spirngs their car works best with 5-7 degrees down..... I don't disagree.....
69dartgt360- i think yuo are dead on.that article said leaf spring cars 5 to 7 down.i must stupidly say iv'e never checked mine .this winter i will may be some et in that!!!.by the way,bought a set of solid leaf spring eye bushings (solid aluminum)from mancini over the summer,never put them in.your thoughts??
Mine don't run as hard as you guy's cars do. But I still picked-up .1 when we set the PA at 6* down. I do use SS springs. 60's are now low 1.80's Jim
Have you optimized the shock settings for the first position you used? What is the car doing now? If we can get some more info, maybe we could get it dialed in without screwing with the front holes, and having to do welding and grinding to reangle the rearend. There must be an easier way to get your car hooked up. Could we get a full rundown of your combo, latest 60fts, and any observations? Thanks.
what I did for my car was to make a lowering block out of solid aluminum about 1 1/2in taped top half put in a stud driled bottom half to fit pin from spring milled bottom at a 5 degree angle
hardcore..... thanks for the input.
Eric....ive been thinking of going to Cal-Tracs but not yet, no $$$ for it, saving up for Indy heads, etc. still have my stock springs out in the barn if i ever do decide to use em.
Greg....im running the 865/866 SS springs w/ NO snubber, they are the 3300 lb springs. was running MP long drag shocks, pulled a best 60 foot of 1.600 early this spring, ran in the 1.61-1.62 range then slowly fell down to 1.64-1.65. i believe its gettin time to buy new slicks. i put on my old CE adj. rear shocks w/ extensions and my 60 foot the last time out were 1.62-1.61 again. atleast i know these softer shocks work better w/ worn slicks. i launch at 3000 rpm, footbrake. ive tried launching off idle, fast idle, etc. the 3k launch works best.
69dartGT360.......my pinion angle is at 0 degrees now. this is w/ 2 degree shims on it. i put em back in the lower hole, where ive been running them since day one. ive never run the car w/ them in the upper mount hole. it launches fair now, left front will e up about 5", right front comes up just enough to skim across the pavement and let the car make a slight veer to the right off the line. you really got me thinking of resetting the pinion angle now!!!! i want some serious whels up action like yours!!
running a best ET of firstname.lastname@example.org and a best 60 foot of 1.600, how am i doing as far as the 60 foot?? am i wrong about thinking i should be in the high 1.5s?
traction on the nitrous is nonexistent, but not worried about that. all the info ive given yall is for the motor only passes. dont worry bout the nitrous, its about to be sold to fund my indy head, solid cam, dominator, 10 sec on motor upgrade im planning! thanks yall, CHIP
From all I have heard/read, SS Springs should not be used with Cal-Tracs. Ideally, the fiberglass mono-leafs, next best, Stock Leaf Springs.
They do make/sell longer Spring Center Bolts. When I shim'd my SS Springs and 8 3/4-Rear, I was able to place a couple small OD Hardened Flat Washers under the Spring Center Bolt to Bush it up, but this only goes so far.
As far as the adjustment of the angle goes, with shims, as you alter the Spring/Rear Housing/Pinion angle, the D/S angle changes as well and it is not putting a 2-degree shim raises the angle 2-degrees.
Instead, both the pinion and D/S angles change. You usually need to play around with it a bit to get it right.
Example: Mine was off by 2-degrees, Nose-Up on the combined Pinion-D/S angle.
To get to 7-degrees Nose-Down, you might think that tyou would need to use 9-degrees of shim, but you'd be wrong.
It actually took only one 4-degree shim on each side to bring the Pinion-D/S angle down, as the D/S angle moves down with the Pinion.
Also, there is a lot of misunderstanding and inacurate information out there about Pinion Angles.
Ideally, (for Drag Racing) you want to achieve a Zero angle under a Hard launch, when the U-Joints, etc are under the greatest stress.
This 5-7 degrees Nose-Down actually refers to the Pinion-D/S Working Angle. The True angles are a bit more involved and need to be taken/adjusted at the transmission with shims under the Trans Mount and welding the Spring Pads on the housing tubes at the correct angle.
Regarding the correct procedure for checking/setting Pinion Angle, I have read the information in the “Mopar Performance Chassis Manual,” “DoorSlammers, The Chassis Book” by Dave Morgan, The Inland Empire Driveline Brochure and a few more chassis books on the subject.
Here is the passage which explains much of what is involved in checking/setting the pinion angle:
In addition to the vibration that is caused by the operating angles of the universal joints, there are a couple of other reasons to be concerned with these angles. First, the greater the operating angle the more rapidly the joint will wear. Second, the greater the operating angle, the less torque the joint can withstand. Throughout the history of hot rodding, it has happened countless times that a car was fitted with a rear axle of a different origin, with little or no regard for the operating angle of the rear universal joint. If the guy was really lucky, he had no problems. If he was a little bit lucky, he experienced a vibration only under hard acceleration or deceleration, and rapid joint wear. If he was unlucky, he experienced a vibration most of the time, and even the strongest of joints would blow apart under hard acceleration.
Checking and correcting universal joint operating angles is really not difficult, and should always be done on any vehicle that has seen any type of rear suspension modifications, driveline component swaps, or sizable horsepower boosts. This includes the installation of Super Stock springs and many rear-axle swaps. Many unmodified vehicles can benefit from this as well, to compensate for production tolerances, body and frame sag, spring sag, and more. If nothing else, correcting these angles provides peace of mind, reduced vibration, and helps to assure long joint life.
Whether you have access to a commercially available universal joint angularity gauge, or choose to make your own as shown here, before measuring the angles you need to take some precautions. First, remove all cargo from the vehicle. The spare tire and jack can stay, but everything else must go. The gas tank should be full. The specifications for universal joint angles are always given for a vehicle that is sitting at rest on a flat surface. Checking the angles with the vehicle raised and the suspension hanging will assure erroneous readings. The rear suspension must be at its normal static position in relation to the body of the vehicle. To that end, the use of a pit or a drive-on rack will give you plenty of access to the underside of your vehicle while maintaining a normal suspension attitude.
But satisfactory results can be achieved with four jack stands or a combination of jack stands and ramps. Raising the rear of the vehicle and supporting it with jack stands placed under the axle tubes will keep the rear suspension somewhat loaded, but to be properly loaded, the front must be raised as well and supported by the tires with ramps or by the lower control arms with jack stands. Supporting the front of the car by the K-frame with a floor jack is not only dangerous; it will place more of the vehicle's weight on the rear suspension, since the K-frame is ahead of the front wheels. The rear suspension will droop somewhat lower than normal. Supporting the vehicle by jack stands placed under the front frame rails will remove some of the weight from the rear suspension, causing the rear of the car to rise. Either way, your readings will not be accurate.
Typically, for a relatively stock vehicle, the front universal joint operating angle should be between zero and one degree. The specification for the rear joint typically calls for between 2 and 3 degrees. A greater angle is specified for the rear joint because, under acceleration, the leaf springs allow the rear axle to rock backward a little, which causes the pinion to rise slightly. This movement, called leaf spring windup, puts the pinion and driveshaft more in line with each other than when the vehicle is at rest. Drag racers are especially concerned with the rear universal joint angle, for leaf spring windup is very pronounced during a hard launch. Typically, they desire a static reading of 5 to 7 degrees "nose down" in order to maintain a reasonable operating angle when leaving the starting line.
"Nose up" or "nose down" refers to the position of the pinion in relation to the driveshaft, not the ground. For example, if the driveshaft ran from the transmission to the rear axle at a 10 degree angle in relation to the floor, and the center line of the pinion pointed upward toward the transmission at a 7 degree angle, the operating angle of the rear universal joint would be said to be 3 degrees nose down. Even though the center line of the pinion is pointing upward, it is still on less of an angle than the driveshaft. And since we want to express the relationship between the centerline of the pinion and the driveshaft, it is said to be nose down.
Correcting the universal joint angles is accomplished with shims. Starting at the front, if the angle is less than specified, no action is required. Adjusting the front universal joint angle is accomplished by installing shims between the transmission extension housing and the rear transmission mount. Each 1/8-in. shim installed will reduce the joint angle by approximately 1/4 degree. You can either fabricate shims from flat steel plates or use Chrysler spacers, part number 3410700, for this purpose. Correcting the rear universal-joint angle is done with tapered shims placed between the leaf springs and the rear axle spring perches.
(Remember to support the vehicle by the frame before cutting the U-bolts loose!) These wedge shaped shims are available from just about any speed shop and come in 1, 2, 3, and 4 degree values. Installing the shims with the fat end forward will rotate the axle rearward and cause the pinion to 11 nose up," while installing the fat end rearward will rotate the axle forward, causing the pinion to "nose down."
Whenever a correction has been made at either end of the driveshaft, always recheck both universal joint angles. If you need to correct both, always start with the front joint. Changing the front universal-joint angle will likely have a significant impact on the rear joint angle, but changing the rear joint angle usually has a negligible effect on the front joint angle.
Sounds like you need new tires, but also could use more tuneability. What angle are the rear hangers at as it sits? This can have a tremendous effect on the springs ability to plant the tires. If the upper half is straight over the spring eye, giving you no angle at all, it will not show much rise. Put a longer shakle on there , with the upper mount farther forward to create an angle of 30 to 40 Degrees, and as the car trys to launch it will have the added leverage of that back shackle raising the car up. Then to compensate, a good adjustable shock to slow it down enough for your combo should fill the bill. My dart had leafs on it for several years, with the shackles the way i discribe, and had all the body seperation i could use.
your going to need atleast 5 degrees nose down i like 7 degrees
my 28x9 ss spring dart 60' times are in the 1.46 range with 7 degrees only ran 1.51 to 1.53 with 5 degrees
you will need to cut the old spring perches of and re weld to get the correct angle
if you want to lower the car set the pinion at 7 degrees in the uper hole and you should still have 4 in the lower hole if you need to raise the car