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So my car is 99% together. I have a Midwest chassis Fab 9 with the welded in tq arm mount. If someone can point me in the general direction or reply here on setting up pinion angle and such as everything is new. Thank you
Pinion angle is all about creating smooth movement of u-joints. Drive shaft joints should have equal and opposite angles at each end for smooth movement. The suspension must be loaded when you take the measurements. You don't need to overcompensate with more angle at pinion because your torque arm is so rigid that the angles will hold under hard acceleration.
The location of torque arm front mounting point determines instant center and how the rear suspension reacts to acceleration and braking. Pinion angle has nothing to do with torque arm geometry (you just need to correct the pinion angle after changing torque arm geometry).
FYI - I don't know anything about the torque arm you bought but Midwest chassis has a bent toward drag racing and torque arm geometry for drag racing doesn't work well in corners and braking situations. I think you're trying to build a corner carver, right?
Pinion angle is all about creating smooth movement of u-joints. Drive shaft joints should have equal and opposite angles at each end for smooth movement. The suspension must be loaded when you take the measurements. You don't need to overcompensate with more angle at pinion because your torque arm is so rigid that the angles will hold under hard acceleration.
The location of torque arm front mounting point determines instant center and how the rear suspension reacts to acceleration and braking. Pinion angle has nothing to do with torque arm geometry (you just need to correct the pinion angle after changing torque arm geometry).
FYI - I don't know anything about the torque arm you bought but Midwest chassis has a bent toward drag racing and torque arm geometry for drag racing doesn't work well in corners and braking situations. I think you're trying to build a corner carver, right?
Thanks for the response. Not building a corner carver. I'm trying to understand the concept of setting pinion angle. I have the car on ramps in the garage. Trying to measure at the output shaft trans I have about 1-2 degrees down. The rear pinion I have about 1.5-3 degrees up.( Need to get a better tool just using an angle finder app.) I have no driveshaft because I need a custom unit. I installed the rear got it close. The rear trailing arms have an in and out adjustment both ends plus there are 5 mounting points up or down on the rear axel side as well for the arms. The tq arm is welded to its mounting point at about 6-8 inches behind the trans tailshaft output . This also has an an adjustment up and down at this point 5 mounting holes. Plus In and out on tq arm end and two adjustment points top and bottom on pumpkin housing. If pictures would help better explain I can post them. Just want to get ahold of this. Once I get my bearing I'll make it work.
You need a more accurate tool to set pinion angle.
Moving instant center will change anti-squat.
* Torque arm front mount: Locating higher (up vertical) will move the instant center rearward and increase anti-squat a bit, and vice versa. It's changes just a little though, not a very strong factor.
* Torque arm length: Shorter torque arm moves instant center rearward and will increase anti-squat a lot, and vice versa. It's a strong factor. Be careful because you can induce brake hop.
* Control arm height: Moving axle side of control arm mount to a lower position will raise the instant center and increase anti-squat by a large amount, and vice versa. It's a strong factor. Start with a 1 to 2 degree slope down toward axle. You can really jack up handling with control arm settings though, i.e., lose control of car in a tail wag, brake hop, etc....
The torque arm mount at axle side has two threaded rods. The top rod is just part of the torque arm itself, not really an adjuster. The bottom rod adjusts pinion angle. There is only so much adjustment available so if you run out of adjustment then you'll need to change the height of the front torque arm mount to bring things back inside the fence you can work in.
Make sure things don't get bound up when adjusting or something is going to break later on. That's where the top rod can be used to help relieve some stress if things get bound up.
Thank you for getting me started. Just picked up a digital level with the degree angle feature. All my other measurements changed.
So you touched on instant center slot. What is instant center? This package runs the shorter arm than the 4th gen kits, and much shorter than stock. Alot of info thank you.
Both the control arm and the torque arm have pivot points that constrains axle movement. The axle moves along an arc that is the combined effect of both those suspension links. The center of that arc is called the instant center. Basically it helps define the path that the axle will travel as the suspension goes through its movements. It is also one of the factors that goes into figuring out whether you're increasing or decreasing anti-squat with suspension adjustments.
No amount of words are going to put this concept together if you've never heard of it. You've got to hunt down an illustration so you can visually see how it works and then it will start to make sense.
Just keep in mind that analysis of a torque arm suspension is different because the torque arm doesn't apply force to the chassis in fore-aft directions, it applies force in the vertical directions.
It's actually kind of difficult to find good information on the web about torque arm suspension. I think Herb Adams or some other GM suspension engineer wrote a book in the '80s that is one of the best reference tools.
Thank you both. I have looked around for books on the subject. Doorslammers came up as a good book but tq arms I read are not mentioned in the book. It is tough to find info in tq arm cars. Plus those in the know esp in the buisness wont go too much into depth on this as well, for buisness sake I assume. Any good reads I can pick up besides doorslammers?
So did alot of measurements today and see if I'm on the right track in terms of pinion and driveline angles. Trans is 3.4 degrees shaft is 3.5. Rear pinion is 4.3. So it gives me a working angle of .1° at the front and a working angle of .8°at the rear. Under the 3° recommended. So here is where I'm heading to see if I'm on the right track. Adjust another 1.5° out of the rear pinion get 2.8° to adjust for under power twist of a solid mounted rear. Which will give me a working angle of 1.5° under throttle. Am I off here?
I think recommendations like that are with a bent toward drag racing where there is gobs of traction and severe loading on suspension.
I drive my car on the street so the pinion spends a lot of time teetering between light throttle and light deceleration. I'd rather keep my u-joints happy in that mode. My torque arm just isn't going to allow much flex even if I stab the throttle. And I'm sure as heck never going to manage lightning 60' times.
So my car is 99% together. I have a Midwest chassis Fab 9 with the welded in tq arm mount. If someone can point me in the general direction or reply here on setting up pinion angle and such as everything is new. Thank you
Hey man I know this is super old but what subframe connectors did you use to weld that MWC torque arm crossmember to?? I only ask because I just received my 2 piece race arm and crossmember from MWC and recently ordered up their fab 9 rear housing and axle package to get rid of my current QP 9" housing
Hey man I know this is super old but what subframe connectors did you use to weld that MWC torque arm crossmember to?? I only ask because I just received my 2 piece race arm and crossmember from MWC and recently ordered up their fab 9 rear housing and axle package to get rid of my current QP 9" housing
I'm done with the car and its going to the alignment shop in a few weeks. But I have old Mac subframes, been on the car for years. I had the tq custom installed by a chassis shop. Let me see of I can find the pics to give you an idea.
Last edited by IROCZ1989; Jul 23, 2021 at 05:27 PM.
I'm done with the car and its going to the alignment shop in a few weeks. But I have old Mac surfaces been on the car for years. I had the tq custom installed by a chassis shop. Let me see of I can find the pics to give you an idea.
The torque arm adjustment is just to adjust the rear u-joint angle, nothing else. You want it equal and opposite of the front u-joint so both joints pivot through roughly the same angle, and you don't want them to be 0* because that will mean that the same rollers are in the same place all the time causing premature wear.
As far as instant center goes, a traditional torque arm (NOT WHAT WE HAVE), the front pivot determines the instant center, it is the instant center and the lower control arms are inline with the axle so they don't do anything but locate the axle fore and aft. A sliding link torque arm is what we have and the front link sets a vertical line which a second line drawn through the pivots of the LCA's crosses that line is the location of the instant center. So basically the fore/aft location of the front mount and the angle of the LCA's entirely determine the instant center, it doesn't move fore and aft like it would with a 3 or 4 link suspension.
The torque arm adjustment is just to adjust the rear u-joint angle, nothing else. You want it equal and opposite of the front u-joint so both joints pivot through roughly the same angle, and you don't want them to be 0* because that will mean that the same rollers are in the same place all the time causing premature wear.
As far as instant center goes, a traditional torque arm (NOT WHAT WE HAVE), the front pivot determines the instant center, it is the instant center and the lower control arms are inline with the axle so they don't do anything but locate the axle fore and aft. A sliding link torque arm is what we have and the front link sets a vertical line which a second line drawn through the pivots of the LCA's crosses that line is the location of the instant center. So basically the fore/aft location of the front mount and the angle of the LCA's entirely determine the instant center, it doesn't move fore and aft like it would with a 3 or 4 link suspension.
