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  1. #1

    Default rear suspension info...

    I'm looking for a link or a sticky with good info on eaech piece of the rear suspension and how it works. Bacisly I'm pretty new to this set up and I want to learn about it, how to adjust it, which pieces to upgrade first and such.

    thanks
    78 Z28:406ci roller, w/ Tremac 5 spd
    96 WS-6: LT1, M6, BBK mid, magna catback, daily driver

  2. #2
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    Wow that's a pretty broad question! I'll start with basics and we can go from there.

    Our cars have a torque arm (TA) suspension. This means they have traditional lower control arms (LCA's) which attach the rear end to the sub frame of the car via the lower bracket on the axle tubes. Instead of having upper control arms we have a TA which mounts above and below the pinion on the front of the differential and parallel’s the drive shaft (DS) attaching to a bracket on the tail shaft (output shaft) of the transmission. There is also a pan hard bar (PHB) which attaches to the rear end on the driver side and the sub frame on the passenger side.

    The TA is what keeps the rear end from rolling upward when the car accelerates. The LCA's hold the rear straight under the car and do the pushing upon acceleration. The PHB keeps the rear end centered under the car.

    Most people will replace all three of these when upgrading the suspension. The stock stuff will work in a stock car but when you start demanding more performance from parts manufactured to handle stock power levels you'll end up disappointed and probably with broken parts! The stock TA, LCA's, and PHB are not boxed and have rubber bushings which makes them prone to bending, twisting, flexing and all other kinds of stuff. Most people will convert to urethane bushings and boxed or tubular components some even with rod ends instead of bushings. These components are much stronger and are able to transfer energy faster with less flex resulting in better suspension performance.

    LCA's - The lower control arms on our cars are not at the best angle from the factory. Basically you want your LCA to be mounted so it will push upwards toward the car (the mounting point on the rear end lower than the mounting point on the car). Stock most LCA's are slightly upward but after years of use the springs settle and the LCA become almost level. This is bad because when you accelerate the rear end will wrap up creating axle hop. Axle hop is what WILL kill your parts and your ET if you’re a racer! This condition is worsened on cars that have been lowered. The solution is LCA relocation brackets which can be bolted or welded to your stock mounting point on the rear end lowering where your LCA mounts. You can also just buy an aftermarket rear with multiple mounting locations already installed, which most will eventually do! Adjustable LCA’s can be used to help with centering the tires in the wheel wells and squaring the axle under the car. They come with rod ends, polly bushings, and a combination of both. They are also available in single and double adjustable. Doubles have the ability top be lengthened or shortened as needed on the car which makes changes easier and less time consuming.

    TA- The stock TA is known to flex and is usually the first thing recommended to change. There are two basic types available, long and short. The long TA is like the stock one and is mounted in the same fashion. There are also kits available to move the front mounting location from the transmission to the trans cross member, this takes the stress of the rear end pushing the TA up off the tail shaft and transfers it into the frame/ body of the car. The short TA works just like the long one only like it's name it's shorter and is mounted to it's own cross member between the trans cross member and the rear end. Drag racers usually prefer the short arm because of its ability to react quickly, however there are several very fast cars using a long arm. It really comes down to the car and HP levels and even trans type. The front mount of the TA can be relocated up or down from the stock location if using one of the earlier mentioned alternative mounting locations. This is used to determine how aggressively the torque hits the tires, higher and the tires are hit harder but unload quicker. Lower and the tires aren’t hit as hard but will stay planted longer. The location will vary with cars as each setup is different.

    PHB- the PHB is a pretty much a must change when a car is lowered though some have been able to make the stock one work. You want the PHB to be level when the car is sitting. As the suspension travels up and down the PHB will actually move the rear end left to right under the car. Imagine a capital "H", say the horizontal part of the "H" is our PHB, the right side is the car and the left side is the rear end. As the left side moves up and down independently of the right side the vertical lines are drawn closer together the more they move up or down. They then separate as the PHB moves back to the center "level" position. When a car is lowered the PHB is usually no longer level making the rear end off center under the car. This is fixed by and adjustable PHB.


    Pinion Angle- This is a topic that will always be argued as there are many theories and methods of measuring and calculating it. Many people confuse driveline angle which is the working angles of the entire drive line and pinion angle which is the working angle of the rear u joint at the pinion. The pinion angle is the angle the driveshaft points at the pinion yoke (the angle the rear u joint is forced to work). Optimum angle is zero degrees, the driveshaft and pinion are in a straight line. You want zero degrees when the car is driving; this requires little work for the u joint resulting in longer life and will minimize driveline vibrations. Since the nose of the pinion wants to roll upward upon acceleration a negative pinion angle is required when the car is stationary. It’s generally accepted that -2 degrees pinion angle works well for most cars. This means the nose of the pinion is pointing down 2 degrees from whatever angle the driveshaft is pointing towards the pinion. Example: your driveshaft is level from the trans to the pinion which is 0 degrees. You will want the pinion pointing down 2 degrees (-2) so when the car accelerates and the pinion wraps upwards (front of rear end housing) the driveshaft and pinion achieve 0 degrees. This is measured by getting an angle finder available at all hardware stores and measuring the angle of the driveshaft vs. the angle of the pinion. Most people use the bottom of the TA mount to measure the pinion, you just need a flat surface that’s square with the pinion. To adjust the angle you need an adjustable TA, move the adjusting nut accordingly. The car must be sitting on its suspension (loaded suspension) for this to be measured or adjusted. Clear as mud right! Your suspension type and hp level will determine what pinion angle is best for your car.

    Well I've already typed this much I might as well give a brief description of instant center (IC). Imagine your car from the side. Look at the angle of your LCA (up towards the front I hope!). Draw a line from the point where your LCA mounts to the rear end and extend that line along the angle of the LCA past the front of the car. On a four link rear suspension you would then do the same thing with the upper control arms which would be at a slight downward angle. The point where those two lines intersect is your IC. On our TA suspension the TA acts as the upper control arm on a four link and like a ladder bar. Since the car will ultimately try to balance on the axles start at the rear axle center line (the center of your axles) and draw a line forward along your TA. Continue this line through the center of the front TA mounting point. The point where your lines cross is your IC. The IC is the "lifting point" where your rear suspension is aiming its energy. Our cars are slightly different though. Our lifting point is going to be where ever the front of the TA mounts to the chassis, much like a ladder bar setup. Imagine your LCA's pushing forward along that line as the TA is lifting upwards (pulling back on a four link). Adjustment can be made to the height of the TA mounting point but not location forward and back without actually physically relocating the mounting point (long vs. short TA). You can use the LCA’s to adjust what direction the forward energy is going to push. Now that you know what your IC is it's easy to tell why it's important. If you’ve ever had you car scaled you can easily find where your car's center of gravity is (the balancing point of the car from front to back). If your IC is too far forward of the center of gravity you will likely not get anything but tire spin, if it's too far behind it you'll probably hook and unload the tires quickly (bog then spin). The IC in the correct location makes for optimal weight transfer onto the rear tires and 100% weight transfer = wheel stand! By moving the front mounting point of the TA and the rear mounting point of the LCA's there are many possible IC's. No two cars will react the same and keep in mind these are just basic principals. What your car will want is all based on weight, HP level, trans type, tire, TA style, etc, etc. Seat time and logging how you car behaved on every pass is the only way to figure out what your car will want! Remember to only change one thing at a time and keep a log of your results!


    I hope this answers your question and doesn't leave you more confused!

    If I've missed anything or have given incorrect info please add to this or let me know so I'm not leading every reader down the wrong path! I'm by no means an expert and am still learning about chassis and suspension design

    Last edited by 96LT1355Z28; 07-16-2011 at 02:10 AM.
    -Josh
    co-owner of BDBRacing.com
    NMCA OC 9004
    96, N/A 385, Holley EFI, Faceplated M6, AI TFS heads, LE SR cam, MWC Fab 9
    10.16 @ 136 1.50 60'........still workin on that 60' shootin for 1.4's!

  3. The Following 4 Users Say Thank You to 96LT1355Z28 For This Post:


  4. #3

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    that really helps. I had been confused about LCA angle from reading other posts, but i thinking i get the theory now. I'm setting my car up for daily driver/drag 1-2 times a month. It will never see a road course. Which should make it easy becuase i can focus in one direction instead of trying to do two different setups (road and drag) which usually are counter to each other in set ups.

    For a drag car with bolt ons and a cam/stall after the tires, i should start with TA, then LCA from what I just read? I'm on a budget so i might explore boxing my own parts before i upgrade them, as i progress over time. As is most things money is the limiting factor so one piece at a time once i get it running.

    I appreciate your help 96 you are the man.
    78 Z28:406ci roller, w/ Tremac 5 spd
    96 WS-6: LT1, M6, BBK mid, magna catback, daily driver

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    I've heard of people buying urethane bushings for the stock LCA's and boxing them in. I've never done it nor do I know anyone who has so I can't give you advice or tips on that. You could probably find a used set of LCA's for a decent price. I'd reccomened doing your LCA's with brackets and the TA first. Decide what your long term goals are for the car and then buy or make your parts accordingly. This will help in preventing you from buying boxed non adjustble urethane bushed LCA's now and in a year wishing you'd got adjustable rod ended ones! As far as order of parts I'd say like this:

    -LCA's w/ relocation brackets
    -TA
    -PHB if ride height is changed, alot of companies will offer a package deal with multiple componet purchases
    -Tires
    -Adjustable shocks

    Hope this helps!
    -Josh
    co-owner of BDBRacing.com
    NMCA OC 9004
    96, N/A 385, Holley EFI, Faceplated M6, AI TFS heads, LE SR cam, MWC Fab 9
    10.16 @ 136 1.50 60'........still workin on that 60' shootin for 1.4's!

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    I just started on my rear suspension, I bought tubular LCAs, tubular sfcs and adjustable phb. I think its gonna stiffen it up quite a bit. Ive also been pricing KYB adjustable shocks for the rear.

    Cammed, bolted, Geared
    LE, UMI, Strange

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    ^^ Good start, I completly forgot about sub frame connectors. They're pretty much a must if you want to stiffen up the chassis.
    -Josh
    co-owner of BDBRacing.com
    NMCA OC 9004
    96, N/A 385, Holley EFI, Faceplated M6, AI TFS heads, LE SR cam, MWC Fab 9
    10.16 @ 136 1.50 60'........still workin on that 60' shootin for 1.4's!

  8. #7

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    Quote Originally Posted by 95LT1Z28 View Post
    I just started on my rear suspension, I bought tubular LCAs, tubular sfcs and adjustable phb. I think its gonna stiffen it up quite a bit. Ive also been pricing KYB adjustable shocks for the rear.
    sounds like a good plan, what type did you buy? Did you get the adjustable "on the car" versions? what i'm trying to decide is how much is the adjustable on the car worth vs just adjustable, or non adjustable. I think the cheaper adjustable will be sufficent. but thats mostly becuase as much as I'd love it, those full on car adjustables are expensive.
    78 Z28:406ci roller, w/ Tremac 5 spd
    96 WS-6: LT1, M6, BBK mid, magna catback, daily driver

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    The only adjustable piece I have is the phb and it is on car adjustable. The phb is spohn, the sfcs are umi and the lcas are bmr. I also have a strut bar from umi. And as far as expesive ness all that less the strut bar came to about $420. Im not going to autocross so i didnt think adjustable everything would be worth it or necessary.

    Cammed, bolted, Geared
    LE, UMI, Strange

  10. #9

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    i found a set of tube bushing BMR LCAs, should i get a set of reloaction brackets? My car is at the stock height, aren't relocations for when you lower the rear, to get the alignment back?
    78 Z28:406ci roller, w/ Tremac 5 spd
    96 WS-6: LT1, M6, BBK mid, magna catback, daily driver

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    Its not to get the alignment back, that would be the phb's job. The lca brackets are for changing the angle at which the contol arm operates. When you lower the car it will be at more of a straight angle, the brackets give it that needed angle much like it had at the stock ride height.

    Cammed, bolted, Geared
    LE, UMI, Strange

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