Suspension tuning - brake dive

[gerno]

I have been a member for a long time but I rarely post so I'll give a quick intro. I'll start by saying I'm not an engineer so please use smaller words with me if you are nice enough to reply with advise. I have been reading a lots of information about suspension setup and I think I should be focusing on anti-dive with my car but not really sure. I am trying to figure out how to effectively upgrade components on my car and not just add every bolt on that is sold even though I think I have bought most of them....

The car is a 72 Camaro weighing 3500lbs with an aluminum headed sbc, 6spd, Pro touring F-body upper control arms, boxed factory lower control arms, QA1 coil over front, factory front sway bar, C5 front brakes, G-braces, DSE subframe connectors, Bolt in roll bar, Hotchkiss leaf springs, QA1 staggered rear shocks with a custom mount to the axle to clear my LS1 calipers. I don't recall the alignment spec but it is close to what I hear most people run with the aftermarket control arms.

The issue with my car is that I feel it's either diving very bad under hard braking or the rear end is lifting hard under hard braking. I have ad the car a Thunderhill and also autocrossed the car this weekend. Thunderhill the car felt fairly stable but some push on tight corners and slippery overall.

At the autocross the tight corners really showed me the issues and specifically the dive/lift made the car very unstable braking to enter turns. I'm not the best driver either so it could be normal and I need to get used to it. It didn't help that the brakes are far too touchy and easily locked on me (I'm adjusting the linkage closer to the pivot first then swapping MC if it doesn't fix the brake issue). It was probably due to entering the corners too fast but I also had a very hard push that I would use power to kick the rear around and straighten the car. I was on radials and it was very slipper, lots of fun but the car also seemed very easy to anticipate. I assume making some changes would make me faster or do I just need to focus on driving the car better first?

I have not added a rear bar because I heard some advice that it is not always needed. I didn't want to "go-cart" my car and make is stiff as I can. I wanted to put together a system that worked all around since I also drive the car a lot. Should I look into a rear bar to reduce the brake dive? I have the factory rear bar at home I could build some mounts for to clear my exhaust.

I am also curious if the QA1 coilovers are part of the issue since the spring is so small. Would swapping to a full spring with the same or higher rate possibly help? I have a set of Hotchkiss front springs at home as well. They were too tall for my stance so I swapped to the QA1 for adjustability but I could cut the front springs as needed.

I've heard about moving the front leaf mount up ~3/4" by redrilling to help with the anti-dive. Should I try this?

Would spherical front leaf bushing help articulation and help any of the issues I have?

Any other areas I should look into first?

Thanks and sorry for the novel...

Steve

[manny z]

Originally Posted by gerno

I have been a member for a long time but I rarely post so I'll give a quick intro. I'll start by saying I'm not an engineer so please use smaller words with me if you are nice enough to reply with advise. I have been reading a lots of information about suspension setup and I think I should be focusing on anti-dive with my car but not really sure. I am trying to figure out how to effectively upgrade components on my car and not just add every bolt on that is sold even though I think I have bought most of them....

The car is a 72 Camaro weighing 3500lbs with an aluminum headed sbc, 6spd, Pro touring F-body upper control arms, boxed factory lower control arms, QA1 coil over front, factory front sway bar, C5 front brakes, G-braces, DSE subframe connectors, Bolt in roll bar, Hotchkiss leaf springs, QA1 staggered rear shocks with a custom mount to the axle to clear my LS1 calipers. I don't recall the alignment spec but it is close to what I hear most people run with the aftermarket control arms.

The issue with my car is that I feel it's either diving very bad under hard braking or the rear end is lifting hard under hard braking. I have ad the car a Thunderhill and also autocrossed the car this weekend. Thunderhill the car felt fairly stable but some push on tight corners and slippery overall. Ok, for one what kind of QA1 coilovers are you using? Did you just get them "off the shelf"? or were they built for YOUR car? What spring rate are you running on these coilovers?

At the autocross the tight corners really showed me the issues and specifically the dive/lift made the car very unstable braking to enter turns. I'm not the best driver either so it could be normal and I need to get used to it. It didn't help that the brakes are far too touchy and easily locked on me (I'm adjusting the linkage closer to the pivot first then swapping MC if it doesn't fix the brake issue). Instead of changing your pedal ratio, why not use a proportioning valve? Or do you know what size the piston is in your MC? You know one of the issues you could be having is, the MC piston might be a little to small, and creating to much pressure when you step on the brakes, making your brakes to touchy. It was probably due to entering the corners too fast but I also had a very hard push that I would use power to kick the rear around and straighten the car. I was on radials and it was very slipper, lots of fun but the car also seemed very easy to anticipate. What kind of tire are you running, what size, and what ait pressure? I assume making some changes would make me faster or do I just need to focus on driving the car better first?

I have not added a rear bar because I heard some advice that it is not always needed. I didn't want to "go-cart" my car and make is stiff as I can. By adding a rear bar, you are not going to change the ride quality of your car, unless you are always turning. haha.. Adding anti-roll bars(sway bars) or getting bigger ones, will change the way the body rolls in a corner. I wanted to put together a system that worked all around since I also drive the car a lot. Should I look into a rear bar to reduce the brake dive? A rear bar, will do nothing for brake dive. I have the factory rear bar at home I could build some mounts for to clear my exhaust.

I am also curious if the QA1 coilovers are part of the issue since the spring is so small. Would swapping to a full spring with the same or higher rate possibly help? I have a set of Hotchkiss front springs at home as well. They were too tall for my stance so I swapped to the QA1 for adjustability but I could cut the front springs as needed. The diamiter of your springs on the coilovers will affect your ride bud. I run 1100 lb coilover springs on our viper comp coupe, with nary an issue.

I've heard about moving the front leaf mount up ~3/4" by redrilling to help with the anti-dive. Should I try this? The adj for anti-dive are made up front. And before you get into changing something like your anti-dive, you should look at the areas I mentioned.

Would spherical front leaf bushing help articulation and help any of the issues I have? Again, look at the other areas before you start throwing parts at your car. No offense but, if you are not well verced in suspension set-up, you are just going to make you car not fun to dirve.

Any other areas I should look into first?

Thanks and sorry for the novel...

Steve

Just look at these to start. Put up the answers to the questions I asked.

[Sieg]

What are your spring rates and shock compression settings?

[Vince@Meanstreets]

I agree, look to matching your spring rates up first. Being QA1's I'd assume the standard 350 lbs spring.
Most likely coming down on your bump stops and unloading the rear end.

If you are serious in performance stiffen up the subframe and look into a different spring and shock set up. Rear should be fine.

Support down bars for the front, cross bar right above the sway bar and weld up your subframe seams.

I'd like to see a video of your runs.

[Vince@Meanstreets]

Originally Posted by manny z

Just look at these to start. Put up the answers to the questions I asked.

manny you got to break that up, didn't see your advice till now....maybe change the color?

[gerno]

Thanks for the replies. I extracted many of the questions and here are they details.

Ok, for one what kind of QA1 coilovers are you using? Did you just get them "off the shelf"? or were they built for YOUR car? What spring rate are you running on these coilovers?

They are off the shelf parts. I used HAL-GMP3350-3 which is spec'd below.

Suspension Height Adjustment Stock
Coil-Over Kit Position Front
Recommended Front-End Weight 1,701-1,900 lbs.
Shocks Included Yes
Adjustable Valving Yes
Internal Design Twin-tube
Gas Charged No
Number of Valving Selections 12
Shock Body Material Aluminum
Shock Body Finish Clear anodized
Bushing Material Polyurethane
Bushing Color Black
Coil-Over Springs Included Yes
Spring Rate (lbs/in) 350 lbs./in.


Instead of changing your pedal ratio, why not use a proportioning valve? Or do you know what size the piston is in your MC? You know one of the issues you could be having is, the MC piston might be a little to small, and creating to much pressure when you step on the brakes, making your brakes to touchy.

I have an adjustable proportioning valve for the rear but the issue is that the pedal is too stiff. The MC has a 1 1/4 bore off an astro van and I have an extra MC sitting around off an S10/Regal/Malibu that has a smaller bore. Based on what I was reading I beleive the smaller bore makes the brake less touching. For some reason I always get confused with the efffect of MC ratio on the brakes.

No offense but, if you are not well verced in suspension set-up, you are just going to make you car not fun to dirve.

I agree completely which is why I'm asking the questions now. Before I start buying all new stuff I'm hoping a little advise on my current mismatched parts will point me in a better direction.

I agree, look to matching your spring rates up first. Being QA1's I'd assume the standard 350 lbs spring.
Most likely coming down on your bump stops and unloading the rear end.

If you are serious in performance stiffen up the subframe and look into a different spring and shock set up. Rear should be fine.

Support down bars for the front, cross bar right above the sway bar and weld up your subframe seams.

I'd like to see a video of your runs.

I'm also thinking the light coilovers aren't helping me. I have the subframe fairly stiff but have not welded the seams as of yet. I did add some down bars and also welded in a supprt bar near the sway bar.

I have some video but they didn't turn out well at all and you can't really see what's going on. I wish my Replay XD had a video screen so I could test in advance.

[manny z]

Originally Posted by gerno

Thanks for the replies. I extracted many of the questions and here are they details.

Ok, for one what kind of QA1 coilovers are you using? Did you just get them "off the shelf"? or were they built for YOUR car? What spring rate are you running on these coilovers?

They are off the shelf parts. I used HAL-GMP3350-3 which is spec'd below.

Suspension Height Adjustment Stock
Coil-Over Kit Position Front
Recommended Front-End Weight 1,701-1,900 lbs.
Shocks Included Yes
Adjustable Valving Yes
Internal Design Twin-tube
Gas Charged No
Number of Valving Selections 12
Shock Body Material Aluminum
Shock Body Finish Clear anodized
Bushing Material Polyurethane
Bushing Color Black
Coil-Over Springs Included Yes
Spring Rate (lbs/in) 350 lbs./in.


Instead of changing your pedal ratio, why not use a proportioning valve? Or do you know what size the piston is in your MC? You know one of the issues you could be having is, the MC piston might be a little to small, and creating to much pressure when you step on the brakes, making your brakes to touchy.

I have an adjustable proportioning valve for the rear but the issue is that the pedal is too stiff. The MC has a 1 1/4 bore off an astro van and I have an extra MC sitting around off an S10/Regal/Malibu that has a smaller bore. Based on what I was reading I beleive the smaller bore makes the brake less touching. For some reason I always get confused with the efffect of MC ratio on the brakes.

No offense but, if you are not well verced in suspension set-up, you are just going to make you car not fun to dirve.

I agree completely which is why I'm asking the questions now. Before I start buying all new stuff I'm hoping a little advise on my current mismatched parts will point me in a better direction.

I agree, look to matching your spring rates up first. Being QA1's I'd assume the standard 350 lbs spring.
Most likely coming down on your bump stops and unloading the rear end.

If you are serious in performance stiffen up the subframe and look into a different spring and shock set up. Rear should be fine.

Support down bars for the front, cross bar right above the sway bar and weld up your subframe seams.

I'd like to see a video of your runs.

I'm also thinking the light coilovers aren't helping me. I have the subframe fairly stiff but have not welded the seams as of yet. I did add some down bars and also welded in a supprt bar near the sway bar.

I have some video but they didn't turn out well at all and you can't really see what's going on. I wish my Replay XD had a video screen so I could test in advance.

I am going to start from the top. BRAKES: With the brakes you are using, the MC piston size is a little on the large side. When I first set up the wilwoods on my charger, I had a 1 1/8" MC piston size, it wound up being the big. I down sized to a 1", and the brakes feel better. Are you manual brakes, or power?

You front shocks, get those 350 lb springs, and use them to hold your hood up. lol.. < just some humor. Way to light for that car man. I would start with at least a 650-700 spring. Like was mentioned, with that small of a sring rate, you are more then likley diving pretty hard, and unloading the rear of teh car.

[manny z]

Originally Posted by Vince@MSperfab

manny you got to break that up, didn't see your advice till now....maybe change the color?

I know. I set it on red, but it came out black. haha..

[gerno]

Thanks for the guidance. I'll be swapping the MC this week to the smaller bore. I had forgotten I had an extra one sitting around. I'll also swap my smal block (600lb) Hotchkis springs in this week for the QA1 coilovers. I figured since many other people were using them they would be ok but apparently not so much. For now I'll use the shocks alone with the other springs but will eventually sell the coilovers and get some good shocks

[Smoker03]

With a small block and the QA1 coilovers, you can get them to work very well. You have the 350lb spring which is a little light. Up the spring on the coilover to 450 or 500 max and it will work great. You do not need 700lb springs on a coilover. If you had a separate spring and shock in the stock location, a 700lb spring would be a good option. I would keep the coilovers and up the spring rate to 450 and see how it does. The rear sounds fine. I also agree with goin down in size on the MC.