Finally got the 62 Nova on the road, its fun but...

[JRouche]

Yeah, its great to finally have the Nova on the road but its a lil squirrely so Im looking for advice, one that is not "stay out of the throttle", cause that one is difficult for me to abide by.

The car. A 62 Nova. The engine, mild 350. Rear end and trans is a ford 9" with 3:70 gears and posi and a 700-R4. The suspension. Art Morrison parallel four link with air ride tech shockwave air springs at the rear and Mustang II front with shockwave springs. Double adjustable shocks on the front and single adjustable on the rear. Speedway engineering sway bars front and rear. And a watts link to control lateral movement. Tires are 235/45/17 front and 285/40/17 rear, goodyear f1 gs-d3.

I have the car setup so it handles really well for various road conditions and it handles pretty darn good. Good amount of predictability and it has some great turning feel. It hugs the road. I like the setup for the shockwaves and shocks, I did adjust it for handling on the road so the tires are in full contact over ALL the road conditions.

My problem, and I dont like it, is the tendency for the rear end to come around to the left (drivers side) when Im on the throttle and it shifts from first to second under HEAVY acceleration. The trans is not extreme. Its a simple crate unit from B&M. Doesnt have a heavy valve package. The engine is not overly powerful, might be close to 425hp and not a lot of torque. I was driving it today and thats when the ugly became more of a problem. Yes, speed was a factor. But I still think there should be some tuning of the four link that could help.

I was all alone on a road. It was a stop sign. I hammered it from the stop and was crossing a six lane road. The trans shifted into second after I was just through the intersection. Problem, the cross street was crowned some, not much and I think it unloaded the rear enough so the normal slip of the rear tires was more than usual. So the rear came around way more than I like and actually placed me into the right lane of the two lane road, I started in the left lane. If there was a car there or if I was already in the right lane it would have been crunch time. Luckily that lane was open and once the tires bit I was good to go.

So I see it as a rear end suspension setup. I have driven plenty of loose cars and they tended to strip the rear meats in a linear fashion. Meaning the car wasnt pushed sideways by the rear end, at speed anyway, this is happening at speed, not a stalled burnout, Im prolly at 40mph or so when second hits at 7000rpm. I do have posi, and its working.

Im done with the sideways "float" when second hits. On a level clean road the second gear "chrip" still pushes the rear to the left WAY to much. It shouldnt. Im thinking I need to adjust my rear links, they sound like they are off.

And YES, Im working on the shift point problem with the trans. 7000rpm is WAY too high. This engine starts dropping power at around 5200rpm. So yeah, its shifting at a lower HP. Thats an entirely diff issue thats also difficult to fix.

So my question FINALLY!!!! For any of the folks here in the know about how to set up a four link Id LOVE to hear some advice.

I dont know much about parallel four link suspensions. But it seems like Im planting the right tire more than the left? So I am thinking about checking ALL the links, I thought I measured them correctly. If so do I extend the left upper link so it will dig the left tire into the ground more? Im gonna keep the lower links equal for now. I dont want to create more pulling around and ruin the cornering. I just want to plant the left tire more so it gets more push.

This is what Im thinking. The upper links are pushing against the frame during power on. So the link can be placed to push down "into" the frame or up into the frame.

I think I need to adjust the left side upper link to push down on the tire a lil more. A slight adjustment is gonna happen. Four link suspensions can be a bear to set up. You have the link length and the various link mounting holes on the frame. The variables are staggering!!!

Anyone want to chime in? ALL the help is good help. As long as its NOT about staying off the throttle, thats obvious :) JR

[exwestracer]

J,
If it's driving the car to the right, the left rear is hitting harder... Stop and think about it a minute, it'll make sense.

I would start by triple checking the wheelbase and square measurements. Rear axle flange registers to lower balljoints is a good way to measure this.

Don't ASSUME anything... When you've verified wheelbase and diagonal, then let's look at the 4 link... If you just start putting preload in it, your left/right handling balance will go all to hell and the car will be very unpredictable.

[exwestracer]

J, can you post a link back to your rear suspension build thread? The search function wouldn't bring it up.

[parsonsj]

I would start by triple checking the wheelbase and square measurements. Rear axle flange registers to lower balljoints is a good way to measure this.Me too. If that checks out, then move on to corner weighting. Check it with you in the car, if possible. Verify that the vehicle's weight is squarely distributed. Good luck, and let us know how this unfolds. It'll be a great object lesson in vehicle tuning after the car is done.

[exwestracer]

BTW, the upper links do not push under power. Ever.

[Bryce]

Remove all preload on the sway bars. Balance cross weights.

If you have a change in ride height from one side to another you will have a different A/S from side to side. This will show its self under impulse loads.

[FlyDoc]

As you said there are so many variables with a 4link, in addition to other suggestions, tire pressure may need to be adjusted & unequal R/L pressure may be needed. Adjusting your IC may be needed.
Check out Performance Trends and there suspension analyzer, you will need a PC not a Mac
good luck & don't bend something!
www.performancetrends.com

[John Wright]

Nothing loose in the watts link? Is the rear stable laterally?

I had a TR7 that drove exactly the way you are describing...I for the life of me couldn't drive that car very hard without white knuckles. Short wheelbase and it felt like the rear end was loose in the links somewhere and wouldn't hold the rear laterally during hard accel and shifting to second without lifting almost guarranteed that I was going to be pointing in the direction where I just left from. Feels like it's steering from the rear.

[MonzaRacer]

If its steering left find local shop with later John Bean Visualiner or a Hunter DSP or Hawkeye. Have them put your car up and give you printout of the rear axle set back it should give them a true reading on which side is farther back, also look for thrust angle.
Take this information, and scale the car to make sure its ok on all 4 corners, right rear may need a few lbs more than left to hook. Also how much pinion angle do you have, on a 4 link sitting at ride height a typical 4 link needs no more than 1.5 degrees down in relation to the driveshaft. Generally as little as 0.25 degrees can be difference between hook or spin. never run less than 0.5 down pinion angle I have found if less you get vibration, and trans should be same angles more or less but opposite. .
As long as heights dont vary much different psi may make it hook. also sway bar should not bind either. Actually have found many air ride cars with 4 "channel" lines that didnt even need a rear sway bar. Odd but true. Made rear end too stiff and cars never hooked. also I like to see and feel the rear end LIFT when you get on it.

[MrQuick]

Remove all preload on the sway bars. Balance cross weights.

If you have a change in ride height from one side to another you will have a different A/S from side to side. This will show its self under impulse loads.

i approve this reply....i'd also look at any lower link convergance difference

[Bryce]

i approve this reply....i'd also look at any lower link convergance difference

HAHA, this message has been approved by the office of MrQuick. Thank you sir.

[JRouche]

J,
If it's driving the car to the right, the left rear is hitting harder... Stop and think about it a minute, it'll make sense.

I think yer right, I was looking at it wrong. This morning while laying in bed watching the sun come up. I was thinking about the slip of the left rear tire and NOT about the direction it was pushing the car. If the rear end is swinging to the left I just assumed it was the left tire slipping, I was thinking of a sliding sideways movement, WRONG. But the end product was the rear was moving left so that would mean the left is getting MORE traction and trying to drive the rear end forward more than the right, right? So with the left tire grabbing more it wants to push the left side forward more than the right side? End result, rear end moves to the left under hard acceleration.



I would start by triple checking the wheelbase and square measurements. Rear axle flange registers to lower balljoints is a good way to measure this.

Don't ASSUME anything... When you've verified wheelbase and diagonal, then let's look at the 4 link... If you just start putting preload in it, your left/right handling balance will go all to hell and the car will be very unpredictable.

Squaring the car up was something I paid great attention to while building it. But the problem is I never went back to check it after all was said and dont. Great point. I think thats one of the simpler checks I can do. I just assumed that is wasn't crabbing down the road because it didnt seem to. WRONG!! I should make sure Im all squared up. Thanks for the great info. JR

[JRouche]

J, can you post a link back to your rear suspension build thread? The search function wouldn't bring it up.

WOW!! The entire post is GONE!! I actually saved the link to it. It was https://www.pro-touring.com/forum/showthread.php?t=55420

Its GONE!! And I did some additional searches for what I KNOW what the subject line was and its not there. Seems Pro-Touring has had a computer DUMP!! Too bad, Ill bet there were many useful posts lost. Thats why I always save great posts locally, never know when the server here or anywhere might take a dump.

Ok, I also posted the same info on Steves Nova Site. And If you are interested for what work was done here is the link to that thread. http://www.stevesnovasite.com/forums/showthread.php?t=121172
JR

[JRouche]

Me too. If that checks out, then move on to corner weighting. Check it with you in the car, if possible. Verify that the vehicle's weight is squarely distributed. Good luck, and let us know how this unfolds. It'll be a great object lesson in vehicle tuning after the car is done.

I have a set of Longacre digital scales. Been waiting to finally play with them. I think its time. Ill check the squareness of the car first then roll her up on the scales. I have a feeling its gonna be pretty equal side to side for the rear and the front, I tried to make sure to balance it out when I built items in or moved stuff around. Like I do have the batt in the trunk, so I put the air tank for the air ride on the other side. The fuel tank is centered. But I think its time to use the new scales just to see. Thanks for the input!! JR

[JRouche]

BTW, the upper links do not push under power. Ever.

Another error from a guy NOT in the know. This is my first and only car I have worked on and so Im learning from ALL you guys.

I thought with power on, the torque from the driveshaft would transmit to the rear gears and try to rotate the rear housing counter clockwise looking at the car from the drivers side, car facing left, and push the upper links.

Simplified... Where is the torque applied? The clockwise rotation of the driveshaft meets a resistance. The pinon gear first. It doesent transmit the force into angular force. Its only seeing linear force. Ok, next down the line. The ring gear. Now we are getting into the meat of it. So the pinion is trying to force the ring gear down, thats where some of why I thought the housing was forced counterclockwise and pushing the upper links when under power. My bad!!!

What I REALLY dont understand is where is the ACTUAL rotational force. The force that acts on the housing. Because if you think about it the housing is separated from the force of the drive shaft and the tire with bearings. It looks like the housing is separated from the force of the drive line force and the resistance force of the tires with bearings.

What causes the forces to act on the housing? How are the rotational forces imparting the resistance to the housing when its basically a housing for the axle and drive line supported with bearings? It seems like it should be a free floating bearing holder and its NOT. It does have some rotational resistance, and thats what we are talking about, the rotation of the axle housing. Its ALL new for me... Anyone have a simple explanation for the simple guy, ME.... JR

[JRouche]

Remove all preload on the sway bars. Balance cross weights.

If you have a change in ride height from one side to another you will have a different A/S from side to side. This will show its self under impulse loads.

I do have an issue with my rear sway bar. Its not great. My bar is not great. My mounts are the problem. They are not perfectly square so I have a slight amount of bind in the bar. Not severe, its noticeable though. Something I will have to fix but its not causing my rear end waggle. Thanks for helping. JR

[JRouche]

As you said there are so many variables with a 4link, in addition to other suggestions, tire pressure may need to be adjusted & unequal R/L pressure may be needed. Adjusting your IC may be needed.
Check out Performance Trends and there suspension analyzer, you will need a PC not a Mac
good luck & don't bend something!
www.performancetrends.com

Ill check the tire pressure. Im not that advance to get into the IC. Good advice but thats a lil beyond my capabilities. JR

[JRouche]

Nothing loose in the watts link? Is the rear stable laterally?

I had a TR7 that drove exactly the way you are describing...I for the life of me couldn't drive that car very hard without white knuckles. Short wheelbase and it felt like the rear end was loose in the links somewhere and wouldn't hold the rear laterally during hard accel and shifting to second without lifting almost guarranteed that I was going to be pointing in the direction where I just left from. Feels like it's steering from the rear.

The Watts link is still secure. I drove it 150 miles then checked ALL the suspension links and connectors. Everything is still secure and tight. Thanks for the help. JR

[Bryce]

https://www.pro-touring.com/showthread.php?55420-Air-ride-Watts-link-and-Sway-bar-build-(long)

here is a link to your build thread. Not lost.

[exwestracer]

Just out of curiosity, how are your rear bags plumbed? If they are tee'd, it may be part of your problem... Let's get back to that later.

Simplest way to look at what happens with the links under acceleration: Whatever the tires do, the housing does the opposite. Tires turn forward, housing turns backward. If the housing is trying to turn backward, the lower links are placed in compression, and the upper links are in tension. Only the lower links push the car forward in any type of link suspension.

That takes us back to the IC, which you said you weren't ready for yet...

[JRouche]

https://www.pro-touring.com/showthread.php?55420-Air-ride-Watts-link-and-Sway-bar-build-(long)

here is a link to your build thread. Not lost.


Ha,ha,ha.. You have MAGIC fingers my friend. I looked high and low and could NOT find the post. Yes, the link has changed, it used to be ok with the original link. But even doing some word specific searches I couldn't find it. Yer a master of yer craft. And thats speaking of your car work also, not only the ability to dig up info.

Thanks Bryce for digging up the new thread link.. Saved me some work of having to try and remember what to write for a new thread. Yer a life line buddy!! JR

[JRouche]

Just out of curiosity, how are your rear bags plumbed? If they are tee'd, it may be part of your problem... Let's get back to that later.

Simplest way to look at what happens with the links under acceleration: Whatever the tires do, the housing does the opposite. Tires turn forward, housing turns backward. If the housing is trying to turn backward, the lower links are placed in compression, and the upper links are in tension. Only the lower links push the car forward in any type of link suspension.

That takes us back to the IC, which you said you weren't ready for yet...

The air bags are independent. They have their own line and solenoid.

For the torque applied I understand the forward rotation of the tires produces a backward rotation of the axle housing.

What Id like to learn is WHY. Where is the torque point from the drive shaft to the tire contact on the road?

I didnt really get torque transfer till I was in the Navy. An enginemen showed me the torque thrust bearing for the main drive system. It was really cool. The ship had two LM2500 gas turbines feeding a massive reduction gear box then to the main drive line that drove the one prop. I had always thought the transmission was the focal point for the torque. NOT.

The way he showed me was the torque was transferred from the engines, through the gear box, down the line, to the prop and back to the thrust bearing that was securely mounted to the ships structure. He said ALL the thrust was applied to that. And yes, the main prop shaft was running through that bearing housing.

And it made sense at the time. But I still dont understand the torque or thrust point on a car. Where is it? Is it the ring and pinion gears, is it the pinion, is it the transmission or the engine itself?

I kinda understand the theory of torque transfer. And its NOT a theory for cars. The guys in the know can explain it.

I dont understand it. Id love to know in simple terms why the clockwise rotation of the drive shaft produces a clockwise rotation, or force on the axle housing with the tire resistance. Because I see the axle housing as not much more than a housing with bearings and a couple of shafts going into it. Forget about any limited slip centers, look at it with a solid center, like a solid spool.

What causes the housing to want to rotate clockwise (as looked on from the drivers side)? Where is the force felt on the housing to force it to rotate? It has to be in the center section, but its still free to rotate from the housing with bearings. There is no mechanical connection with the rotating shafts and the housing. There are bearings there. So why does the housing have any force? It does. But how? JR

[rossmacd]

It's the pinion trying to climb the ring gear. Ths pinion isn't 'attached' to the case, however it's still in contact with it, albeit with a bearing in between. The pinion climbs the ring gear on acceleration, imparting vertical force to the case, viola, you have housing rotation. It rotates clockwise as seen from the driver's side, which means the lower links push, the upper links pull.

[exwestracer]

That's it in a nutshell.

Let's say you had to pull something attached to a rope; so you throw the rope over your shoulder, dig your feet in and start pulling. Every bit of force you apply to the ground is also applied through your legs, up through your hip joints, spine, and finally at your shoulder where the rope is attached. The same is true with the car. All the force required to overcome inertia is applied at the rear tires, but the "equal and opposite reaction" of that force is applied at the ring gear, pinion shaft, suspension links, driveshaft and motor mounts.

[JRouche]

That's it in a nutshell.

Let's say you had to pull something attached to a rope; so you throw the rope over your shoulder, dig your feet in and start pulling. Every bit of force you apply to the ground is also applied through your legs, up through your hip joints, spine, and finally at your shoulder where the rope is attached. The same is true with the car.

I think you are correct and I was missing the force issue. I saw the floating axle housing being separated from the force of the drive line, and it IS!! There is NOT friction there to rotate the axle housing.

I think I am limiting my view of the entire process. The force that rotates the axle housing comes from the car body and NOT the drive line.

The drive line does NOT rotate the axle housing. The product of the force and resistance from the car body to move is what makes an apparent axle housing rotation. The axle housing doesnt rotate! The car rotates, or tries to. As you get on the power the car moves in a forward direction but also tries to move in an upward direction due to the resistance of the road. So as the car body tries to rotate clockwise (looking at it from the right side) under power the forces seen on the links will be like the axle housing is trying to rotate. But the axle housing CANT try to rotate, its separated from the drive line forces with bearings.

So... The body DOES try to rotate with the power applied. And the axle housing IS attached to the body through the links. So its NOT the axle housing that is applying the force to the links but it IS the body applying the force to the housing through the links.

Its like an after thought in a way. The force has to go from the drive line to the gear set to the axle, to the tires and road. The road resistance acts on the entire car and frame right to the links that are mounted to the frame.

So under braking the links will see a force and under power the links will see the opposite. The drive line itself DOESN'T impart ANY twisting force on the axle housing, the CAR does.

A light went ON here people!! I finally got it!! Thanks for all the help. You guys opened my eyes and now I see the process...

Thanks abunch... JR

[exwestracer]

Actually we do tend to look at the reaction force rotating the axle housing as coming through the driveline, if only for ease of making a mental picture. And the housing does move slightly before the car does, more or less depending on what type of suspension is under the car. Inertia is holding the car in place, and the suspension gives the pinion gear some degree of freedom to climb the ring gear. This "climb" is transmitted to the housing itself through the pinion bearings, and to the chassis through the suspension brackets and links. The only place the force is applied to the road is through the tires, so the cycle of motion has to start there. If you were sitting on ice, the suspension wouldn't load the chassis at all, because there is NO reaction force available.

That's why we don't worry so much about correct geometry on hot rods with skinny tires. They will typically smoke the tires long before they can generate enough reaction force to get the suspension out of whack...

BTW, this is also why a stick axle always has the potential to plant the tires harder on launch than IRS...note I said potential. The IRS has no solid connection between the pinion bearings and the wheel hubs, so it can't offer any anti-squat reaction force through the links to the chassis.

Merry Christmas. Enjoy your light bulb! :idea: