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Old 03-16-2012, 07:07 PM   #1 (permalink)
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How Do You Tune Rear Suspension??

Out of every leaf spring car I've ever seen at the track, I have never seen one react like mine does. Whenever I hit it, the rear end rares up and stays up until a gear shift, then it drops a bit, and rares right back up under power.

I'll post some videos that I've taken over the past year or so but first, here's my setup.

-351W with a World Class T5
-aluminum driveshaft
-Nodular 9" 4.30 28 Spline Detroit Tru-Trak
-255/60/15 Drag Radials with usually 17-20psi
-Caltracs (about a full turn of preload on both sides)
-9-way adjustable Calvert Racing shocks (setting: driver #6, pass #8)
-slap worn out stock leaf springs

Here is the link to all of the videos of my car.
Pictures by hepcat351 - Photobucket

The rear of the car is not supposed to come up is it? Unfortunately I've had very little time to play around with the rear suspension of the car as I only make it to the track maybe 3-4 times a year. I have tried to go both ways with the shock setting and I've only been able to make it worse i.e. spinning and a slower 60'.

I'm going to try and make it out to the track hopefully sometime toward the middle of May, if school and work permits, and I'd really like to have an idea on what to look at to get the rear end planted, shave my 60', and possibly get both tires off the ground









Thanks in advance to all you guru's out there!
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12.63 @ 107mph 1.70 60'
-3 '66 Fairlanes - soon to be 1...one day
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Old 03-16-2012, 07:15 PM   #2 (permalink)
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Re: How Do You Tune Rear Suspension??

Almost forgot, here is a quick pic of my last/PB time slip so yall can get an idea of what times it's putting down.

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-69 Mustang - 351W AFR 185, Vic Jr, .512 @ 232, 750 Holley, WC T5, 4.30 TruTrac, CalTracs
12.63 @ 107mph 1.70 60'
-3 '66 Fairlanes - soon to be 1...one day
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Old 03-17-2012, 03:57 AM   #3 (permalink)
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Re: How Do You Tune Rear Suspension??

I see nothing horrible about the way your car launches. It does have some separation, but at least its in the right direction showing that the body is moving forward at launch-that tells me that the car is trying to plant the tires hard. What you don't want it to do is squat.

You could try loosening the shocks a click or 2, but watch for wheel hop/wheel spin. Not sure how that will affect your radials during launch though. Also, anything you can do to help the front rise more will help too at the car would shift more weight to the rear.

Calvert would like to see a full 5" of lift for the Caltrac system to work properly. That comes back to 90/10 shocks, light coil springs, roller spring perches, and removing or disconnecting 1 side of the front sway bar. You should also remove any excess weight from in front of the driver or move it to the rear, such as putting the battery in the trunk.

Someday borrow a set of bias slicks with rims to try at the track. You might be surprised how they work at launch and their consistency.

I also suggest that you paint a line on your rear tires and also train you photographer to zoom in and film your car as close as possible and from different angles (both sides and rear) as a diagnostic tool so you can see more of the what has gone on during a run. That, along with the corresponding timeslip, can tell you the results of any tuning that you have done.
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My little 65' Stang street car:



Dart 428W NA, 4 Spd, 4:33, on pump gas pushing 3550lbs.

10.553@127.81 with a 1.466 60'

Last edited by dennis111; 03-17-2012 at 04:13 PM.
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Old 03-17-2012, 05:35 AM   #4 (permalink)
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Re: How Do You Tune Rear Suspension??

"Slap worn out stock leaf springs"

Well there's your problem. The body separation isn't too bad. I've seen worse. As dennis said, the motion is in the correct direction. You just need to control it a little better. A new set of leaf springs could help out a lot. I would suggest calling Calvert and get a suggestion from John. He sells some nice mono leaf springs or you could go with another muti leaf set but I'm guessing you need to be stiffer with the springs. Also making the rebound stiffer on the rear shocks will control the separation better with your loose springs.
Once you get the rear springs stiffened up you will probably need to back off the preload from the caltracs and shocks. Then you will have some adjustability to tune to track conditions.

As for the front suspension you need it to be free moving. 5 inches of travel measured at the wheel well. If you have adjustable shocks in the front they need to be set on loose. Then adjust stiffer from there as needed.
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Old 03-17-2012, 08:12 PM   #5 (permalink)
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Re: How Do You Tune Rear Suspension??

I've already moved the battery to the back, removed the heater core/evaporator unit, removed the sway bar, and I have 90/10's in the front. I have a set of set of 28/10.5 slicks that I have run at the track once, but that's all the action they are seeing until the T5 gets swapped out for a TKO600.

As of last weekend, I'm picking up the LF tire a few inches so I guess I've got 5" of travel.

Yesterday at work, a customer told me about a '66 6cyl parts car he has and said I am free to have the front coils. Will these fit/work okay in a '69? That's the only thing I can think to snag off of it. I might see about getting the spring perches and building my own roller perches.

I'll also see about backing the shocks off 2 clicks or so. I'm currently saving up for a TKO600 and I'm about halfway there. If the T5 holds up, I might just use some of those funds to get some mono leafs from Clavert. We'll see..
Thanks again guys.
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-69 Mustang - 351W AFR 185, Vic Jr, .512 @ 232, 750 Holley, WC T5, 4.30 TruTrac, CalTracs
12.63 @ 107mph 1.70 60'
-3 '66 Fairlanes - soon to be 1...one day
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Old 03-18-2012, 04:04 AM   #6 (permalink)
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Re: How Do You Tune Rear Suspension??

Quote:
Originally Posted by hepcat69 View Post
As of last weekend, I'm picking up the LF tire a few inches so I guess I've got 5" of travel.
Cool to be getting the wheels up, but that is not an adequate test. You need to actually measure the wheel well clearance difference by jacking up the chassis on both sides.

Quote:
Originally Posted by hepcat69 View Post
Yesterday at work, a customer told me about a '66 6cyl parts car he has and said I am free to have the front coils. Will these fit/work okay in a '69? That's the only thing I can think to snag off of it. I might see about getting the spring perches and building my own roller perches.
I believe that they physically fit-just have a different spring rating. The price is certainly right to do some experimentation.

Quote:
Originally Posted by hepcat69 View Post
I'm currently saving up for a TKO600 and I'm about halfway there.
Thanks again guys.
The TKO is tough, but it will not shift like the T5. They typically don't like high speed shifts without being internally modded. Also it will require some severe mods to your transmission tunnel to accommodate its size AND to get the driveshaft angle right. Do your research.

A Gforce or Astro upgrade for the T5 (or even a wide ratio toploader) might be a better choice for less overall work.
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My little 65' Stang street car:



Dart 428W NA, 4 Spd, 4:33, on pump gas pushing 3550lbs.

10.553@127.81 with a 1.466 60'
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Old 03-19-2012, 08:00 PM   #7 (permalink)
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Re: How Do You Tune Rear Suspension??

It looks like too much seperation to me. Clamping each leaf in front of the axle will help. Moving to the top hole will help too if it is not there already. Mine has the same problem. I clamped the springs since the video and also moved to the to top hole. Hopefully in the next couple months I can retest with a little more power. You don't get much weight transfer if the rear raises as much as the front.

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Old 03-19-2012, 08:23 PM   #8 (permalink)
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Re: How Do You Tune Rear Suspension??

The rear lifting is a function of the lifting point of the suspension....in other words, "instant center". On leaf sprung cars, IC is usually at the front spring eye. Caltracs can help and you already have them. But IC is still the spring eye, more or less.

When thinking of IC, think of pushing a fridge. If you push at the top, it has a tendancy to fall over. If you push at the bottom, you're trying to push the bottom out from under it, wasting energy and the top has a tendancy to fall backwards on top of you if pushed really hard and fast. Somewhere in the middle is where you want it. Just like rear suspension in a drag car.

Changing the position of IC can help a ton. However on leaf sprung cars, it's not so easy. About all that can be done is to get the front end up, transfer the weight and KEEP it transferred to the rear, which counteracts "anti-squat".

There are two things that had a major influence when I was messing with leaf springs in my Maverick. First....I limited front suspension travel. Sounds odd...kind of backward of transferring weight. However, limiting the travel helped the car to move forward, quicker, than using torque to lift-or "pitch rotate" the chassis. There was .15-ish in limiting travel, in the 60' alone. Seems like .2 or better 1/8 mile. The other major change that happened was going to a longer rear shock. I was literally separating so hard, so quickly that it was pulling the shocks to the limit of their extension travel. Found some Rancho's that had a little more travel and that helped. Later when I added some HP and torque, I put the stock length shocks back on and had NO problem after that. Mainly because it was planting the tires hard and lifting both front tires a little, and carrying them, which put all the weight on the rear anyway. Only problem is that hitting the rears that hard wears them out. Faster. Was lucky to get 125-130 passed out of them before they were getting inconsistent.


And finally...I backhalfed it. 4 link. Leaf spring problems were gone forever. Much more consistent, smooth, faster, predictable and easy to tune. And tires last longer at least for me.
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Old 03-19-2012, 08:23 PM   #9 (permalink)
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Re: How Do You Tune Rear Suspension??

Another thing you can do is add a main leaf to the pack. I got some free leafs off another 67 and robbed the main leaf, cut off the eyes and added it to the pack. If you can get video it will help a ton. There is a caltrac sticky on The Bullet with some sharp guys and lots of info.
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Old 03-19-2012, 08:32 PM   #10 (permalink)
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Re: How Do You Tune Rear Suspension??

Mavman, what tires, 60", ET, MPH?
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Old 03-20-2012, 08:11 AM   #11 (permalink)
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Re: How Do You Tune Rear Suspension??

Brian can I hire your camera guy?!

Dennis, I'm looking into going with the G Force upgrade. Do you know what all is involved, price and if the stock case will hold up? I emailed them but no response yet. I'd like to buy the kit and do it myself. One because its cheaper, and two, I'd like to get a full manual trans rebuild under my belt. I've done minor things like change shift forks and stuff like that but never spilled all the guts out and stuffed it back with new ones.

Also, I see what yall are saying about the leaf springs. I was thinking about clamping them but then again, I'm also looking at the Calvert mono leafs. I haven't thought much about limiting the front end on my car. I've seen it on plenty of other cars that were making a lot more power and going much faster. What did you use for a strap mavman? Where did you attach it?
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-69 Mustang - 351W AFR 185, Vic Jr, .512 @ 232, 750 Holley, WC T5, 4.30 TruTrac, CalTracs
12.63 @ 107mph 1.70 60'
-3 '66 Fairlanes - soon to be 1...one day
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Old 03-20-2012, 03:44 PM   #12 (permalink)
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Re: How Do You Tune Rear Suspension??

Quote:
Originally Posted by hepcat69 View Post
Brian can I hire your camera guy?!

Dennis, I'm looking into going with the G Force upgrade. Do you know what all is involved, price and if the stock case will hold up? I emailed them but no response yet. I'd like to buy the kit and do it myself. One because its cheaper, and two, I'd like to get a full manual trans rebuild under my belt. I've done minor things like change shift forks and stuff like that but never spilled all the guts out and stuffed it back with new ones.
The T5 is not in my realm, but a friend of mine builds his own for racing and they seem to hold up decently behind his 408. He absolutely swears by the Hanlon Motorsports video which walks him through the rebuild, plus it offers helpful tips: T-5 | www.hanlonmotorsports.com

I suggest that you contact 289Nate with your questions as he recently acquired the Gforce gearset and is now in the process of installing it in his T5.
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My little 65' Stang street car:



Dart 428W NA, 4 Spd, 4:33, on pump gas pushing 3550lbs.

10.553@127.81 with a 1.466 60'
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Old 03-20-2012, 04:33 PM   #13 (permalink)
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Re: How Do You Tune Rear Suspension??

I'll get a hold of Nate and see what kind of light he can shed on the subject.

I've found a bunch of exploded views and how to's on how to disassemble and assemble the T5. I don't imagine it'd be much different with the new parts..
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-69 Mustang - 351W AFR 185, Vic Jr, .512 @ 232, 750 Holley, WC T5, 4.30 TruTrac, CalTracs
12.63 @ 107mph 1.70 60'
-3 '66 Fairlanes - soon to be 1...one day
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