Rear Camber in a Live Axle Car

[bsim]

Actually Keith, we don't differ there either. I'm one of the ones that want full disclosure of everything (no secrets on my car) - and yes, I was jazzed when I got sent to the dyno at Buttonwillow.

 

I dunno, maybe I'm a little too paranoid about the unanswered tech question, but at least we don't have a 'formal protest' clause in our rules.

 

WTF is this 'carpet pad' protest? That's BS, and the kind of crap we have to avoid. 270 HP on the dyno is one thing, but that's another altogether.

 

Is my car legal? 100%, you betcha. But then again, I've never measured rear camber and toe. Better check that...

 

Nice segue back to the original point of this discussion, huh?

[Keith]

Yeah, I would never protest on the amount of carpet in a car. Period. However, that's only me and I will never underestimate the power of frustration when someone doesn't finish as well as he/she feels he should.

 

The issue of inspection isn't an "issue" in my mind. If you have no doubts that your car is legal when you show up, then it's a matter of registration procedure and nothing more... In our regional events, I really don't care all that much. However, in a National event, I am hopeful that we are all comfortable that the cars on the track are legal. I want to see what sort of spread in lap times we can see in CMC and we've never had the opportunity to check this in our local events. Yet...

 

BTW - NASA's CCR does indeed have a protest procedure. I have only seen it used twice in three years (in both instances it was in AI).

 

I am still interested in tech - I want to make a genuine effort in making the car better while minimizing the risk of rendering the new rear useless to me. Anyone?

[mitchntx1548534714]

Does tech ever measure the camber in the rear at the CMC races?

 

 

 

... at an SCCA Runoffs, and presumeably a NASA National event, you better meet the letter of the rules in every category. I doubt that any regional NASA event has the capability of accurately measuring the rear camber within 1 degree, let alone less. However, at the NASA National I expect nothing less than pin point accuracy on any measurements taken and the opportunity for competitors to check their cars beforehand to insure compliance.

 

So, should he get it close or spot on?

[Richard Pryor1548534703]

I adher to the SCCA standard when it comes to exact specifications and legality....if the maximum spec is 1.0000 you CANNOT legally be 1.0000000001....with all measurements that are specified the extreme measurements are just that with NO extra tolerance...in this case if rear camber exceeds the maximum allowable by ANY amount, it's illegal so my advice to those who are concerned with exact legal specs to keep within the rules...and my advice to those who go to any CMC weekend I've attended, I wouldn't worry about an extra .25 degrees of neg camber as I no one I've encountered at a CMC event would protest you and no tech or impound I've seen would DQ you as they have never measured rear camber/toe (they had enough trouble with the front)...it all boils down to two philosophies as I've outlined above...me, I'm easy going and relaxed in everyday racing, but when a title is on the line, I'll make certain everything passes teardown...I won three Pacific Coast Road Racing Championship titles in Camaros with SCCA (these were one race end of season West Coast shootouts) and two of the three wins ended up in teardowns all the way to the inner engine block! just like the Runoffs and all the suspension and rear too...the first one in 1990 took over 6 hours in impound to be cleared....and I won...same two more times....but, no longer would I be interested in sticking around at a cold and windy track tearing apart my car...just personal taste and experience...been there done that and now in my old age I just like to come out and watch the pretty cars go round and round...rp

[Al F.]

Richard, you gotta get out of Carmel more often. Those half caf double caramel mochas are getting to you. On the west coast we've done rear axle camber checks twice with a random set of cars (ie, not post race inspection) just for courtesy. I wouldnt be surprised to see this happen on a regular basis during tech from now on...and .25* is not close enough.

 

Keith...back when I was building little off road cars we used to bend the tubing for the cages by making "molds" out of wood, then heating the tube and bending it around the mold. It worked great in the absence of a real bender. You could apply the same logic here: make a housing bending jig out of a steel beam and some other metal parts. Have you called around and priced this out? My understanding is it isnt that expensive if you dismantle and reassemble the thing yourself.

[Keith]

Now we're getting to where I am headed. I am wondering if I shouldn't let some one who has done this before do it for me.

 

The Herb Adams procedure (in a nutshell) states that heating 6 inches cherry red should be enough for -0.5 degrees. For safety, I was thinking that I should simply heat 5 inches. The problem with that is that the rear may already have negative camber to start and I guess I need to check first. Maybe I need to make some precise measurements and do the math to convert from length to degrees by measuring the top and bottom distances between the brake backing plates.

 

Al, maybe a way to remedy a mistake would be to use the technique that you describe.

 

My alternatives are:

1) Check with the local speed shop that specializes in f-bodies and vettes. Problem here is that they only seem to have experience with street and drag cars (when I did my dyno there last year, they were adding twin turbos to a C5 Z06)

2) Talk to the local cage builder. They do great work and might see this as a challenge.

3) Talk to Sam Strano - He has probably never done this but could do it. He's only about 3 hours from here.

4) Talk to the local SCCA race shop. The only problem here is that this shop is always filled with Japanese products.

[JKnight]

Keith, Nick had this done on his AI car and might be able to provide some data. I have no idea how this will translate to a CMC car, but thought you could use a point to some real data.

 

Jason

[King Matt1548534716]

How far are you from the lovely village of Phoenixville, PA? I hear there is a shop there with some experience building 4th gen F-bodies.

[mitchntx1548534714]

How far are you from the lovely village of Phoenixville, PA? I hear there is a shop there with some experience building 4th gen F-bodies.

 

Pheonix racing?

 

I saw their prepared cars ... I was NOT impressed.

 

No welds on the top of the halo bars, the wiring looked like a rat's nest, it would fuel starve with 1/2 a tank of gas ...

Edited December 21, 2005 by Guest

[King Matt1548534716]

I only mentioned them because I know this guy at GM who has had pretty good luck with their cars in the SCCA for the past few years.

[Keith]

I don't know where Phoenixville is but if it in PA, it can't be more that 5 hours away, worse case...

 

The local f-body tuning shop recommended a rear end shop about 3 hours from my house.

 

BTW - picked up the rear and just got back to the inlaws a couple of hours ago. The guy threw in a spare, new gear set and a bunch of other stuff. I haven't been this happy since I got the Red Ryder under the Christmas tree as a kid.

[Richard Pryor1548534703]

Be careful..you'll shoot your eye out!....man, I love the movie CHRISTMAS STORY and the source matarial by Jean Shepherd...if anyone out there enjoys nostalgic ('40's/'50's) humour find a copy of WANDA HICKEY'S NIGHT OF GOLDEN MEMORIES on eBay for a buck or so...you'll be glad you did..or IN GOD WE TRUST ALL OTHERS PAY CASH...or at Amazon...only a few bucks each and hilarious (well, if you know my sense of humor that's a recommendation or warning)....rp

[jeffburch]

more info;

http://www.stockcarproducts.com/rear25.htm

 

jb

[Carson]

Hey rp. luv chinese for Christmas dinner or lickin da flag pole ?

or bendin your rear end part ...

[trackboss]

Clowns eh? Somebody sure has a big mouth around here. You may be right about the cars, I don't know, but unless you know someone don't shout out nonsense about them.

[kevin67]

Thanks Mitch. I thought you were a nice guy when we met that cold day in Dallas, alas I was obviouslly mistaken. Your comments on the cars may or may not be correct. Your comments On Keith and I are obviously wrong. You may now delete your post, if you care to keep some decorum.

[Keith]

Just to close this out.

 

I checked and Phoenixville is about as far away from here as you can get and stay in PA. Mapquest claimed 5.5 hours...

I checked with the rear end specialty shop about 3 hours from here and they make custom rears for street rods. The guy said that they have a rear straightener setup and never had actually bent one on purpose and he didn't know what to charge me (I actually didn't even ask). He suggested that they were busy and I should call in a couple of months. They didn't sound interested.

I talked to the local race/cage shop (one exit up the Interstate from me) and again they made me feel very comfortable to work with. I should have called them first. We are going to make up a jig and do this right on December 28th. I don't know why I didn't call them to begin with.

 

I plan on documenting this work for anyone that might be interested. Later on in the winter, I will also take the car to an alignment rack to confirm the setup on the car. I want to pick a time that there isn't so much snow/salt on the roads since I will either drive the car to the rack or take it on an open trailer. Two years ago, I towed the car to Akron for my annual tech in a snowstorm and I vowed to never do that again!

[Tri-Agan]

Richard,

 

Go to the following link to buy the funniest Christmas decoration available. You will have all your neighbors cracking up as they drive by.

 

It comes in the same huge wooden shipping crate "as seen on TV." You also receive a real telegram in the mail that says you won a special prize.

 

 

http://www.leg-lamp.com

 

See ya

 

Kent

[mitchntx1548534714]

Thanks Mitch. I thought you were a nice guy when we met that cold day in Dallas, alas I was obviouslly mistaken. Your comments on the cars may or may not be correct. Your comments On Keith and I are obviously wrong. You may now delete your post, if you care to keep some decorum.

 

How's that? Decorum been restored? I apologize if you took offense to my assessment.

 

And Kevin, I am a nice guy. I'm also very honest and opinionated ... my achilles heel.

[Richard Pryor1548534703]

Kent...ow, wow...I just emailed Santa that I WANT one of these...thanks for the post...it'll look great in the movie room next to the Maltese Falcon...I just had a great idea for the racer with lots of garage room...pick up a gutted, lousy condition Camaro, Mustang, etc....gut the interior to race standards, number and decal, bolt in a seat, roll cage and your extra set of dead Goodyear GSCS and install a 72" monitor on the hood and a computer in the passenger side and replace the steering column, shift stick and pedals with a computer set, plug in your favorite racing game and put on your nomex and helmet and belt yourself in....instant cool race game environment...hmmm...richard

[Keith]

I already do this with my current car.

[Tri-Agan]

Richard......I am cracking up. I love the idea of setting up a car just for racing on the computer. A few of the CMC guys out here have hooked up in the past racing on the computer and it was a blast. It would be great to have a cup holder with a bourbon and coke in a partial stang hooking up with the fellas doing race games. (My wife would probably think I was more nuts than usual, but so what, it's a lot cheaper than going to the track.)

 

What was this post about anyway? I saw the Christmas Story part and that was all I remember. I absolutely love that movie. By the way...if you have kids you may want to go back to the link and buy a bar of the genuine "lifeboy" soap that was in the movie. I don't want to pay shipping so I figure that Lever 2000 soap will suffice if my kids ever say the wrong thing.

 

I hope to meet you at the nationals.

 

See ya

 

Kent

 

Kent

[Pat Stone1548534713]

Yes we have been checked for rearend camber at the race track. I would make sure you are within the specs. I think they would DQ you on the west coast if you are not in compliance with the rules. I'm sure they will check most tech stuff at nationals. If we drive all the way out there to race you guys we want it fair and even for everyone. That's what makes CMC a great race series. Pat Stone

[Keith]

Just to close this one out, for the time being.

 

I cambered and toed the rear the day-before-yesterday and installed it on my car yesterday. We went with a piece of aluminum channel bolted to the brake backing plates as our measuring point. While we were looking for measuring accuracy in the range of 1/64", the tape measure only included 1/16" so there may be some error in all of this. The work will be will confimed when I put the car on a 4-wheel alignment rack in the spring. I suppose that there is also the possibility that the aluminum was not straight, but it looked pretty good to me.

 

First and foremost, we used the procedure as described in Herb Adams' book titled "Chassis Engineering" (page 81) for heating the axles tubes. We biased the heat a little towards the front of the axles tubes to get a little toe-in at the same time that we got the camber, though we didn't measure the toe change.

 

The owner of the shop took some digital pictures of what we did but I don't have them yet.

 

We put the rear end on 2 jack stands, supported as close to the brake backing plates as possible to encourage a little bending by the sheer weight of the rear end once the tubes were heated. We levelled the rear end-to-end then also used a floor jack to locate the pinion at the approximate angle that it would be when installed on the car. We marked both ends of the aluminum pieces 13" up from the centerline of the axle tube and 13" down from the centerline of the axle tube as our reference points. According to my calculations, reducing the distance between the top of the aluminum pieces and the centerline of the diff housing by 0.113 inches would be 0.5 degrees of negative camber, or the maximum that we wanted. It was clearly impractical to measure to the centerline of the diff so we only used the aluminum pieces. This meant that we were looking for a total change in distance between the aluminum channels of 0.226 (between 3/16 and 1/4 inch) with the assumption that shrinkage would be even per side. I hope our ASSumption is correct. We decided to shoot for 3/16 for safety and to account for the fact that this was the measuring resolution available to us.

 

The distance (both top and bottom) between the two aluminum pieces, both top and bottom, was exactly 63 inches to start - zero camber. This measurement included the width of the aluminum itself to give us a straight edge for accurate measurements with the tape measure.

 

On the first pass with the torch, we only did the passenger side and were very conservative. We originally decided that doing just one side would tell us what we would need to do to the other side. As we continued, it became obvious that this was going to take much more time than we had so we abandoned this approach in favor of trying to do the same thing to both sides in one shot later on.

 

Anyway, after the first pass and once the tube cooled back to room temperature, the change in distance was barely perceptible on the tape measure. So, we did a second pass and got more aggressive, yielding only slightly more movement after cooling. On the third pass, we ensured that we got more of the circumference of the axle tube itself and hit both sides at the same time. Still not as much shrinkage as we were looking for after cooling. So we put an old engine block on the engine stand and sat it on the diff housing to encourage more (clock was ticking and the day was passing us by).

 

With the final agressive heat and the additional weight on the housing, the tape measure showed somewhere between 3/16 and 1/4 of change. This was much closer to the limit than I wanted to be but the time we were spending was getting to be a bit much and we got a little aggressive on that last pass. According to my calculations, I should be right around an average of 0.5 degrees of negative camber per side assuming that the change in dimension was symmetrical on both sides.

 

It appears that Herb Adams' rule-of-thumb that 6 inches of heating should yield 0.5 degrees of camber is near correct. In our case, we needed to put some weight on the diff housing and this helped more but it's hard to say how much was due to more aggressive heating and how much was due to weight since we did both simultaneously.

 

Like I said, the only way to know for sure is to put it on a 4-wheel alignment rack in the spring.

[Al F.]

Fabulous info. Make sure you let us know what happens when you get it on the rack.