'Splain this, Lucy!

[Paul Workman]

Stability afforded by C-beam plates...Really??? How???:icon_scra

I'm not dissing the plates; they're worth every penny if for no other reason than to greatly simplify removing and installing the beam to do drive shaft, transmission, or clutch work.:thumbsup: But, forgive me for being dubious, I don't quite get it as far as the claim for improved stability goes. (Don't get me wrong! I'm not doubting anyone for saying they work in that regard; truth is where you find it: If in fact chassis stability is improved thru the use of the C-beam plates, then so beit...But is it really?)

The "thing" is stability (lack of movement) of the joints between the C-beam/differential and again at the C-beam/transmission joint - establishing a rigid relationship fore and aft (as it were). To my way of thinking, the friction between the C-beam and its respective joint contacts with the diff/trans is the key to the rigidity. So, as long as those joints do not move, I don't understand the dynamics of how capturing the bolts at each end of the bolts (with C-beam plates) affords any change in chassis stability as long as the contact between the beam and the diff/trans does not shift.

But, what if the joints are not entirely stable? How is having the plates going to change the chassis behavior then?:dontknow:

About the only thing I can think of is "cold flow" - (metal) displacement over time and pressure - the squeezing of the aluminum out from under the pressure of the bolts. A demonstration of the phenomenon (sort of) can be seen by anyone who has ever over-tightened the sheet metal valve covers on a SBC. The gasket "squirts" out from under the bolts - much the same as metal will do (if the pressure is great enough). In the case of metal fasteners, when a nut or a bolt is removed and there is a ridge formed around the circumference of the washer - some displacement (cold flow) has resulted. Do the steel plates simply eliminate the displacement (of the aluminum) and subsequent loss of tension, or is there more than that going on here?

Well, like I said...I'm not "casting dispersions" on the beam plates - I use them and recommend them myself. But, as for the claim of improving chassis stability?? Hmmmmm.... :icon_scra

P.

[RHanselman]

P.

I'm not going to claim I know how they work and frankly I don't care...

All I know is that after I installed the Beam Plates (on my First Z) the rear end stopped stepping out to the right when I launched at the drags. I have 3 more Z's that I've installed the plates on and each had the same result... Just my small sample size.


BTW - What I experienced is what Bill says in his website description. I had no idea it was in there however it's exactly as I've experianced...

From Bill's website:

These multi-purpose drive-line support reinforcement plates can be used on all 1984 through 1996 model year (C4 or 4th Generation) Corvettes. We have found that most C4 Corvettes inherently experience a slight amount of twisting at the fastening points of the support beam to the transmission and differential housing connection surfaces. Although fastened with high grade bolts, self-locking nuts and adhered with factory sealant, the drive-line components of the C4 Corvette still experience some level of counterforce load-induced lateral deflection between the members while under heavy loading. This allowance of flex in the drive-line beam fastening joints creates a condition where the chassis structure must additionally contend with. One common side effect of this phenomenon is where the rear of the vehicle tends to kick out to the right during aggressive high RPM gear shifting. Notice that the C5 or 1997 and newer Corvette was redesigned so that lateral deflection of the drive-line is practically non existent. The C5 Corvette drive-line consists of a drive shaft within a tube that has a bell housing fused to each end.

Q) How does lateral deflection between the drive-line members affect the vehicle handling?.

A) The immediate area of the drive-line beam around the bolt and nut heads where the beam fastens to the transmission and differential are prone t flexing a finite amount. With the slightest amount of flex or deflection occurring at these joints, counter-force torsion energy is off-loaded to the chassis. This brief spike of counterforce energy causes unnecessary deviation of the suspension planes. A brief change in the drive wheel thrust angles is the root cause for the C4’s inherent response of the rear end kicking out to the right when aggressively shifting during heavy acceleration.

Q) How do the C4 Beam Plates improve the vehicle handling?

A) By installing the ZR51 Performance C4 Beam Plates, the drive-line system becomes more rigid and less apt to affect the suspension system during extreme loading.

Bill's tightening procedure does not have you over tightening the bolts...

Tighten support bolts at carrier to 80 Nm (59 lb. ft.)

Tighten support bolts at transmission to 50 Nm (37 lb. ft.).

Hope this helps your delema...

Cheers,
RH

[ZR1Vette]

I am with Paul... just would like to hear an 'engineering' analysis of how they work...like Paul, not casting doubt just like to know the details. Also, I have heard that installing the plates reduces drive line vibrations...something about changing the relationship angle of drive shaft to output shaft...am I crazy and dreamed that up :icon_scra

[RHanselman]

Well you'll be waiting for a long time if you want the right answer...

Bill is not an engineer, he was looking for an easy way to re-install the bolts. It just happened that the plates had other benefits as well.

Unless you get get someone to do an scientific analysis all you will get is guessing, some of it will be educated and some of it won't... but, it will be guessing...

[XfireZ51]

I installed C beam plates on my 84 after 85K miles on it. Just looking at the C beam bolt holes it was clear it was moving around because the holes were oblong. I would think the plates assist in applying greater and more consistent clamping force across the interface between the beam and the trans/diff.

[secondchance]

I am not a structural engineer but generally when you beef up bolt to mounting area with a plate, plate will distribute any force/torque over wider area (area of the plate) resulting in reduction of localized flexing. I think the plate would definately make the whole assembly behave more as a single piece resulting in reduced twisting between trans to rear diff under servere torque.

[tccrab]

:dontknow:
They work.

/thread.

TomC
'Crabs

[WB9MCW]

the rear end stopped stepping out to the right when I launched

I FOUND THE SAME

I installed C beam plates on my 84 after 85K miles on it. Just looking at the C beam bolt holes it was clear it was moving around because the holes were oblong. I would think the plates assist in applying greater and more consistent clamping force across the interface between the beam and the trans/diff.

YES SOLVES THE DREADED OBLONG HOLE THING

I am not a structural engineer but generally when you beef up bolt to mounting area with a plate, plate will distribute any force/torque over wider area (area of the plate) resulting in reduction of localized flexing. I think the plate would definately make the whole assembly behave more as a single piece resulting in reduced twisting between trans to rear diff under servere torque.

YES SOLID NOW NO MORE FLEX LESS TWIST -- VERY HAPPY USER MYSELF

OUR PRESIDENT RON K IS A BIG PROMOTER OF THESE AS WELL

[rkreigh]

when you look at the beam it's "fish mouthed" at the mounting points

the beam plates better distribute the clamping and stiffen up the mounting

they also keep the bolts from digging into the soft alum and losing torq

plus as mentioned they make mounting up the beam MUCH easier by capturing the nuts

funny story when I first got the LSV, I was romping the car pretty hard, the rear end stepped out so bad that I hit my head on the glass and almost knocked myself out

after mounting the beam plates, that doesn't happen

one customer didn't believe it would work either (I was among those as well) Bill told him, well, mount them up, try them and if they don't work send em back.

he mounted them, they worked, took them off, noticed the difference, and put them back on!

honestly, if you never drive the car hard, you won't see any difference at all. if you launch the ZR-1 they help!

it won't keep you from spinning, or reduce wheel hop, but the car will track straighter.

nice mod, let me know if any of you need a set, bill gives me a bit of a discount

155 shipped, I think I have 3 more sets