[FC] FC Transverse Spring

[Dale Dewald]

At 12:39 12/15/2008 -0500, RoboMan91324 at aol.com wrote:

>I am not challenging you but your answer raises another question.  If the
>side to side difference in rear springs on the '64 model cars was to 
>compensate
>for engine offset, why were the springs on pre '64 models the same?  Did they
>change the engine offset in the '64s?

All of the 60-64 cars were slightly heavier on one side (the driver side I 
assume) because of engine offset, driver weight, etc--by maybe 100 lbs or so.

Consider this: The EM Corvair weighs about 2400 lbs and has a 40/60% weight 
distribution F/R.  That means the rear suspension supports about 1400 lbs. 
With the 60-63 design, each rear coil spring is supporting approximately 
700 lbs. If we take 60% of the imbalance (the amount supported by the rear 
suspension) the left rear spring will be supporting 60 lbs more than the 
right rear. Therefore the difference in spring compression between the left 
side holding--say 730 lbs and the right holding 670 lbs--is less that 10% 
of the total load and apparently not large enough to be noticeable.  Ken 
Hand states that the '64 traverse leaf spring supports about 40% of the 
rear suspension load, or about 600 lbs.  In this case each rear coil spring 
would have to support only about 400 lbs.  An 60 lb difference from side to 
side, 430 lbs left and 370 lbs right, is proportionally quite a bit of 
difference and apparently makes a very noticeable side to side difference 
in ride height; therefore the need for different rate springs.

>To answer your question, another list member wanted to know how to use a car
>transverse spring on an FC.  I can't answer for him but it may be that he
>already had the '64 car springs and wanted to improve the FC's handling.

The track width of the FC is greater than the car (I think by 2 inches), 
therefore a car traverse spring will not fit.  However, any decent spring 
shop should be able to make a custom leaf spring that is 2" longer.  It 
would help to bring a car leaf spring along and say, "Make one just like 
this, except 2 inches longer."

>   As for
>myself, I already own an aftermarket transverse spring for an FC and would
>prefer to use it eventually rather than buy new equipment.  Obviously, 
>this would
>be the most attractive alternative if I do not need to modify coil springs
>etc.

Are you sure what you have is a traverse leaf spring and not a camber 
compensator?  If you installed a transverse leaf spring with stock coils 
the rear ride height would be greatly increased, creating excessive 
positive camber and overall poorer handling.

>   Since the subject of using a transverse spring on an FC came up, I had
>hoped that someone on the list would know the aftermarket FC spring well 
>enough to
>advise me on coil springs etc.

I do not think much information is available, other than how the '64 car 
was set up.

This is how I would build a '64-style FC rear suspension:
1) Make sure my FC has a '64 style differential housing.
2) Obtain a set of 60-63 car rear springs.
3) Obtain the '64 traverse leaf spring mounting hardware. Modify the A-arms 
to accommodate.
4) Measure the empty rear ride height of my FC on level ground.
5) Add 500 lbs of weight (bags of cement, Sand-in-a-Tube, etc) to the 
vehicle directly over the rear axle.  Measure ride height again to obtain 
the effective installed spring rate.
6) Remove FC springs and install car springs.  Repeat steps #4 & 5 to 
calculate the spring rate for the car springs.
7)  Use the difference in spring rates to determine the spring rate needed 
for a special FC transverse leaf spring.  Take this information to a spring 
shop along with a car leaf spring so they have some idea of what is needed. 
(Remember that the FC spring will need to be 2" longer)  Have them make a 
custom spring.
8) Install the custom spring but be prepared to have a second spring made 
up in case the first one does not quite meet expectations for ride height.
9) Make sure to install an ADCCO front anti-roll bar to compensate for the 
reduced roll stiffness of the transverse leaf '64 suspension design.

Dale Dewald
Hancock, MI