Front Spring Weight

[34ford]

Anybody have spring rate for the front coil overs on a 34 Ford coupe running small block, aluminum heads and aluminum radiator. Come to find out the chassis came with #350 which is to light as it's compressing the spring and ruining the bushings in the shocks and is causing the problem with the ride issue I asked about earlier in the summer.  Aldan site says  generally 400,  Heidt's says 450 if the 350 don't work. Just trying to get a real time weight from someone who might be running a front coil over setup.  The front end is a Heidt's Super Ride setup and they said the front end should have a heaver spring. Yogi's says they will get it fixed, just want to do this once not a lot of trial and error.

thanks

bob

[enjenjo]

Any place close that you can weigh the car? If you have the front weight, and the suspension travel, you can calculate the proper spring weight. I don't think changing the sprinds will help the coilover bushings, unless they are bottoming out.

[34ford]

I am going to weigh the car tomorrow.  Friend has a set of electronic scales so that will be the easy part. The guy from Alden seems to think the 350# are to light and I have them wound to tight causing the bushing failure. Also told me to mark the top of a coil with a grease pencil and then drive it and see if the mark shows up on the bottom of the coil above it. I have the lower a arms level or parallel with the ground.  Having it set that way I have 1" of thread showing on the bottom of the shock. They are 656 shocks with 9" springs.

[34ford]

Did weigh the car this weekend.  Neighbor just bought a nice set of digital scales for his drag car so we did it Saturday. Weigh on the front is #1336 and on the rear is #1352. So the scales tells that it is 49.7% on the front and 50.3% on the rear. Cross over weight is #1354/50.5%.

Did the zip tie on the shock shaft to see if it was bottoming out the shock and it was still about 1/2" down from the shock bumper on the shaft.

Put a grease pencil mark on the top of the coil to see if the springs were compressing complete down and did not find the mark transferred to the bottom of coil above it.

The shock has 13 threads showing below the shock which sets the bottom a arm parallel with the ground.

Shocks are 12" center to center on the mounting points as recommended.

The coils have about 3/8" between them as the car now sets. The fronts are #350 and the rears are #220.

Have to see what the tech guys say now. Must just be wound to tight and causing it to be too stiff causing a bad ride and bushing failure.

[enjenjo]

How far is it from the shock body at rest, and where the zip tie is after driving? This will give you the amount of suspension movement.

[34ford]

Here's a sketch. The shocks are aldan 656 which have a 3.5" travel.

There is 2.5" from the top of the shock to the bottom of the top mount.

The zip tie moved up 1.25" up on the shock shaft.

The balance of travel left to go before bottoming out is 1.25".

So in reality the zip tie moves to the center of the available travel length.

At ride height the shock is compressed 1".


thanks
bc

[enjenjo]

1 1/4" at the shock, is roughly 2 to 2 1/2" at the wheel, which is in the high range of what it should be. A bit stiffer spring wouldn't hurt. It does sound like there is some thing else going on that damaged the top bushing.

[34ford]

Frank,

Both the top and lower bushings were split.  

Think the rough streets around here don't help either. Some of the main ones are like a roller coasters.

[34ford]

Well talked to the guy at Aldan today and give him all the information and he says the #350 springs should be right. Should be 1/4 of the front end weight. Says there is something else going on and the bushings could be bad batch. I don't buy that theory, I think the spring are to compressed and there is not enough "bounce" in it to smooth out the ride set as tight as it is. I measured today and I can barely get a 5/16 drill bit in between the coils with the car setting on the ground.

Then I called Mike at Heidt's and talked to him and he says the springs should be #450 with the weight I have on the front end. I asked him about the heavier springs not having to be set so tight to get the a frame level and still having some "bounce" and he said that was true, although you'd think it would ride rougher with heavier springs.

So Yogi's is sending me a set of #450 springs and a return label to send the #350 back at no charge. They are great people to work with. It is 10 years this month since I got the roll in chassis and body from them.

So well see what happens with the stiffer springs and some new bushings.

to be continued

bc

[Rex Schimmer]

34,
If you jack the front end up and let the axle hang by the coil overs is the spring lose on the shock? Or have you had to "pre-load' the spring to get the ride height that you want? If you have pre-load i.e. you have the spring compressed by screwing the lower spring collar up and compressing the spring, then this pre-load has to be over come by the suspension travel before the spring starts to compress. Makes for a pretty rough ride an could be causing the bushing problem. The wheel rate related to the the spring is dependent on the motion ratio of the wheel movement to the spring compression squared. So if the the wheel moves 2 inches and the spring moves 1 inch the ratio is 2 to 1 and the wheel rate is therefore the spring rate divided by the motion ration (2 in this case times its self (squared) equals 4) So the wheel rate would be the spring rate divided by 4. So using your car as an example with approx 675 lbs on each wheel and if the motion ration was 2 to 1 and with your spring rate of 350 lbs/inch the wheel rate would be 350 divided by 4 = 87.5 lbs/inch. Using this number and the corner weight of 675 lbs the wheel, once the spring is seated would travel 650 divided by 87.5=7.4 inches before the spring held the weight and the spring would compress 3.7 inches. If your case is somewhat like this, i.e. your car ride height was to low and you screwed the lower spring collar up until you got the right ride height you preloaded the spring and this makes for a harsh ride and possible bushing problems. The cure is a heavier spring or a longer 350 lb spring. Measure the length of your lower control arm and then measure the distance from the arm bushings to the spring mounting bolt. Divide the arm length by the distance from the spring mount to the arms bushings and this is your motion ratio. From there you should be able to come up with a wheel rate that you want and also the spring required to give you that rate.  If the coil over is slanted at less than 30 degrees you don't need to consider the angle.

You mention that there is approx 5/16 inch between the coils when the car is on the ground, and I would guess that the spring probably has between 8 to 10 coils, this would certainly mean that the spring is not in coil bind, what you probably need to do is to add some spacers below the coil to do the inital ride height set up (get it close) and then fine tune it by turning the spring collar.  If you are preloading the spring to get the desired ride height you need to measure the length of the spring when you have the weight off of it  and then subtract that from the spring free length and that is the amount of spacers you would need.

Rex

Rex

[34ford]

Rex,

Or have you had to "pre-load' the spring to get the ride height that you want? If you have pre-load i.e. you have the spring compressed by screwing the lower spring collar up and compressing the spring, then this pre-load has to be over come by the suspension travel before the spring starts to compress.

Yes this is what I've been trying to explain to the Aldan tech guy.

The front end is a Heidt's Super Ride. It came set up on the rolling chassis with the 350 springs. I would think the geometry would be right and the right length of shocks.

Here's a pic of the front end.

bc

[Rex Schimmer]

BC,
This is going to be pretty rough but I took some measurements from the picture and it looks like the motion ratio squared is approx 1.8 so if you have 350 lb springs then the wheel rate is 350 divided by 1.8= 195 lbs/inch. This is probably pretty close that would mean that the suspension would compress, assuming that your wheel weight is 1/2 of the 1334 # front end weight (667#), approx 3.4 inches. You can check this by raising a front wheel off the ground, take the tire off and then set the front end back down on something like a wooden block that is either under the lower arm outer pivot of the spindle its self.

Looking at the picture it certainly looks like the spring is to long to allow you to lower the spring collar and add spacers. You may want to go to a shorter 350# spring. The other thought is going with either a 400 or 450 # spring. Going with the 400 # would put your wheel rate at 400 divided by 1.8= 222 lbs/inch which would then make the amount of wheel travel to be 3 inches which would raise your car about .4 inches with out preloading the spring. Going with a 450# spring would make the wheel rate 250 lbs/inch and the travel to compression would be 2.7 inches which would raise your car about .7 inches. Of course going to heavier springs does make the ride more firm but it does eliminate the preload which makes the ride very harsh until the preload is over come.

Rex
Rex

[river1]

OK while googleing "motion ratio" i came across this page maybe it'll help.

http://www.proshocks.com/calcs/imotion.htm

later jim