New name and and new engine for Mina: an e30 for the GF

[Andy.B]

e28 3.25 diff is in, and rear coils are in:



I think I am going to cut up a hockey puck to make a better centering ring for the spring, but as it sits, the bump stop will keep it from falling out. I think that with shorter shocks (probably camaro rears), it will be captured nice and snug.

The e28 rear/e30 auto front driveshaft combo will fit. CSB mount is about 1.5 inches too far forward, but I may be able to just weld a bolt in place and bolt it in, as it still sits on the 'shoulder' type mount area for the CSB.

All that is left is to shorten the shift carrier and selector rod, bolt in the drive shaft, and weld the m30 downpipes to the e30 exhaust. Hopefully we will have it driving in the next couple of weeks.

[Mr. Tasty]

I'm not saying that. The material has its own properties that effect spring rate, but an inch of material X does not have the same flexibility as 2 inches of material X just because they are made of the same material.

I think you are over thinking this.

I figured flexibility would be the same for the coils after the dead coil, because of the similar vertical compressive forces. That's why I said I wanted to see actual force graphs, not that I doubted you. I understand Hooke's Law but I didn't think that would apply here.

[Andy.B]

No moment of inertia involved in a spring, but I can kind of understand your points. You are saying it has nothing to do with the material properties that would normally provide spring rates, but revolves around forces sitting on top of of spring coils?

I'm not saying that. The material has its own properties that effect spring rate, but an inch of material X does not have the same flexibility as 2 inches of material X just because they are made of the same material.

I think you are over thinking this.

[Mr. Tasty]

Think of a diving board. The farther out you walk, the bouncier it gets. When you get to the end, it will be drooping towards the water just by standing on it. It's because the spring rate of the board acting against your weight is lower the farther out you go from the fixed end. That is why driving boards usually have rollers underneath to roll towards or away from the middle. It allows the diver to adjust the diving board to their desired spring rate.

A coil spring works the same as a diving board. It's just wound into a coil instead of being straight. If you took that same piece of coil spring and straightened out out you would have a piece of metal with the same spring rate. By cutting it in half, there is less metal to flex, raising its spring rate.

You don't need real world testing. It is math. I know it can seem counter intuitive, but that's how it works.

No moment of inertia involved in a spring, but I can kind of understand your points. You are saying it has nothing to do with the material properties that would normally provide spring rates, but revolves around forces sitting on top of of spring coils?

[Andy.B]

Think of a diving board. The farther out you walk, the bouncier it gets. When you get to the end, it will be drooping towards the water just by standing on it. It's because the spring rate of the board acting against your weight is lower the farther out you go from the fixed end. That is why driving boards usually have rollers underneath to roll towards or away from the middle. It allows the diver to adjust the diving board to their desired spring rate.

A coil spring works the same as a diving board. It's just wound into a coil instead of being straight. If you took that same piece of coil spring and straightened out out you would have a piece of metal with the same spring rate. By cutting it in half, there is less metal to flex, raising its spring rate.

You don't need real world testing. It is math. I know it can seem counter intuitive, but that's how it works.

[Ether-D]

Whenever I am about to make a particularly questionable decision regarding a worryingly cheap diy solution, I just ask myself, "What would Ether-D do?"

I just lolled so hard. Thank you! I may have to sig that shit. Yep…

With money, being a badass is easy. With no money, being a badass takes skills bitches! (and a certain willingness to try just about anything)

[Mr. Tasty]

http://www.eatondetroitspring.com/cu...scalculations/

Interesting concept, I would love to see some "real world" testing with loads to test it.

[Andy.B]

Spring rates are an intensive property, why would halving a 10 inch 375lb/in spring double the spring rates? With the lb/inch rate, you are goings to have two, 375 lb/inch springs now.

http://www.eatondetroitspring.com/cuttingcoilspringscalculations/

[efficient]

oh my that strut. must suck living in ny and owning a rusty car.

[Mr. Tasty]

Spring rates are an intensive property, why would halving a 10 inch 375lb/in spring double the spring rates? With the lb/inch rate, you are goings to have two, 375 lb/inch springs now.

[jt223539]

Any pictures of what you are doing on the rear for adjusters? I am looking for a affordable way to get adjusters in the rear of my e30, and you may have the solution I am looking for.

[Andy.B]

Hell to the yes.

Whenever I am about to make a particularly questionable decision regarding a worryingly cheap diy solution, I just ask myself, "What would Ether-D do?"

[Andy.B]

Update: ordered a 10" 375# spring from summit on sale for $32.50.

$47.88 for the 2.5" coilover kit
$32.50 for the rear spring(s)
= $80.38 for a coilover adjuster kit with 550# front and 750 rear springs.

[Ether-D]

Hell to the yes.

[Andy.B]

To solve the first problem, I took a two pronged approach:
Step one: wire wheel all the dirt and rust off the strut housings up front to minimize the interference.
Step two: get creative with some sand paper and to open up the ID of the adjuster a tiny bit:



I taped a strip of sandpaper to a socket that just barely fit inside the adjuster, wrapped the sandpaper around the socket, stuck it inside the adjuster, stuck it on an impact wrench, and pulled the trigger. After a few minutes, and a cloud of aluminum dust (wear a respirator if you attempt this) I had a slightly larger opening on the sleeves.

I then put a little grease on the strut housing, and drove the sleeve down onto the strut housing. It took a little elbow grease (probably should have spent more time sanding), but I got the sleeves seated snugly on the strut housing.

The next issue was to fix the length issue. This was easy enough with a cut of wheel... I just cut it down even with the top of the strut housing:



The final issue up front was that the hole in the spring hat is small for the e30 strut inserts. This was easily fixed with a 37/64ths drill bit:



A quick check of the fit of everything:



Everything looks good, so it's time to toss the spring on and bolt it back together:



The front is buttoned up, but I still have to tackle the back end. Fortunately, the rear is a much simpler job. I just need to get some 4 to 5 inch springs and cut the adjuster down to fit. In keeping with my theme of bad judgement driven by a lack of money, I am going to buy an 9 or 10 inch 400#ish spring, and cut it in half to end up with two 800#ish springs.

All in, I'll have spent about $105 and 4 hours of my time to end up with a coilover kit for the e30 (not counting shocks). While it's not an easy bolt on job like GE or GC coils, it will work just the same.