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Discussion Starter #1
I mentioned in another thread that it is relatively easy to convert to rear coil-overs on our 105/115 cars for ride height adjustment and corner weighting. Since I had a few PM's with questions, I thought I'd just start a new thread. Here's what it takes:

(1) remove the spring pan from the trailing arms. (2) weld on Coleman coil-over mounts (see picture) directly over the original shock holes on the top of the trailing arms. (3) Source an appropriate coil over shock with an eye mount at the bottom and a bayonet mount at the top. (4) Source coil-over springs in the rate that you think you need. (5) Fabricate an aluminum adaptor to bring the upper spring seat down to the size of your coil-over spring.

The attached picture shows the mount on the trailing arm.

Of course this would all be overkill for a street car, but well worth the effort for a race car or autocrosser. On my pretty-serious vintage race GTV, I am running Carerra (now QA1) 8264 shocks. These are an aluminum-bodied coil-over shock that are not adjustable, but are revalvable. The springs are 300 pounds in rate and 8-inches in length. Depending on your overall set up, you may need different shock valving, different rate springs, or even shocks with different compressed and extended lengths, so measure carefully before buying the shocks! A great side benefit of the conversion is that coil over springs are available in about any rate you want and are pretty cheap.

Hope that helps anyone considering the project!

Erik
 

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Erik,
Did you have to shorten your axle rebound straps at all, to keep the springs from falling out of their seats at full droop?

I had to do this on my car after fitting shorter springs, and I'm kind of upset about loosing droop travel. I'm wondering what it'll do for handling.

After many weeks of fiddling with various springs, I finally got my GTV sitting nice and low in the back (I know... it's just a street car, but now it looks cool!).

I ended up with 11- or 12-inch springs... about 160 lb/in. But with the stock spring perches, they need to be at least 13" long to mantain enough preload to stay in their perches with the stock limit straps. So, vanity taking precedance over function, I shortened the limit straps to keep my 12" springs slightly preloaded, and lost almost 2" of droop travel. Hmmm...

I still haven't driven the car (fuel system and steering are all apart), but I'm thinking it might create traction issues or sudden oversteer at the limit.

What do racers do?

George
 

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Discussion Starter #3
The limit straps on my car are long gone due to a rear end collision (previous owner!) and repair. It now has cables in place of the limit strap. With a coil-over set up, you can alway add a "tender" spring if the springs don't stay in tension. The tender spring goes under (or on top of) the regular spring. It has essentially a zero spring rate and will collapse entirely at ride height. But it will keep the spring in place at full droop.

Erik
 

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Ah... I see the cable in your picture now.

Roughly how much droop travel do you have? The stock amount, or less?
Can you give me an estimate... say, from center of rear axle to fender lip? (or from edge of tire to fender lip... but this varies with tire choice.)

Yes, I may need to convert to 2 1/2" springs with tender springs to get the right combination of ride height and reasonable street spring rate. Or... my limited droop travel might be fine, in which case I'm set already.

BTW, I'm actually using a set of Honda Accord springs in the rear (5" x 14" stock, about 135 lb/in), which fit the stock perches perfectly and are progressively wound, so they act a bit like tender springs would. I've trimmed 1 1/2 coils off to get the car lower and raise the spring rate to around 160 lb/in. Cost me $16, which is a nice way to experiment without spending hundreds for the usual Alfa springs.
 

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Discussion Starter #5
I have about 2 inches of droop travel from normal ride height position in the rear right now. I'd want more on a softer sprung street car.

Erik
 

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do you have any pictures of the top, or anymore pics of the process? Also where did you get the coilover style shocks?
 

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.. a question.. genericwood.. i have noticed you rear brake mounts.. are you using diff. rear calipers..i am using nissan 300 zx rear ..on closer inspection.. it looks like you are using front calipers of a 105/115 car..am i getting close:):)
 

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Erik,

Thanks for a great post. Your rear coil over arrangement looks tempting but the necessary trailing arm modification is prohibited under SCCA Autocross rules except in the Prepared and Modified classes. Cars running in Stock, Street Touring, Street Prepared and Street Modified classes must use stock shock attachment points. Too bad...

... Of course this would all be overkill for a street car, but well worth the effort for a race car or autocrosser...
 

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Erik,

Thanks for a great post. Your rear coil over arrangement looks tempting but the necessary trailing arm modification is prohibited under SCCA Autocross rules except in the Prepared and Modified classes. Cars running in Stock, Street Touring, Street Prepared and Street Modified classes must use stock shock attachment points. Too bad...
George
I thought that rear suspension work was virtually free- which is how you justify using the solid bushings... (this assuming a live rear axle, where the rules are pretty liberal for Street Prepared)

The way I read the rules- I can change upper and lower control arms, add or delete any, plus add or delete any later load hardware.

And if I change the lower control arms, then it seem to be logical that one could change the mounting style.... Perhaps I'm reading that wrong?

Eric
 

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Discussion Starter #10
That's what I was thinking Eric. "Stock attachment points" can be interpreted in many ways. I would interpret it to mean you couldn't change WHERE the shock attaches, but you could change HOW it attaches (i.e. stud versus rod end). Then again, I have been accused of "creative" rules interpretation before!

Erik
 

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Erik,
I saw your post on the other thread about, where you mentioned this set-up... Thanks for creating this thread. It is a very interesting alternative. There is another (older) thread in the Spider forum, where someone had custom coilovers (front and rear) made for his car, but the set-up was expensive. How long have you been racing with this set-up?

Best regards,
 

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Discussion Starter #12
Enrique, I had this on the car I crashed last Fall (no fault of the shocks!) for the last 2 seasons. The shocks I've used are Carrera 8264. The 82 is the shock series for the aluminum small body shock, the 6 is for 6" of stroke, and the 4 is the valving. They have been matched with 300 pound 2.5 x 8" coil-over springs. Again, the real benefit is easy ride height and scale adjustments.

As with the substitution of any aftermarket shocks not specifically made for a particular car. I would carefully check the ensure that the droop limit straps protect the shocks when they are fully extended, and that the suspension travel doesn't allow the shock to become fully compressed. Six inches of stroke should be plenty, even for a street car. But you really need to check it on each specific application.

As to the question on what the top looks like, it is a simple aluminum plate with a small lip on the top to center it on the sheet metal of the chassis, and a small lip on the bottom to center the spring.

Erik
 

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Hi Eric and Erik (or is it Erik and Eric?),

Sorry for the late reply, the BB was a little cranky yesterday. Here are some SCCA autocross rules vs. Erik's neat coil-over rear suspension for his race car:

"Shock absorbers
Any shock absorber may be used... mounting brackets which serve no other purpose may be altered, altered, or replaced provided that the attachment points on the body/frame/subframe/chassis/suspension member are not altered. The installation may incorporate an alternate upper spring perch/seat and/or mounting block (bearing mount). The system of attachment (for this) may be changed.

"Live axle suspension allowances:
1. Addition or replacement of suspension stabilizers (linkage connecting a De Dion to the chassis, which controls lateral suspension location) is permitted.
2. Traction bars or torque arms may be added or replaced.
3. A panhard rod may be added or replaced.
4. The upper arm(s) may be removed,replaced or modified, and the upper pickup points on the rear axle housing may be relocated.
5. The lower control arms may not be altered except as permitted under 15.8.C, or relocated (This is a bushing allowance, see below).

"Suspension:
Suspension bushings may be replaced with bushings of any type material (except metal) as long as they fit in the original location.... This does not autorize a change in type of bushing (for example a ball and socket replacing a cylindrical bushing)...the replacement bushing may not be changed to accomodate a spherical bushing involving internally moving parts....


As I interpret this, there is nothing that allows removal of the trailing arm spring pan and replacement with a mount for a rod end shock absorber. Further, there is no mention of anything that allows replacement of front upper/lower arms.

This is all pretty nit-picky, and there are SCCA autocross cars that don't comply with requirements. It kinda depends on where you sit in the results; first place cars tend to be scrutinized, while lower finishers don't get as much attention. While this is all supposed to be fun, the difference between winning and loosing is measured in thousands of a second so some people get really engaged in rules and regulations - especially at the national championship level. While Dee and I spend most of our time running SCCA events, I really like the AROC autocross/time trial rules where individual modifications have point values and classes are established at different point breaks (a little off topic there...sorry)



George
I thought that rear suspension work was virtually free- which is how you justify using the solid bushings... (this assuming a live rear axle, where the rules are pretty liberal for Street Prepared)

The way I read the rules- I can change upper and lower control arms, add or delete any, plus add or delete any later load hardware.

And if I change the lower control arms, then it seem to be logical that one could change the mounting style.... Perhaps I'm reading that wrong?

Eric
 

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Hmmm, looks like on the 2008 PCS, Prep 2, it specifies that shocks have to be in the stock mounting point and using the stock system of attachment. Erik, what shock do you run up front?
 

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Hi Erik

How many inches of bump travel do you have in the rear? Do you use the factory bump stops? Shock towers extended?

Thanks

David
 

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Discussion Starter #17
Pete, I haven't done much with front shocks yet. On the old car, I was running some steel-bodied Carerras that were on the car when I got it. On the new one, I'm going to start with some Yellow Konis I have.

David, with the set up I had on the old car, I had all the bump travel I needed. But I would have liked to have more droop travel. This was with a "doubled up" shock tower "cap" and shocks with 7" travel. I'm working out the rear suspension measurements on the new car right now. I will probably use some 1" shock extenders to give me more droop at the expense of bump. Again, 7" of overall travel should be way more than you need at the rear of a race car. But of course you have to be at the right point in that 7" range at ride height!

Erik
 

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Why are you worried about protecting the shock from full extension?. All the single seaters, etc. use the coil over shock to stop the suspension coming apart at full extension, ie. a jump.

My last club car just used the shock too on all four corners ... and it had a Ford beam axle in the rear obviously with coil overs ... no limit straps of any form on any corner (just like every other car I have seen with coil overs).

Best
Pete
 

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Discussion Starter #19
Why are you worried about protecting the shock from full extension?. All the single seaters, etc. use the coil over shock to stop the suspension coming apart at full extension, ie. a jump.
Pete
Good question, Pete. I previously protected the shock with a limit strap under the thought that shocks are expensive and limit straps are cheap! But on the latest project, I'm planning to run without limit straps just to make things easier. I assume most race shocks will handle the load. If they have decent rebound valving, they wouldn't hit full droop with too much speed anyway.

Erik
 
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