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I have a lowering spring which came with 2 cars I purchased 30+ years ago. I am trying to determine the drop of this spring. The photo shows the arch from the bottom of the spring eye to the center of the spring. Does this help or is there another way to determine the drop?
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1973 Opel GT
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How much a spring lowers the car requires it to be installed. If you upload a pic of the whole leaf spring, we can probably tell you roughly how much lower the front end will be. Opel GT Source has an image comparing stock vs 1” vs 1.5” drop leaf springs. The larger the drop, the flatter the spring.
 

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A couple of things affect the ride height with the transverse spring. One is the spring’s arch, the other is the spring rate. Without knowing both, there’s no way to guess the final ride height.

However, that said, most of the GT springs that were on the market in the 1980’s and 1990’s had a 1.5” drop.
 

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I get dropping the front end, but does it improve handling? Thanks
It is a lot stiffer than stock. So it will improve handling.
 

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I get dropping the front end, but does it improve handling? Thanks
Yes and no. Just making something stiffer is no guarantee it improves handling. The GT already understeers badly by virtue of bad suspension geometry, and from the binding of the stock leaf spring.

That said, the lowering spring has one thing going for it. It’s nearly flat. So it doesn’t bind like the OEM spring, which pretty much goes solid.

Other considerations when using a lowering spring are:

1) Did you trim the bump stops? If not, the standard bump stops very nearly touch the control arm with a lowering spring. Which means that once the bump stop starts to impact the arm, it becomes the spring…

Therefore, either cut-down bump stops, or shorter aftermarket bump stops are mandatory for any lowering spring.

2) Did you install shorter-travel shocks with higher rebound dampening? Off the shelf KYB’s, though stiffer than stock, don’t have enough dampening to to control the higher spring frequency. So ride and handling are actually worse with softer shocks. (Note, compression dampening does NOT need to be increased).

3) What has been done to correct alignment? Camber? Caster too…

4) Bump steer. A stock GT has it. A lowered GT is absolutely horrible. Racecars normally measure bump steer in 1/16” of an inch. Lowered GT’s have darn near an inch of bump steer throughout the front suspension’s travel. It’s literally one of the worst cars on the road in this regard.

High offset wheels exaggerate the negative impact from the skewed steering geometry.
 

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Bob:
I have read several older threads that reference a "kit" you put together to improve the front suspension on a GT. I believe it consisted of some gussets and brackets that need to be welded. Do you still offer something like that?
 

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Bob:
I have read several older threads that reference a "kit" you put together to improve the front suspension on a GT. I believe it consisted of some gussets and brackets that need to be welded. Do you still offer something like that?
I used to sell a Manta/Ascona gusset kit. My neighbor in my old rental shop had a CNC plasma cutter and used to cut out sets for me. He later upgraded to a much faster/more accurate CNC laser cutter, but the NC formatting/programming was completely different, therefore my original patterns were lost forever.

Last year Keith Lundholm asked my permission to replicate my old kit, which I said okay to. He apparently had one of my kits from around ten years prior to sczn

I never sold a GT kit, though I did generate a couple of one-off kits for one of my cars and a friend’s. Years later, OGTS sold a kit which was sold by Splendid Parts, and marketed as a ‘Steinmetz’ kit. Ironically, it was VERY close to the reinforcements I developed back in 1992 for myself. I’m not saying it was a copy, but it was darn close. And I’ve never seen an actual set of those reinforcements on a period-correct Steinmetz GT.

Given that I freely post pics of the stuff I build, it’s possibly an updated copy of my stuff. Maybe, maybe not. I don’t care either way, otherwise I’d have never posted pics.

I believe Keith Lundholm also made a batch of these GT kits last year, as OGTS and Splendid were out of stock for an exceptionally long time.

There’s a whole bunch of other GT suspension mods and upgrades I do too, but I usually don’t get too technical disclosing specifics there since a lot of it is beyond an average tinkerer’s garage capabilities. Not everyone mind you, but most folks…the consequences of doing it wrong can be dangerous. It’s not a safe place for hand drills and 110-volt flux-core welding!
 

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1969 Opel GT 1.9L.
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4) Bump steer. A stock GT has it. A lowered GT is absolutely horrible. Racecars normally measure bump steer in 1/16” of an inch. Lowered GT’s have darn near an inch of bump steer throughout the front suspension’s travel. It’s literally one of the worst cars on the road in this regard.
Is a b/s gauge relatively common in alignment shops, or are they mainly seen in hi-po racing shops?
 

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Is a b/s gauge relatively common in alignment shops, or are they mainly seen in hi-po racing shops?
Race shop only. Production cars have no bump steer adjustability, so a repair shop has no reason to check it.

Race cars are often designed with adjustments in mind. A bump steer gauge usually consisted of a small hydraulic jack to cycle the front control arms up and down (with spring removed), and a plate that bolts to the hub, with another plate and two dial indicators to measure toe movement during suspension cycling.

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Wow, quite a scathing review of GT's there by Bob.

Personally, I LOVE the 1" lowering spring and I consider it to be one of the ESSENTIAL first mods all GTers should do. The stock GT spring often suffers from the "55mph shimmy", the steering mysteriously starts to shake or vibrate as you transition from 50 to 60mph, then mysteriously goes away after 60mph. The stock spring also goes absolutely nutz when driving over stutter bumps or lots of small bumps close together. Stock GT's seem to bounce when you press down on the fenders and the front end can severely dive going over dips in the road. The 1" spring don't bounce. I also use the KYB heavy duty shocks and love them. Just my opinions and experience......
 

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Wow, quite a scathing review of GT's there by Bob.

Personally, I LOVE the 1" lowering spring and I consider it to be one of the ESSENTIAL first mods all GTers should do. The stock GT spring often suffers from the "55mph shimmy", the steering mysteriously starts to shake or vibrate as you transition from 50 to 60mph, then mysteriously goes away after 60mph. The stock spring also goes absolutely nutz when driving over stutter bumps or lots of small bumps close together. Stock GT's seem to bounce when you press down on the fenders and the front end can severely dive going over dips in the road. The 1" spring don't bounce. I also use the KYB heavy duty shocks and love them. Just my opinions and experience......
Really. My Gt had the 55mph shimmy. When I drive it around I usually go like 50mph so it doesn’t shake. But in Springfield when I got on the highway for dinner and going like 65mph it didn’t shake. Charles thought it was the old bushings. But you say that it is the spring? Well maybe I need to order a lowering spring someday.
 

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While I quite detest the phrase "...from what I understand or have been told..." , in this case, as I understand it, the "55 mph GT shimmy" is related to a natural harmonic generated in the GT's front lower control arms. That became "known" to Opel engineers, and they implemented a fix for the 1972 model year. They changed the lower bushings on the front LCA's, by making the inner sleeve a bit thicker. That resulted in the rubber in the bushings to be slightly thinner.

The result was to stiffen the front LCA's bushings, which moved the harmonic frequency (stiffer would presumably make it a higher frequency).

Installing urethane bushings in the front LCA's eliminates the 55 mph shimmy. But the sleeve bushing thickness (actually the sleeve OD) must be known so that the correct urethane bushing ID is installed.
 

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We installed the 1" lowering spring on the front and the lower coil springs on the rear. Koni reds on all four corners. Poly bushings.
I'm with Gordo, we both love the steering response. We probably don't drive it hard enough to notice the b/s.
 
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