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Opeler
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Discussion Starter · #1 ·
Last night I attempted to swap out my rear shocks and rear springs. I figured it was time to refresh these suspension items because on my recent test runs after installing the Sniper unit, just trying to drive the car in & out of my driveway produced a rough ride in the rear, and I’ve felt too rough a ride for a while anyway....so what better time than now to make the switch!?

The shocks that were on the car were Monroe 5753ST shocks, and they were shot. I could take my hands and position them to any height I wanted and they wouldn’t move...anywhere from fully compressed all the way to full extension, they’d just stay there. I replaced them with KYB343039 shocks. Simple install, with the exception that the bushings were too thick to allow the shocks to be installed at the top. I had to trim down a bushing to allow the threads of the shocks to be visible andable to have the nut grab them. As you can see from the picture, the new shock has a much shorter top stud than the old one, and the difference in extended heights are quite noticeable as well. Old shock on the left, new KYB on the right in the picture below....

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The rear springs have me puzzled though. The old (have to be original) springs came out fine and they were very crusty and so were the spring seats and hats. One huge difference I noticed was the difference in heights of the old springs vs the new stock height springs from OGTS. The ones I took out measured ~11 1/2” and the new ones are ~12 3/4”. I attempted to put the new ones in but haven’t been able to gain enough clearance to fit the new ones in.

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I am concerned about how this will affect the ride height of the rear end. I’m wondering if I should try to go for a shorter spring knowing how much difference there is between what I’ve had in the car and what I was planning to put in. I am including a side profile picture of my car for everyone to see what the ride height looks like with original springs and Monroe shocks and if making the switch in springs will change this for the worse.

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Thanks for any useful info you could share or other input anyone may have...

Eric
 

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Note the closely-wound coils at the end of the OGTS springs. Those are essentially ‘dead’ coils, they do nothing except take up space. They aren’t active when under load, they will be stacked together tightly.
 
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Opeler
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Discussion Starter · #3 ·
Note the closely-wound coils at the end of the OGTS springs. Those are essentially ‘dead’ coils, they do nothing except take up space. They aren’t active when under load, they will be stacked together tightly.
Thanks for the reply Bob. So, you’re saying there’s nothing to be concerned about when it comes to ride height differences?
Appreciate all of your help!
 

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Just Some Dude in Jersey
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I find the stock rear springs to be just fine. I installed the lowering progressive springs in the rear and I now find that I bottom out the rear on speed bumps and dips easier. It looks like you still have the stock front spring. You should replace that with the 1" lowering,if you haven't already. It's a major improvement in handling. First thing I do to all my GTs. I also use the KYB's and like them. I've never tried the Koni reds. My new car has the Koni yellows and I'm told that the car will ride like an ox cart with them.
 

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First off, were the old shocks worn out (as in no restriction to jounce or rebound), or did they simply not expand? If those are the same as the Munro "Classics" I installed, they are not gas charged, and will NOT expand. Not worn out, just not gas charged.

Second, where did you get those new shocks? They do not seem to be the correct ones. What is the compressed height compared to the Munroe's? If they are too tall, they will not allow full travel (especially jounce) and might even cause the rear end to sit high, with no jounce. Too long a shock will allow the differential to drop too much, and the coils will fall out

Third, what is stopping the new coils from being installed? No need for a spring compressor. Simply disconnect the shocks with a jack under the diff, and the differential should drop WAY further than needed to fit the coils. Sometimes a sticky Panhard rod will restrict the drop, so loosen that.

Last, I suspect that the coils you have will be too tall for your liking. I had exactly the same coils, the OGTS progressive coils, and I installed OGTS's 1" drop front leaf. I knew I likely had to shorten the coils, but I wanted to do it in steps.

The first photo is the measured OGTS coil next to a couple of other coils I had.
The next photo is the result. Definitely too high at the tail
Next is the first cut down coil in the middle, compared to the original on the left, and a cut-down Kadett Wagon coil on the right. The Wagon coil is quite a bit thicker and higher spring rate. Height was good, ride was HARSH!
Next is "how to cut a coil".
Final photo is the end result.

HTH
 

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Opeler
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Discussion Starter · #7 ·
First off, were the old shocks worn out (as in no restriction to jounce or rebound), or did they simply not expand? If those are the same as the Munro "Classics" I installed, they are not gas charged, and will NOT expand. Not worn out, just not gas charged.

Second, where did you get those new shocks? They do not seem to be the correct ones. What is the compressed height compared to the Munroe's? If they are too tall, they will not allow full travel (especially jounce) and might even cause the rear end to sit high, with no jounce. Too long a shock will allow the differential to drop too much, and the coils will fall out

Third, what is stopping the new coils from being installed? No need for a spring compressor. Simply disconnect the shocks with a jack under the diff, and the differential should drop WAY further than needed to fit the coils. Sometimes a sticky Panhard rod will restrict the drop, so loosen that.

Last, I suspect that the coils you have will be too tall for your liking. I had exactly the same coils, the OGTS progressive coils, and I installed OGTS's 1" drop front leaf. I knew I likely had to shorten the coils, but I wanted to do it in steps.

The first photo is the measured OGTS coil next to a couple of other coils I had.
The next photo is the result. Definitely too high at the tail
Next is the first cut down coil in the middle, compared to the original on the left, and a cut-down Kadett Wagon coil on the right. The Wagon coil is quite a bit thicker and higher spring rate. Height was good, ride was HARSH!
Next is "how to cut a coil".
Final photo is the end result.

HTH
Thanks for the post Keith.

These shocks are the exact same model of KYB shocks that OGTS sells (you can read the number in their picture of them) but I bought both of these somewhere else for less than the cost of 1 shock on OGTS website. These are the same ones that have been mentioned over and over in threads here. The Monroe’s that were on the car aren’t the proper shocks for our cars, that much I found by doing some cross referencing and researching. It was another reason that I opted for new shocks.

I’m going to try to tackle the springs tonight. I think I went about it the wrong way last night. I jacked up the rear end by jacking it up under the differential and put jack stands on the jack points in front of the rear wheels. I didn’t jack it up high enough to allow the wheels to drop low enough when I lowered the differential with the jack. And the panhard rod nuts haven’t cooperated at all yet! I’m concerned it will be too high too, but it’s the stock height ones...not any of the progressive ones you mentioned. I’m guessing 50 years time have weakened the springs a bit. I haven’t done anything to my front suspension yet, so everything is still “stock” all around on the suspension, even if “stock” is super old and maybe saggy/weak.
 

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Won't KYBs raise the back end a bit all by themselves? At least when new...
 

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... I’m concerned it will be too high too, but it’s the stock height ones...not any of the progressive ones you mentioned.
Au contraire, the coils you showed are progressive.

What are the extended and compressed heights of the new KYB shocks compared to the Munroe's? The Munroe's I bought were (as you mentioned) not QUITE the correct shock, and a bit too short for the stock coils, although Munroe spec'd that shock for the GT. With the stock coils, I added extenders. With the 1" ride-reduction, the Munroe shocks work perfectly without the extenders. The key is to ensure that the shock isn't too long as to interfere with jounce or allow the coils to fall out :rolleyes: , nor too short to interfere with rebound.
 

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Opeler
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Discussion Starter · #10 · (Edited)
Au contraire, the coils you showed are progressive.

What are the extended and compressed heights of the new KYB shocks compared to the Munroe's? The Munroe's I bought were (as you mentioned) not QUITE the correct shock, and a bit too short for the stock coils, although Munroe spec'd that shock for the GT. With the stock coils, I added extenders. With the 1" ride-reduction, the Munroe shocks work perfectly without the extenders. The key is to ensure that the shock isn't too long as to interfere with jounce or allow the coils to fall out :rolleyes: , nor too short to interfere with rebound.
I’m not following you on the springs. The springs I received are new stock springs from OGTS. Here’s the link. https://www.opelgtsource.com/search/2576/details
Why do you say they are progressive and not stock??

The shocks are on the car now. So, I’m not going to take them off to measure them. They are KYB 343039 shocks and the low pressure ones OGTS sells, so I can’t imagine that they are not right for the car. The Monroe ones, we agree that they are not quite right.
 

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Über Genius
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Your differential will drop lower if you disconnect the panhard bar and loosen the torque tube mount about 5 turns.
 
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Opeler
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Discussion Starter · #12 ·
Your differential will drop lower if you disconnect the panhard bar and loosen the torque tube mount about 5 turns.
I wish I could disconnect the panhard bar. I’ve been hitting it with penetrating fluid a couple times a day for the last two days, and I still can’t get a nut to budge on it.
 

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Über Genius
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I wish I could disconnect the panhard bar. I’ve been hitting it with penetrating fluid a couple times a day for the last two days, and I still can’t get a nut to budge on it.
This will be a difficult thing to do but somehow make a reservoir surrounding the nut area and fill it with evaporust. Let sit for 2 days. It works wonders on rust but the part has to remain saturated.
 

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I’m not following you on the springs. The springs I received are new stock springs from OGTS. Here’s the link. https://www opelgtsource com/search/2576/details
Why do you say they are progressive and not stock??
"Progressive" means the coil has a variable spring rate, and is created by the difference in the coil spacing at one end. The stock coil is not progressive. I assumed it was obvious by the photo you posted

The shocks are on the car now. So, I’m not going to take them off to measure them. They are KYB 343039 shocks and the low pressure ones OGTS sells, so I can’t imagine that they are not right for the car. The Monroe ones, we agree that they are not quite right.
Umm, if you don't want to take the shocks off to measure them, then why bother asking? No worries, good luck with however this turns out.
 

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Opeler
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This will be a difficult thing to do but somehow make a reservoir surrounding the nut area and fill it with evaporust. Let sit for 2 days. It works wonders on rust but the part has to remain saturated.
I do this on stuck nuts too and it is very effective. I use plumbers putty to form a little "swallows nest" reservoir around the threads, then fill it with a good penetrating oil and walk away fora day or two.
 

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Opeler
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Discussion Starter · #16 ·
"Progressive" means the coil has a variable spring rate, and is created by the difference in the coil spacing at one end. The stock coil is not progressive. I assumed it was obvious by the photo you posted


Umm
, if you don't want to take the shocks off to measure them, then why bother asking? No worries, good luck with however this turns out.
I’m asking questions because it’s the first time I’ve done this and there are answers to questions that I don’t know. You don’t need to respond condescendingly, I’m trying to learn and do this on my own. I appreciate the help that anyone is willing to offer, but I don’t think that the answers need to be delivered in a manner that is made to make me feel like a moron for not knowing something and trying to learn.

Im sorry I didn’t want to take the shocks off to measure them and do double the work. I personally didn’t feel it to be necessary when I installed the model of them that is made for a GT and sold by OGTS. I did however look up the info on KYBs website for you, or whomever else to see.

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Opeler
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Discussion Starter · #17 ·
This will be a difficult thing to do but somehow make a reservoir surrounding the nut area and fill it with evaporust. Let sit for 2 days. It works wonders on rust but the part has to remain saturated.
I do this on stuck nuts too and it is very effective. I use plumbers putty to form a little "swallows nest" reservoir around the threads, then fill it with a good penetrating oil and walk away fora day or two.
Thank you for the tips! I’ll try to create something around it and fill it with the fluid to let it soak.
 

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Just Some Dude in Jersey
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You pretty much HAVE to remove the shocks to allow the rear axle to drop low enough to slip the springs in. You should be able to loosen and remove them at the axle with ease. And it's likely that you'll have to remove one end of the pan hard rod, also.

The pan hard rod is attached at 2 locations with nuts holding them on. Are BOTH nuts resisting your efforts to get them off? They are massive nuts on giant bolts/studs, there should be little chance of them stripping or breaking, certainly you should be able to break them loose with a 1/2" drive ratchet or breaker bar or even simply a 12" adjustable wrench. There's no need for them to be torqued massively, the rod barely pivots and applies very little unscrewing force. Keep trying the Liquid Wrench-type products.

"Progressive" springs have some of the gaps between the coils smaller than what most of the other coils of the spring have, usually just at one end. The gaps between the coils on normal springs are roughly all about the same distance.
 

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Opel Rallier since 1977
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Eric,

Take a caliper and very carefully measure the wire diameter of the new coil vs the old. Very small differences is wire diameter will make a very large difference in spring rate. For example a 5% smaller wire diameter will result in a 19% lower spring rate. A spring with a lower spring rate will need a longer free length to end up at the same ride height when you put weight on it, so if the new springs have a slightly smaller wire diameter, then that is why they are longer.

As noted, the new spring is a progressive rate spring, and the tight coils will compress more easily. A progressive winding is done to give a less-harsh ride when the car is lightly loaded but not sag too much when you add full passengers plus luggage. The 50 series Opels came from the factory with progressive rate srping in the rear. IDK on the GT's but would not be surprised if they do also. I don't know if the springs you removed are originals or not.

BTW, you can go to the local box auto parts store like O'Reiilys and borrow a set of spring compressors on their tool loaner program, or get a cheap set from Harbor Freight. I am guessing that it will not take much compressing to get these in with the shocks out.....so a cheap set ought to work like these:

(BTW, I would not use these for serious spring compression but for lighter springs, they are probably safe.)
 
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