A bunch of questions

[MonkeyNutZ]

I know you folks love questions!

I've got a 73 GT that's mostly stripped out, the only thing left is the glass and the rear suspension. Now I was looking through the suspension sub-forums and I was formulating a plan. What I'd like to do is build a set of spring shackles to solve the understeer and binding problems, however looking at the front suspension has got my thinking that nothing is keeping the whole leaf spring from shifting to one side. Could I drill a center hole and run a bolt through it? (Or weld a center shaft through it to allow the spring to move up and down.)

The shackle also lowers the car and I was curious what that does to the front end geometry as far as camber changes throughout the suspension travel? Would I also have to lower the rear end? Do I need shorter front shocks?

Finally, what effect do the shackles have on tire/wheel choices, I was thinking about R200/50-70/14s?

[BQS4]

Why not do this?

Neue Seite 1
Look at "bilds" 11-14 where a Kadett C or Isuzu-Opel front was grafted onto a GT. The man that did it will be in TX later this month, Uwe Klippert.

[heimue]

Originally Posted by BQS4 Why not do this? Neue Seite 1 Look at "bilds" 11-14 where a Kadett C or Isuzu-Opel front was grafted onto a GT. The man that did it will be in TX later this month, Uwe Klippert.

Probably not, because it is quite hard and expensive to get a Kadett C front axle to Ohio, and the Izusu front axle comes from Japan and looks different than the Opel axle...

Dieter

[SantaClaw]

For a front suspension, I'd suggest short steering rack from Quaife Engineering + the large sway bar from Lenk + full set of polyurethane bushings..

works great..

Opel GT :: stabstagforran.jpg picture by santaclaw - Photobucket

It makes the GT feel like the sports car it should have been from the start..

[MonkeyNutZ]

I'm still going for a somewhat original car, I've got a complete rebuild order lined up from OGTS and I was looking at some sway bars from Addco.

I was just trying to reassure myself if the shackles were the way to go. I've got the drawings and a brother who could weld the moon in place so the fabrication isn't a problem.

[RallyBob]

Originally Posted by SantaClaw For a front suspension, I'd suggest short steering rack from Quaife Engineering + the large sway bar from Lenk + full set of polyurethane bushings.. works great.. Opel GT :: stabstagforran.jpg picture by santaclaw - Photobucket It makes the GT feel like the sports car it should have been from the start..

Where do you see a fast rack to fit an Opel GT? I can only find the Manta/Ascona B and the MK1 Vauxhaul Kadett. Just curious...

As far as the Lenk sway bar, it is made here in the US for Opel GT Source, so no reason to get it from Europe! As well Opel GT Source manufactures the front and rear polyurethane bushings that Lenk and many other German tuners sell.

There are many other things than can be done to improve the GT's handling, and most are listed on this site already. The biggest issues are with the OEM geometry and design. If you are willing to make modifications, the GT can be made to handle decently, however the compromise is a rougher ride quality.

Bob

[SantaClaw]

Originally Posted by RallyBob Where do you see a fast rack to fit an Opel GT? I can only find the Manta/Ascona B and the MK1 Vauxhaul Kadett. Just curious... As far as the Lenk sway bar, it is made here in the US for Opel GT Source, so no reason to get it from Europe! As well Opel GT Source manufactures the front and rear polyurethane bushings that Lenk and many other German tuners sell. There are many other things than can be done to improve the GT's handling, and most are listed on this site already. The biggest issues are with the OEM geometry and design. If you are willing to make modifications, the GT can be made to handle decently, however the compromise is a rougher ride quality. Bob

I'll ask for the part nr but i've got the fast steering rack for my GT so I KNOW it can be done..

I also have a Quiafe gearbox in my GT, that's the stock 4 speed, with Quiafe internals, straight cut gears, and close ratio.

I'd suppose it's this one for the Kadett MK1(A) with left hand drive:

Opel Kadett Mk1 quick rack and pinion kit 2.7 - Quaife Engineering

But that's just a guess, I've sendt a message to the guy who bought it for me...

I've got:

- New balls & bearings
- Poly bushes - Everywhere.
- Lowering kit from lenk.
- Lenk 25mm front sway bar
- Watt link bar in the rear.
- Kadett C 20 mm steering rack with a short steering kit from quiafe.
- Gabriel Red rider shocks. for a comfortable ride compared to stiffer shocks..
- Rear Axle from Manta GSI with difflocker.
- The body has been strongly reinforced with both a roll cadge, "rally welding", 3 cm weld, and 3 cm pause in al the body panel gaps, and reinforcements like this:

Opel GT :: stagunderplate.jpg picture by santaclaw - Photobucket

I promise you it rides like a dream...

Rigid and stiff, but not hard...

Oh.. and the body has been widened to allow for wider wheels/tires...

Info regarding the short steering rack

Ok, the short steering rack is for Kadett C !

It's got the complete steering rack from a Kadett C, that's 20mm compared to the 18mm that's stock in the GT...

[MonkeyNutZ]

I discovered why my GT was in a scarp yard in California, it seems that the right front wheel fell off at some point and the car may have been dragged for quite a distance.

All I know for sure is that the eye of the leaf spring has been ground off and there is some (repairable) damage to the lower control arm and disc brake "dust cover" that correlates to my wheel failure theory.

OGTS recommends just replacing the spring with their intermediate sport spring and that it will eliminate the spring binding and understeer. Does anyone have any experience with this spring? Does it still cause the shimmy relating to repeated bushing compression (from the leaf widening during suspension travel)?

Sorry if it seems like I'm being a bit precise, it's in my nature.

So my options are as follows,

1. Repair or replace the leaf spring and leave it stock
2. Repair or replace the leaf spring, fabricate a set of shackles and a center bolt to keep it from shifting
3. Buy the intermediate sport spring from OGTS

[SantaClaw]

I would not reccomend welding on the spring itself, as you may change the hardening of the spring.

I'd go for lowering springs, both in the front & rear.

[trlmr]

I have the intermediate spring and poly bushings and the ogts sway bar - front & rear. The spring is fairly stiff so you really don't get much suspension travel. All of these things were put on at the same time (along with 15" wheels and tires and new shocks). I don't know whitch item did the most change to the way it drives but it is a different car. I don't notice much understeer now. I do think it put some negative camber in the front end.


Hope this helps. Tom

[RallyBob]

Originally Posted by MonkeyNutZ OGTS recommends just replacing the spring with their intermediate sport spring and that it will eliminate the spring binding and understeer. Does anyone have any experience with this spring? Does it still cause the shimmy relating to repeated bushing compression (from the leaf widening during suspension travel)?

I would go this route rather than mess around with the OEM spring. The car will be lower, the spring is stiffer, the spring is easier to install, and the spring has less arch therefore it doesn't abuse the control arm bushings as badly. Don't forget that if you go this route (or any lowering for that matter), you need to cut down the bump stops on the front of the GT. I don't know how many GT's I've seen with the lowering spring up front and stock bump stops...the car is always 1/8" away from riding on the stops! If that's the case, yes....the ride quality is doggie-doo, since you're running on undampened rubber bumpers, and the spring rate is nearly infinite at that point. Cut the bump stops to half the OEM height, and you're all set. Do not be tempted to just remove them, if you bottom out metal-to-metal, bad things will happen!

HTH,
Bob

[trlmr]

Hmm...... I will look at my stops again. It's been a few years since the spring was installed and I remember looking at them. I thought it looked like about an inch clearance at the control arm. I don't know what that would translate to in actual suspension travel but it is worth another look.

Thanks for the info Bob.

[markandson]

I have the intermediate spring in my car also, along with 15" wheels, Koni Reds, stock rear springs, front and rear sway bars, and poly bushings all over the place. The ride is stiff but the car handles very nicely, the faster you go the better it feels. I can let go of the wheel at cruising speeds and the car tracks perfectly with almost no vibration or shake in the wheel.

[MonkeyNutZ]

Thanks guys, I'm sold.

Now a quick question for markandson and trlmr what tire sizes are you running and do you think I'd be better off with 14" wheels? I'm a fan of big thick tires so I was thinking about 200/70/14s.

[trlmr]

I have 195/50/15's They have a fairly small side wall. that might be one of the reasons it drives differently. There are a few pictures of it in my album on this site. I'm no tire expert so I won't comment on what your size would be like. I don't know how many rim choices there would be in a 14" either.

[markandson]

My tires are Goodyear Eagles 195-45 15 front and rear. I would like to replace the rears with 205-45. The 70 series tires will have too much sidewall flex for good handling and also I don't think they will fit the wheel wells if you use 15" wheels, I don't know about 14's. I would go with 15's or 16's personally.

[neuropel]

Good thread...Sounds like I need to check the bumpstops on my GT to see if they're cut down because the ride quality is very poor. It has poly bushings front and rear, the OGTS front and rear sway bars, and I "think" it has the OGTS spring. Not sure about shocks - I haven't spent enough time with it to note that much detail. Handling is OK for a GT, but it's far too harsh for my liking. Tires are Yokohama 205/50/15 on the front and 225/50/15 on the rear, but they were manufactured in 1995! If you cherish your teeth, I'd recommend going with a little more sidewall (which you can do with the 14" wheels). I think you could still get very decent handling and not have to compromise the ride quality so heavily. Years ago, I had another GT that had the OGTS intermediate spring and poly bushings with 195/50/15 tires (but no sway bars) and I recall the ride being a LOT better, so I suspect sway bars kill the ride quality. The sway bars do, however, make a notable difference in handling...just can't have it all I guess.

[MonkeyNutZ]

Based on some rough calculations I did, a 195/60/14 will be about the same size as a 195/50/15 (about half an inch larger total) but will have .75" more sidewall height and I'm thinking that that extra 10% in thickness will make quite a difference in ride quality.

[Paul]

Sway bars should yield no added harshness in ride quality, since they do not add to the spring rate at the wheel. The only time a bar comes into effect is when there is a change in location (up/down) of the wheel WRT the other side of the car, such as in corning. The shock valving has more to do with ride quality. Having the correct valving, in compression and rebound, for the spring rate and suspension travel is key. Too much compression valving will prevent the wheel from being able to move up in the fender well and absorbe the energy of the bump. Like wise too little valving will allow the suspension to bottom out. Similar issues with rebound....


And as Bob stated earlier, when the suspension hits the rubber bumb stop, the total effective spring rate curve changes with the spring rate of the rubber added to the spring rate of the spring. And, the rate for the rubber is not linear, its more expenential. Under normal conditions, the shock is not valved to handle these rates. I say normal circumstances, because back in the day when the 1st Gen Neon's were so dominate in Road RAcing and Auto-xing, the hot set-up was to have the compression of the struts lowered so much that the car would sit down on the rubber bump stops and the rebound was valved around the spring rate of the rubber!!! Very Trick and very fast!!!

[neuropel]

Hmm...well, after reading Paul's thesis, I guess either my shocks are more harsh in my current car or else my butt has gotten more sensitive . So you guys are saying to just hack off half of the bump stops (with the OGTS lowering spring)? I've lowered the ride height of my Manta with new springs and shocks, but I haven't cut the bump stops on that car yet either. MonkeyNutZ, I'd still go with the 14" wheels and 195/60/14 tires with more sidewall, as you have suggested. I actually have a set of 16" wheels I was going to use on a GT, but I now think they will be put to better use on a Manta. I've seen a few GTs with 17s...if they're using performance shocks and the OGTS spring, they must ride like a wheelbarrow!

[Paul]

Originally Posted by neuropel Hmm...well, after reading Paul's thesis, I guess either my shocks are more harsh in my current car or else my butt has gotten more sensitive . !So you guys are saying to just hack off half of the bump stops (with the OGTS lowering spring)?

Todd, you MAY be getting soft in your old age..... On both my GTs with the OGTS sport Spring, I cut the stops shorter and at an angle to give a "progressive" rate increase. Seems to work very well. One has Koni's and the other GR-2s

Originally Posted by neuropel I've lowered the ride height of my Manta with new springs and shocks, but I haven't cut the bump stops on that car yet either. !

Todd, from other discussions, I believe you springs don't have as much drop as the ones I'm using on my lowered Manta, but I HAD to cut the stops by75% and I drilled holes in them to allow them to have some "give" to them

Originally Posted by neuropel MonkeyNutZ, I'd still go with the 14" wheels and 195/60/14 tires with more sidewall, as you have suggested.

I'm running 195/60-14s, and with the right tire, handline is very good and ride quality doesn't suffer

[markandson]

I have Poly bump stops in my GT that are very low profile, they are mentioned somewhere here on the site but I don't remember where. If anyone wants I can look up where I got them. I believe I had to open up the holes just a tad in order to get the studs through since they are not metric thread .

[SpringGT]

Originally Posted by MonkeyNutZ Based on some rough calculations I did, a 195/60/14 will be about the same size as a 195/50/15 (about half an inch larger total) but will have .75" more sidewall height and I'm thinking that that extra 10% in thickness will make quite a difference in ride quality.

Here is what 195/60/14 Pirellis look like on 14" wheels. Overall diameter is about 23.2 inches.

[markandson]

Mis-information disseminated by me....oops....my tires are 195/50 R15 they are not 195/45's as I posted yesterday.

[MonkeyNutZ]

Originally Posted by SpringGT Here is what 195/60/14 Pirellis look like on 14" wheels. Overall diameter is about 23.2 inches.

Is that GT lowered? I'm a little worried about clearance.

EDIT: It seems that there are very few 14" wheels that have the 4x100 pattern. So I'm thinking of switching to 13" any thoughts?

Wheels from BMW 2002s are quite easy to find and would work with 195/60/13s. That'd be the same section width and sidewall height so I doubt the handling would be affected.
http://cgi.ebay.com/ebaymotors/set-o...Q5fAccessories

EDIT2: I'd like to find some '73 GT wheels but I haven't seen any turn up recently, if anyone has a set they'd like to part with shoot me a PM.