Thread: Project Sebring GT Spyder

Tweet

I started out by centering the rack and setting the toe. I pulled the clamps on the rack boots and slid them back so that I could measure the location of the inner tie rod ends. This allowed me to find the true center of rack travel. You can count the turns lock to lock and estimate center, but if the rack teeth are off, you won’t actually be on center. Everything has to be in the same position every time you check it or your results won’t be consistent. I checked the toe every time by laying a straight edge on the rotor and measuring to the frame rails. The toe has to be reset after every adjustment.

There are several charts on line that show how to interpret the toe changes and how to correct it. In my case, I had to raise the rack and move it forward I will say that I was very surprised to see the laser dot move well over 2” toe out the first time I compressed the suspension. That would be over ¼” toe change at the tread! I actually reran that test a couple of times just to see if it was repeatable. Unfortunately, it was. The toe change in droop wasn’t much better, either. Eventually, I was able to get it reduced, but it still wasn’t great.

The charts were telling me that my tie rods were too long. Now I am using 5/8” shorter control arms, but I had just enough thread travel available in the outer tie rod ends to compensate for that. Since this suspension is built completely out of aftermarket parts, the answer must be an incompatibility in the conglomeration of non stock components and altered geometry. After thinking this over for quite a while, I decided to shorten the tie rods and move the steering arms inboard. Luckily, the Wilwood spindles have simple bolt-on arms. The outer tie rod ends were just about bottomed out in the the threads, so I reasoned that if this didn’t work, I could go back and still have plenty of thread engagement.

I kept adding spacers under the arms, cutting a little off the tie rod and rechecking the toe change. Every time I cut a little off, the bump steer curve got better. Finally, after lopping a full inch off, the toe change curve was just about perfect. I had practically zero change, at the tread, in the first inch of travel increasing to about .015 in the second inch. The final inch brought to total change to around .025. That is less than 1/32 of an inch in 3” of travel. This was both in compression and droop, but there was a price to pay for this.

Moving the steering arms in greatly reduced the amount of Ackerman. In fact, I wound up with almost zero Ackerman. This bothered me so I had to call full stop and do some more research and that research really didn’t give me a definitive answer to my questions. I spent a bunch of time looking through the various suspension books that I have and checking out any articles I could find on the internet. As well as other forums.

Now let me say to start, I understand the basic principle of Ackerman. In a nutshell, it allows the inside tire to make a tighter radius than the outside tire so that each tire can follow the radius of a turn without sliding, but it seems that even in published articles, there is no real consensus as to whether it’s actually needed for anything but extremely low speed in a modern car. It was originally invented to keep buggies and wagons (horse drawn) from cutting ruts in soft dirt when turning and side loading fragile wooden wheels. Because early cars were just self-propelled buggies, it transitioned into the automobile era. Over the years cars have apparently been built with “correct” Ackerman of varying amounts, zero Ackerman and even anti-Ackerman.

Supposedly, some sports cars and Formula One cars deliberately use weird Ackerman setups to generate a high slip angle on the inside tire, which, as I understand it, is supposed to make the car turn in better. Essentially, this acts as a turning brake to literally drag the front end into a curve (no, I’m not making this up). I know I have definitely seen factory front steer cars that appear to have zero or even anti-Ackerman. The reason generally given for this is because it’s difficult to get the proper steering arm angles on a front steer car without hitting the tire or wheel, especially with wide tires.

Then there is the situation with pickups, which admittedly are not usually considered high performance vehicles. They are available in various wheelbases, from short bed standard cabs all the way up to long bed quad cabs. As far as I know, they all use the same spindle, which means only one of those wheelbases could possibly have anything close to correct Ackerman. From what I could gather, since a tire will generate some amount of slip angle at anything above low speed, Ackerman is just not considered critical anymore.

In the end, I decided to just give it a try. I’m convinced it’s not going to make the car uncontrollable or dangerous, but it will, most likely, have some degree of tire scrub in a parking lot. Of course, so do a lot factory cars designed by credentialed engineers.

If it turns out to be a situation I don’t like, plan B will be a custom rack. It will have to be built wider (by 2”) between the centers of the inner tie rod ends while fitting a standard Fox body Mustang mount. Flaming River builds custom racks, but I imagine it won’t be cheap. Unfortunately, this is the kind of issue you can run into when you get too far from stock stuff. Suspension geometry is a complex interaction of many parts and this suspension literally does not have a single part from a stock MII except for the spindle bearing nuts. Some kind of issue like this is just to be expected, but at least this one can be corrected fairly easily, but expensively, if needed.

These are the aluminum spacers I machined to move the arms in.

Mike, I really appreciate your explanations of the thought processes you go through, your talents and the solutions! I predict that for this one, at some point you'll overhear some guy talking to his buddy or his girlfriend at a cruise or show, saying "Look at this, the guy put his wheel spacers on the wrong side!" The things you hear when parking lot "experts" are "explaining" things....

I'll agree and echo Mr. Spears thoughts in the first sentence. But, now I'll have to sit and be patient for you to take it for a ride and then give us a report on your findings. Ackerman =YES? or NO? You've got so many nice features built into this chassis, should be a blast to drive.

Thanks folks. I really appreciate the words of confidence.

I will report back on this, good or bad. I've put too much time, money and effort into this thing to just live with something that doesn't work.

BTW - I may have already figured out a way to "fix" this without a custom rack. It would involve machining extensions for the rack main shaft to space the inner tie rod ends out 1" on each side. I'm sure this wouldn't be as simple as it sounds, but I think it's doable and a lot cheaper than buying a custom rack. That's a nice little thinking problem for a later date. Gotta finish this thing first. Debugging (which is ALWAYS required) can come later.

With the basic alignment behind me, I mounted the front brakes. As I said earlier, I’m using a Baer brake kit designed for the Wilwood Pro spindles. They are 4 piston calipers with 11 inch rotors.

I considered both Wilwood and Baer kits, but settled on the Baer’s because the rotors are so much heavier than the Wilwoods. The Baer’s are 1.02 inches thick while the Wilwood’s are just .810. Other than that, the 2 kits were very similar. Both would fit under 15” wheels and had the pistons sealed against road grime. The Baer tech I spoke with assured me, that considering the light weight of this car, I could do track days with just a pad change.



While I was at this stage, I also went ahead with the flex lines and a little plumbing. The hoses are -3 Russel DOT approved parts. It took a little fiddling to come up with a hose routing that would allow full suspension travel and steering without rubbing or kinking, but eventually I got it worked out.

I prefer hoses with female screw on connections on both ends, rather than the hoses that have swaged on banjo fittings. The screw on hoses are usually a little cheaper and they are easier to fit, IMO. You can put a slight twist in the screw on hose to get it to clear things whereas with the crimped on banjo fittings, you pretty much can't do anything except bolt them on and hope you have clearance.



I also did the front crossover line. This needed to be done before the engine goes back in. Trying to route the line with the engine in would have been much more complicated. Because I had plenty of room to work, I was able to do it in one continuous piece.



It made sense to finish the short line from the line lock valve to the front tee while I was making the crossover.

I am currently focusing on things that need to be done to get the engine and trans back in since I need to get the car off my lift. I have to help my grandson put a new (to him) engine in his truck and I need to pull the trans out of my 46 to replace the flexplate. I don’t want to do either of those jobs laying on my back, but there was one thing that needed to be finished on the rear end before I moved on.

One of the things I got back from the powder coater in the last batch was the rear sway bar assembly. I had to wait until the rear suspension was back in to finish the parts. I didn’t have time to do it before I sent the frame out to be coated.

I originally wanted to mount the bar under the rearend, but that wasn’t really possible due to the exhaust. I had to mount it on top and there is just enough space for it with the body on. Changing it will be a pain, but that’s the way it goes sometimes. The available space dictates what you can do.

The bar itself is a 26” torsion bar intended for a mini sprint car and it just squeezes in between the frame rails. The ends are 1” splined. This bar is ¾” diameter and gun drilled. It is in the middle of the available diameters. The nice thing is, the ends all stay the same, so all you have to do is swap the bars.



The arms do look a little chunky, but that is due to the size of the weld on splined ends that were available. That and I just happened to have the tubing that fit them. They are actually not as heavy as they look. Considering that they will be buried way up under the body, I doubt anyone ever sees them if they are not reading this thread.

The bearings are Delrin bushings that are made for these bars and are off the shelf items. This should make it easy to get cheap replacements in the future. I fabbed the steel housings for the bushings and added a grease zerk. They will get silicone grease too.

This is before powder coat and may be a little easier to see.



The end links were modified from some type of side by side suspension struts. I have a friend that was doing some R and D work on an electric 4x4 side by side a few years ago. I was at his shop one day and noticed a big box full of these struts. He gave me a big handful of them saying that they might come in handy one day. They worked just fine for this job.

I bushed the large metric hole down to 3/8” and changed the button grease fitting over to a standard zerk. Because they are so heavy duty, these rod ends should last the life of the car!



The links are different lengths because they attach to the Watts link brackets on the rearend and of course, they are different heights.

I totally forgot to send the lower link brackets to the powder coater, so they will have to go in the next batch of small parts.

Since there is no poly or rubber in the sway bar assembly, there won’t be any lost motion in operation. That should make the bar more effective, but it might make the ride a little harsher.

OK, gang. I found several things that I wrote up quite some time ago and never posted. I was sure that I had put them up and went back and checked the thread, but didn’t find them. Sooo, while I’m busy on getting the engine back in, I’m going to post the stuff I found. Keep in mind as you read them that this was all done months ago. The pictures and wording may seem out of order because they are. At least it will give ya’ll something to look at.

Just for a time reference, these posts should have been made after I got the LeMans style gas cap on and right after I took the first batch of parts to the chrome shop. This stuff was done sometime between March and August of 2020. This was during the time my company sent me home to separate the workers due to Covid and it was crazy thrash time for me trying to get the chassis to powder coat. Guess this stuff just got lost in the shuffle. I’ll post the up a few at a time to give folks time to read them. So here goes.

I also found another set of seats and fitted them. The original seats I used were out of a 1995 M series Miata. They have separate head rests (all other Miata's have one piece headrests and seats), fit the car well and look fairly period to the car. However, mine were in bad shape due to weather exposure and I was missing the Mazda seat adjusters. I added some universal adjusters, but they were just ok. The seating was pure sports car in that I was sitting pretty much on the floor with my feet stuck straight out in front of me in semi reclining position. As my back condition has worsened, this position became unacceptable. I doubt I could have ridden like that for very long. I needed a fairly upright position with a little drop to the floor. It was obvious that I had to change something.

I also found out that the M series Miata's were sold in very limited numbers in the US market. The only padding and upholstery rebuild stuff I could find came from Europe, where they were much more common. I had the choice of either getting custom covers made or getting a kit from Germany by way of the UK. Either choice would cost north of $600.

While I was delivering the parts to Tennessee for chrome, I found another set of seats out of an MX5 with a retractable hardtop. They are black leather and the top had protected them very well. There is one minor scuff on the leather that can be easily repaired. I got both seats and tracks for $300. They are much more comfortable on my back and have better bolstering for lateral support. They are not as period looking as the old seats, but I'll make that sacrifice for better long range comfort.

Here are the new seats:

I also wanted to get some more leg room. I had already pushed the firewall forward a few inches and that helped, but I still felt cramped up. I would have to move the seats back to gain anymore. I needed to do some modifications to fiberglass section behind the seats anyhow, since after I got the body sections aligned, the rear bulkhead section wouldn't touch the floor.

If you've been following along since the beginning, you will remember that I found the rear body mounts were bent down and I straightened them out. I thought this was due to the rearend taking a hit since the bumpers and brackets were bent like they had been in an accident. I don't think this was right. The car had obviously been hit in the rear, but I think that whoever built this car ran into this same issue and bent the mounts down to get the rear section to touch the floor pan.







Before I could work on rebuilding, I had to get rid of more of the same "horsehair" looking crap that was used as insulation on the firewall. I don't know what type of silicone was used to glue this junk down but it doesn't give up easily. Once again, I had to resort to a stiff wire bush on a grinder to even touch it. It was even better bonded to this part than it was to the firewall.





Eventually I got it clean enough to work on.

The first thing I had to do before getting the seats in, was patch the holes I had cut in the floor to access the new rear suspension mounts I welded on earlier in the build. Not much drama here. Just straight forward pattern making and welding.





I bent a lip on the rear of the patch for a little extra strength.









You can see how much extra length I added to the floor here by the notch in the foreground. The vertical leg of the notch was where the original floor stopped. This notch was filled too, but I didn’t get a picture. This may not look like much extra room, but, every little bit helps when you're talking about leg room.

Here you can see the extra room that Classic Roadsters left behind the rear bulkhead. I’m not sure why they did this, unless it was to have the rear floor follow the contour of the laid back seats. What it did was waist a lot of potential extra room. I could fix that by changing the angle of the rear bulkhead and tieing it into the little extra floor length I had added.



I also had another issue to correct. The wider wheels were contacting the inner interior tub. They bolted on fine and appeared to fit, but when the suspension was articulated, like one wheel hitting a big bump, the tire would just contact the body. I could fix this by adding a tiny wheel tub. This would allow me to keep as much interior space behind the seats as I could. Besides, trying to go bigger with the wheel tub would cause issues with the fuel tank. I was about as deep in the wheel well as I could get without major surgery.

This is looking up where the tire was contacting the body tub. Not much contact, but any is too much.



Here you can see how much I had to cut out to clear the tire. You can also see the big hole I had to cut to clear the new wider seats.


This shows the clearance I gained by relieving for the tires.

Getting this stuff posted hasn’t been as easy as I had hoped. I switched computers a few months ago and some of the pictures got lost or jumbled up. I’ve had to hunt them down to upload them. Here are a few more of the old stuff.

I suppose I could have dummied up some kind of form and laid glass over it to reform all this stuff, but as I said earlier, I don’t particularly enjoy working with ‘glass. Besides, building the form would have been almost as much work as building out of metal and I would have still had to lay up the fiberglass, smooth and paint it.

Of course, that meant that the new metal parts would have to be riveted in or panel bonded to the fiberglass with adhesive, but that wasn’t a big issue. I decided to just rivet them in and seal the joints. If I have trouble with the rivets loosening, I can always use one of the new panel adhesives to bond them in. I think with enough rivets, this won’t be an issue. Since I would be installing a bunch of pop rivets, I went to Harbor Freight and dropped a 20% off coupon on pneumatic pop rivet gun. Man, it sure does make things quick and easy.

By riveting all these pieces in I could assemble them in sections under the car and I also had the advantage of being able to remove them easily if I ever needed to. Not sure if I would ever NEED to do that, but at least I have the option, and considering how difficult the rear shocks are to access, that option might come in handy one day. Also, the upper link mount is behind the seat bulkhead and that might need some kind of attention one day.

There was one small tool I had to make before I could tackle the sheet metal. That was a tipping wheel for my bead roller. I had to make some odd bends on a few parts that I couldn’t do in my brake. The tipping wheel makes this a lot easier than trying to rig up something on my welding table to do it.

I welded a hub onto a piece of steel plate that was actually an old slug from a hole saw. I almost never throw those things away, since they come on very handy. The hub was some kind of mystery alloy (probably 4140), so I had to bury it in a bucket of oil dry to keep it from cooling too fast and getting brittle from the welding heat.







Then I machined it up and here it is in action. I also made both a steel and a polyurethane “anvil” roller for it to pinch the metal between. I machined a recess in the die and made a custom flush mounting washer that would allow me to tip the flange almost to a 90* bend. I could finish it up with a hammer and dolly. The tipping die also has the advantage of being able to tip curved flanges.

There were many small parts required and almost all of the small angle tie-ins had to the curved to fit the existing fiberglass panels. I used the shrinker and stretcher for these. When these go in for the final time, they will get a bead of silicone to between them to seal the joint. I also have some brush on seal sealer that I may use. All of the metal and fiberglass will eventually be covered in marine carpet, so the pop rivets won’t really be seen. Some of the parts were welded together.

I made all these parts out of 18 gauge steel. I had it on hand and I feel a little better having steel between my back and the tire. I rolled a few beads in to give it a little support.
This is the bulkhead that goes behind the seats.





This is the finished inner tub and the filler panels for the seat clearance.





The parts that you see in the interior are only a small section. They are actually the inner fenders, too. I made some aluminum extensions to tie the steel parts into the outer fiberglass body section. A rubber lip seal will attach to the edge of the fender and press against the body to seal out road grime.







I made the fenders in two parts like this because I’m thinking of adding wider rear fenders in the future. There is a company making body parts for this car in limited numbers. The MX version of this body had fenders widened an extra 2” or so. I’ve talked with the owner of the molds and he says he can do just the outer rear quarters. This would get me the wider rear body kit and allow for wider tires. If I do decide to do that, all I have to do is remake the outer sections of the fenders that tie into the body contours.

Very nice work there!

Ditto Nice work, and glad to see your working on this, I'm doing carb work on mine today!