|LIFE OF A GT
|November 17, 2009 - So, while I wait for suspension parts to arrive, time to look at the brakes.|
I'll be mounting a set of Miata rear calipers and discs. I hadn't really thought too carefully about how to do this before, but I could have started as soon as the new axles arrived. As it turns out, it's going to be fairly straightforward.
entry 210 - tags: brakes
|November 17, 2009 - The beginnings of a rear brake bracket.|
Most of my axle uses 2.625" tubing, and it's impossible to find a 2.625" hole saw. This meant lots of grinding for my trailing arm brackets. Are they trailing arms or radius rods? I'm not really sure. Anyhow...
A look at the end of the axle tube revealed that there's a step in the tube size, dropping down to 2.5". That size hole saw I have! And with the axle removed, I can slide my bracket right over the end of the axle tube so I can get a full 360 degree weld. Excellent. The bracket is made of 0.25" steel, nice and beefy. The two mounting points for the caliper are in the same plane, so all I need to do is drill two holes in the right place and weld this on.
Well, almost. Naturally, the bracket uses 10mm metric bolts. I have a 0.375" drill, but 10mm is 0.394". I'd rather not go oversize (7/16 is 0.438") so I'll have to see what my options are for opening up the hole slightly.
The bracket also ends up very close to the end of the tube, so I'm going to put a 0.25" spacer to move it inboard a bit and get more room for welding. That'll also give the mounting bolts for the caliper a bit more meat around them to help them resist shear.
It's kind of funny - I've taken the Seven to two magazine tests over the years. One was in the company of a bunch of other Locosts, the other was to compare against a $75,000 supercharged Atom. In both cases, I was called "a ringer" because of my purported access to equipment and tools not available to mere mortals. Want to know what I've been using for all of my recent fabrication? The holy trinity of a good drill, a sawzall and an angle grinder. Yes, a MIG welder, stick welder and a torch have also recently come in to play, but they're not exactly unusual tools for fabricators. I don't even have a bandsaw. The car is on jackstands in my garage, a far cry from the bead-blasted perfect shell on a rotisserie that some people might expect.
My point here is not to say "oh, poor me", but to point out that you really don't need a lot of equipment to do this kind of work. This bracket isn't as pretty as it might be, but a bit more time with the grinder will fix that.
entry 211 - tags: brakes
|November 19, 2009 - The brake brackets are ready to weld on to the axle tube.|
I'd been trying to figure out the best way to ensure the holes were in juuust the right place. I needed to get the radial location of the caliper just right. Measuring wasn't going to work well as I was dealing with curved surfaces everywhere. After a bit of cogitating, I came up with a cunning plan. Naturally, I wasn't bright enough to take pictures of the process, so I'll have to try to explain.
First, I used a transfer punch to mark the center of the two holes in a piece of 1"x0.25" strap. This is my 0.25" spacer. I drilled those out (I found a step drill that was close enough to 10mm to solve my previous problems) and checked that they were accurate on the caliper.
I then took a couple of bolts and cut them down into short studs, which protruded out of the caliper by 0.25". This way I could hang the spacer on them and butt it up flush against the face of the large bracket piece.
Now the axle and brake rotor were mounted to the rear end. I placed the caliper in the perfect location and held it in place by tightening down the adjuster screw Mazda thoughtfully provided, clamping the caliper in the right spot. Now it was a matter of assembling all of my pieces - the bracket on the axle (loose) and the spacer hung on the caliper. I lined everything up and tack-welded the spacer to the bracket. Now, I had my holes lined up! I drilled the rest of the bracket to match, welded it up and voila.
The second was easier. Now that I had one accurate bracket, I used the transfer punch (wonderful things, these are) to put the holes in the same place and stuck it all together.
Now all I have to do is figure out just how I want to clock the calipers on the axle. I'll mount the rear end to the car and find out if there are any potential interference points with the body.
entry 212 - tags: brakes, rear axle
|November 19, 2009 - A big box full of MG suspension parts arrived in the mail!|
Well, I know they're MG suspension parts. Most people probably wouldn't identify them as such.
A collection of swedged rods for my trailing arms along with 4 left-hand thread ends. I'm sure I ordered the latter back in the summer, but they're nowhere to be found. At worst, I have some spares.
I also picked up a couple of weld-in bungs so I can build the Panhard bar. I'm pretty close to that point. Cool.
entry 213 - tags: rear axle, suspension
|November 20, 2009 - Time to assemble the rear and attach it to the car!|
First off, with the differential, axles, brakes and trailing arms attached, it's really heavy. Yowza. Lifting this thing off the workbench was an excellent illustration of unsprung weight.
entry 214 - tags: rear axle
|November 20, 2009 - The axle in its new home!|
It took a bit of fiddling around with trailing arm length to get it in just the right place, and I think I'm going to have to pick up some lower ones that are an inch longer. No worries, they're only about $12 each. I'm actually really liking these, I'm trying to think of other cool places to use them. It's super-easy to adjust the pinion angle and the rear axle angle.
In this picture, I have the jackstands at different heights - the arms are usually parallel! I also took the shot before I went on a major garage cleaning binge. That's how it usually works, right?
entry 215 - tags: rear axle, suspension
|November 21, 2009 - With the axle actually attached to the car, I was able to move it through the full range of motion.|
As I suspected, at full compression the upper link hit the bottom of the car. After a bit of fine metalwork, I had that problem solved! Right now, maximum compression is actually a bit more than was available on the original suspension. My tires are a smaller overall diameter but since they're further outboard, getting this much travel is going to involve quite a bit of surgery to the wheel wells before the fender flares go on. The plan to to build the car to allow this much travel, then use spacers to limit it to less if that should become necessary for any reason.
It was very cool to be able to put the axle through its paces and see how things worked, then simply reach up and tweak the pinion angle or the fore-aft location.
entry 216 - tags: rear axle, suspension, travel
|November 21, 2009 - I'm still playing around with places to put the coilovers.|
This rod is the same length as a fully compressed AFCO shock with 5" of travel. With the suspension at full compression, it helps me determine my worst-case scenario for mounting points. I'm starting to lean towards putting the shock in the wheel well. It'll take up a bit of space that could be used for tire, but on this axle there aren't really any options for moving the tire inboard much anyhow. As long as I have an inch or two of clearance, it shouldn't cause any real problems.
If I do decide to narrow the rear axle to allow more tire - since this is a street car, not a drag or track car, I don't need monster rubber - I can always move the shock. The good thing about this setup is that I'll have more ground clearance and I'll have a much easier time welding in a strong upper mount for the shock than if I tried to use the mount for the travel limiting strap.
entry 217 - tags: suspension, rear axle
|November 24, 2009 - There won't be much work done on the car over the long weekend - my parents are coming to visit.|
Thus the massive and long overdue garage cleanup!
Still, I'm spending a lot of time designing things in my head. Next is the Panhard bar. Ahead or behind the axle? I also spent some time designing the front end bracing in my head on the way to work this morning. I really enjoy the process of working through problems mentally.
|November 30, 2009 - The weekend wasn't completely without progress.|
I got all itchy to do something productive so I figured out how to mount the Panhard bar and also welded the brake brackets on to the axle. One step closer. I'll do the messy fabrication work for the bar this week and get it all put together.
I also took advantage of a Black Friday sale at Discount Tire Direct and picked up some new tires for the car. The eventual plan will probably involve some 15x8 wheels in the rear with 225/45-15 tires, but I'll probably have to shorten the rear axle to do that. For the initial build, I'll stick with my current setup of 14" wheels with 195/60-14 tires. Yes, miniscule by modern standards and the skinniest tires on any vehicle I own when I think about it. But I have the wheels, they look appropriate on the car and I have the wheels. The tires are a set of Falken Azenis RT-615s, and I got the full set for $176 delivered. Can't beat that for value. They might be small, but they're pretty sticky for a street tire.
I also just ordered the shocks. Things are moving along. I'm thinking the Christmas holiday will involve the dissection of a certain Camaro.
entry 219 - tags: rear axle, suspension, tires
|December 1, 2009 - Panhard rod mount!|
As I've mentioned, I'm using the Fast Cars suspension as a base for my design - albeit with a bit more adjustability built in. In that case, the Panhard bar mount is in front of the axle. This means it has to be fairly tall, and it has some support braces to keep it from flexing under side loads. The roll center of the rear axle is the center of the Panhard bar, and the usual geometry means the bar should be in line with the center of the axle at ride height. Thus the long bracket design.
I've decided to put mine behind the axle. This lets me use a straight bar instead of having a bend to clear the nose of the differential. It also means I can take advantage of the contours of the body and use a much shorter mount. It's also a bit of an odd shape and will have a very solid connection to the body of the car. It's made of 2x3 tube instead of the 2x2 in the Fast Car setup and the extra width is in the right place to resist lateral loads. It should be significantly stronger but there's not much clearance for the bar. I think I'll be able to pull it off though.
I should have this welded in to place shortly, I just have to pull out a bit of carpeting inside the car so nothing catches on fire. You know, the usual.
While underneath working this out, I think I figured out how to mount a sway bar to the rear. Hmm.
entry 220 - tags: rear axle, panhard, suspension
|December 2, 2009 - The Panhard bar mount welded in place.|
This is one solid sucker, I'm very happy about that. The bend in the body makes it good and strong.
entry 221 - tags: panhard, rear axle, suspension
|December 2, 2009 - With the body mount in place, it's time to build the one on the axle.|
I welded one of the threaded bungs into a length of 1" pipe and attached it to the body. Then the axle got put into place and I measured the distance from the bar to the axle. That gave me what I needed to figure out what the mount on the axle should look like.
I went through a number of possible designs for this. The final one - shown - has a bracket made of a section of 2x2 bar with a nice thick wall. It's welded to a support made of 2x3 bar, reshaped to meet up. There's a nut welded on the back side of the bracket. A lot of designs I see in circle track catalogs put the bolt in single shear instead of double like this, but I prefer this design.
entry 222 - tags: rear axle, panhard, suspension
|December 2, 2009 - And voila!|
The rear suspension linkages are all in place. The axle is sitting quite a bit lower than usual to show off the bar. In case you're wondering what a Panhard bar does, it provides the lateral support for the axle.
The two outer (lower) trailing arms keep the axle straight in the frame and transfer the brunt of the power to the chassis. The center link at the top of the diff keeps the whole thing from rotating under power and lets me set the pinion angle. And the Panhard bar transfers the side loads into the frame. With this whole lot in place, the axle can twist up and down to let the wheels follow the road, but it will always stay properly aligned to the chassis. Cool.
It's not completely finished, of course. I tucked that Panhard bar into a pretty tight spot, and it only clears the back of the axle by a millimeter or so. More importantly, the bracket on the axle hits the body of the car. A bit of reshaping will solve that problem, of course, but I think I'll have to pull the fuel tank to do it properly. No worries, that looks like a pretty straightforward job.
entry 223 - tags: panhard, suspension, rear axle
|December 2, 2009 - The tank came out without much fuss at all.|
No recalcitrant fasteners, no further dismantling required for access. Thank you MG.
Of course, I had filled the tank with fresh fuel a year and a half ago when I was trying to run it on the original engine. So I had to drain out an amazing amount. Note the approved containers of fuel in the background.
|December 2, 2009 - Here's the interference between the body and the Panhard bar mount.|
It's not dramatic, there's only about an inch of up travel left anyhow. It'll be simple to add the space I need without any real consequences anywhere else.
At the top of the picture is the bracket that originally held the straps for travel limitation. I'm thinking it'll be a good place to put a sway bar end link.
entry 225 - tags: rear axle, suspension, panhard
|December 10, 2009 - After filling the garage with smoke and setting the car on fire a couple of times, the body is reshaped to clear the Panhard bar mount.|
The welding's a bit ugly as I had a bit of trouble getting a wire wheel in to clear up the floor properly, but it's not terribly structural so that's not important. I'll clean it all up with seam sealer before it gets repainted anyhow.
I'm not sure what to repaint with. There's some sort of goo or tar in there that isn't factory and likes to make a mess of my clothes - you can see some overspray on the bottom of the panel just above my new patch as well as the variation in color. This part of the trunk is hidden beneath the trunk floor and is just used for spare tire storage. It's big, though, and I'd love to put it to work for me somehow.
entry 226 - tags: trunk, rear axle
|December 16, 2009 - The shocks are here.|
They're a set of custom single-adjustable T2s from AFCO. I worked with AFCO on the suspension for the Targa Miata and I was really happy with the process. Not just the final result, but the experience of working with the company. They're very responsive and willing to do all sorts of oddball things.
The custom shocks weren't that expensive, either. In fact, I probably would have spent more by going with a non-adjustable off-the-shelf coilover setup from someone else like QA1. I have a good collection of springs from previous projects, so I should be able to use those to get into the right ballpark. Most shocks in this price range have a fixed valving, which won't let me experiment with the suspension to get the ride and handling sorted out. Since I really don't have a clue what sort of rates I'll be running - particularly in the rear - I need the ability to swap springs around. The T2 has a huge adjustment range, so I won't have to get them revalved if I swap springs. I went with a single adjustment (rebound) as that's the more important one. If I want to upgrade them to a double-adjustable setup, that's a fairly easy change to make.
The shocks in the picture are for the rear. They've got a 5" stroke for some decent suspension travel back there. The upper perch comes off in seconds without tools, making it very easy to swap springs. The rubber bumper on the shock shaft isn't intended as a bumpstop, as I'll be using the factory MG one attached to the frame. The rubber's just there to protect the shaft seal in case of problems. The shocks are rebuildable if necessary. Oh, and the aluminum body is light, not that this is a big factor with a big heavy live axle.
Overkill? I don't think so. I like my cars to handle. The MG isn't just going to be a straight-line car. I picture it as a great touring car that just happens to have the ability to rip up a series of corners without breaking a sweat.
entry 227 - tags: suspension, shocks
|December 16, 2009 - After a bit of cogitating, I built this lower shock mount for the rear axle.|
I'm not completely happy with it, it's not as elegant as I'd like. But it should be strong enough. It's 1/4" plate, welded to the lower trailing arm bracket as well as to the axle tube. There's a triangular reinforcement taking care of some fore-aft strength. I'm still redesigning it in my head, we'll see. That lower shock mounting point carries the entire load of the car (well, 1/4 of it). Assuming the car is around 2600 lbs and evenly balanced (possibly both fairly big assumptions), that means there's 650 lbs on that perch. If it's designed for a 3g load, that means it has to support approximately 2000 lbs. I'll definitely be monitoring this!
The upper mounts will be attached to a plate that will spread the load somewhat. At least, that's my plan. We'll see how that works out.
Underneath the bumpstop, you'll see part of the original MG axle sitting on top of my axle tube. This means I'll have the same bump travel as the original suspension. I'm estimating a bit here, trying to set the shock up so it doesn't quite bottom out at full compression. I expect to have to do some fine-tuning in this area.
entry 228 - tags: rear axle, suspension
|December 16, 2009 - The front shock mounting is much easier to figure out.|
The shock is basically the same design we worked out for the Miata application, but fitted with a different upper mount. The bottom bolts right in to the Miata control arm, and a simple bracket will take care of the top. Lots of clearance. I left that upright on the frame for this purpose, looks like I got the dimensions just about perfect. It'll be tied into the unibody and hopefully cross-braced across the engine bay once I know how much room is available to me.
entry 229 - tags: suspension, front suspension