| LIFE OF A GT |
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 | |  | April 15, 2008 - There's a shield that usually covers the brake master cylinder pushrod.
One of the screws that holds it in place had been damaged by a previous owner, but after a bit of work I got it free. And here's what greeted me underneath. Yuk.
So it's a good thing I ordered a master cylinder rebuild kit yesterday. Moss says the master can't really be rebuilt, but I'm willing to give it a try. It's the difference between a $270 part and a $18 kit.
On a similar note, I got a call today from Gordon Strickland of the B Hive, confirming some of the slightly odd quantities in my order. He was very helpful, discussing some slight differences in the badges that might cause difficulties in my planned grille design.
entry 21 - tags: brakes | | |  | April 23, 2008 - Time to stop messing around with badges and grilles and time to fix a real problem.
The brakes. The master cylinder leaks badly and has to be rebuilt. I picked up a rebuild kit from The B Hive.
The first step is to remove the master. It's a bit of a puzzle really. It will come out, but you have to discover just the perfect way to twist it. I went a little further in disassembly than I really had to, but I got it out!
entry 38 - tags: brakes | | |  | April 25, 2008 - The master is out of the car and on the bench.
Time to rebuild it!
entry 40 - tags: brakes | | |  | April 25, 2008 - The first thing I did with the master was stick it in the bead blaster.
I haven't actually done anything to repair it yet, but it looks almost new now!
One thing I did do was install some Time Serts into the mounting flange. The factory used nuts and bolts here, and the lower nut is almost impossible to access. The Time Serts - similar to Helicoils - will let me use bolts that thread right into the master cylinder. Much easier. These particular inserts are too long to be ideal, but they'll work. Tapping the holes in the flange would probably also have been just as effective.
entry 41 - tags: brakes | | |  | April 25, 2008 - The master is mostly disassembled.
There are two snap rings that could be easier to reach! A pair of small needle-nose pliers did the trick, though. There's also a nylon spacer that is very reluctant to come out, so I borrowed a trick from the MG Experience forum and inserted a couple of screws to yank it out. A replacement came with the rebuild kit.
The next step was to take the piston apart to replace a couple of the seals. This was the most difficult part of the job. The assembly is held together by a couple of tiny roll pins, and it's difficult to gain access to them without marring the steel. It took a lot of effort (and some frustration) but I eventually won. I used a modified "precision screwdriver" as a punch and ground it down to the perfect diameter after some trial and error.
entry 42 - tags: brakes | | |  | April 25, 2008 - The inner bore of the master looked very good, much to my relief.
So I gave it a quick hone with this honing tool then put everything back together.
Of course, on reassembly, I had to remove the master a couple of times before I was done. Every time it had to come out, it fought me more. More frustration and I never did clean out the pedal box area as well as I should. I'll get the pressure washer in there soon and give it a good blasting.
entry 43 - tags: brakes | | |  | April 25, 2008 - More painting!
This time, the rear brake drums. They were ugly and rusty and very obvious behind the new wheels. So a shot of satin Rustoleum and we're good. You might notice that this is three different types of black paint so far. I used four, but I forget what the other was for! Oh right, the cover for the pedals.
So, how did the brakes turn out? Well, it took a bit of cleverness to get them bled properly with the dry master, but once we got a bit of fluid moving through they pumped up nicely. So it looks as if my brake master was a success, at least in the short term.
entry 46 - tags: paint, brakes | | |  | April 27, 2008 - Time for that all-important first drive!
This is always a big moment in resurrecting an old car. With Basil, it was a late-night run around the block at night with no brakes. Hopefully this one will be a little less exciting.
First off, the car's a bit of a slow starter when cold. I just haven't learned the magic ritual yet. Still, it does eventually roar into life. Yes, roar. There are more holes in the exhaust!
The clutch feels good and the gearchange is really nice. The steering feels good underway, although there's a bit of internal friction. It's as if someone overtightened it to get rid of some play. I'll check that out. The stiff (solid might be a better term) rear suspension certainly affects the experience though. I never knew there were so many bumps on my street!
The brakes have a solid pedal, but need a very strong push. There's probably a bit of rust on the pads, and I think it was getting better. Still, we were mostly cruising along and didn't spend much time on the brakes. I'll bed them in and see if that helps.
The engine seems healthy but the carbs probably need tuning, as the idle never drops down below about 1100. There's also a flat spot on rapid tip-in. Not a big deal, just a bit of fettling required. Oil pressure is strong and all of the gauges work with the exception of the engine temperature.
So, all good then? Well, not quite. The car's spitting out radiator fluid. And it looks foamy. Uhoh. The oil looked fine when I drained it, but either the stock radiator cap is completely trashed (possible) or something's pressurizing the cooling system. I haven't investigated this fully yet. It could be a head gasket, although there's no smoke. Further checking will tell the tale.
On top of that, there are also the usual oddities. The turn signal/high beam stalk is stuck on high beam. There are some weird lights stuck on and others that don't work, so I have to disconnect the battery whenever it's not running. But that's okay, that's part of the fun.
In other words, it's a basically decent little car. It has a list of things that need to be sorted out, but it's all doable and at a good level of difficulty.
entry 53 - tags: driving, brakes, suspension | | | December 15, 2008 - Not much actual work on the car, but lots of planning.
I'm going to go with a three-link rear after talking with a number of road racers and other folks on the Grassroots Motorsports forum. The lateral motion of a long Panhard bar isn't a big deal at all it seems, and it's free of bind and easy to fabricate. So there's that settled. I just have to do it!
I'm also starting to plan the brake system. Very little of it will be MG by the time I'm done. In fact, it's possible it will all be custom. I'll have to wait until the motor position is determined before I can finalize this but it's fun to build it in my mind. Brakes are important to me, and I like putting together good systems.
This is actually a very entertaining part of the build. I have all of the major components so I can start legitimately planning and figuring out how to do things. On top of that is the anticipation of the first big steps coming up - I'm looking forward to that first chop of the frame rail with anticipation and a little frisson of nerves. This is the stage where the whole car comes together in concept, making it a complete machine instead of just a collection of bits that are a reaction to unforseen problems.
I love this part.
entry 108 - tags: suspension, brakes, rear axle | | |  | June 28, 2009 - The new axles have arrived.
Now I can mount the Miata brake rotors and wheels to the S10 rear housing and that opens up a lot of potential work. The picture shows what needs to be done to fit the brakes to the housing - I'll weld a new bracket on to the tube. I'm not sure if I'll try to cut the original one off or not, it'll be a huge amount of work if I do. Depends on the access I have for welding the new one.
I have one wheel mounted on the rear now, I'll install another one soon and roll the whole thing under the car to see how they sit. I already have a pretty good idea, but of course I'm still eager to see it.
entry 190 - tags: rear axle, brakes | | |  | 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 | | |  | January 22, 2010 - It's time to make sure I have room for some real brakes.
The car originally came with unboosted brakes, and long-time readers will remember that I rebuilt the master cylinder. That was back when I thought I'd be driving the car as a four-cylinder for a while. Ah, those were the days.
Purists, of course, claim the unassisted brakes are superior in almost every way. But those who are sensitive to subtle hints may have noticed that I'm not much of a purist. I have several cars with unassisted brakes (interestingly, they're all British or replicas thereof) but this car will have a fairly intense power/weight ratio, and I want power assist. Besides, the whole braking system has been replaced with Miata parts, and my rear discs take more pressure to operate than the previous drums.
The problem is twofold - first, there's not much room for a booster underhood. And secondly, the original pedals put the masters above the driver's feet - so there's simply no room for a booster at all in that setup. There are such things as remote boosters which are intriguing. A number of newer vans (and other packaging-challenged cars) also use a "hydroboost", which steals hydraulic pressure from the power steering pump for assist.
But there's an easier way. In 1974 or 75, MG added power assist to the MGB. And in order to do so, they used a very small brake booster, a master cylinder with an angled top to clear the hood, and a different pedal box that put the brake hydraulics in front of the pedal. And it's a simple bolt-in to the earlier cars - although most MG owners go the other way, installing the unassisted setup. I found a complete pedal box, booster and master on the MG Experience website and had it in my hands a week later.
The first trial installation showed that it's a perfect fit. The front outlet is fairly close to my shock tower mount, but a well-placed divot would take care of that. The rubber line that runs close to the booster is actually the vacuum line on the engine. It's just sitting there, I can easily route it with lots of room.
I need to do a bit of figuring with pedal ratios (looks like it's in the 4:1 range) and master cylinder sizes (0.75", apparently) and see what that does for my brake pedal travel. I may want a larger master, as the Miata has a similar (4.1:1) pedal ratio but runs a .875" master. I'll measure the MG one more carefully tomorrow. Luckily, mounting a Wilwood unit is fairly straightforward. So there may be no reason to put that dent in the sheetmetal anyhow.
First, I'll stick this setup in the bead blaster and make it all pretty!
I've been puzzling on the best way to package this for a while, looking at various booster combinations. But I'm really happy with this result. I think it's going to be very clean.
entry 258 - tags: brakes, hydraulics | | |  | January 24, 2010 - I love my bead blaster.
That's the pedal box for the boosted brakes on the right, with the unassisted setup on the right.
entry 259 - tags: brakes | | |  | January 24, 2010 - After a fair bit of calculation, I'm starting to figure out my brake options.
From my measurements, it looks like the MG brake pedal has a ratio of 4.48. That means that 100 lbs of pressure on the pedal is transformed into 448 lbs on the master cylinder. It also means that it takes 4.48" of pedal movement to move the master cylinder pushrod by 1". Basically, it's the same as a gear ratio. The Miata pedal has a ratio of 4.1 according to the manual.
I know the Miata setup pretty well, and the Targa Miata uses the hydraulics from a later Miata setup. The standard Miata master cylinder is a 7/8" unit, and the Sport master is 15/16".
As you can see from the picture, the stock MG master cylinder is 13/16".
So, based on pedal ratios and master cylinder sizes, I compared how much force on the pedal is needed to get 250 psi of line pressure. Why 500 psi? No reason, it's just a constant so I can get an idea of how the different setups would compare in feel for the same amount of braking. I also figured out how far the pedal would have to move in order to push 1 cubic inch of brake fluid, as the leverage ratios and hydraulic multiplication always trade off travel for effort. Here's what popped out of my spreadsheet:
- MG pedal, MG master: 57.87 lbs, 4.32"
- Miata standard setup: 73.3 lbs, 3.41"
- Miata Sport setup: 84.2 lbs, 2.97"
- MG pedal, 1" Wilwood master: 87.7 lbs, 2.85"
So no surprise here, the further you move the pedal the less you have to push on it. Simple leverage. And if you're doing these calculations at home, remember that it's a dual circuit system so you'll get half the pressure and twice the fluid flow as you would with a single circuit of the same size.
According to my calculations, a 15/16" master on the MG pedal (77 lbs, 3.25")would be pretty much right between the two Miata types. But the dual circuit remote reservoir master cylinder available from Wilwood is a pretty unusual piece, and only available in a 1" bore. I need the remote reservoirs to clear the hood, I believe. I do have a few other single circuit master cylinders I can use for test fitting for clearance.
Still, since Janel and I both prefer a nice firm pedal, I'll probably go with the Wilwood 1" setup.
But of course, there's a catch. The booster. All the calculations above give the numbers for an unassisted brake setup. The booster will multiply the force on the pedal to give more force at the master. If the booster has a 2:1 boost ratio, that means it would only take a bit less than 44 lbs of force on the pedal to generate my 500 psi of line pressure, instead of 87.7. And here's the problem. I don't know what the boost ratio of the MG booster is. The Miata one should be around 4.6 according to the manual.
So the end result is going to come down to trial and error, with a bias towards a too-firm pedal instead of a too-soft one.
This stuff is fun. I get to learn all sorts of things.
entry 260 - tags: brakes | | |  | January 24, 2010 - Sometimes, you have to walk away from a problem for a while.
I don't know why I didn't think of this - the Miata comes with either a 7/8" or a 15/16" master, depending on the application. It has a plastic reservoir that can be removed and turned into a remote setup. And while the bolt pattern isn't correct for the MG, its close enough that I think I could make it work.
I'm also going to make sure the Miata booster won't fit on the MG pedals. If it does, then life is very simple. I'll have a complete Miata brake system with a slightly different pedal ratio. I'll find out tomorrow.
entry 261 - tags: brakes | | |  | January 26, 2010 - So, while trying to figure out a few things about the MG booster, it was suggested to me that I try to fit the Miata booster.
As with everything else in this car, make it more like a Miata! Well, my initial reaction was concern that it would fit - the MG part is silver and the Miata one is black in the picture. There's nearly 2" of diameter difference involved.
But I had to try.
entry 266 - tags: brakes, packaging | | |  | January 26, 2010 - And voila!
Some light massaging of the inner fender with a 2 lb sledge (about the only part of the inner fender I haven't actually cut off by this point), a new bolt pattern on the pedal box and some clever twisting and turning of the assembly to get it into place, and there's my Miata brake booster installed in the MG.
In researching this, I found that there are actually three brake boosters that have been used over the years, with three different boost ratios. I'll be able to fine-tune my braking effort nicely. Now I just need to source a 15/16" master cylinder from a 2001-05 Miata. Easy enough.
There's just one problem with the fitment of the new booster.
entry 267 - tags: brakes | | |  | January 26, 2010 - The booster and the engine end up very close to each other.
Very close. That little port on the head is only about 1/4" from the edge of the booster. It's normally connected to vacuum line that runs from one head to the other, I suppose to prevent pressure buildup on one side.
I looked at a later LS1 and an LS3 in the shop, and I got bitten by the 1998 donor again. In 1999, the heads and valve covers were changed to a center bolt design instead of the peripheral bolt setup I have. This means I can't use a particular Edelbrock coil cover I thought would look great, but that's not important right now. On my engine, both valve covers are the same casting. The little port on the driver's side that's causing me problems is where the oil filler is placed on the other head. On later engines, the driver's side valve cover has a much stumpier protrusion for this port which would give me lots of clearance. This is not a big problem, I'll just whack it off and weld it up. If I decide to keep the connection from head-to-head, I have a few options. So it's not a show-stopper, it's just a bit more work. And it means I'll have to pull that valve cover off - easy to do, just something I was hoping to avoid.
Still, the final result is good. Other than a slightly different pedal ratio, I'm basically running a full Miata brake system. And I know Miata brake systems!
entry 268 - tags: brakes, packaging | | |  | August 29, 2010 - As promised (threatened?
), the rear axle has been installed. It's full of fluid, has the axles installed, brakes bolted up - it's all looking quite serious now! I still have a few things to do back here, such as working out how to make the Miata and the MG emergency brake systems and locate the platform for the bumpstop. You can see it here sitting on top of the axle. The bumpstop is installed on the chassis. I have to set things up so the bumpstop reaches full compression right before the shock bottoms out. Thus the lack of a spring, so I can do range of motion testing.
I pulled one of the bumpstops off a while back to play with it, and haven't been able to get it back on since. They fit over a mushroom shaped stud, so they have to deform to pop into place. Well, I finally got a brainstorm - I sprayed a bit of Simple Green on the bumpstop (great for lubricating exhaust hangers as well), held it in place, then used a jack to push the axle up. The axle pressed the stop into place with an easy little pop. Sometimes the thinking is much harder than the doing!
entry 371 - tags: bumpstop, rear axle, brakes | | |
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