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PostPosted: July 23, 2013, 2:08 pm 
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Always Moore!
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rrobb wrote:
It happened right as I let out the clutch going to second.


I wonder if it hadn't started to fail and the shift into second just finished it off?


cheapracer wrote:
You have some chassis issues going on there, either an ackerman issue or your RC axis angle might be too shallow.


The front KRC is 3" above the ground and the rear is 6". The rear used to be 4" but I added another adjustment.

When I built the car I thought I was careful making sure the steering points where correct. Your post got me second guessing myself so I went downstairs, clamped two pieces of tubing to the outside of each front tire, marked points 12" and 24" forward of each tire's leading edge, turned the steering wheel, and took some measurements.

Both sets of points were 64" apart*. That explains quite a bit like why the car was actually pretty good on a real track but not so much on tight autocross turns. I guess the stickier tires allowed for more weight transfer which minimized the negative impact of the inside front tire.

Time to design some new steering arms: good call CR. I probably won't get them done for the next event so maybe I'll just add a little more toe-out and see what happens.

*On the plus side, my front track is 56" and the tire has a section width of 8" so apparently the rest of my build tolerances were pretty good!

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PostPosted: August 16, 2013, 11:15 pm 
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The Locost hit the track again:



Following on from this thread, I added an oil cooler prior to the outing. I decided to build a plate to replace the stock oil fitting and the only way to have a port to use for a pressure reading was to use a T-fitting. A smaller one worked with the stock aluminum piece so I figured adding a larger one would be fine.
Attachment:
IMG_1195.JPG



Of course after the second session my buddy pointed out a few drops of oil beneath the car. I saw the fitting was wet and figured it needed a little turn of the wrench. Low and behold the fitting completely sheared off. I guess it was cracked and tightening it finished it off (the weight of the line and the senders probably didn't help.) Time to roll the car onto the trailer and head home. :BH:
Attachment:
IMG_1211.JPG



I decided to go back to the old set-up and a filter bypass adapter. Hopefully this fixes everything.
Attachment:
IMG_1205.JPG

Attachment:
IMG_1208.JPG



I've thought about calling this build "complete" but the car just doesn't seem to agree - there is always something!


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PostPosted: August 17, 2013, 6:55 am 
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you may get more toe out in a turn by reducing your caster?

the oil fitting shown, well look at it, come on, it has all that weight on it and a sharp corner at the base of the thread and i would not be surprised if the one holding the switch and sender arn't far behind either.

come on Andrew, you are better than this, every time you go on the throttle that tee moves up and down, every time you go over a bump it does the same, too much weight hanging on a bit of brass casting.

go back to the first piece that you made, turn it over and machine a groove in the back then drill and tap a third hole.

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PostPosted: August 17, 2013, 9:37 am 
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Those tee's are known to fail when used that way. Vibration is bad for copper and brass fittings, they work harden quickly and then fatigue. It reminds me I should take a look and see what my FF uses for this, I think I have the same switch...

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PostPosted: August 17, 2013, 10:17 pm 
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I was going to tap and drill the center of the plate but there isn't enough room between the 10AN fittings for the gauge sender and the light switch goes too far into the hole and plate isn't thick enough.

I'm not that shocked that it didn't work since it was a concoction of plumbing but I don't think the 3/8 NPT tee-fitting failed purely due to fatigue. It happened way too fast and the break surface doesn't exhibit signs of a fatigue crack (its not a clean break at all). Looking back I think it was self induced; I wasn't able to get a wrench on the tee-fitting when I was tightening the hose and I probably started the crack. Maybe I need to stick to Home Depot stuff of unknown specs since the 1/4 NPT tee-fitting has survived over 4,000 miles. :mrgreen:

I think I need to do one of these to be truly safe:
1) Buy a forged steel 1/4 NPT tee-fitting from McMaster to replace the one that is currently on the car.
2) Buy a different oil filter bracket and mount the gauge sender to it and eliminate the 1/4 NPT tee.
3) Beg/borrow/steal to get access to a mill and make a really nice custom adapter fitting with as many ports as I want.

Eurospeed apparently makes something kind of like what I want but it still does not have a port for a sender. If they offset the ports in the other direction it would leave enough room to tap and drill on the return side.
Attachment:
getrempic3.jpg


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PostPosted: August 18, 2013, 12:07 am 
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Andrew,
If you need a special plate made, we have a Bridgeport sized vertical mill at PJ's and I have a tabletop mini mill at the house. Will be happy to make a piece if you make a reasonable drawing of what you need for sizes and locations. Speedymetals.com or onlinemetals.com are good sources for 6061T651 starting material. Let me know if I can be of help. Also have alum. & steel welding machines and ONE pretty good welder.
PJ and I made supercharger adapter plate for his 4.3 going in the Land Cruiser on his mill.
Old machinist Don


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PostPosted: August 24, 2013, 11:42 pm 
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Nice! That sounds like a fun project.

Thanks for the offer. I'll have to figure out what I want to do and get some drawings together. I'll be in touch. ;)

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PostPosted: December 4, 2013, 12:13 pm 
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Andrew, i'm new on this board and for some reason can't send you a PM. I have a Duratec / Mazda 6-speed going in to an old English Ford and am wiring up the speedometer (well, looking to). The transmission I bought didn't have the pigtail on it, so I am trying to locate one of those for the Speedometer sensor wiring. Looking at the transmission, is the speedometer sensor the clearish/light green sensor? Where did you get the sensor harness /pigtail for your car? Was the wiring to the aftermarket speedometer straight forward?

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Bryan


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PostPosted: December 4, 2013, 7:26 pm 
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Hey Bryan - my transmission actually did not even have a sensor; I believe the NC Miatas use the wheel speed sensors for the speedometer. It did have a plastic plug that was the same shape as the sensor but it did not have any of the electrical parts inside and I do not believe the shaft behind it had any teeth. I just looked through my archive of build pictures and I do not have a good photo but it is located near the tail end of the transmission on the driver's side just forward of the shifter and is white. Here is a blurry picture I cropped out of another:
Attachment:
speed sensor.JPG


If yours is a real sensor the dealer may be your best option. I found that Ford was really good at having pigtails available - maybe Mazda is the same or maybe a Ford connector will work?

I had a spare crank sensor for an F4i bike engine laying around and I attached it to the differential so it would trigger off of the ears for the driveshaft yoke. It is a typical VR sensor that is oil proof so I figured it would work well for the application (plus it was free - here is a picture: download/file.php?id=15790 ).

I used an aftermarket speedometer so wiring was very easy; just power, ground, and a wire to one side of the VR sensor (the other side of the sensor is grounded). The aftermarket speedometer has you program it so it knows how many teeth it is reading. If you want to keep the stock gauge cluster this probably won't help you.

BTW new members have limited capabilities for their first few posts. You've met the limit so you should have full access now.


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PostPosted: December 5, 2013, 9:37 am 
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Adam, thanks for the reply. While I was waiting for my post to get approved, I found your post about your cam sensor set-up you did and the sensor being a dummy. Mine is the same way, it was confusing me when I was looking at it because everything I found online LOOKED like it, but was black with actual pins, and mine didn't have pins so I was like how the F do wires hook to it...........SO, i'll either have to do like you, or there is a guy that did a 6-speed MX-5 gearbox in an old Escort that I asked how he did the work.

I was going to ask about the cam sensor set-up and how it knew what it was reading to translate into speed......but you answered with the programming of the speedometer.


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PostPosted: December 5, 2013, 12:03 pm 
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Would an aftermarket GPS speedometer not work for you? I think it would eliminate a lot of problems.

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PostPosted: January 12, 2014, 11:59 am 
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Small update - I've been running with an open differential since day one. It was sufficient for the street and even autocrossing with the stock ECU/intake. Once the MS and the ITBs were installed and a little more power was available, it was evident that unloading was a real issue for autocrossing and track days.

I purchased a Miata Type 2 Torsen a few weeks ago so hopefully this is the fix. So far the swap into the RX7 housing has been pretty painless. Once I get some larger calipers and set the bearing preload everything should be ready to go back together.

Before:
Attachment:
IMG_1564.JPG


After:
Attachment:
IMG_1571.JPG


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PostPosted: January 12, 2014, 1:33 pm 
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Andrew,
You may need a whole new driving style. Might have LOTS of oversteer like the solid axle go-karts I used to run. Can you say sideways? Ta-dah!!!! Maybe we'll get out to see you this spring?
Don


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PostPosted: January 14, 2014, 1:31 pm 
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I'm kind of figuring something will change - hopefully for the better.

I still need to add more ackermann to the front. I'm crossing my fingers and hoping that the geometry change will help the mid-turn front grip and the LSD will reduce some of the on power under steer along with keeping the inside wheel from unloading. The Sprite has a spool in the back so if nothing else it will be good training.

You guys definitely need to make it out. Steel Cities posted their schedule and autocrossing is tentatively scheduled to start on May 11th.

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PostPosted: May 13, 2014, 5:15 pm 
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After the first event of the season I'm happy to report that the Torsen swap was a success. I've never assembled a differential before so I was a bit nervous about missing something and having it whine like crazy or do something else bad.



The on-throttle characteristics are noticeably different but much better and you no longer need to drive around the inner rear tire's grip.

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