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PostPosted: February 25, 2019, 2:02 pm 
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Miata, I'm not married to that axle, I only bought one to confirm spline fitment. I am kind of married to the Blazer outer hub bearing and the Chevy splined diff. I could not find great information on what CV axles have what splines and took an educated guess that that axle would fit both my diff and hub bearings. It just needs to be 8" longer. I'm open to other CV axle options.

This render shows the steering rack design. I bailed on the full tube design because I felt it needed support out on the ends and there wasn't enough room for full stroke to clear from the welded support to the eyelet.

I noticed on that rack, it gets a little bindy when you push off axis, so I think it needs support out as far as you can get.

The flats were already on the stock rack and the boots originally went past those. I plan on keeping the support bushing just shy of that during full stroke and the clevis does not go into the support bearing at full lock the other way, so I'm happy with that.

I could go with a solid rod and thread both ends, use a stud to connect to the stock rack. Then bolt a 1/8" thick U bracket on the outside, that would probably be about as beefy as it could be made.

Thanks for the ideas and criticism, don't hold back!


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PostPosted: February 25, 2019, 3:12 pm 
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I don’t know. That still sounds like marriage to me. :lol:

I guess you have a 28 spline, Eaton “Detroit True Trac” for a 7.5 to 8.6 inch ring gear, straight axle application and small blazer, 27 spline, front wheel bearing hubs. Modifying what you have looks to be the most cost effective option. You could weld vw cv flanges to the wheel and diff cups to fit Porsche 930 cvs and 3x3 bus axles at 19.5” or 20.5” but it will cost a lot more by the time you are done. Might grind a small chamfer in the cv inner race for if you ever need to pull it apart again.

I think a street legal formula vee would be cool, with the bec driveline sideways, fit a hawk driveshaft adapter and a single ujoint to couple to an R160 diff flange, matching axles, and hub bearings if the rotation and ratio would be acceptable.

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PostPosted: February 26, 2019, 1:22 am 
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Yeah, the diff is for a Chevy 28 spline 7.5". That brand sounds right, it's got the helical type gears, and is mostly sealed off so I can just plug a few holes and run it in the air. It looks like they run fine on grease so I'll add a few grease zerts to it also.

I guess my inner-hill-billy came out there for a second. I'll try not to let that happen again. :oops: It's not like I was gonna leave it in there looking like that.


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hillbilly_tierod.png
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PostPosted: February 26, 2019, 1:39 am 
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Now that I have the steering somewhat figured out, I tacked in a few more braces. At least it's starting to look like something other than a steel canoe.

The roll hoops (steering and helmet) have me a bit stumped, I don't think I can make them without a mandrel tube bender. Is there a good place I can just send a CAD drawing to and have them shipped to me? And I'll trim the ends to fit. They have the same radius.


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PostPosted: March 1, 2019, 4:48 am 
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There may be fab shops in your area that can make what you need or you can try by mail.
Ask about the equipment they use so you can determine the limitations for od, gauge, mat, and radius before telling them what you need.

Mandrels are not normally used. Smaller od, thicker wall, less than 180 all help.

A few online:
https://secure.chassisshop.com/partlist/19412/
https://store.windingroad.com/custom-ro ... p1035.aspx
https://www.swracecars.com/store/Custom ... R_508.aspx
https://race-crafters.com/roll-cage-and ... s-experts/

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PostPosted: March 13, 2019, 1:47 am 
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I already changed the design a bit, but this is my plan for mounting the diff. There's a layshaft in the middle which allows centering the engine and the diff and having the same length drive shafts. The swinging plates will allow chain adjustment and mounting the rear calipers relative to the rear axle if I go inboard brakes. With a layshaft I need to be able to adjust both chains, the layshaft will have eccentrics, the rear has the swinging plate.

There will be an adjuster of some sort between the lower right holes. The upper right hole will just have a shaft that holds the plates apart.

I'm gonna turn into a Butter Burger if I'm not careful.


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PostPosted: March 13, 2019, 7:54 am 
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Considering the output rpm, you may want to eliminate the lay shaft (and bearings) and use a slack side tensioner on a single chain. Also eliminates the need for all the machine work to be able to mount a replaceable sprocket on the layshaft that can handle the torque.

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PostPosted: March 13, 2019, 11:51 am 
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Not quite sure what you mean. But to clarify, the engine sprocket and the diff sprocket are offset maybe 3-4". I could move the diff over that 3-4 inches, but that would result in different length axles. The BEC book suggests this, but I don't like it. moving the diff sideways would also screw with how the diff gets held to the engine, the diff bearings line up pretty close (width wise) to the rear engine mounts.

Believe me, I would like something simpler.

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PostPosted: March 13, 2019, 3:59 pm 
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Check the primary reduction and gear ratios to determine the max rpm the drive sprocket will turn in high gear. The layshaft will be turning close to this rpm because you don’t have much room for a reduction. Capacity of the bearing goes down as rpm goes up and the shaft od and length is another consideration along with the seals, grease type, etc. Nail down the parts specs and cost. You might also contact the bearing mfg for recommendations after reviewing their specs. Most high quality bearing mfgs have their design catalogs online:
https://www.timken.com/wp-content/uploa ... alog-1.pdf

As for the 3-4 inch offset, split the difference. Use a stock Colorado axle ( I forgot the length difference) on the left with a custom on the right for more savings. Move the engine over the last ½-1 inch or whatever is necessary. Just a thought. Unequal axle length is not ideal but not a problem either.

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PostPosted: March 14, 2019, 12:40 am 
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The output spline on the engine is 30mm. I haven't picked a bearing for the layshaft yet, but I have space for a big one (or 2). I guess I was just gonna use a 30mm and find a similarly splined shaft so I could use standard sprockets (or what ever the Honda uses). I had planned on a 12 tooth on the engine and an 18 on the layshaft. I am assuming I can find splined shafts somewhere.

My calcs show the output shaft on the engine spins at 2300 RPM at 11,000 RPM in top gear, so not too bad.

The book suggests simply using different length axles, I'm just not sure I can bring myself to do that :lol: I know in RC cars that axle angle can effect the suspension action under load. I think the book addresses that too, and says the effect is minimal. My axles should be level at ride height and are pretty long so probably even less effect. But I'm kind of a symmetry freak...so...

The offset is 3.0225". :lol:

The input shaft of the layshaft is cantilever, the output sprocket is close to one side and the other end of the shaft is in a bearing. If I put 2 bearings on the input side I can reduce the cantilever a bit, maybe make the eccentric adjuster on that side super beefy (technical engineering jargon).

Oh, I cut the axle in half and turned it a bit to see if I can get a good fit to the extender tube (which I don't have yet). I must have gotten lucky with the tool and lathe setup cause I got an amazing finish on it. Maybe because it's chromoly or something. Hardness was a bit much for HSS but carbide cut it fine. I was amazed for a mini lathe. The most difficult part was getting a center hole in the cut end...a Dremel was involved.


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diff_01.jpg
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axle_cut.png
axle_cut.png [ 776.5 KiB | Viewed 1201 times ]

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PostPosted: March 14, 2019, 6:58 am 
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Thanks for the drawing. I see now.

The output rpm of 2300 rpm sounded low so I searched for cbr1000rrspecs and found the primary reduction is 1.604 with high gear/6th is 1.16 for about 6,000rpm at 11,000 engine rpm. Not as high as I expected. First gear is 2.538 for 2700 at 11k. I don’t know what year model these specs are for.

https://hondanews.com/releases/cbr1000r ... mode=print

I think the cbr1000RR spline profile is only used on Honda’s, and only those in the750-1000cc range.

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PostPosted: March 14, 2019, 1:01 pm 
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Yep I mis-calced the RPM, you're right, it's about 6000.

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PostPosted: March 14, 2019, 4:08 pm 
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Is a keyed shaft like this going to be sufficient? 1.25" 1/4" key.

https://www.thebigbearingstore.com/1-1- ... yed-shaft/

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PostPosted: March 14, 2019, 5:24 pm 
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The size yes, the single key, no. That is essentially what I am using on the 1100cc diesel (around 25hp) reverse trike with a polaris cvt except mine is 4130 tubular for a kart axle and QD bushed.

You might consider welded flanges to mount sprockets or weld sprockets directly between the bearings to the same size axle. Plain universal gears and axle are cheap. You could also keep the design you have by installing the bearing before welding. Make a spare at the same time.

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PostPosted: March 14, 2019, 5:34 pm 
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I'm not a fan of single key when the hp goes up.

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I can't tell you how many things I broke on the A Mod with a CBR600RR and chain drive. All those things survived years with a snowmobile motor and CVT clutch. The CVT does a lot to dampen the shock loads to the system.

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