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Learning how to build Lotus Seven replicas...together!
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PostPosted: May 26, 2015, 5:55 pm 
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Location: S.W. Michigan
Ive been looking up possible ways to put inboard brakes into use with all the wearable parts being available off the shelf without modification. I think i found a pretty ingenious solution, but id like to see if anyone could see any problems with it.

A walkthrough of the picture:
1. Diff: The idea here is to cut down a solid axle as short as possible. This would leave the braking mounts and everything available for any typical upgrades of the donor.

2. Brake disk: Preferably the differential would have disk brakes, but they could be changed or upgraded pretty easily.

3. Wheel spacer: There would most likely need to be a wheel spacer added here to make room for the halfshaft stub and nut.

4. Extra bearing and hub: The wheelbearing shouldnt actually be required but is an option for people who would feel better with it there to help support everything. the hub would spline with the halfshaft allow it to bolt to the spacer/rotor/differential section, would probably require extended studs.

5. The halfshaft: halfshaft would be for a miata or if it fits possibly an rx7. this is only because of the tulip cup for the upright side that i found is made for a miata. If another could be found or made it would allow any halfshaft to be used, but they would likely be quite expensive.

6. Outer Tripod tulip stub: This is readily available from FSAE suppliers (RCVpeformance.com is where i got my information for it). Weighing in at just over a pound and without any rotors and calipers there is a massive reduction in unsprung wieght.

7. knuckle: Can be much lighter now that it doesnt have to support the torque of the brakes being applied and doesnt have to mount anything but the control arms and wheelbearing. Control arms can also be lighter weight now that the hub doesnt try to twist them apart when the brakes are applied. This means no more broken and bent control arms from hard braking or trailbraking.

8. Wheels and tires: These can now be any size since there are no brakes to consider. for example 13" wheels and 14" cobra rotors are an option, lol

there is a decent amount of rotating mass added by doing this, but unless power is a limiting factor it shouldnt be an issue. most of the mass is speed dependent and also not far from the rotation axis, so it shouldnt be much of an issue.

Looking for any suggestions or constructive criticism, thanks


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PostPosted: May 26, 2015, 6:16 pm 
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Jaguar did something similar.

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PostPosted: May 26, 2015, 6:45 pm 
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Military HUMMVEE's have inboard brakes as well. It would be great if you could pull it off as that would allow for much smaller spindles and therefore wheels and tires.

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PostPosted: May 26, 2015, 7:11 pm 
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I thought about something similar, maybe a future mod for way down the line.

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PostPosted: May 26, 2015, 7:42 pm 
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But if you do it make some removable panels so that you can get to the calipers to change pads from the inside.

Also you'll need to find a way to duct some more air to the brakes. It gets very hot under there and diff fluid and seals can have a limited life.

I haven't had inboard brakes on a 7ish for at least 12 years but I swore that no matter how good it sounded on paper it just wasn't worth the trade offs.

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PostPosted: May 26, 2015, 7:43 pm 
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get a vw transaxle cut off the bell housing then remove the gear box just keep the diff and the pinion shaft.

modify the pinion shaft to take a drive shaft, now you have a magnesium cased diff with output flanges for independant axles using cv joints several different sizes are available to suit this transmission.

now follow my mod to fit inboard discs to a vw transaxle

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PostPosted: May 27, 2015, 4:19 am 
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I think there are more for`s than against`s in favour of the inboard brakes. Unsprung weight is a big factor and removing all of the torsional twisting forces that an outboard setup imposes on the wishbones another. The inboard accessibility is not a problem if its part of the design as is extra ducts to compensate for the lack of cooling . There are also no flexi brake lines needed and very short handbrake cables both of which are a pain to route to an outboard system.

Bob

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PostPosted: May 27, 2015, 11:54 am 
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You still need flexible lines for something that doesn't get torn down between every race. ... It may seem like you don't but you do.
Mounts flex, calipers flex, heat causes expansion of metals, etc.
Air ducting isn't horribly difficult but it does need to be addressed, caliper/rotor heat taking out shaft seals is a major problem on inboard brakes.

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PostPosted: May 27, 2015, 12:28 pm 
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I will go with that flexy pipe theme Jack but it can be as simple as the way citreon did it with a loop of copper brake pipe. The image below is how they piped up the suspension on some of their models, if those coils are all it needs to soak up the full suspension travel of a Citroen then one loop would cope with the flex of a rear suspension set up or a caliper.

Bob

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PostPosted: May 27, 2015, 1:55 pm 
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Thanks for the nod of approval guys. Another option i had before i thought of this one is to use a supra differential but between the unique bolt pattern and the need to find a way to mount the calipers to it i was just never happy with it. short of mounting calipers to the chassis (this didnt sound like it would work well) i couldnt think of a solid fix.

i heard of those VW's made to use inboard brakes but i hadnt seen any pictures, that looks like an impressive setup, what kind of power can that expect to hold?

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PostPosted: May 27, 2015, 9:07 pm 
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the one shown is a standard beetle trans, it is usually the trans itself that fails before the diff.

as to the amount of torque that could be forced through just the diff, i have no idea.

you didn't say in your original post that you were in the 500 ft.lbs. league.

if you need something really tough, then merkur scorpio or xr4i, you could use the mounting holes to bracket the calipers from as well as mount the diff to the chassis.

these are good for a cosworth sierra 500 in europe, see pic.
Attachment:
cossy sierra.jpeg
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good for about 500 hp
Attachment:
sieera diff.JPG
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PostPosted: May 27, 2015, 10:19 pm 
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The Jag XJ lump is a good choice in my opinion, basically it's a Dana 44 with odd sized bearing races.

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PostPosted: May 30, 2015, 8:52 pm 
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main downside of inboard brakes is that the heat generated by the brakes cooks the seals on the output shafts on the diff. I have a 69 E Type, ask me how I know
cheers
Doug

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PostPosted: May 31, 2015, 3:11 am 
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I had a 64 Etype and in road form never had issues with cooking brakes or seals, I was never really very kind to it and it was driven in anger . That said it was modified to the later xj brakes with vented fronts and girling rears. The XJ rear end with inboard brakes is used in 90% of all the Cobra kits built in the uk , for general road use and the odd track day everything is fine . I suppose if its an original heavy jag track only car the rear discs would need changing for bells and vented discs with cooling ducts. It also needs pointing out that the weight of the cars being built here are a fraction of the two and a quarter tons of the originals weighed, that alone would reduce the heat build up by a massive margin, couple this to the fact most of these cobra`s have found the rears to be overbraked and had to fit bias to reduce the rear`s which is probably why the Cobra`s raced here dont have issues either.

Bob

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PostPosted: May 31, 2015, 11:45 am 
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Inboards pass all your braking forces through your half shafts, joints, etc. For what that's worth.


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