Inboard Rear Disc Brakes - Plausibility

[dd-ardvark]

First off guys, not that your insight isn't any good on this forum, and I do want you to prove me wrong on that statement. It's just the question that I'm posing is generally not in the street scene of things. "Inboard Rear Brakes", If their so good, why don't you see them more. I know this question may not be for this site, but I'd like to run them on my Speedster Kit car. If you have insight into these..., Please enlighten me. I know their a high dollar item, so besides cost, what's the down side, you know..., the bad things to using them.

Is their a problem with transmission output stub axle flex and breakage?

With respects to hanging the caliper and disc in close proximity to the transaxle..., does it cause excessive overheating of the trans?

Is cooling a problem for the rotor / caliper itself?


I can see the plus side, that mounting the assembly inboard -vs- at the wheel would allow a very light unsprung wheel, although rotational mass would remain close if not the same.

I remember seeing these a lot in the early to mid eighty's on off road racers and a lot of European road race cars. Again please enlighten me with comments and criticisms.

Thanks, dd-ardvark

[Panelfantastic]

I don't know the tech reasons why OEM wouldn't do it but I'm willing to throw out some ideas about retro fitting a set.
I bet racers don't do it to keep the heat out in the airflow and to keep the clamping force close to the largest area of rotatating mass and for design/packaging reasons (they usually run big rotors and calipers).
The only place you see it in the aftermarket are street rods where cost is usually not a concern, you would have to have some pricey billet pieces made and you would have to design everything yourself.

[DORIGTT]

I've always considered doing a conversion like that for the 'coolness factor' but for practicality, my lowly Ghia doesn't have the performance specs or room to effectively do it while being cost effective. But here are some pages to check out on it.

http://www.jag-lovers.org/xj-s/book/InboardBrakeUpgrade.html

Various cars with inboards standard to check out their system.
http://www.answers.com/topic/inboard-brake

A company that has kits for sprint cars. http://www.sanderengineering.com/cat26.htm

Scroll down to the lower items for Wilwood inboard kits.
http://azracemart.com/store/brakes.html

[Tedzbug]

it's a stretch, but the military HUMVEE has inboard brakes also.......... not that it helps you much..... just FYI

[R2.0]

Inboard Brakes Advantages:
- Reduces sprung weight/helps handling
- protects brakes from damage (fewer lines ansd flex lines)

Disadvantages:
- Takes brakes out of airflow/cooling problems
- Makes the rear assembly more complex (Only works with IRS, needs extended stubs with more support, etc.)

[yetibone]

The only production based cars I know of that use inboard brakes were Jaguar XKE, XJ6, and XJS. Mabye others within that marque as well.

Replacing the rear rotors on those is no fun at all. Most labor guides say it's a 10 to 12 hour job.

I believe the benefit of lower unsprung weight is outweighed by the complexity, inability to shed heat, and difficulty to service.

Also, in a VW, you may also have to use shorter axles.

[volkdent]

They would also put a tremendous amount of stress on what would be the CV joints, in the Jags they had heavy duty UV joints.

[tom'72]

My mother has an '85 Citroën 2CV that has stock inboard brakes, never thought they would be better in any way then regular brakes really.

[Steve C]

Hi

The old Audi 100s had inboard discs. Its a nice idea but I feel its not worth the effort.

Steve

Audi 100http://www.arch.kth.se/~a98_don/images/audi100.jpg

[CPRcubed]

I did my college senior project by putting inboard rear disks on a '69 Baja. I used 914 calipers, Type III rear hubs, and machined the other parts (rotor hats, rotors, and mounts). Caliper mounts bolted to the transmission side cover studs. Rotor hats mounted to the tranny CV flange (using longer CV capscrews). The setup saved about 14 lbs unsprung weight per side. The brakes worked well, although since all braking force is now transmitted through the CVs and axles, it is very hard on those components. I ended up breaking one of the CV "bearing cages" due to the constant loading (I imagine applying the brakes is like launching the car from a dead stop all the time). Caliper orientation is also limited under there. I could not get them oriented to where the bleeder was at the high point. I had to unbolt the calipers to bleed them correctly. My calculations showed a very small improvement in suspension reaction with the reduced unsprung weight which probably is not worth the cost and effort associated with such a conversion. Cheers!

[Wally]

Hi

The old Audi 100s had inboard discs. Its a nice idea but I feel its not worth the effort.


So did the Alfa 155 models over here. I am sure other Alfa's used them as well.
Its a very good idea IMHO.
I don't really get the airflow concern for cooling? :
Airflow is much better at the trannny ends than encapsuled inside a big wide wheel :rolleyes:

The service issue is probably the reason for most factories not to use them.

[dd-ardvark]

Have you guys had a look at http://www.transworks.biz/ before. Seems that they may have come up with a new way of skinning a cat.

:cool: On their site, they machined IRS type1 side covers to accept outboard bearings to carry the weight of the carrier and output shafts, that by doing this it stopped stub axle breakage associated with IRS high HP type1 trans applications..., and consequently their running Inboard brakes as well.

Have a look, it's under FLANGE BEARING RETAINER, here's the link http://www.transworks.biz/TWP.html http://www.transworks.biz/brakes1.jpg

dd-ardvark / David