Possible project: inboard cv joint mount disc parking brake?

[Piledriver]

Possible project: inboard cv joint mount disc parking brake/s

Laser/waterjet cut rotor, 90 or 100mm CV joint pattern. (T1/914/T2/T4)
Use the cheap/simple mechanical spot calipers, probably a floating caliper mount bolted to the trans side cover.

Allows using the excellent and extremely light std Wilwood etc calipers in std outboard location, rather than the brutally heavy OEM setups with the cable operated parking brake, which are admittedly ~trivial to use even with factory parking brake cables.

I vaguely recall seeing this discussed ages ago but I cant find a disc or kit to buy.

Currently running Passat etc calipers out back, picked up some very similar design Ford late model 2.3L Mustang units ...but they still weigh a ton (compared to Dynalites) even in aluminum, but can be trivially modded to handle .810 vented rotors.

Factory Ecoboost 2.3 rotor is ~.5"ish solid if I am not misteaken, but theres a ton of meat in the pad carrier, which is under little>no load in the required milled areas, looks like they designed pad frame for a wider rotor as an option, only requiring a quick mill pass to widen. The floating piston/pad clamp part is plenty wide as-is.

Discuss?

[Ol'fogasaurus]

Disgusted before here.

The main draw back to this is that if there is a busted half-shaft or stub axle then that side's parking brake won't work. Inboard braking system, as you know, have been around for a long time so the parking brake has been a point of contention hence they have moved from place to place. I have even seen them mounted on the rear U-joint in front engine cars (busted R&P anyone?). When some companies used axle keys and/or tapered axles w/axle nuts the e-brake there was less of a problem as the wheel and brake drum would usually fall off the can and it would be parked that way (axle keys being sheared may not cause the axle to break so the e-brake would work... more of less especially if the an axle key had been broken many times and the drum or axle had gotten worn down; been there done that).

Check to see but as I remember mechanical parking brakes and I think outboard e-brakes might be part of the DOT thing, or at one time they were. It is a safety thing like not allowing the in-line POS out there.

I did a quick search which was interesting; you have to look hard and long to find much. Commercial vehicles are better covered than passenger vehicles and modifying vehicles I saw some half-way good in some states and almost zilch in other states.

The states rules are interesting and usually vague at best as there are only partial contingencies given the rest would be discussed in a court of law I suppose.

https://www.law.cornell.edu/cfr/text/49/393.41

Look at #3... interesting

[aircooledtechguy]

Would this simply be as a parking brake or would it be for all braking too?? Does the Wilwood caliper have a separate mechanical P-brake or would you simply run a hyd p-brake?? I can tell you from experience that hyd p-brakes don't hold for more than 20 minutes after you walk away from the car due to brake fluid cooling and releasing the pressure. It's also illegal for that same reason.

[Piledriver]

The idea was to use mechanical spot calipers inboard, as I know the hydraulic locks, don't.

A lot of street rods simply add a second spot caliper outboard, is likely a simpler option, but is ~killing the lighter unsprung weight part of the inboard setup, might as well run the OEM units.

With a solid rear axle it probably doesn't matter.
Given the weight of stock trailing arms it may not really matter very much for us.

[Ol'fogasaurus]

I know that some disc setups have a mechanical brake that works against the inside of the rotor. I am not sure how others do when they claim to have a parking brake. I am debating that right now in case I keep my black buggy but it goes up for sale first.

Lee

[Bruce2]

I like your lightweight thinking! Look to motorcycle discs and calipers for lightweight ideas. You might even be able to use a motorcycle rotor.
I've weighed Al A3 rear calipers at a full 1kg lighter than a 914 iron caliper. Are you trying to go lighter than that?

... if there is a busted half-shaft or stub axle then that side's parking brake won't work.

You're so funny!

[Marc]

I like your lightweight thinking! Look to motorcycle discs and calipers for lightweight ideas...

Also go-kart stuff. Motorcycles are usually hydraulic caliper, karts will have either.
http://www.bmikarts.com/8-Brake-Rotor--Gold-_p_609.html
http://www.kartpartsdepot.com/product_p/kw-k395.htm

[Ol'fogasaurus]

I like your lightweight thinking! Look to motorcycle discs and calipers for lightweight ideas. You might even be able to use a motorcycle rotor.
I've weighed Al A3 rear calipers at a full 1kg lighter than a 914 iron caliper. Are you trying to go lighter than that?

... if there is a busted half-shaft or stub axle then that side's parking brake won't work.

You're so funny!

On inboard brakes, if the connection from the wheel to that sides brake and ebrake ceases to exist Bruce you are SOL on that side.

I seem to remember that that problem has raised its oogly head before. No offence meant Bruce but some times you, metaphoric you, have to think beyond VW and see what has been done before. I've been farting around cars since the mid to late 50s and still have a lot to learn and have forgotten a lot. Sometimes something said will knock a memory lose once in a while.

Lee

[Piledriver]

I know that some disc setups have a mechanical brake that works against the inside of the rotor. I am not sure how others do when they claim to have a parking brake. I am debating that right now in case I keep my black buggy but it goes up for sale first.

Lee

AFAIK all the modern OEM brake calipers with integral parking brake are floaters, so they effectively squeeze from both sides, unlike a 914 calipers parking brake setup. (fixed caliper, I consider it a failed first attempt)


The "most popular" calipers (and the ones in most of Wilwoods kits) are the Wilwood Forged Dynalites, in most piston sizes and widths the caliper is ~3 lbs, the pads are pretty huge area though so I'd add ~another pound for a new set of pads.
Everyone and their dog make pads in many compounds for these, reasonably priced in most cases.

They are not bad, probably feel ~as good as any OEM caliper at 1/3-1/2 the weight, black anodized finish is std, SS pistons.

They use spacers (and different cross bolts) to set the caliper width: no spacers is for 3/8" rotors.

The higher end Superlights weigh about 5 lbs, but are a far more rigid caliper design.
They don't use spacers. They use more bolts and are longer, and have the option for a bridge bolt/spacer as the pad guide for additional stiffness.

I need to remember to buy a fishscale to weigh this stuff.

[Marc]

...On inboard brakes, if the connection from the wheel to that sides brake and ebrake ceases to exist Bruce you are SOL on that side...

100% true of course, but hardly life-threatening if its only purpose is to function as a parking brake.
There've been plenty of production cars with inboard service brakes, from the lowly Citroen 2CV through the Audi 100LS to multiple ~200MPH supercars....it's a consideration, but not one really worthy of losing sleep over IMO.

[Piledriver]

If you have to use your parking brake in an emergency stopping situation, in most cases you would be far better off trying to miss or just brace for impact...

Yank that sucker at 70 MPH (down the middle of an EMPTY freeway perhaps, or giant empty parking lot) and see how that goes.

Its a PARKING brake.

[Ol'fogasaurus]

"I know that some disc setups have a mechanical brake that works against the inside of the rotor."

Poorly written on my part. In the past I remember seeing a single shoe e-brake (not VW based) but it didn't work well based on what I remember reading. I should have said double shoes is what I remember seeing the few times I have done a search for them. My blue buggy's pan started to crack in the e-brake hole in the tunnel. It was professionally welded up but cracked again. Finally the area got to the point were a doubler was put on the tunnel in that area so I dropped the idea of an e-brake there (it was one of the factors to changing over from a street and sand buggy to a sand only buggy). I really haven't looked into them much since then but I may want to when I get home.

Now days you can get bathroom scales almost as cheap as fish scales and should read higher weights unless you are going for sharks and whales. One advantage is you can put a box on the scale, weigh it the dump you stash in, weigh again and subtract the weight of the box.

"https://www.law.cornell.edu/cfr/text/49/393.41

Look at #3... interesting"

Lee

[Marc]

IMO disc brakes make poor parking brakes compared to drums - the latter are generally better since they offer better self-energizing/"wedging" action. Some production cars use a "drum-in-hat" setup that puts a small set of shoes inside (e.g. Porsche 924/944, some Chrysler products) to take advantage of this...but if minimizing unsprung weight is the goal they aren't exactly the best way to go.
My concern about Piledriver's plan is how to go about mounting the inboard rotor...could be that the best way to go would be to just weld a rotor to the periphery of the CV flange. Lateral runout's not going to be a big deal if it's just going to be a parking brake, and that way it's easy to retain the vital rim surrounding the CV joint - that'd be a problem with attempting to simply make a bolt-in sandwich deal.

[Ol'fogasaurus]

'Pile, whoa-ing her down from anything above not very fast and, especially, only having an e-brake on one corner is going to be a thrill you'd never forget. I think "drifters" would appreciate it though.

Remember that off-roaders put handles on the e-brake to turn with and that was pretty wimpy at the best and then as things work it got worse. It also wore the single e-brake shoe (of the pair) down very fast and that, in-turn, also screwed up the rest of the braking.

Not trying to be too negative but I have had fun things like that happen to me.

[Piledriver]

IMO disc brakes make poor parking brakes compared to drums - the latter are generally better since they offer better self-energizing/"wedging" action. Some production cars use a "drum-in-hat" setup that puts a small set of shoes inside (e.g. Porsche 924/944, some Chrysler products) to take advantage of this...but if minimizing unsprung weight is the goal they aren't exactly the best way to go.
My concern about Piledriver's plan is how to go about mounting the inboard rotor...could be that the best way to go would be to just weld a rotor to the periphery of the CV flange. Lateral runout's not going to be a big deal if it's just going to be a parking brake, and that way it's easy to retain the vital rim surrounding the CV joint - that'd be a problem with attempting to simply make a bolt-in sandwich deal.

Actually that setup is pretty common, you just don't notice it often as its well hidden.
Many Vettes, Ford Crown Vic, trucks... many examples.
Porsche has used the drum-in-rotor setup on almost most models since the 356C.
They can be ~easily retrofitted to 914s, one of the few that did not have them. (possibly the ONLY one)


I was thinking more of a giant CV bolt multi-hole washer, over everything, probably with a 5 "tooth" VSS ring ~right near the CV to keep Subaru ECUs happy, and ~useable on everything else. Slightly longer CV bolts would be easy, but not needed if kept thin at center.
It would probably have to go on the axle before the boot/CV are installed, which really isn't that hard.
(Over the CV boot flange)

O'l Fog, I was just pointing out that ~any "emergency brake" I have ever seen is next to useless in any actual emergency braking situation, unless you need to keep a parked car from rolling away from the scene of the accident.
They are more commonly called "parking brakes" for very good reason.

The 914 caliper parking brake does actually only push on one side of the rotor. Failed attempt, probably the same idiot who designed the odometer reset... (breaks the odometer if you are moving and try to reset the trip meter)


The setup on some Subarus might be of some use as they are on the front wheels, or once were.

For steering brak use, you could put one on each side, and even use small hydraulic calipers if you just wanted a steering brake.
Would be the safest way to do that as it would be entirely separate from the primary braking system, i have heard strange tales of setups that tie into the std brakes hydraulics. (just ...Yuck... if that's true)

Even the cable operated steering brake setups with stock drums have an effect on the pad adjustment as the cables stretch.