Rear Disc Brakes

Hello all,

* Do you have rear disc brakes? (as the ones listed
at CBperfomance.com)?
* If you do, which master cylinder did you use?
* Which front disc brakes do you have?
* Did you have to add residual pressure valve(s)?
* Did you use a porportional valve (to change bios front to rear)?

I just put CBperformance's rear disc setup on my Vintage Speedster. It's OK, but I had lots of trouble fixing leaking fittings at the calipers.

I lost some pedal travel or lack there of that I had with rear drums.
Even with the recommended residual pressure valve in place, the pedal is solid more toward the middle rather than at the top of its travel.

Greg B.

Greg, I have CBs rear disc brakes too (Roto Hub). I'm not running anything extra. I just put the rear brakes on and away I went. Pedal goes down about as far as yours, or just a bit less. The car stops great, so I can put up with a bit more pedal travel. I also have front discs.
Ron

Greg: I installed the CB Roto-Hubs rear kit as well. I used the residual valve for the rear circuit. I adjusted my master cyl. plunger to .001 clearance to piston for better pedal. John Steele advised me to bleed the fronts first then the rears when bleeding lines.(because of residual valve to rear).In addition to the front discs, I'm most happy with them.
As far as I know I'm running a normal bug master cyl.

BD

Yep, what Bill said via John Steele, although I am not so sure you need the residual valve if you follow his reverse bleeding suggestion. It raised the pedal on mine.

Do the rear disc kits affect the wheel clearance at all? My car has drums at the rear and about 1/4 of clearance for the tires to the fender.

Brian

Henry told me that the purpose of the residual valve is to prevent the calipers from backing off when new. If they back off, that gives lots of pedal travel until they break in. If you can deal with it, the pedal will firm up after a 100 miles or so. He also said always parking with the hand brake on helps break the calipers in as well.

Brian,

According to the service tech I spoke with at CB Performance, RotoHub disks do not change the width, however, I am not so sure about that. When you don't have much clearance to begin with...

My eventual plan is to order two Beck Spyder rear 5.5" rims, their offset has been changed allowing you to run wider tires.

Eric, I've got 7" rims with 205/55 tires. What can you fit with the Beck rims?

In previous threads concerning a change of clearance, the worry was widening the track towards the fender. I actually lost 3/8 or so inwards after I put my rotohubs on.

BD

Brian,

Another poster here installed the Beck Spyder rear 5.5" rims when the standard offset 5.5 rims limited his tire selection. Maybe he will post what he found, but it seems like he said he could fit tires as large as 205/60's, though he went with 195. Certainly buying the rims which are in stock at Beck would be cheaper than having Stockton Wheels reweld yours. Earlier I bought a set of the seven inch rims from IM but decided against using them.

I haven't purchased the Beck rear rims yet, will shortly.

Erik,

What is the offset on the Beck rims? Are they 5x205 stud pattern?

I'm still looking for some more clearance at the back of my car, having fitted mangel wheels with an offset (ET) of 25mm that I had to wait 6 months for (standard offset is 15mm, compared with 4x130 stud pattern cars 25mm). My 195/60 tyres clear by just a few mm.

Here in Europe, I believe Custom and Speed Parts (www.csp-shop.de) are the best source of after-market brake parts led by the strict TUV requirements of the German market.

Their rear discs are on my wish list (I already run their front discs) - the fact that they narrow the track each side by 10mm (on an IRS car, 5mm on a 68- swing axle car, and 3.75mm on a 58-67 car) may lead to me upgrading prior to upgrading my engine (and wanting(needing?) the braking performance)

They also sell master cylinders designed for for cars with rear disc brakes.

Simon,

I haven't bought the Beck Spyder rims yet. Am sure the info re offset can be obtained from Beck easy via an email. The rims stay in stock.

If not mistaken Beck buys his Brazilian rims from the factory with the offset made by them. I don't know if they are five or four lug, however, my guess is both are in stock.

Mr Shammly,
I think you have, or had the same exzact problem I did. I got Henry at Im to make me 2 6x1/2 rims out of Beck rims and I got 3 more stock 5.5s from Beck for the front and the spare.
The offsets match all around, I did add 30mm spacers to the front rotors from CSP and their 60 mm lug studs. .

If my budget had been worse, or I wanted to be able to rotate tires all around? I would have bought all Beck 5.5s and ran 185/60s all.

I also have CB disc all around. I need to snoop CSP again to see just what master cylinders they now offer, Maybe I can improve my petal some more.

Thanks for the feedback. Everything noted here is what I'm finding to be true (about the residual valve and brake pedal height).

As far as the spacing on the CBperformance Roto hub rear discs here are the results of my set up.
I started with short axle swing axle with 4 bolt drum brakes (with the snoot cut down on the drums for the short axle). The wheels are fake fuchs (same offset as 15" or 16" x 6" wide real fuchs. They had 1/4 in. tire clearance with two 5/16" spacers.
After the RotoHub assy. was installed the same wheels and tires and one 5/15" spacer achieved the same (or a little less) clearance.
SO:
the roto hub rear disc brakes (at least in my case) ended up 5/16" wider per side.

Greg B

Barry,

There is a good master cylinder application table on their website.
For front and rear discs they recommend going to a larger bore master cylinder - 20.64mm. This should help your pedal as it'll move more fluid.

Simon

Simon,
Which Website do you reference for the mastercylinder recommendations.
CBperfomrance or ??


Thanks,
Greg B

Greg,

The CSP (custom and speed part) site.

They have an application guide: Browse to master cylinders and then select the tech tip

Try this link:

www.csp-shop.de/shop2/frame_nachladen.php?func=agb&agb=techtips/hbzinfo&wkid=54200319908&rub1=Wheels+/
+Brakes&rub2=Master+Cylinder,Mounting+Adapter&artnr=20826a

I was reading on another VW forum that a type 3 master brake cylinder was the way to go with rear disc brakes. So far mine work fine with the stock beetle master cylinder.
Ron

If not mistaken bigger master cylinders would be necessary for heavier cars, but not for our lightweights. Four wheel disk brakes on our slim fast cars is a L-O-T of stopping power.

If you are making a ton of HP and drive race track speeds by all means look at converting to the Porsche 944 system or one of the beefy after market setups.

The bigger cylinder does displace more fluid though, so would remove excessive pedal travel due to having larger slave cylinders.

I agree that its easy to get enough braking force to lock the wheels - and thats all you need.

I also believe that the standard master cylinder has a residual pressure valve on the rear circuit (to stop the drums retracting) that is not desirable with rear discs?