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Empi Disc Brake conversion
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blackivory69
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PostPosted: Tue Jun 19, 2018 4:38 pm    Post subject: Empi Disc Brake conversion Reply with quote

Hi everybody. It’s been a long time since I post but I got bitten by the bug again so here I am. I’m currently converting my 70 Crew Cab from drum to disc using the Empi disc conversion kit. I know, why Empi, but that is all I can afford.
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Everything is well until it’s time for me to replace the master cylinder. The MC in the kit is exactly what’s in the picture which I think it’s for 1971 and later because it meant to be installed with a booster. I have a few options. The ports of this new MC is different from the original, so if I’ll use this I have to re-route my metal brake lines. And then since the reservoir is sitting on top of the MC, I have to make a hole on the floor so that I can refill the reservoir when needed. I cringe just thinking of cutting a hole on my floor. That’s my 1st option. My second option is to buy a 1971 MC and a booster and do some cutting underneath for the booster installation, but to tell you the truth, I don’t really need or want a booster because my legs are strong enough. Now, my last option is to use my existing MC but someone told me that I have to disassemble it and take off some kind of a small valve inside the MC or I’ll run the risk of locking up my disc brake. I like the 3rd option but could someone please verify me if I have to modify my OEM MC (take off that “valve”) or I can use it AS IS for my converted disc brake? Thank you very much in advance.
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airschooled
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PostPosted: Tue Jun 19, 2018 4:52 pm    Post subject: Re: Empi Disc Brake conversion Reply with quote

Good to see you back here!

Disc bus brakes without a booster are SIGNIFICANTLY harder to press than a four wheel drum brake bus. The physics involves the double leading shoe design where both shoes “energize” themselves from being pulled out into the drum, like the front shoe does by itself without the help of the rear shoe back in the rear brakes on every bus. No other vehicle on the road utilized double leading shoes like VW did to my knowledge. Because of this designed-in mechanical advantage of stock bus drums, you will likely not be able to lock the front discs with your stock master cylinder, even if you did take the residual valves out like you mentioned in option number three.

Any time you change the stock brake balance, you’ll also want a proportioning valve to avoid prematurely locking the rear tires in a hard stop. Also, when the balance is altered, the master cylinder bore displacement has to match the requirements of the front/back systems.

Good luck!
Robbie
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raygreenwood
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PostPosted: Tue Jun 19, 2018 10:38 pm    Post subject: Re: Empi Disc Brake conversion Reply with quote

asiab3 wrote:
Good to see you back here!

Disc bus brakes without a booster are SIGNIFICANTLY harder to press than a four wheel drum brake bus. The physics involves the double leading shoe design where both shoes “energize” themselves from being pulled out into the drum, like the front shoe does by itself without the help of the rear shoe back in the rear brakes on every bus. No other vehicle on the road utilized double leading shoes like VW did to my knowledge. Because of this designed-in mechanical advantage of stock bus drums, you will likely not be able to lock the front discs with your stock master cylinder, even if you did take the residual valves out like you mentioned in option number three.

Any time you change the stock brake balance, you’ll also want a proportioning valve to avoid prematurely locking the rear tires in a hard stop. Also, when the balance is altered, the master cylinder bore displacement has to match the requirements of the front/back systems.

Good luck!
Robbie


He will be able to lock the brakes just fine. The lack of a booster does not change the output pressure of the MC. It just increases the effort to produce it. Diameter and stroke is diameter and stroke. Plenty of bigger and heavier vehicles without power boosters worked fine.

But.....if not using power.....it WILL be somewhat easier to go to a non power MC. Ray
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PostPosted: Tue Jun 19, 2018 10:56 pm    Post subject: Re: Empi Disc Brake conversion Reply with quote

raygreenwood wrote:
asiab3 wrote:
Good to see you back here!

Disc bus brakes without a booster are SIGNIFICANTLY harder to press than a four wheel drum brake bus. The physics involves the double leading shoe design where both shoes “energize” themselves from being pulled out into the drum, like the front shoe does by itself without the help of the rear shoe back in the rear brakes on every bus. No other vehicle on the road utilized double leading shoes like VW did to my knowledge. Because of this designed-in mechanical advantage of stock bus drums, you will likely not be able to lock the front discs with your stock master cylinder, even if you did take the residual valves out like you mentioned in option number three.

Any time you change the stock brake balance, you’ll also want a proportioning valve to avoid prematurely locking the rear tires in a hard stop. Also, when the balance is altered, the master cylinder bore displacement has to match the requirements of the front/back systems.

Good luck!
Robbie


He will be able to lock the brakes just fine. The lack of a booster does not change the output pressure of the MC. It just increases the effort to produce it. Diameter and stroke is diameter and stroke. Plenty of bigger and heavier vehicles without power boosters worked fine.

But.....if not using power.....it WILL be somewhat easier to go to a non power MC. Ray


You just got “Airschooled”. 🤓
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PostPosted: Wed Jun 20, 2018 3:42 am    Post subject: Re: Empi Disc Brake conversion Reply with quote

Airschooled...hahahah.
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PostPosted: Wed Jun 20, 2018 4:51 am    Post subject: Re: Empi Disc Brake conversion Reply with quote

On our 69 we did a conversion to Crossover/Late Bay Discs. We don't have a servo booster and it stops fine. But a lot of owners on the EarlyBay forum say that having the servo booster is one of the best upgrades they have done.
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PostPosted: Wed Jun 20, 2018 6:26 am    Post subject: Re: Empi Disc Brake conversion Reply with quote

asiab3 wrote:
Disc bus brakes without a booster are SIGNIFICANTLY harder to press than a four wheel drum brake bus. The physics involves the double leading shoe design where both shoes “energize” themselves from being pulled out into the drum, like the front shoe does by itself without the help of the rear shoe back in the rear brakes on every bus. No other vehicle on the road utilized double leading shoes like VW did to my knowledge. Because of this designed-in mechanical advantage of stock bus drums, you will likely not be able to lock the front discs with your stock master cylinder, even if you did take the residual valves out like you mentioned in option number three


Having put many, many miles behind the wheel of a non boosted euro disc brake bus, I couldn’t disagree any more
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PostPosted: Wed Jun 20, 2018 8:42 am    Post subject: Re: Empi Disc Brake conversion Reply with quote

VWsArent4Hippies wrote:
asiab3 wrote:
Disc bus brakes without a booster are SIGNIFICANTLY harder to press than a four wheel drum brake bus. The physics involves the double leading shoe design where both shoes “energize” themselves from being pulled out into the drum, like the front shoe does by itself without the help of the rear shoe back in the rear brakes on every bus. No other vehicle on the road utilized double leading shoes like VW did to my knowledge. Because of this designed-in mechanical advantage of stock bus drums, you will likely not be able to lock the front discs with your stock master cylinder, even if you did take the residual valves out like you mentioned in option number three


Having put many, many miles behind the wheel of a non boosted euro disc brake bus, I couldn’t disagree any more


Didn’t those buses use a different master cylinder? My point is the brake system is just that, system, and everything has to match.

There are enough people texting and driving; we don’t need to add mismatched brake components to the soup.

Robbie
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OB Bus
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PostPosted: Wed Jun 20, 2018 8:43 am    Post subject: Re: Empi Disc Brake conversion Reply with quote

Is your original master cylinder OK? If so, search “residual valve” on this forum. You might be able to just use your current master cylinder.
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PostPosted: Wed Jun 20, 2018 8:32 pm    Post subject: Re: Empi Disc Brake conversion Reply with quote

Thank god you VW Gurus are still here at Samba. Some people will not know what to do with out you guys and that includes me.

OB Bus; Yes I believe my MC is still in good condition.

Now that I have guidance from you guys, my game plan will be to try to run it with my original set up and see if it’s going to bind. I rotated the wheels after bleeding the system and the wheels are turning. And this was after pumping the pedal a few times, I can feel the resistance of the pad but I think that’s how it supposed to be. So it’s a good sign. If it binds, then my next step is to open the cylinder and bypass that residual pressure valve.

I didn’t have the chance to road test it coz I need to go to work. So tomorrow will be the day and I’m excited. After a 2 year (or so) hibernation, she’ll awake tomorrow. Can’t wait 🙂
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PostPosted: Wed Jun 20, 2018 8:48 pm    Post subject: Re: Empi Disc Brake conversion Reply with quote

You shouldn’t need to open the cylinder to remove the residual valves; they should unscrew directly from the master. The question is: are the MC residual valve bores the same thread as the stock brake lines? I don’t know.

Robbie
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PostPosted: Wed Jun 20, 2018 9:25 pm    Post subject: Re: Empi Disc Brake conversion Reply with quote

Removeing the internal parts of the residual valve for the front disc brakes.
Disc Brake Conversions
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blackivory69
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PostPosted: Wed Jun 20, 2018 9:37 pm    Post subject: Re: Empi Disc Brake conversion Reply with quote

asiab3 wrote:
You shouldn’t need to open the cylinder to remove the residual valves; they should unscrew directly from the master. The question is: are the MC residual valve bores the same thread as the stock brake lines? I don’t know.

Robbie


Hi Robbie. Long time no see. I hope you still remember me. I’m the guy with the red 71 Small pop top reviera.

You are absolutely right Robbie. After some reading here, I found out that residual pressure valve is built in to the fitting. So judging from the photo below, it looks like I don’t have one. Do I?
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PostPosted: Wed Jun 20, 2018 9:50 pm    Post subject: Re: Empi Disc Brake conversion Reply with quote

Of course I still remember your beautiful custom interior and bespoke roof rack system!

Check out those silver looking 19mm~ish fittings where the brake lines fit into the MC. As shown in Tcash’s link, those are residual valves that should be removed for disc brake operation.

Robbie
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PostPosted: Wed Jun 20, 2018 10:19 pm    Post subject: Re: Empi Disc Brake conversion Reply with quote

asiab3 wrote:
VWsArent4Hippies wrote:
asiab3 wrote:
Disc bus brakes without a booster are SIGNIFICANTLY harder to press than a four wheel drum brake bus. The physics involves the double leading shoe design where both shoes “energize” themselves from being pulled out into the drum, like the front shoe does by itself without the help of the rear shoe back in the rear brakes on every bus. No other vehicle on the road utilized double leading shoes like VW did to my knowledge. Because of this designed-in mechanical advantage of stock bus drums, you will likely not be able to lock the front discs with your stock master cylinder, even if you did take the residual valves out like you mentioned in option number three


Having put many, many miles behind the wheel of a non boosted euro disc brake bus, I couldn’t disagree any more


Didn’t those buses use a different master cylinder? My point is the brake system is just that, system, and everything has to match.

There are enough people texting and driving; we don’t need to add mismatched brake components to the soup.

Robbie


Understand.....the power brake booster does NOTHING....to increase hydraulic pressure in the MC. You have X diameter by Y stroke. It creates Z pressure.I

If that cylinder can create the volume required for the pressure your brakes require.....there is nothing that can increase that.


All the booster does.....is allow your leg to create the same pressure its going to create no matter what......using less EFFORT.

Its an ASSIST. Air rushes into a vacuum chamber whem you push the pedal ....giving between 2.5 and 3+ X whatever pressure you put on that pedal (it varies from vehicle to vehicle).
In other words it cuts YOUR effort down....to produce the same pressure....it was going to make in the first place.

I fully agree....do not start swapping cylinders around because the port spacing for each circuit....and the internal spring pressure on each piston set....is what sets your brake BIAS.

However.....if your booster is dead but otherwise you keep the same MC in there.. it WILL stop just as well.....if you learn to put your foot into it. Ray
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PostPosted: Thu Jun 21, 2018 6:42 am    Post subject: Re: Empi Disc Brake conversion Reply with quote

Removeing the internal parts of the residual valve only for the front disc brakes.
Disc Brake Conversions
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PostPosted: Thu Jun 21, 2018 11:44 am    Post subject: Re: Empi Disc Brake conversion Reply with quote

Davydomes wrote:
On our 69 we did a conversion to Crossover/Late Bay Discs. We don't have a servo booster and it stops fine. But a lot of owners on the EarlyBay forum say that having the servo booster is one of the best upgrades they have done.


Not a vanity trip, just remembered! We changed the master cylinder because I think (not entirely sure because it's a few years back) the bore is slightly bigger by 2mm diameter on the later ones.

Probably get schooled now Confused

We also fit the pressure regulator valve that stops the back wheels from locking up causing the bus to snake. I don't think everybody fits these.
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PostPosted: Thu Jun 21, 2018 12:40 pm    Post subject: Re: Empi Disc Brake conversion Reply with quote

So I ended up bypassing the residual pressure valve. Bleeded the system again and put it back. I just finished the road test and holy cow! Big difference from my drum. Just a little pressure and I will lock both front wheels. I can’t feel any binding as well. I need to get used to it coz I’ll end up locking my front wheels every time I brake.

Now my question is, since I need just a little pressure for my front disc, is my back drum brakes working when I brake? I’m thinking it is just because it still has that residual pressure valve in there. That’s actually a check valve so it means that the fluid between my master cylinder and wheel cylinder stays there every time, so it should be working. Right?
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PostPosted: Mon Sep 17, 2018 7:29 pm    Post subject: Re: Empi Disc Brake conversion Reply with quote

Aw cool.. I'm thinking of getting the same kit for my 70 kombi. I put the thing back on the road for the first time in 45 years and well, of course the original brakes leak everywhere, so I could either spend a bit constantly switching out failing original parts (and I do mean original!) or just spring for a kit like this.

As I do need a MC anyway , the empi kit seems the best bang for the buck as it comes with it. I'm none to happy about the filler cap for the reservoir requiring you to cut an access hole under your seat. for realz? What? You can't rig up the original hoses and use the original reservoir under the dash? WTF?

-Tara
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PostPosted: Thu Jul 25, 2019 11:58 pm    Post subject: Re: Empi Disc Brake conversion Reply with quote

Bumping this up from about a year ago.

Just installed these on a '70 Westy. I ended up keeping the original master and I removed / modified both residual valves. I think I was only supposed to modify the front one. Can somebody confirm that is the case? Is there any place these are available for purchase? I looked a little bit and couldn't find one.

2nd issue.. the brake light on the dash is on and doesn't go away. Is that normal after this?

Otherwise, they really do work great. I need to bed the pads a little bit more as it takes a bit of force to get the bus to stop.
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