Brake adjustment after new wheel cyls,hoses,lines,and mcy

[Trikeman72]

[viiking]

OK. Thanks for clearing that up (for me anyway). I don't know much about rails, hence my confusion.

Now the only thing to think about is that when you have discs (on the front), the MC is usually built without Residual Pressure valves which are used to maintain some pressure in drum braked cars. Disc brake MC's have narrowed ports in the MC to achieve the same result. I guess having the discs on the back would be no different.

I assume that you would need to remove any residual pressure valves that you may have re-installed on the new MC and see if that helps. Normally in OEM VW disc brake set ups the RPV had a different thread to the disc brake MC so they couldn't be inserted. But you may have aftermarket bits?

Here's another option. Do you have a MC with three fluid outlets. Usually they have 2 for the front circuit and one for the rears on a Type 1!

If so have you connected the front circuit (with 2 outlets) to the rear discs? I think you may have to, to provide sufficient volume to the rear brake circuit (which in your case is the primary braking circuit?

Failing all of the above reverse your bleeding process and go to the furthest one from the MC first.
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[Trikeman72]

Update

Ok so I adjusted the front shoes out to hold drums then rebled LF RF RR LR


I just noticed that I have the brake line from the rear in the hole nearest front on mcy meaning

Rear brakes and the right front is fed by the front half of mcy
And the left front only is the rear of mcy where cap on mcy is

So asides the fact that I’ll lose almost everything if I blow a rear hose I gather I have to change those around so the rear brakes run off the rear of the resivoir
Then bleed them a frikingain 🤬🤬

Could that be why the brake switch don’t turn brake lights on it don’t build enough pressure it sounds like a reach now I type it but I’m grasping to figure out where the air is that I can’t get out of the system if that is in fact the problem yk?
I’m keeping fronts locked up to change line around but then I will bleed again then back shoes off a touch and see what I have for brakes

[Trikeman72]

[Trikeman72]

Sweet I think I’m getting there now
I know there’s air in it but the brake light comes on with initial pedal press then goes out I’m guessing when the air does it’s part

Hopefully this is the last dang test bleed geez 😒

[Trikeman72]

Well I have all the air out of the rears the brake light stays on now.

Idk what the deal is with the fronts man
I didn’t back off the shoes much at all and I have to pump brakes to get them to kind of hold the tire ☹️

Only thing I didn’t do was change the LF hose idk maybe it’s bad wouldn’t a thought so it’s only a cpl yrs old

[viiking]

I may be completely wrong here so others should chime in.

My thinking is this (and I may not have explained this very well previously).

On a "normal" car the front MC circuit has individual lines going to the primary braking circuit, i.e. one for each side from the MC. The rear (secondary circuit) feeds the rear brakes with a single line which splits into the two lines under the back seat area.

Given your rail is "backwards" and needs the majority of its braking effort at the rear, I think you need to reverse ALL of the braking circuits like so:

1. Front drum brakes are fed from the rearmost port of the MC. This requires you move the T-junction pipe from under the rear seat to the front and run new lines to the drum brakes. That is one line from rear MC port to the T, then two new lines to each of the front rums.

2. The rear discs are fed from the front two ports of the MC. This requires you run two new lines (or extend one plus new one) from the MC to the rear discs. One for each side.

This is inherently safer than what you have. If the front or rear circuit fails you have one whole axle's worth of brakes and it will pull up slowly but at least straight.

The other reason I say this and depending on your MC you have purchased is the "stroke" of the MC. I can only talk about originally designed for VW MC's and not aftermarket. On a dual circuit MC for drum brakes, the front circuit stroke was 15.5mm and the rear 12.5mm giving a total stroke of 28mm. This means that if you use the rear circuit for the discs( and you have noted that maybe yours is set up this way) then there may be insufficient stroke volume for that circuit. This was changed when the dual circuit disc brake MC was introduced so that both front and rear circuits had the same stroke volume, 14mm each giving the same total stroke volume.

It would be good if you could find out this information of your newly installed MC.

As I said this may be the extent you have to go, but I'd leave it till the last resort.

Are there not other forums on here that may help you with your rail?

As I said, wait until others chime in. I'm trying to help but my logic whilst sound to me may be wrong.
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[viiking]

Also bite the bullet and replace that hose. You already have it and it might help. If it doesn't you can keep the one that you have just replaced as being an OK spare for later.
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[Trikeman72]

Ok so after checking and checking some more I found that this M93354 mcy was spose to come from appletree via Amazon for 2wheel disc brakes but When I checked thru Amazon chat they said it’s for 4 wheel drum only 🙄

So I’d prefer to not have to spend some retarted amount of money for a mcy
Like a polished pedal set etc
Sku 16-9554-0 on appletree website is for 4 wheel disc will that be ok with 2 disc and 2 drum ??

[viiking]

Appletree website doesn't specifically say you CANNOT use the MC on discs and drums. It just says that you NEED that one if you go to 4 wheel discs.

The reason for this is often the standard 19mm bore MC cannot deliver sufficient volume to expand the calliper pistons on 4 sets of pistons, i.e. 8 in a single stroke. Depending on the aftermarket discs, the pistons may be larger than what VW originally designed for the disc brake fitted beetles. A simple pi*r squared*stroke of MC gives the total volume of the disc fluid that can be displaced with one push of the pedal. If the pistons are large then the total volume isn't sufficient to close the pistons or build sufficient hydraulic pressure in the line and your pedal can essentially go to the floor.

The one you reference is 20.6mm bore versus a standard bore of 17mm in earlier VW or 19 for later (I don't think you said what year model your rail is actually based on, but I think it originally would be 19mm). This would provide much more fluid volume so would be more that enough. Having too much displaced volume should not be an issue. Not having enough is the real problem.

I would persist with what you've got as you've already said you don't want to spend any more unnecessarily.
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[Trikeman72]

[viiking]

Three quarters is 19mm. My OEM Euro beetle with discs up front has 19mm MC as standard and works fine. For 2 wheel discs, I think that is all you need. For 4 wheel discs you probably need a bigger bore.

Re the RPV. You don't usually put them on any disc brake system because the MC should have the correct internal structure to deal without them.

Have a look at this brief video from Summit Racing and you'll see they mention this.

https://www.onallcylinders.com/2013/10/15/tech-brake-master-cylinder-faqs/

What should you do next?

Yes replace the hoses and try and bleed again. Report back what happens.

I still strongly recommend you change the pipework so that rear discs have individual lines from the MC and the drums the single line with the T piece fitted. Read my previous post again and see if it makes sense.
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[Trikeman72]

[viiking]

Before you start making too many surgical interventions, I suggest you ask (or get this post moved. Glenn might help)in the HBB Off Road forum which has members who run rails. As said I’m giving you my advice as I see the logic of having discs on the back but I have little experience with rails.

People in there may already have done exactly what you have and can advise better. Of course I will follow on there to see how it evolves.
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[Trikeman72]

[Trikeman72]

I noticed socal has a dual circuit mcy that’s a 20.6 bore made for 4 wheel disc brakes. I was thinking if I get this one I could keep my front drums and I could run single line to rear T on one half of the mcy and be good because the front would have plenty of pressure to operate drum brakes it’s made to work front and rear disc yk?

Idk which route to go I’m resigned to the fact I have to buy a 20.6 bore mcy I just want to buy the right one first instead of what I’ve done so far here 🤦‍♂️

[viiking]

I guess not knowing the types of discs you have or their piston sizes all I can say this.

I can only talk about OEM MC's. I assume all of the aftermarket parts are copies of the original VW ones.

So the way I understand it is you have blocked off a dual port MC and cannot get enough retardation from the rear circuit. The rear circuit on a dual circuit MC for drums had (originally) a 15.5mm stroke. For discs this was 14mm.

For the single circuit the stroke was around 33mm! Even though the bore was smaller, the volume produced on the single circuit was a lot more and therefore produced higher pressure FOR ONE CIRCUIT FRONT OR BACK.

Do the maths as I indicated above in one of my posts.

15.5 x [(19/2)squared]*pi -Drum dual MC
14 x [(19/2)squared]*pi - DIsc dual MC
33 x [(17.5/2)squared]*pi. Single MC. This is significantly higher.

Forget the significant figures but you end up with (I think I calculated correctly)

1. 7937 single MC displaced volume at full stroke (remember this was for 2 circuits front and back)
2.4394 drum brake dual MC
3. 3969 disc brake MC

A big difference!

So what I think is the problem is that the calliper pistons are quite large and the volume required to fill the calliper is larger than what can be produced on ONE CIRCUIT OF A DUAL CIRCUIT MC.

In otherwords if the volume of the calliper piston chamber is large you won't develop enough pressure.

So, if you are only driving this off-road and can accept the risk, I would get a single circuit MC and run the discs only at the back with a SINGLE CIRCUIT MC. Blocking off one circuit on the dual will give you significantly less volume.

Alternatively a larger bore dual MC MIGHT give you enough pressure. If you knew the calliper piston size and stroke then you can do all the maths.
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[Trikeman72]

Oh wow no wonder the single circuit mcy he’s using for rear only brakes works good for rear disc only. It’s nearly twice the pressure
It’s road legal but the places I off-road are mostly dunes I don’t bomb thru trees etc like I use to I don’t live there anymore lol the odds of busting a hose isn’t huge then again I know what your thinking or I am anyways. I don’t want to test that theory with a kid crossing the road etc. me crashing me idc about but brake failure on the street isn’t an option
think I’ll get the dual circuit 20.6 bore mcy for front and rear disc. Least that way I know the rears will work for sure and have a better chance of the fronts working as well yk

I’d have to call socal to get the technical info on the calipers for the math.
I appreciate your help on this Viking

[Trikeman72]

The single circuit mcy is 22.5 dang
The local beetle shop is a socal distributor he should have what I need without a wait too so I’ll check on it tomorrow.
Thx again

[Trikeman72]

I called socal where I got the rear disc kit and he said the 3/4 bore mcy should work the rear disc front drum setup and I may need to jack up the rear of my rail to get any air to goto the bleeders??

I guess I’ll try that first uggh