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deronmoped
Samba Member
Joined: November 18, 2006
Posts: 386
Location: San Diego
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 Posted: Wed Nov 12, 2025 6:44 am Post subject: Brake residual pressure valve delete? 1973 and on? |
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How come VW deleted the residual pressure valve from the 1973 and on Bays? Would it be good to add a aftermarket one?
Thanks, Deron. |
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KTPhil 
Samba Member
Joined: April 06, 2006
Posts: 36324
Location: Conejo Valley, CA
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| Posted: Wed Nov 12, 2025 9:35 am Post subject: Re: Brake residual pressure valve delete? 1973 and on? |
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Do you actually mean RPV on the master connections, or do you mean the Brake Proportioning Valve that limits rear fluid pressure on hard braking?
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airschooled
Air-Schooled
Joined: April 04, 2012
Posts: 13624
Location: West Coast, USA
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| Posted: Wed Nov 12, 2025 12:27 pm Post subject: Re: Brake residual pressure valve delete? 1973 and on? |
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| deronmoped wrote: |
How come VW deleted the residual pressure valve from the 1973 and on Bays? Would it be good to add a aftermarket one?
Thanks, Deron. |
Because it’s cheaper to put a spring in the rear wheel cylinders. (I thought the change was 1971; discs do not need RPVs.) If your ‘73 rear wheel cylinders are good, they should have the spring. A couple of aftermarket cylinder makers don’t include the spring.
Without either method, the pedal bite point will be farther down. It does not affect braking or pedal feel once the brakes are engaged.
Robbie
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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 23468
Location: Oklahoma City
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| Posted: Wed Nov 12, 2025 1:05 pm Post subject: Re: Brake residual pressure valve delete? 1973 and on? |
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| airschooled wrote: |
| deronmoped wrote: |
How come VW deleted the residual pressure valve from the 1973 and on Bays? Would it be good to add a aftermarket one?
Thanks, Deron. |
Because it’s cheaper to put a spring in the rear wheel cylinders. (I thought the change was 1971; discs do not need RPVs.) If your ‘73 rear wheel cylinders are good, they should have the spring. A couple of aftermarket cylinder makers don’t include the spring.
Without either method, the pedal bite point will be farther down. It does not affect braking or pedal feel once the brakes are engaged.
Robbie |
To add to that.....NOT having a residual pressure valve as well as NO springs in the rear wheel cylinders makes for much more difficult bleeding. The residual pressure valve makes for easier bleeding when there is no spring in the wheel cylinder to keep minor pressure on the pistons.
Ray
Last edited by raygreenwood on Thu Nov 13, 2025 11:23 am; edited 1 time in total |
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Bnanwel
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Joined: November 10, 2022
Posts: 393
Location: Ft Lauderdale
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| Posted: Wed Nov 12, 2025 4:01 pm Post subject: Re: Brake residual pressure valve delete? 1973 and on? |
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FWIW, 72 has the RPV.
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deronmoped
Samba Member
Joined: November 18, 2006
Posts: 386
Location: San Diego
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| Posted: Thu Nov 13, 2025 8:21 am Post subject: Re: Brake residual pressure valve delete? 1973 and on? |
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I mean the residual pressure valve that was removed from the brake proportioning valve. My BPV does not have the RPV. My BPV does not have the bleeder too. My BPV is the model with the brake in and brake out connections on the top of it.
So I'm thinking I do not have the correct rear slave cylinders with the spring in them. I swapped the braking system out of a 1973 into my 1970 Bus a long time ago. So I'm going to have to see exactly what I have in the way of slave cylinders on the rears. As I know I replaced one of the slaves two years ago and probably went with a 1970 one. |
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deronmoped
Samba Member
Joined: November 18, 2006
Posts: 386
Location: San Diego
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| Posted: Thu Nov 13, 2025 8:25 am Post subject: Re: Brake residual pressure valve delete? 1973 and on? |
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| 1955 to 1971 wheel cylinders are sold. 1972 to 1979 wheel cylinders are sold. So I'm guessing there is a change in the 72 to 79 wheel cylinder as compared to the 55 to 71 units. |
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kreemoweet
Samba Member
Joined: March 13, 2008
Posts: 4145
Location: Seattle, WA
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| Posted: Thu Nov 13, 2025 9:50 am Post subject: Re: Brake residual pressure valve delete? 1973 and on? |
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| deronmoped wrote: |
| As I know I replaced one of the slaves two years ago and probably went with a 1970 one. |
No, 55-71 cylinders can not be used on a later bus brake setup, the mounting is different.
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deronmoped
Samba Member
Joined: November 18, 2006
Posts: 386
Location: San Diego
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| Posted: Fri Nov 14, 2025 6:55 am Post subject: Re: Brake residual pressure valve delete? 1973 and on? |
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"No, 55-71 cylinders can not be used on a later bus brake setup, the mounting is different."
What if I kept my 1970 backing plates? I'm not sure what I swapped over when I converted my 1970 brakes to 1973 brakes. Probably the minimum, just enough newer parts to make the disc brake swap work.
I'm going to pull a wheel to find out. |
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