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Servo Proportional Control Valve And Rear Proportional Control Valve Operation


mk3dub

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I've been across the internet and back trying to find out more information on these two valves. Press material is scant, at best, and the factory service manual glosses right over them aside from telling how to remove/replace them.

I'm not looking to rehash the theory of operation on the LBS, but would love to know if anyone has information on these valves...either from a good source (i.e. Honda) or through your own disassembly. Specifically, I'm looking to better understand how much each valve proportions. This is strictly a mental exercise. Inquiring minds would love to know!

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Have you looked in section 21 of the 5th gen service manual? There's quite a bit of detail in there.

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That's a great place to start, thanks. My sixth gen manual doesn't list this information - very good explanation.

It looks like the part number changed from 5th to 6th gen. I assume they changed the internals, as it looks pretty much identical. Of course, hard to say if the bias changed or if there was some other non-performance change made to the unit. Any ideas?

Similarly, the 6th gen does away with the delay valve on the front fork but incorporates something (similar?) back by the PCV. It's inline with the rear master cylinder and splits the pressure between the rear caliper and the front left. It must do something more than splitting because they could have used a simple fitting for that purpose. Honda also calls that a proportioning valve, so I'm wonder if it delays, proportions, or some combination thereof...

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  • 4 months later...

Hi

Servo proportional valve possible failure?

I have a 2006 V tec, and when I operate the rear brake pedal, the rear braking is low, (via the three pistons in the rear caliper), and due to the linked braking system, the front braking is normal (via the one piston in the left front caliper).

When I operate the front brake, front and rear braking is as should be, (through the five pistons in the front caliper and one piston in the rear caliper).

On looking at the rear calliper with the rear wheel off, all looks normal, and there is no binding of the brakes. Further, I have had the fluid replaced, as I thought old fluid may have been the problem.

There is a unit called the rear proportional control valve, between the rear master cylinder and the rear calliper, and I suspect this is the problem.

There is another valve, called a servo proportional valve between the rear caliper and left front brake calliper, which operates the front left piston, but the front piston is working when the rear brake is operated, so I do not believe I have a problem here.

I would be pleased for any advice on the matter.

Cheers

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  • 5 months later...

Hi again,

Servo proportional valve possible failure?

Further to my posting above, I was hoping that someone else had experienced a similar problem with the rear brake operation, as myself.

I have still to resolve the problem, but have found out that it is not a common problem and only heard that the linked braked Blackbird can have the same problem when they age?.

In conclusion,I am still searching for advice and would appreciate any advice,

Cheers

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  • Member Contributer

Hi

Servo proportional valve possible failure?

I have a 2006 V tec, and when I operate the rear brake pedal, the rear braking is low, (via the three pistons in the rear caliper), and due to the linked braking system, the front braking is normal (via the one piston in the left front caliper).

When I operate the front brake, front and rear braking is as should be, (through the five pistons in the front caliper and one piston in the rear caliper).

On looking at the rear calliper with the rear wheel off, all looks normal, and there is no binding of the brakes. Further, I have had the fluid replaced, as I thought old fluid may have been the problem.

There is a unit called the rear proportional control valve, between the rear master cylinder and the rear calliper, and I suspect this is the problem.

There is another valve, called a servo proportional valve between the rear caliper and left front brake calliper, which operates the front left piston, but the front piston is working when the rear brake is operated, so I do not believe I have a problem here.

I would be pleased for any advice on the matter.

Cheers

Has the rear braking changed or has it always been this way? How old is your brake fluid? My rear brake pedal was like a block of wood with minimal action until I changed to stainless steel hoses and did a thorough flush, fill, and bleed of the brake system. I'm pretty sure my problem was the fluid in the rear LBS system.

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Hi

Thanks for your response and confirm the rear braking had always be fine until now - after changing the brake fluid after some years, the problem has not gone away.

However, I now have presented myself at a local main honda dealer, whose chief mechanic appeared to know all about our brake linked system with all its valves.

Half an hour later in their service bay, he had solved the problem - although I had cleaned the rear brake caliper and was able to push the pistons backwards and forwards, he stated that it was not up to his standard. On completing a full cleaning service on the rear unit and components, he retested the rear brake and all was back to normal.

Therefore, there was no need to investigate further, as under rolling road testing, the rear braking and front braking by the rear brake pedal, is now as should be - problem solved - and in future I shall regularly change the fluid and conduct deep cleaning on my calipers.

Thanks for your responses.

cheers

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