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How To Swap From Servo To Yellow Tag

brakes engine

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#1 Mini_Problems_


    Formally known as Cmontgomeryc

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Posted 13 November 2019 - 01:48 PM

I felt it would be useful to explain all the modifications required to change from servo to yellow tag set up.

Why might you want to change to a seemingly obsolete setup? Well in my case I wanted to tidy up the engine bay and install a brake proportioning valve for the rears.

But wait won't this increase you insurance premium I here you cry? After contacting Adrian flux and explaining to them about my flip front and new non servo brakes setup I can confirm that my premium didn't increase. However any brake proportioning valve must be out of reach of the driver.

But won't this make my brakes rubbish? In my experience braking performance is the same (if not a little better thanks to proportioning valve) however the pedal is firmer and you get more "feel". You have to press harder granted but I prefer the way this feels now I've adjusted.

What will I need to make the change?

Yellow tag master cylinder
Early brake pedal (no extension bar)
Old type larger clevis pin
Early type pedal spring
Early type bulkhead mounting plate
Reel of 3/16 copper/nickel pipe
Brake proportioning valve (optional)
Metric unions 12mm and 10mm
Brake fluid 1l

When changing to this setup beware, some unions are metric some are imperial.The connections on the pdwa valve (if you decide to keep it) are both 10mm. The upper connection of the yellow tag is 10mm and the lower is 12mm.

The front split t piece located on the left-hand lower side of the front subframe is 3/8 imperial.

I didn't have to change my front to rear brake line, however you should note that the splitter and the rear should be imperial.

The wildwood proportioning valve I purchased came in a few different union sizes, I picked 10x1 bsf as I had spare 10mm unions, no adapters required!

It can be a fiddly job getting the brake old style brake pedal and spring to all fit. You may have to remove the heater in order to get the clearance to remove the pedal box main shaft.

The reason most choose a proportioning valve when carrying out this modification is due to the rears having a tendancy to lock up. This means you have to swap your rear brake cylinders out for small diameter ones. I decided the valve was easier and gave more tunability.

You can apparently modify a servo type brake pedal by drilling out the rivet and removing the extension. You would then have to drill out the clevis pin hole to make it compatible with an older type clevis pin as required by the yellow tag.

The mounting plate can also be reworked to fit, however for the £20 for a new plate and same again for brake an early pedal I found this easier.

If you are connecting to the pdwa valve from the yellow tag. The top connection of the yellow tag connects to the rh side of pdwa (10mm to 10mm) and the lower union of the yellow tag goes to oh side of the pdwa (12mm to 10mm).

To bleed the system I used a gunsons easy bleed, for £20 seems like a great investment, comes with the correct caps to do brakes and clutch.

The order to bleed the brakes should be rear near side, rear offside, front offside, front offside. The theory being that you should go from furthest away to nearest.

If you are making your own copper/nickel lines as I did, get yourself or borrow a pipe bender and flare tool, try some practice pieces and don't forget to put the unions on before flaring both ends (yes I forgot to do this)

When fitting the new clevis pins use R clips, you will be happy the next time you decide to remove them, I found removing the heater piping made fitting alot easier.

Hopefully this will clear up some of the confusion I experienced doing this.

Much love, connor

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