silvermine front disc conversion

[Chance]

I decided I'm gonna do a front disc conversion so i don't have to worry about working on drums when im up in the salt belt, I had a question do I need to to do anything with the master cylinder for the conversion or do I just put the kit on and im good? I've seen talk about the residual pressure valves but for rear and front conversions, does this apply to front only conversion? thanks also off topic question should I make a project topic and just keep asking questions on the one topic or just post individual posts? 

 

[datzenmike]

Drum brakes have a stronger 10-12 pound 'residual' valve than a 2 pound disc brake. If not changed to a disc brake residual valve the disc brake will rub too much. Certainly if they don't over heat they will wear out way too fast. A disc brake only need a slight pressure to keep the pad gently against the rotor.

 

Find a Datsun car or a '78-'79 620 that had front disc brakes and get the residual valve from it. It's on the output from the master cylinder.

 

 

 

 

The front brake circuit is the one at the rear of the master. It's marked F. I put a rear disc master on my rear drum car and had to put a drum residual valve in. I could not see any difference between the two so DON'T get them mixed up.

[Chance]

appreciate it Mike

[Chance]

@datzenmike would one from a 1983 720 work? only parts car Datsun around me 

[datzenmike]

Should work. Should look like the ones in my picture.

[Chance]

20 minutes ago, datzenmike said:

Should work. Should look like the ones in my picture.

okay nice, I think ill just grab both front and back just in case.

[Chance]

thought about the silver mine kit? the wilwood and the standard caliper are the same price. 

[datzenmike]

10 hours ago, Chance said:

okay nice, I think ill just grab both front and back just in case.

 

The 720 rears are drum so not much use to you. Again the front brake circuit is marked F and it's the rearmost one on the master.

[Chance]

also i've been reading about people saying for conversions to get a adjustable proportioning valve is this necessary?

[datzenmike]

Front/rear brake bias is designed into the 620 brake system. The fronts do almost all the work as weight transfers to the front tires increasing traction and reducing lock up. Thus more braking can be safely sent to the front brakes. The rears are the opposite, with weight being removed from the rear tires making rear lock up more likely. Generally when full braking is applied all wheels should lock up at about the same time. If you were increasing the braking on the rears then yes the adjustable proportioning valve would be useful for dialing this back but you aren't. In fact not much will change going to front disc other than a LOT less maintenance and adjusting, and much easier changing of pads. The limiting factor in braking is the tire traction. Once maxed out and the tires are locked there is no difference between disc or drum. 

 

I will add that discs are more resistant to heat fade than drums, but this is exceptionally rare in real life.

[Chance]

went to pick n pull and took the residual valve off that but it looks a bit different. 

 

[datzenmike]

They may have changed over the years.

[Chance]

31 minutes ago, datzenmike said:

They may have changed over the years.

you think it'll still work

[datzenmike]

I don't see why not. There is a spring and a valve. When the brake pedal is released brake pressure drops and fluid returns to the master cylinder reservoirs against the spring and valve which captures and retains about 2 PSI in the front circuit.

[Chance]

2 hours ago, datzenmike said:

I don't see why not. There is a spring and a valve. When the brake pedal is released brake pressure drops and fluid returns to the master cylinder reservoirs against the spring and valve which captures and retains about 2 PSI in the front circuit.

okay nice and I just wanted to add I looked at the rear valve that was for drum brakes that holds more pressure and there is no hole in the center on the drum brake "valve" ill post pictures tomorrow to show what i'm talking about just in case someone comes upon this in the future and is wondering haha.

[Slow Loris]

If I may borrow this thread for a moment, so if I seem to have put a master from a disc/drum truck on a drum/drum truck would I be missing out on the extra residual pressure provided by the drum residual valve? To the detriment of my front braking performance?

[datzenmike]

A drum residual valve retains about 10-12 PSI. If used on a disc brake it will be pushing four or five times more than a disc brake residual valve.  Sort of like driving around with you foot resting on the brake pedal. The disc brake may heat up and for sure the pads won't last as long. Best to get a 2-3 PSI disc brake residual valve.

 

The residual valve won't affect braking performance but it will shorten the life of the pads.

 

[Slow Loris]

Yes I’m saying I have a disc/drum master (so presumably the weaker valve in front) but using it with drum/drum brake set up.

[datzenmike]

Then it needs the 10 PSI residual valve. The drum shoes have a lot of slack designed in and the higher pressure in the lines takes up this slack reducing the brake pedal travel.

[Slow Loris]

7 hours ago, datzenmike said:

and the higher pressure in the lines takes up this slack reducing the brake pedal travel.

Then I think that explains some things. Makes perfect sense. Thanks!

 

Chance you may have your thread back!

[datzenmike]

Disc pads are already just against the rotors and there is hardly any movement so a couple of pounds just to keep them shiny.

[Chance]

3 hours ago, Slow Loris said:

Then I think that explains some things. Makes perfect sense. Thanks!

 

Chance you may have your thread back!

all yours brother haha, have a good one and God bless.

[Chance]

hey so I took the residual valve off my master cylinder and its a bit bigger than the one I took off the 83 720 for the front brake conversion will it still function?

Edited July 29 by Chance