Some shadetree mechanics on another forum are telling me that if I convert from drums to disk I will need a new master cylinder in addition to the proportioning valve.

Is this the case?

 

No,otherwise you would need it when you do an axle swap.Just the prop valve.

 

new master cylinder wtf

 

ghey

 

I mentioned that the disks take less hydraulic pressure to operate (therefore the proportioning valve) but they responded saying it was more an issue of volume of fluid as opposed to pressure. At least a few of them own their own shps so I gave it a little creedence.

They mentioned that if I did need a new MC, it would be pretty obvious after installation... pedal would be way off and stuff.

 

i actually just did this swap fairly recently, pain in the *** first off all so be sure u wanna do it, second still useing the same MC, front brake line after the master cylinder going into a line lock then T-ing off too each side, back brakes from MC going into an ajustable wilwood prop valve then back to the rear end and T-ing off to each side hope that helps...oh and LT1 discs in the rear if that was in question, they DO clear stock wheels however i had to grind a little off the caliper to fit my 15x9 5.5bs weld draglites on.

 

The diaphram in the disc prop valve is bigger than the drum.I think the drum valve is like 0.75 and the disc is 1.00.I'll have to find the specs but that's about it.

 

Yes and no, the shadetrees are correct depending if GM has two different MC's (they used to long ago). DB's need more volume and usually have a larger bored MC's.

In the"old days" it was a must, but may not be the case now if the same MC is used on 4w DB, etc.

Everything aside, the way Jessae did it is probably the best, since the front to rear bias on the PV's we have in our 3rdgens suck, plain and simple...assuming the MC can hold enough fluid when the pad wear.

You don't need a different/larger MC, as long as there is sufficient volume in it to keep fluid in it after the pads wear down. Adjustable valve will be your best friend when you convert.

 

Where did you get the Wilwood prop valve? How much was it?

How does the adjustment come into play?

 

Summit, like 30 bux, theres a ****...ill even find a part # for u gimme a sec

 

WIL-260-8419

on summit... enjoy

 

I have one of those in my Firstgen and hate it because it leaks.

I'd tell you to find a disc rear car at your local junkyard and pull the proportioning valve. Install it in your car and have factory fit and NO LEAKS!

 

really im having no problems with mine (knock on wood ofcourse)

 

Thanks Jesse (and Vin). I'd love to get a GM original one but have heard they charge upwards of 100 bucks for a new one. The Wilwood is an attractive option however (name and cost).

If I knew my way around these cars like some of you gents, the junkyard option is the way I would go.

 

Just find a disc rear car in the yard, follow the lines to the prop. valve (metal block looking thing) and you could have it out with a Crescent wrench (although I would recommend flare nut wrenches) in a few min.

No lines to bend for an adjustale, no headaches, no stealership price tag.

 

Hey Terrell, you reading this?

Will you need your old prop valve on that 10 bolt?

 

I think these guys are thinking of older front drum to disk conversions where fluid cunsumption was a much bigger difference than with the rear axle wich takes much less effort to stop. All the rear axle disk conversions kits i've seen do not include new master cylinders. On a different note I would rather upgrade the front disks and leaving the rear alone (rotational drag)

 

Actually you do need the master cylinder too for optimum performance.The piston bore for the disc brake is 1.00" and the drum 0.75".

 

Well dang.

Otimum performance is what this is all about for me. Would this do the trick?

Ebay auction

Is that the valve I need too?

 

Yep,that's the master cylinder and the prop valve.I forgot that I swapped the master too.I took it off the 86 t/a that Eric now has.It wasn't out of poket so I forgot about it.

 

Well, I won that auction. 25 bucks for a master cylinder with OEM prop valve. Not too bad if it's in good shape.

Now for the speedo gear and my stock to hit a decent price.

 

Sweet!I have to do my rear swap asap as my driverside rear wheel is knocking around (bearing)No point in fixing that just to swap it later.I'm leaving on the 7th for vacation in Florida for 2 weeks so I'll have to do it when I get back.