I replaced my drum rear with a 4th gen disc rear. I kept the stock master cyl. and ran the single brake line to the back into a t-block.
My original idea was to install a preportioning valve on the 2 lines feeding the front calipers, restrict the flow there, resulting in more rear bias......?

I spoke to a mechanic today who told me I had it all wrong. That i'd need a late model master cyl. and will have to run a line to each rear caliper in order to get enough ''umph'' back there. (to put it in his words)

Those who have been through this swap, or just know a bit about brakes, PLEASE give me some input. I barely have enough pressure back there to keep the rust off my rotors!

Thanks alot.

 

I too am redoing my brake system, you need a proportioning valve for the rear summit has one for 47.99 but I don't have the part # handy. I have the same rear as yours and I had the same problem you have now I don't.

 

Ok, can you explain where it was installed in relation to the master cylinder? I don't see how placing a proportioning valve between the master cylinder and the rear brakes could increase pressure. There isn't a stock proportioning valve that has to be eliminated, is there? Sorry, I don't know squat about brakes.

 

As I understand it, the aftermarket adjustable prop valve is installed on the rear brake line AFTER the stock valve, and it's intent is to DECREASE the line pressure for the new disc rear - drum rears require more pressure and thus the stock valve will provide too much pressure and lock the rears too early if left stock (like I said, it's what I read on here).

For my 4th gen rear disc (LS1) I just ordered and got the stock proportioning valve for a rear disc car from the dealer - a search on here will reveal the part number. Then it's a simple swap of proportioning valves. HOWEVER - I have read here also that certain year cars had different thread sizes on the prop valves than others - mine is a 1992 and the threads were the same.

Those aftermarket adjustable proportioning valves require alot of either a) adapters or b) self-made flares and fitting ends on your existing lines in order to work, as they all come with something like 1/8 NPT fittings (which will NOT connect directly to the brake lines in the car).

So in short, the dealer part is (usually) a simple swap but not adjustable, and the aftermarket stuff is adjustable but requires a knack for double-flaring your own lines and installing new end fittings.

Another FYI - depending on which 4th gen rear you have, you may need a new spare tire - I have 16inch 3rd gen wheels (camaro), but my spare will not clear the LS1 brake discs.

 

Just keep you stock master and use a prop valve from a 91-92 Fbody 4whl disc car and be done.

 

That sounds painless. Did the 3rd gen 4 wheel disc cars have the same master? Only one line feeds fluid to the rear brakes?

 

Just use a prop valve from a 91-92 they were all the same disc or drum.I have one if you need.Or I can just sell you the whole setup booster,master and valve for $70 shipped.

 

This is just the opposite of what I am experiencing. Seems to me like my new disc rear needs a good deal MORE pressure.

 

Disc brakes (on the rear) need a LOT more fluid pressure to work, as compared to drums, because drums are self-acting once the brake shoe contacts the drum. Discs don't work that way.

So in a car with front discs & rear drums, a proportioning valve is used to reduce the fluid pressure to the rear drums. If you swap the drums for discs, you either need a new proportioning valve intended for 4-wheel discs, OR, the stock proportioning valve needs to be altered to allow high line pressure to the rear brakes.

Some time ago (link below) I posted here how 94-96 Caprice 9C1 // Impala SS owners have altered their proportioning valves to suit the 4-wheel-discs brakes on their car BECAUSE the factory used the same proportioning valve on the 9C1/Impala SS as they did on the disc/drum Caprice. In those cars, the proportioning valve is part of the so-called combination valve (combi valve).

https://www.thirdgen.org/forums/brak...ighlight=combi

 

Im running all LS1 brakes from a 99 Z28. Im also using the booster and master cylinder from that car.

Front brakes:
Im running a line from the mater, to a line lock, to a t-fitting, then to each front caliper. ALL 3/16 line.

Rear brakes: Im running a 1/4" line from the master, to a willwood adjustable proportioning valve, then back to a t-fitting on the axle. That is still 1/4". AFTER the t-fitting, Im running 3/16 to each rear wheel.

I bought a kit from SJM Manufacturing that had all the fittings and pre-bent lines, line lock, and prop. valve needed to put it together. The kit is for a 4th gen...but with alittle tweaking works fine.

This kit was designed to delete the ABS on a 4th gen. SO... there is NO other proportioning valve in the system. Should stop just fine, and Ill have adjustment over my rear.


On another note... I have a 94 Jeep Cherokee which I offroad. I fitted rear disc brakes on that as well. Stock everything else. I ditch the prop. valve and ran the lines the same way that Im running them in my TA. It stops 33" mud terrains on steel wheels better than stock.

Just my 2cents and experience.

Justin

 

Thanks for the help guys. I've got it sorted out. My rear will basicly be setup like Ghettocruiser's, with the stock master/lines and a Wilwood adj. valve.

 

Hello. I am basically doing the same thing , installing a 2001 rear end (with the big disc brakes) in my 1989 (rear drum brakes) camaro rs. trouble is, i'm not at all that experienced.
if i get it right, the simplest way would be to get a prop valve from a 91-92 camaro, and keep everything else as it is. WOULD THAT WORK ?? WOW

so I get to keep the booster, master cylinder and stock brake lines ? In that case, I sure am interested in that prop valve you have available. How much do you ask for that one ? (I live in Blasdell, NY) Thx

 

Yes. No point in all the aftermarket stuff.

For that matter, your existing prop valve will work fine. The hydraulic requirements of the PBR calipers are pretty similar to drums (unlike the earlier model cast-iron Saginaw calipers); and your drums are no different from 91-92 drums; and therefore your prop valve is not significantly different from a 91-92 one.

I have PBRs in my 83 car that originally came with drums, with the original (well, original replacement, anyway...) MC & PV. Works great. The rear pads wear at about 60-70% of the rate of the fronts, and they lock up at almost exactly the same point, so I'm inclined to think that they're balanced reasonably well.

 

this rear end swap sounds like its going to be a breeze
thanks for the enlightening advise

 

91-92 prop valves are all the same, disc drum, or disc disc??? Is this true?? Doesn't seem right. Any info on this? I just picked up a disc rear end, and found a 91 prop valve from a disc drum Camaro. Any info on this would be much appreciated. Thanks!