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Hello, sorry if this topic has been discussed many times!
I have a 1971 Olds Cutlass S with power drums all around. I made my drum brake stuff all new. All lines, hoses, distributor block, shoes, hardware etc. It brakes good, but i want to convert to front discs just to get better and saver braking performance.
im in Austria, and here its a bit heavier to get parts for a car like this, all has to be shipped from the US. Because of this, i want to ask for some help and recommendations in Parts gathering (rockauto?) Just to order the right parts.
i recently purchased original GM disc brake spindles, discs, brake calipers, brake calipers mounting plate, steering arms and the tin metal disc guard plates from an 71 chevelle. They work fine with my 14" olds rally wheels. Just have to refresh and repaint these parts.
- Can i use my current brake booster for a disc/drum master cylinder?
- which master cylinder do you recommend?
- do i have to use the current distributor/switch block from the drum/drum system or just a proportioning valve for disc/drum (from OPGI?) Or do i have to use both?
- for sure, i know i maybe have to do some replumbing of the brake lines, but i would love to keep my big front-to-rear line.
are there some other points i should keep in mind with this project?
Yes, you can use the original brake booster.
I just use a replacement disc brake M/C for the car. There's no need to get exotic.
A 1971 would have come with a combination valve from the factory, which includes the functions of the distribution block, the metering valve, and the proportioning valve in one (hence the term COMBINATION valve). If you don't care about being optically correct, get one of the aftermarket brass ones instead of the OEM cast iron. The cast iron ones will rust in the bore, causing the piston to stick.
You will need the correct brackets that hold the frame end of the rubber caliper hoses. These have a different shape cutout for disc hoses than for drum hoses.
If you plan to do the plumbing yourself (as opposed to buying a pre-bent kit), you'll need the flare nut assortment that has the non-standard thread sizes that GM used. You won't need all of these, but this is an example.
Thank you! I think the small mounting stuff for the brake hoses-to-frame is no problem to for me to made them by myself.
So, i would prefer to keep all my existing brake lines from the distribution valve to both front wheels and the larger line to the rear of the car. They are brand new and the one to the right front i bent by myself so get far enough away from my headers.
in this case, all i need is a disc/drum master cylinder and the correct proportioning valve for disc/drum between the master cylinder and the distribution valve? This would be great, because i can mount the proportioning valve right next to the master cylinder and route the 2 lines from there to the distributioning valve and keep all my lines to the wheels and rear.
will this be correct? For sure, i want to go the easiest way to do this
in this case, all i need is a disc/drum master cylinder and the correct proportioning valve for disc/drum between the master cylinder and the distribution valve? This would be great, because i can mount the proportioning valve right next to the master cylinder and route the 2 lines from there to the distributioning valve and keep all my lines to the wheels and rear.
will this be correct? For sure, i want to go the easiest way to do this
You can keep the stock distribution block and use an aftermarket inline prop valve in the line from the M/C to the rear brakes. That won't give you the metering valve function to the front brakes, however. It's possible that you can replace the distribution block with a combo valve and reuse the existing lines from the distribution block to the wheels with minor rebending and possibly some inverted flare adapters. I've done that before. You'll be better off making new lines from the M/C to the combo valve, which isn't difficult.
You can keep the stock distribution block and use an aftermarket inline prop valve in the line from the M/C to the rear brakes. That won't give you the metering valve function to the front brakes, however. It's possible that you can replace the distribution block with a combo valve and reuse the existing lines from the distribution block to the wheels with minor rebending and possibly some inverted flare adapters. I've done that before. You'll be better off making new lines from the M/C to the combo valve, which isn't difficult.
Ok, i think i prefer the just-use-a-combinatipn valve-way.
I found at Summit Racing the SUM-760186 proportioning/combo valve.
Inlets are 1/2 - 20 inch and 7/16 - 24 inch,
outlets for front are 3/8 - 24 inch and the outlet for the rear is 9/16 - 18.
Is this like the stock combination valve with front disk and rear drums?
my current distribution block is the one from OPGI for drums all around. I cant remember the thread sizes of it, but i hope that theyre the same to keep - or just a little rebend - my existing lines.
i think ill order a box with a few brake line fittings too, like the set you posted.
BUT, way more easier is the 1970 in - line prop valve solution, i just have read your Low cost disk brake thread.
Are there any points which make the combination valve way better than the 1970-in line prop valve?
As i said, all my lines are brand new and one is made by myself because of headers and i even relocated the new OPGI distribution block a bit away from the headers. So the 1970 solution is getting more and more attractive.
im not into the complete original way to go, i mean, original in my car are 4 drum brakes and if this works the same way as the right 1971 style comb.valve works, i dont care if this solution isnt correct for 1971.
The 1967-70 cars did not use a prop valve. The metering valve next to the M/C controls application of the front brakes. It does not proportion front-to-back balance. That was done through careful selection of wheel cylinder sizes and lining friction.
The 1967-70 cars did not use a prop valve. The metering valve next to the M/C controls application of the front brakes. It does not proportion front-to-back balance. That was done through careful selection of wheel cylinder sizes and lining friction.
Thanks a lot for your help!
So this tells me, the better way is to use a 1971-style comb./prop valve and re-plumb the lines?
Are there some recommendations which brands/part numbers to use for the combination valve, M/C and fittings assortement?
Again, thanks a lot for your help. I wish we would have the same easy access to parts for these cars here in Europe. Every small fitting has to travel over the ocean
Would the correct master cylinder for a '71 power disc/drum application have a longitudinal single bale on the top or a two bale design? I'm about to replace mine and I'm uncertain which is correct. Thanks!
Would the correct master cylinder for a '71 power disc/drum application have a longitudinal single bale on the top or a two bale design? I'm about to replace mine and I'm uncertain which is correct. Thanks!
Yes, 1971 would have come with the rectangular single bale M/C.
June 24th, 2020, 02:03 PM
