I need a little help plumbing my brake lines from the master cylinder to the frame mount proportioning valve. The car is a 69 Cutlass. I have converted to disc brake fronts using the Speedway kit.

I am using an aftermarket master cylinder / booster assembly which came with a MC mounted proportioning valve.

So, I am wondering what my brake line plumbing options are.

The simplest
option to me seems to be to just not use the proportioning valve which came with the kit and run the lines from the stock frame mounted proportioning valve from the old drum brake system. Would the disc brake system function properly this way and would it look correct.

or

Use only the MC mounted valve and run all new lines for the entire car or tie them in elsewhere.

or

Use both proportioning valves in line using new lines from the MC mount valve to the frame mount valve.

Pics are attached. Any help much appreciated.

 

I believe the old valve is not a proportioning valve. Drum brakes do not use them and that is just a brake warning switch. At any rate I would use the new one and fabricate all new lines.

 

^^What Patrick said.

 

Ok, but the "switch" also serves as a "distribution block" for the brake fluid coming from the master cylinder and connecting to the three front and rear brake lines. I have two 69's the one we are discussing was originally a drum brake car. My other 69 I believe was originally a disc brake car and the switch / distribution block / proportioning valves both frame mounted in the exact same location appear to be identical.

If I use the proportioning valve provided with the aftermarket kit how do I tie in the two lines leaving the MC mounted proportioning valve to the three lines needed (two to the front and one to the rear ) that would now bypass the frame mounted "switch". I guess the rear could be one continuous new line from the valve to the rear end. But the line to the front wheel cyls would have to be split.

If in fact the frame mounted valve is just a switch how would I harm the system by using it as the method to continue to split the lines ?

 

The brass combo valve that came with your kit has EXACTLY the same ports as the factory combo valves used on the 1971-up cars. There are two inlets to the combo valve that connect to the ports on the M/C. Your photos show that you already have the short lines to do that. There are THREE other ports on the combo valve, two on the front for the two front wheels and one on the back for the rear wheels.

Remove the stock distribution block. It is NOT a proportioning valve and must NOT be used in series with the new combo valve. Either fabricate new lines to replace the current brake lines (by far your best bet) or use inverted flare couplers to attach extension lines to the existing hard lines that reach to the new combo valve. The wire for the differential pressure switch that connected to the old distribution block now connects to the same connector on the new combo valve. Done.

The inverted flare couplers are available at any auto parts store.

 

Joe,

I just got done reading a response from you to someone on the Hotrodders forum from 2012.

In that post you stated that the 67-70 models used a hold off / metering valve in addition to the distribution block. Would that valve have been upstream from the distribution block near the MC ? What does it look like ? as I don't recall seeing one on my disc brake 69 ?

Part of what I was wanting to avoid here was having all that extra plumbing attached to the MC. Could I not just purchase a hold off / metering valve correct for my 69 and keep things more factory looking
and still be properly safe and functional.?







[/QUOTE]

 

Joe or Patrick or anyone,

Is there any reason why I could not frame mount the proportioning valve that came with the kit to solve this problem ?

 

The metering valve for the 67-70 cars looks like this:



Note that it also mounts on the master cylinder, though in this photo the distribution block is incorrectly mounted under the M/C as well. If your 69 truly did not have one, it was either converted incorrectly or the valve was removed by someone who was clueless.

The correct metering valve plumbing hard line looks like this:



Inline Tube and others sell repro metering valves. I don't see how this solves your problem, however, as you will still need to replumb the lines from the distribution block to the M/C.

Like this?




Again, you will still need to run new lines, and some of the inverted flare fittings are likely to be different sizes.

Bottom like is that you can either use the combo valve (in either location) or the original distribution block with the 67-70 external metering valve. All of these options work exactly the same way. None of them get you out of bending new lines. And of course, the combo valve or distribution block on the frame in the stock location usually interferes with headers if you plan to install them, which is why many aftermarket kits mount it under the M/C.

 

Joe,

Thanks so much for all this info. I like this option best as it allows me to keep the look cleaner at the MC and makes it look as correct as can be for using the after market valve as a frame mount application. I knew some replumbing would be involved but had hope to avoid replumbing the entire car. I am running a 455 with stock manifolds not headers so the frame mount should work nicely for me.

As far as Inline Tube goes. I had a very bad experince with them recently involving the attempted purchase of a gas pedal mount detent cable which they sent a carb mount cable claiming that there was no such animal as a gas pedal mount detent cable for an Olds. The carb cable was returned and they refused to refund my money. Each person I spoke with became ruder and ruder. The trouble was that I could find no one at IT who had any knowledge about Oldsmobiles and it just turned into a big mess. This was my 6th or 7th order with them but I will never use them again for anything. I know you were just mentioning their name as one of many.

I will double check the coupe and look for the metering valve. I suspect that you may be right in that someone long ago did a disc brake swap and did it wrong. If so then I will remedy that error and will be replumbing the
P valves on both cars.

Thanks again, for the a very helpful post. And Patrick thanks for your response as well.


I like this option and will use it.
Like this?




Again, you will still need to run new lines, and some of the inverted flare fittings are likely to be different sizes.

Bottom like is that you can either use the combo valve (in either location) or the original distribution block with the 67-70 external metering valve. All of these options work exactly the same way. None of them get you out of bending new lines. And of course, the combo valve or distribution block on the frame in the stock location usually interferes with headers if you plan to install them, which is why many aftermarket kits mount it under the M/C.[/QUOTE]

 

Joe or anyone,

In looking at this pic particularly at the line to the rear end there is a large loop as it leaves the valve. Is there a purpose for this loop ? Same question re: the short line to the left front wheel ?

And what is the purpose for the coiled shields that slip over the lines to the MC ?


Thanks

 

I simply stole this photo off the web (thanks, Google Images), so I can't justify the workmanship. I'm sure this is simply a case of whoever installed that valve bought overly-long pre-flared brake lines at the auto parts store and didn't want to cut and reflare them, thus the loop-back to use up the extra length. The brake fluid neither knows nor cares about the loops.

They are stone protectors, so that small stones thrown up by the tires won't damage the brake lines.

 

Not relevant to this pic, but loops like that are also used where hard lines go between surfaces that would move or vibrate to allow movement without causing cracks. The coils usually found in the lines leading from the MC to the frame for example. Plumbers installing a gas stove would leave about 10' of copper line coiled behind the stove to allow it to be pulled out.

 

Which is not the case when both the combo valve and hard line are firmly bolted to the frame rail.

 

OK thanks Joe.

I was looking at fittings today and the original ones appear to be 3/8 24
thread while the ones on the kit and the ports on the kit valve appear much coarser like 18 or 16. I know you mentioned having to possibly change fittings on the existing lines.

Sorry to beat this subject to death but would it be an option to run a stock GM combination valve from a 71 or 72 or up to 77 ( I think ) Which would frame mount, replace the metering valve, and still work with the original inverted flare nuts ?

 

All disc brake combo valves use different flare nuts from the drum brake distribution block. This was to prevent mistakes on the assembly line. Just go to NAPA and search through their drawer of "master cylinder adapter fittings". Or, you can order them on line. Be sure to get fittings that have inverted flare threads on both sizes (female and male ends). Do not use NPT adapters.

http://www.oreillyauto.com/site/c/se...delmann&mc=EDE

http://obrienbrass.thomasnet.com/vie...nder-adapter-2

https://www.hydraulicstore.com/index.php?loc=items&data[catalog]=1&data[grp_id]=4104

 

Thanks Joe, awesome help as always.

Brad

 

Joe or anyone,

It appears that I have brake lines in different sizes. On the old drum system there was a 1/4 line from the the MC to the distribution block for the rear wheels and a corresponding 1/4 line from the distr block to the rear axle.

The line from the MC to the distr block handling the front brakes is 3/16 and the two lines from the distr block to the front wheels (formerly drum now disc) are also 3/16.

Is this correct ? or with disc brakes now does everything need to be 1/4

 

Front lines are 3/16 in all cases. Back is 1/4.

 

Great Thanks!!!!!!!!!