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Discussion Starter · #1 · (Edited)
When upgrading the brake system on a Gen 1, what is the best donor vehicle to get a combination valve from?

By combination valve, I mean one with these functions:

1. Metering Valve, to compensate for rear drum slop time.
2. Pressure switch. To indicate if front or rear MC has failed.
3. Proportioning Valve. To limit the pressure to the rear brakes to stop them from locking.

It would also be great if the proportioning valve was adjustable, but I don't think factory units are.

The plan is to mount it right next to the Master cylinder

One alternative is to use a valve without a proportioning valve. In stead I would add an external proportioning valve But this would mean I would need a valve which only has the metering and pressure switch functions. Any suggestions?
 

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welcome..
if you are going from 4 wheel drums to a disc/drum combo, just use the stock drum/drum one that's on the car and add an adjustable prop valve on the rear line.
it is just a splitter and a brake light switch and does no metering.
 

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Discussion Starter · #3 ·
I'll confess, this is actually for a 63 vette. The vette has a single chamber master cylinder and then a distribution block to all four wheels. Its a dangerous setup and I'm upgrading to a dual chamber master cylinder. I have also upgraded the front drums to disc, so now I have disc in the front and drum in the back.

To connect the MC to the rest of the system I need to find a combination valve as described, or separate pieces that result in the same.

Thanks, :beers:
 

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Split,

For your car, I think you'd use a 71' and later brass Disc/Drum combination valve with built in rear propotioning and front "hold off". Two lines in from your master, 3/16" front, 1/4" rear. Two 3/16" lines out to the front left and right brakes. One 1/4" line out to the rear. Includes a pressure failure switch. Brackets to mount it off the booster and under your master are commonplace.

About $80 to your door, ebay. Brackets extra.



Probably not required, but you could add an adjustable Proportioning valve to "fine tune" the rear braking force. Just plumb it into the rear line, just after the line leaves your Combination valve. It would have to have 1/4 inlet/outlet though. You need the volume for drums. I think you can get these in 3/16 or 1/4.

About $50 to your door, ebay.



Cheers, Mark.
 

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Discussion Starter · #5 · (Edited)
cdnpont,
Are the Camaro combination valves from '71 on to today all the same?
In my system the front left and right 3/16" lines connect to a block near the left front A-arm. A single 1/4" line from this block then goes to the front Master. The back brakes combine and have a single 3/16" line to the front also.

Can I get adapter fittings which will convert from 3/16 to 1/4 and visa versa? Will I be able to use just one of the front brake outlets on the combination valve? What are the male and female tread styles? For example, 1/4" NPT?

I should be able to find a dirt cheap combo valve off a camaro at a wrecking yard, esecially if they are all the same from '71 on.

oh, do you happen to have a diagram of this combo valve or know a link to one? I just need to understand which ports do what and go where.
 

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i got what you need. i got a adjustable valve for the rear brakes. goes in front a single line from master cylinder to rear of car. cause drum brakes and disc brakes stop differently from each other. you adjust the rear pressure to where you like how car stops.ricks first gen got them also ill sell you mine for cheaper still brand new i bought a kit and had 1 in also so i got an extra 1.
 

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Sorry about the length,

As far as I know all the combination valves of this post 71' style shared the same internals. Although some may have been valved slightly different due to different vehicle weights and performance requirements. I don't really know. But I do know that any valve that I've seen for sale doesn't make any distinction as to " Vehicle Type". Except that it is for Disc/Drum or Disk/Disc. All GM vehicles after 71' had at least front discs as standard equipment.
The Disc/Disc simply lacks the Disc/Drums Metering portion, in that it no longer needs to perform any "hold off" action on the front discs, when the rears are also disc. There also could be a different front/rear proportion ratio between both types. I belive the Disc/Drum has at least a 1/4" outlet passage to the rear brakes. I'd think the Disc/Disc should have a 3/16 rear outlet. Not sure, I'm actually waiting for a proportion valve from Inline tube for my own conversion.

Do you have rear discs? You say you have a 3/16 rear line, that would be disc if I'm not mistaken. I'm not up on 63' Vette's.

I would disconnect your right front 3/16 line from the small dist block. Attach 1, 3/16, 3/8-24 female coupling to the male end of that old line. Make a small line with two 3/16, 3/8-24 to run from the new coupling up to the combination valve, connecting to the upper front 3/16 outlet (the one on a angle). Remove the left side connection from the flex line to the dist block and discard. Make up a small 3/16 line to run from the flex line to the combination front lower(almost directly below the upper one).

I think I would follow this rather than trying to block off one front combination outlet, to adapt your 1/4 dist block inlet line into the one remaing 3/16 front outlet. Let the valve split the flow. Many different line adapters are available, better to keep connections to minimum imop.

The bolt like item protruding from the left of the valve pictured is the rear brake outlet. You cant see it's exit. 1/4 line for drum. 3/16 for disc.
The three holes seen on the top are, from left, Rear brake inlet from master ,1/4 line, Fitting ? Front brake inlet from master,3/16 line, Fitting? Front outlet, 1/16 line, (should be) 3/8-24 fitting.

Buy a new (or at least reman.) valve. Don't chance a wrecker valve.

Google " GM combination Valve". You'll find good info, it's out there.

Cheers, Mark.
 

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Discussion Starter · #10 ·
Here is an interesting wrinkle..... Was searching on ebay for combination valves.
Found this one, although there were many others listed just like it.
http://cgi.ebay.com/ebaymotors/GM-S...105426840QQcategoryZ33565QQrdZ1QQcmdZViewItem
The interesting part is that it is claimed to have a "self-adjusting" proportional valve function? This would sure explain why GM provides no adjustability. Is there any truth to this and how does this self adjustment work?

Also, it's described as having a "zinc coated finish". I had assumed that these were all made of brass?

:beers:
 

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I can tell you the photo they're using is of a Disc/Disc valve. It's missing the small black plug or button on the front. Disc/Drum has the plug. I think it's where the front metering valve is installed and the fitting is covered for protection.

I think "self adjusting" as described has to do with line pressures from the master, front and rear entering the valve. As overall pressure to both front and rear brakes rise, the line pressure to the rear is proportionally reduced, the fronts increase. This to avoid rear lockup seeing as generally the weight of the car is being transfered onto the front wheels (brakes) during hard stopping, unloading the rears. A good guess really!

As far as I know the Factory valves were either Steel with zinc plating, Brass or Aluminum. Brass looks nice for advertising and that's what I'd want, but you might just recieve a plated steel one. Send him a message asking just that question!
 

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Discussion Starter · #13 ·
I can tell you the photo they're using is of a Disc/Disc valve. It's missing the small black plug or button on the front. Disc/Drum has the plug. I think it's where the front metering valve is installed and the fitting is covered for protection.
It could be that the vendor is reusing the same picture for disc/disc and disc/drum, as he is selling a lot of these. Here is another one that I think is showing the front button
http://cgi.ebay.com/ebaymotors/GM-S...096510649QQcategoryZ33566QQrdZ1QQcmdZViewItem

I think "self adjusting" as described has to do with line pressures from the master, front and rear entering the valve. As overall pressure to both front and rear brakes rise, the line pressure to the rear is proportionally reduced, the fronts increase. This to avoid rear lockup seeing as generally the weight of the car is being transfered onto the front wheels (brakes) during hard stopping, unloading the rears. A good guess really!
I read somewhere that if you mess with the factory suspension, it might alter the performance of the self-adjusting proportioning valve. This would seem to point to some mechanical force feedback rather than pressure. But you know, you can't trust what you read on the internet. Hence after searching for an hour, I decided to post my previous message. THe other day, someone sent me a link to a picture which showed the internal layout and functions of the combination valve. But I have not been able to find it again.
As far as I know the Factory valves were either Steel with zinc plating, Brass or Aluminum. Brass looks nice for advertising and that's what I'd want, but you might just recieve a plated steel one. Send him a message asking just that question!
I did send the one vendor such a message, I also asked him what "self-adjusting" means.
 

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Discussion Starter · #14 ·

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There are a lot of different combination valves. I'd just get the adjustable rear valve and skip the metering and saftey switch, or use separate ones, BUT, if you must get a combination valve...

There are lots... LOTS of different ones which look and fit the same, but are different internally. The most popular by far is AC-Delco # 173-1353 (GM 25509419). It's listed for F bodies, X bodies, Trucks, G bodies.... It costs about 50-60$ new. It is also the one pictured above with the 'B' stamped in it, though many sites use that pic and sell a poorly made reproduction.

After some study of these valves and their applications, this one seems to be used on vehicles with comparatively large rear brakes and/or cylinders or large weight transfer.

Go to http://ac-direct.com/
open parts catalog
click 'vehicle list'
type 172-1353
81 pages of vehicles.
as new as 1991, as old as 1974 (website's lists only go to '74)

Also try the numbers 172-1350, 172-1351, 52, 54
They are also listed for many A bodies and others.
The first site will provide you with GM#s if you use the search. The parts catalog can show pictures. I have a crossreference for about 50 of these valve blocks.

Any might be a viable candidate for your disc/drum vehicle... it all depends on how close your brake ratios and weight ratios are to the donor.

Eventually I'd like to test these different valves and record the actual proportioning and metering pressure numbers.... someday ;)

edit: http://www.442.com/oldsfaq/ofbrk.htm reports the 1350 (GM 1257177) valve to not actually have rear proportioning in it, just front metering and pressure switch. But it looks the same.
 

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Discussion Starter · #16 · (Edited)
Found some interesting info:
http://www.stoptech.com/tech_info/wp_proportioning_valves.shtml
http://piratejack.net/proportioning_valves.html
http://piratejack.net/Images/ebay/pv2.html
http://pg.photos.yahoo.com/ph/pearlfootprints/detail?.dir=d9df&.dnm=2535.jpg&.src=ph
http://www.inlinetube.com/articles/Out of Proportion.htm

In the end, its a bit of crap shoot as to the proportioning ratio needed and the one in the valve. I have found no additional info on the self-adjusting proportioning function....not sure its real.
 

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I would not get any of the piratejack combination valves unless they are truly delco valves.
stoptech=good info
yahoo= mine
inlinetube= OK... I just skimmed that but i found several mistakes, and one (semi correct) statement contradicts another on a sales part of their site about the "third valve".
 

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I have a 1353 valve in front of me.
Rear to front, left to right, the 'B' is upside down.
The code is HJ 02 233 9419
The last 4 digits correspond with the GM part#

The two letters seem to be used in the parts manuals for superceding. (HJ replaces DX etc...)
so here's the AC to GM list for 1350 through 1357
> delco Part# / ...GM#
> ACDELCO 1721350 / 01257177
> ACDELCO 1721351 / 25515634
> ACDELCO 1721352 / 25510208
> ACDELCO 1721353 / 25509419
> ACDELCO 1721354 / 25509418
> ACDELCO 1721356 / 25515631
> ACDELCO 1721357 / 25515632
 

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Discussion Starter · #20 ·
There are lots... LOTS of different ones which look and fit the same, but are different internally. The most popular by far is AC-Delco # 173-1353 (GM 25509419). It's listed for F bodies, X bodies, Trucks, G bodies.... It costs about 50-60$ new. It is also the one pictured above with the 'B' stamped in it, though many sites use that pic and sell a poorly made reproduction.
Using the ACDelco search tool, I have been looking at which proportioning valve the camaros used, after around '77. Generally, I find no listing. The 173-1353 seems to be used on very heavy vehicles, trucks and blazers, so I'm hesistant to use it. I'll continue to see if I can locate something that more closely reflects the Disc/Drum setup and overall weight and type of vehicle. Do later model Camaro have rear drum.....or did they switch to all disc?
 
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