65 GT350 Proportioning Valve

[shelbydoug]

No, they were used on every Mustang. Not Shelby installed or specific. Totally needed on any disc brake equipped car of any make or model if you have a disc / drum combination.

  The valves were set to work with "hot" brakes. If you set the valve to make the brakes effective when cold , they will lock up FOR SURE if run at a competitive event where they see heat. "Street driving " is not enough.
   In drag racing , I ride the brakes when smoking the tires before the starting line. The holding power on the starting line is far better with the rear brakes heated and stopping at the end in great too.

Aren't the valves overkill on the street then? They should be R model only then?

Every Mustang had a non-adjustable valve. The 65-6 Shelby's had a version of the Corvette adjustable valve. It had it's own S1MS part number.

The only use I can think of for it would be as Randy stated, "for race use".

Even today typically the rear brakes don't need to be done often. Every 75,000 miles or so. Fronts every 30,000. It's about a 2 to 1 ratio.

Lots of things were done on the '65s apparently with the presumption that they were all race cars

[Bob Gaines]

No, they were used on every Mustang. Not Shelby installed or specific. Totally needed on any disc brake equipped car of any make or model if you have a disc / drum combination.

The proportioning valves that were used on the 65 and 66 GT350's were different in that they were adjusted to compensate for the larger 2 1/2 inch drums and the more pressure needed to activate them in proper relation. Those special proportioning valves adjusted differently had a different Ford engineering number consequently Kelsey Hays identified them by painting them black instead of the typical battleship gray. That was most likely so that they could be told apart by assemblyline workers from the regular valves given that there was no other distinguishing features.

[gt350hr]

    Doug ,
       NOT the same valve as a Corvette. They had bigger fitting/tubing sizes. True both versions were made by K/H and used the same raw casting.

    Royce , YES same valve as C5ZZ "except" the S1MS version was "preadjusted" for use with 2-1/2" metallic rear lining. The C5ZZ valve was set for 1-3/4" organic lining. If you had an original C5ZZ and S1MS side by side , the difference in adjustment is obvious. This is also noted in the partial blueprint Jeff S posted earlier in this thread.
    For '67 and later , metallic shoes were dropped and standard inline , non adjustable prop valves were used.

[Royce Peterson]

Right, the 67 and later Shelbys had the standard size rear drums. I did not know the prop valves for Shelby were readjusted for the 2 1/2" rear drums but it sure makes sense. Those would lock up big time without a proportioning valve.

Thanks for straightening me out!

    Doug ,
       NOT the same valve as a Corvette. They had bigger fitting/tubing sizes. True both versions were made by K/H and used the same raw casting.

    Royce , YES same valve as C5ZZ "except" the S1MS version was "preadjusted" for use with 2-1/2" metallic rear lining. The C5ZZ valve was set for 1-3/4" organic lining. If you had an original C5ZZ and S1MS side by side , the difference in adjustment is obvious. This is also noted in the partial blueprint Jeff S posted earlier in this thread.
    For '67 and later , metallic shoes were dropped and standard inline , non adjustable prop valves were used.

[Bob Gaines]

Right, the 67 and later Shelbys had the standard size rear drums. I did not know the prop valves for Shelby were readjusted for the 2 1/2" rear drums but it sure makes sense. Those would lock up big time without a proportioning valve.

Thanks for straightening me out!

    Doug ,
       NOT the same valve as a Corvette. They had bigger fitting/tubing sizes. True both versions were made by K/H and used the same raw casting.

    Royce , YES same valve as C5ZZ "except" the S1MS version was "preadjusted" for use with 2-1/2" metallic rear lining. The C5ZZ valve was set for 1-3/4" organic lining. If you had an original C5ZZ and S1MS side by side , the difference in adjustment is obvious. This is also noted in the partial blueprint Jeff S posted earlier in this thread.
    For '67 and later , metallic shoes were dropped and standard inline , non adjustable prop valves were used.

Royce,actually 67 had 2 1/2 inch rear drums too. 68-70 had the smaller regular Mustang drums.

[gt350hr]

  +1 Metallic lining is the KEY.  "Cold" metallic brakes stop poorly . Once they get some heat they work well. The average driver doesn't get enough heat in them to utilize them as intended by SAI. Renters of Hertz cars complained about poor brakes to the point where SAI had a "brake test group" which sent cars to San Francisco and LAX for monitoring. My Hertz was one of those "test cars" where organic (2-1/2) linings were substituted at some point.  When I reinstalled the original metallic linings , I had WAAAAY too much front brake apply and had to readjust my prop valve.
   Randy

[Helmantel]

Right, the 67 and later Shelbys had the standard size rear drums. I did not know the prop valves for Shelby were readjusted for the 2 1/2" rear drums but it sure makes sense. Those would lock up big time without a proportioning valve.

Thanks for straightening me out!

    Doug ,
       NOT the same valve as a Corvette. They had bigger fitting/tubing sizes. True both versions were made by K/H and used the same raw casting.

    Royce , YES same valve as C5ZZ "except" the S1MS version was "preadjusted" for use with 2-1/2" metallic rear lining. The C5ZZ valve was set for 1-3/4" organic lining. If you had an original C5ZZ and S1MS side by side , the difference in adjustment is obvious. This is also noted in the partial blueprint Jeff S posted earlier in this thread.
    For '67 and later , metallic shoes were dropped and standard inline , non adjustable prop valves were used.

Royce,actually 67 had 2 1/2 inch rear drums too. 68-70 had the smaller regular Mustang drums.

I seem to recall that the 428 CJ cars got the rear drums upgraded to 2,25". Is that correct and does that apply to Shelbys too?

[Royce Peterson]

Not correct.

Right, the 67 and later Shelbys had the standard size rear drums. I did not know the prop valves for Shelby were readjusted for the 2 1/2" rear drums but it sure makes sense. Those would lock up big time without a proportioning valve.

Thanks for straightening me out!

    Doug ,
       NOT the same valve as a Corvette. They had bigger fitting/tubing sizes. True both versions were made by K/H and used the same raw casting.

    Royce , YES same valve as C5ZZ "except" the S1MS version was "preadjusted" for use with 2-1/2" metallic rear lining. The C5ZZ valve was set for 1-3/4" organic lining. If you had an original C5ZZ and S1MS side by side , the difference in adjustment is obvious. This is also noted in the partial blueprint Jeff S posted earlier in this thread.
    For '67 and later , metallic shoes were dropped and standard inline , non adjustable prop valves were used.

Royce,actually 67 had 2 1/2 inch rear drums too. 68-70 had the smaller regular Mustang drums.

I seem to recall that the 428 CJ cars got the rear drums upgraded to 2,25". Is that correct and does that apply to Shelbys too?

[shelbydoug]

I've used stock 1-3/4" rear drums with organic lining, Velevet-touch mettalic, and 2-1/2" rear drums with metallic linings.

In my experience, those metallic linings are so hard, they hardly seat and you can't lock the suckers up at all either with the  65 "add on" proportioning  valve or the stock (in my case '68) proportioning valve so to me, the adjustable is unnecessary on the street no matter how hard that you drive it.

As a matter of fact, the stock proportioning valve is just right for the Lincoln rear discs as well.


"68 GT350 Lives Matter!"

[gt350hr]

    My "regular Mustang" 68.5CJ has 1-3/4 rear shoes.These were never used on SA vehicles , 350 or 500s.

[KR500]

    My "regular Mustang" 68.5CJ has 1-3/4 rear shoes.These were never used on SA vehicles , 350 or 500s.

Randy
PM sent.

[gt350hr]

  Looks like I was "off" on my statement about 68.5 brakes on SA vehicles. I apologize to those I misled. I was going off of the last one I changed a diff in. Probably changed by a PO. My bad.

   I could have easily suffered a bite from a coralsnake if left uncorrected. LOL