proportioning valve question for balance of brakes

[Babydriver]

Hi Guys,

Got a 66 coupe restomod.  Lowered 1 inch with dual master power discs up front  and drums at back.  Pedal is always soft so did a full triple power bleed and not much better.  Rear drums have slight (correct drag) on them.  Inspected and great with no leaks etc. (car has done little work since full rebuild).  The front set up is SSBC plain rotors. This is a c4 auto with a warmed 289 std rear 8".  My question: what balance should I have between rear and back brakes.  There is so much poor info out there on this. The car is fitted with a SSBC proportions valve.  I have experimented with this and the pedal appears to be a bit better.  Under heavy braking from 60kph the car now will make some tyre noise from the front but no lock up.  Currently can get no lock up on back or front.  What is correct procedure to look for.  Do I look to get a lock up at full tramp in front.  I understand that lock up is not a desirable point to reach but  none achievable at all makes me feel the brakes are short of where they should be. Another little issue is that now when the brakes are jumped on hard there is a whistle sound from under the dash pedal box.  The car is for general street use and highway use, no track. Yes I know under the pussification laws proportioning valves are taboo, but I have one anyway and it is correctly plumbed in.
Any procedures or troubleshooting ideas please.

Many thanks
CK

[lukep6470]

When I bought my car the brake booster had a fault where it would get a vacuum leak when you pressed the pedal but was OK otherwise. 

If the engine idle changes from you pressing the pedal down and holding it down then it could have the same fault.

[USA066]

I also have a 66 couple with C4, running XF Falcon 11" slotted rotors and single piston calipers on front with 7" dual power booster and drums on rear. I rebuilt the drums and upgraded the front disc pads to Bendix med/soft compound. No proportioning valve installed, but brakes work fine for street and highway use. I question the need for a proportioning valve for this setup other than if you are breaking heavy. The whistling sound may be normal or may mean your booster is passing. I have similar, but not really noticeable.

[Babydriver]

 Booster is good no issues with idle etc.  The valve was put on when I was building the car so I could do some burnouts, never put the posi rear 9" in so never happened. Car gets babied most of its miles. Basic question still remains... tune till fronts begin to lock without backs locking?  So guessing if it had a dial - 70 -20 maybe 80-20.

[shaunp]

4 piston SSBC fronts or single if they are single make sure they are on the right side as they are left and right handed and wont bleed if they are wrong. Your complaint is not uncommon on this type of brake swap. What size rear cylinders do you have?

[Babydriver]

 Single piston up front not sure on size of cylinders back but they are standard size that came with the car.  No size upgrade but all new.  Will check the LH verse RH set up.  Are they marked?

CK

[shaunp]

Single piston up front not sure on size of cylinders back but they are standard size that came with the car.  No size upgrade but all new.  Will check the LH verse RH set up.  Are they marked?

CK

 No not marked you need to make sure the bleeder is at the highest point, The mustang rear cylinders are bit big  you need smaller ones I normally put falcon ones in  as the single piston fronts are pretty much the same as a Falcon. Falcon rear cylinders are 13/16 which generally work ok on post 66 car with no prop valve, 65/66 cars need 5/8 which is an old falcon ute/gt size which are no longer made. Though Knights old school brakes in Brisbane modify normal ones to this size. Make sure your fronts are on the right sides  first and foremost or the brake we never work correctly.

[Babydriver]

just checked and bleeder are upside so they are right. Will investigate rear cylinder option/issue.

[Dwayne]

Shaun, what size cylinders would you run with the KH 4 piston calipers?

I've also got an adjustable prop valve and 10psi residual valve for the rear drums.

[shaunp]

Shaun, what size cylinders would you run with the KH 4 piston calipers?

I've also got an adjustable prop valve and 10psi residual valve for the rear drums.

They falcon 13/16 they are cheap, so they are like XY/XA it think the bolt pattern changes at XC

[unilec5544]

Shaun, what size cylinders would you run with the KH 4 piston calipers?

I've also got an adjustable prop valve and 10psi residual valve for the rear drums.

The 10lbs valve was used by Ford in the 60's to maintain a slight pressure behind the piston seal to stop them leaking, not really needed today, but still not a bad idea.

[unilec5544]

just checked and bleeder are upside so they are right. Will investigate rear cylinder option/issue.

Are you still using the non boosted brake pedal?

[Dwayne]

I haven't installed the residual valve yet (or any of the lines), so is it even worth doing?

[unilec5544]

I haven't installed the residual valve yet (or any of the lines), so is it even worth doing?

Its up to you, the newer piston seals are a lot better than the old ones, but if you are fitting a proportioning valve, I wouldn't bother.

[Babydriver]

Yes using booster that came with the SSBC set up. Drove tonite and pedal is still way too soft. There is no air in the system at all.  The car stops ok around town but with 80 kph and a sudden stop... well I reckon she stopped better before it was restore with non power drums all around.
 

[unilec5544]

Yes using booster that came with the SSBC set up. Drove tonite and pedal is still way too soft. There is no air in the system at all.  The car stops ok around town but with 80 kph and a sudden stop... well I reckon she stopped better before it was restore with non power drums all around.

I'm referring to the brake pedal, if its the old non boosted pedal the issue will be the pedal ratio, it needs to be 4-1. Back when 65-66 mustangs came out there was no provision for a power brake pedal until Ford realized there was an issue in 1967 when 2 brake pedals were on offer one non boosted and one for boosted power brakes. Some people don't have an issue but most do.

[Aussie-67]

Don't know if this is of any help, but looks to be a similar issue.

http://www.allfordmustangs.com/forums/classic-tech/913714-1967-mustang-disc-brake-not-working.html

Tony

[Babydriver]

 ok so looks like an email to SSBC and another brake pedal to suit.  Hope the existing booster can still be used.  Will see what the US  Mustang suppliers sell .  Would never have picked this as a problem. So thanks guys... Seems poor that they offer many front disc brake upgrade from drum options for 65 66 cars but none seem to mention a different pedal is needed.  Cheers

[unilec5544]

ok so looks like an email to SSBC and another brake pedal to suit.  Hope the existing booster can still be used.  Will see what the US  Mustang suppliers sell .  Would never have picked this as a problem. So thanks guys... Seems poor that they offer many front disc brake upgrade from drum options for 65 66 cars but none seem to mention a different pedal is needed.  Cheers

Doubt if you will get any joy from your supplier, if you look at the 67-70 pedal box there is a pair of holes in the top of the box for the longer pedal for power brakes, unfortunately the 65-66 did not have provision for this upgrade. i have used a chev pedal for my application, but you may be able to use a 67 power pedal, but I am not sure if you have enough room to get it high enough, but if you have an auto then it may not matter, the manual need the clutch and brake pedal to be on the same plane.
What size is your master cylinder, should be 1"?

[unilec5544]

If you look at this photo, you can see the top holes I am talking about.

https://secure.cougarpartscatalog.com/1919pobrpeha.html

[Babydriver]

 I will start investigations.  It is an auto car. Not sure on master cylinder will check and get back to you all.  If needed will the 67 pedal box mount easily to a 66?

[289 vert]

All I did to sort the wrong pedal problem was to grind the weld on the brake pin, punch out the pin, drill new hole in correct location, insert pin and weld.
I don't recall what the measurements were to determine the new hole location. If no one else can tell you in the meantime, I will measure it next week.