'64 Galaxi power disc conversion - doesn't feel quite right

Hello!

I finished a 4 wheel disc conversion on my '64 Galaxie recently and just took it for a drive. The car stops very well, but the pedal doesn't feel quite right. When I hit the pedal, I get maybe 1" of travel, then it's like it hits a stop, and no matter how hard I press, the car doesn't stop any quicker. I REALLY laid on them a few times, and I could not get the wheels to lock up, either front or rear.

I checked the brake pedal ratio, and it's 6:1, exactly what it should be for manual brakes (which the car had), but not the 4:1 it should be for power brakes.

I'm also running a 4 wheel disc proportioning valve, but it's non-adjustable.

Could the manual brake pedal setup be causing the blocked pedal feel? I don't know how much travel it takes manual brakes to fully engage vs. power brakes. More? Less?

If I have to change the pedal ratio to 4:1, can I simply redrill the brake pedal shaft and angle the MC push rod down.

If I cannot angle the push rod down, will fabricating an offset work? I will have to drop the fastening point of the MC push rod down 1" to get a 4:1 pedal ratio.

Should I look into an adjustable proportioning valve? The rear discs have wear marks on them that tell me that the pads are hitting the rotors, but it seems as if the front brakes are bearing most of the load.

I bought the MC/front disc kit off of Ebay from Tom's Cl***ics in Isanti, MN. If you search for Galaxie disc on Ebay, they pop right up. The rear brake kit came from The Rod Shop in CO.

Thanks in advance.

Chris

 

Anyone? Beuhler?

 

sounds like the powerbooster nots working
with the engine of press down the brake pedal
and start the engine if you dont feel the
pedal sinking when the engine starts the
Booster is not working

 

Yup, sounds like the booster.

 

Thanks. How do I test the booster?

 

Not enough information.

What size master cylinder?

Which calipers front & rear?

How much engine vacuum at idle?

B.

 

Ok, saw the first response. I'll try that...any other suggestions?

 

Hop in the car, engine off. Push down on the pedal. Observe the pedal feel. Release.
Turn the engine on. Push down on the pedal. Observe the pedal feel. Release.

If there is no difference, then the booster is either hooked up wrong, or it does not work. If the pedal is softer with the engine running, the problem lies elsewhere.

Where do you have the vacuum line for the booster attached?

 

Where do you have the vacuum line for the booster attached?[/QUOTE]

I have a T in a line from the bottom of the carb. Also runs a PCV in the valve cover. I pulled the PCV valve out of the grommet with the engine running, and there's strong vacuum.

Chris

 

I have a T in a line from the bottom of the carb. Also runs a PCV in the valve cover. I pulled the PCV valve out of the grommet with the engine running, and there's strong vacuum.

Chris[/QUOTE]

The booster will need a direct, non-shared vacuum source. Try connecting it directly. See if there is a plug or fitting in the manifold where you could connect it.

 

Will do. Thanks.

 

after that, check and be sure you don't have the valve in backwards. I know I know. Sounds stupid. But it does happen.

 

I've never heard of a non adjustible proportioning valve on 4 wheel disc setups. What's it off of? I would remove it to see if that is your problem.

Testing the booster - With the engine off, pump the pedal about 10 times. Press down on the pedal and start the engine. You should feel the pedal drop. If not, make sure vacuum is getting to the booster, if it is the booster is bad.

 

This is very important. Brakes are a system. If the master cylinder is too large it will make the pedal short and hard. If the calipers are sized incorrectly front to rear the bias will be wrong, no change in the proportional valve is going to fix that.

Master power sells a unit and there are several cheap Chinese knock offs that are similar. It's simply a preset unit. Not ideal for maximum braking power.

This is the easiest way to test the booster.

 

I have 4wpdb and it was tricky to get them where I wanted them.

what kind of carb and have you looked at the manual for where you're supposed to plug in the booster? I think I had mine plugged in the wrong port at first.

I ended up using a powere brake pedal, dual 11" booster, and 1 1/8" dia MC with an adjustable prop valve that I have full open, I have no idea if it does anything at all.

I can't get my car to lock the brakes because when I stomp on them my face hits the steering wheel. d

 

Update:


Found out that I have a 1" piston MC. Good? Bad?


Vac*** is connected to the bottom of the carb, which is a 600cfm Holley with vac secondaries and electric chock. I checked the PCV valve before I disconnected it, and there was a TON of vac***.


I plugged the T going to the PCV valve to give the booster full vac***, got in the car, pressed on the brake pedal and started it up. I felt the pedal soften a bit and drop about 1/2", so it appears as if the booster is NOT bad.


I took the car for a ride, and the brakes seemed about the same, so it does not appear as if vac*** is an issue.


Spoke with the brake guy at Auto City Cl***ics (aka Tom's Cl***ics on Ebay, Isanti, MN), and he confirmed that I have a 7" diaphragm booster. He said that the 7" might be a bit small for my Galaxie, so he offered to swap me an 8" dual diaphragm booster at not charge, so that's what I'm going to do for now.


I asked him about relocating the actuator rod going to the brake pedal to decrease the pedal ratio to 4 from 6. He said that he's never done on it any Fords he's ever done, and has never had a problem, so I'm going to leave it where it is for now.

I also check the swing on the brake pedal with the actuator rod disconnected, and it swung all the way to the floor, so there's no trave/interference issues with the pedal itself.


We'll see what happens when I get the new booster.


Chris

 

I would go to an 11 inch booster. The 1" mc should be adequate. Especially since you're getting a firm pedal but not full lock up it leads me to believe you are moving enough volume of fluid but just need a bigger booster.

 

A 1" should be fine with a booster, not so good with manual discs unless you have lots of caliper piston volume and a mc that can keep up. If the new 8" booster does not help go after the prop valve next imo.

A 6-1 pedal ratio should make it easier to stop over a 4-1 , not harder.

Forgot to add... Make sure the 8" booster is a dual diaphram or it may not provide enough help.

 

Thanks for the input. It IS a dual-diaphragm booster, but I'll check to see if he has anything larger.

One thing to note - I checked the brake lights, and they do not come on until I have a substantial amount of pressure on the pedal. The Galaxie uses a switch mounted on the proportioning valve/block. Don't know if the heave pedal pressure necessary to actuate the lights means anything.

Re: the proportioning valve - it's actually a solid br*** distribution block/non-adjustable proportioning valve. Speedway Motors sells what appears to be the exact same unit for about $69.00. I did check the valve to see if it had "popped", but it had not.

Thanks...

Chris

 

Still have no idea how much caliper volume you have.

With a stock manual brake leverage, you should be able to lock the brakes with the booster disconnected. Brakes should be firmer, but functional all the way to lockup.

You say the pedal travels to a point then stops solid. There are a few possible causes:

Mis-adjusted pushrod / booster combination running out of travel.

Too small on the Master Cylinder volume - it simply bottoms out before the calipers have max pressure.

A bad valve to the rear brakes that p***es nothing. This would stack up maximum pressure on the rear circuit without moving the caliper pistons.

Check for rear brake operation. Jack up the rear end, have someone step on the brakes while you try to turn the wheels.

Crack the rear line loose at the MC, and try the brakes (in the driveway!) - do they feel the same?

Is your dual master cylinder plumbed correctly?

B.

 

Okay, from looking at the guy's ad on eBay - it's all GM hardware. Can't tell the original caliper application or bore from that pic. The big-car GM calipers have I think two different possible bore sizes. It looks like decent hardware but it's in no way an improvement over using, say, a set of '70-72 Galaxie disc spindles and related hardware.

If you've got what's in the pic it's a very small booster. Something bigger may help.

Measure the caliper piston diameter.

I don't see any rear disc listings from him, what are you using for the rears? Once again, original application and piston size for the caliper is important.

A fixed-ratio proportioning valve may be good or it may be bad. Depends on the original application and how it's set up.

What pads are you using? Did they come with the kit?

Whether a 1" MC is big or small depends on the caliper piston size.

More mechanical advantage (pedal ratio) means less pedal effort at the expense of longer pedal travel.

I'm becoming quite fond of hydraboosts, myself, but an early Galaxie power steering pump won't be able to drive one.

I'm also currently cutting on a set of late Galaxie drum-brake spindles to hang 14in Coleman rotors and 6-pot Porsche Cayenne calipers on 'em, but admitting all that will bring purists' bats down upon my head...

 

Well, if they are the big GM calipers they have about 11.87 square inches of piston area all by themselves.

That means to advance the pistons .050 on each caliper you need to move 1.187 cubic inches of brake fluid.

1" master cylinder? Well, with .785 cubic inches per inch of travel that cylinder must travel more than 1.5 inches. You may be bottoming out the master cylinder or other mechanical parts before you get full braking force.

Still need to know about the rears, and the plumbing.

B.

 

Bohica -

Wanted to clarify a point...I may have been unclear in my first post.

When I push the pedal, I get maybe 1" of travel, then it feels almost solid...I can push really hard, and the brakes will seem to apply a little more, and the car stops well, but it feels odd because I get a what seems like a tiny increase in braking power when I almost stand on the pedal. Every other car with power brakes I've driven will have an increase in braking power until the wheels lock up, and I cannot get my brakes to lock up at all.

I will get the specs on the front and rear calipers tomorrow and post them. It may be that my MC isn't moving enough fluid for 4 wheel discs, along with a booster that's a bit too small for a heavy car like the Galaxie, but I will let the experts comment when I post the caliper specs.

Thanks...

Chris

 

Make sure that if you have an adjustable pushrod that the jam nut is tight and not allowing the pushrod to work its way out, making it longer. This would make your pedal travel shorter before the system bottoms out before it should. We just corrected this on a shake down.

 

Sounds like you are running out of travel. Unless you have the body of a POW after the Bataan March, you should be able to lock the brakes with the booster disconnected from the vacuum source.

Do you have a dual master cylinder? Which port are the front brakes connected to?

B.

 

Is that Disc or Drum?

The tricky thing about Drum brakes is modulation is poor. Once the shoes grab they self energize and pull into the drum. Kind of hard to work on that threshold braking when the drums just want to snag and lock.
With all drums, the bias was taken care of by the drum and wheel cylinder sizing, no need for a proportional valve.

Ideally you do not lock the wheels. A locked wheel while the car is still moving is not going to provide any slowing power. If you can test what you want is the front tires to lock and not the rears. If the rear wheels lock this will put the car into a spin.

 

That sounds like a m***ive mismatch between MC and caliper bore - that is, a MC much too large for the caliper pistons. Or far too little mechanical leverage on the pedal. We still need to know the piston diameters on those calipers, front and rear, and I'd suggest actually sticking a caliper into the bore at the rear of the MC to check the bore diameter, if you haven't already, rather than ***uming that what you're told about it is correct - those tubby GM master cylinders come in a bunch of different bores up to as much as 1 1/4in that all look quite similar, and it's possible you got the wrong part.

Remember, a 1 1/8" piston is not 12.5% larger than a 1" piston, it's ~22% bigger, and a 1 1/4" piston is ~60% bigger than a 1".

It could be a pushrod/adjustment problem as others have noted, but if you're able to generate more braking with more force (that is, both feet...) you're probably not bottomed.

Or some sort of brake pads with very poor mu (friction) at cold temps, but that's kinda unlikely - there used to be some old Performance Friction 'street' pads that were nearly useless when cold, but I haven't seen those in a decade. Real race pads typically have plenty of bite when cold, but they eat the rotor like it was a cheese wheel in street use, not to mention making pedestrians dive for cover from the noise.

 

Ok, spent a half hour on the phone and here's what I've got:



Front calipers are from a 1978 Chevy K10. Bore size is 75mm, which is 2.96".



Rear calipers are from a 78 - 85 Eldorado/Riviera/Toronado. Bore size is 54mm, which is 2.13"



Non-adjustable proportioning valve is listed on Speedway Motor's website as a GM disc/disc proportioning valve. Here's a link to it:

http://www.speedwaymotors.com/GM-Disc-Disc-Proportioning-Valve-for-1-2-20-9-16-18-Outlets,13539.html



Both calipers came loaded with pads. I don't know what kind they are (semi-met, ceramic, or organic).



I do NOT have an adjustable pushrod from the pedal to the booster.



My MC is dual port. Front port on the MC goes through the proportioning valve and into the factory br*** distribution block on the frame. The other port in the proportioning valve for the front brakes has a plug in it. Same setup for the rears, rear (closest to firewall) master port into the proportioning valve, with a single line to the rears, split at the factory br*** block on the rear axle.



I checked the rear rotors, and I can see wear marks from where the pads hit the rotors, so I do know that the rear calipers are working, but I don't know to what extent. I will check that tomorrow.



I'd appreciate any additional advice. I want to drive the car, but I'm kinda funny about wanting the brakes to be right.


Chris

 

I'll now go for the bottoming theory.

Those are BIG pistons. That's basically the same hydraulic ratio (maybe the same front calipers, probably the same front pads) as a '94-96 Impala SS/Caprice 9C1 - 75mm fronts, 54mm rears.

Those use a 1 1/4" bore MC to move enough fluid and get the forces right. A 1" MC would need a very long stroke with pistons that big.

Measure the MC bore.

 

JEM -

I'm going to pull the booster tomorrow to send it in for a bigger one. A few questions:

I asked the guy at Motor City Cl***ics if he had a booster bigger than 8", as the Galaxie is a big, heavy car (it's a ragtop, so it's got a boxed frame). He said that he has a 9" dual diaphragm MC that he could make work with the existing bracket.

Would I be better off with a 9" dual diaphragm booster vs. and 8"?

I've never had a MC apart, so will I be able to measure the piston diameter from the rear of the MC? I recall that there was a "plug" going into the bore with a depression for the rod when I bench bled it. Is that bore the bore of the MC? Sorry if it's a stupidly obvious question, but I'm in new territory here.

The guy also said that he could send me a 1 1/8" bore MC for about $35. If this MC has a 1" bore, should I just order the 1 1/8" one? I can ask about a 1 1/4" as well.

Thanks...

Chris