95 F350 very hard to stop

[Peroni]

Been helping to try and sort this truck out but am about out of ideas on it. It's a 95 F350 with a 02 rear axle swapped in with hydroboost added. It is very difficult to stop, about have to stand on the pedal even at lower speeds.

All 4 calipers are rebuilt NAPA Eclipse, pins and sliders are lubed and moving freely. Flexible lines are new braided stainless from Crown. Hard lines have been thoroughly inspected and didn't see any pinched or kinked spots. Have good flow of brake fluid from each bleeder.

Rotors up front are cryo treated slotted Frozen Rotor brand. Rears are slotted Raybestos pro grade. Has the blue Motorcraft superduty pads front and rear, they are not binding in their guides and do not appear glazed.

Hydroboost unit is a new Motorcraft part. I modified his brake pedal to F Superduty standards so the pedal rod lines up right. All hoses are new with no leaks or kinks. Master cylinder is a Raybestos brand with the larger bore.

Still using the C2 style power steering pump but the one in there is a brand new not reman unit and actually is working very well. Using Ford Mercon fluid as well as Ford branded brake fluid.

What I've done so far besides a visual inspection is to vacuum bleed all the brakes again. Also went through the hydrobooster bleed procedure while pulling a vacuum on the reservoir. The pedal is hard with no excessive travel or noise from the pump and does not sink to the floor. With truck off I pumped the pedal a few times, held it down then started engine and pedal kicked back so the booster is working. Have not observed any leaks anywhere. Only thing I haven't messed with yet is the RABS valve. Was thinking of bypassing it to see what happens. Has no brake or ABS light on.

Does anyone have a clue as to what might be wrong or can think of something I missed? This truck's braking system is very similar to mine yet my truck stops great and this thing is an absolute bear!

 

[79jasper]

RABS valve shouldn't have much to do with it. You should still get decent braking, at least from the front.
What about the pushrod between the booster and master? Maybe you need to adjust it?
Some reason I seem to recall needing to bleed hydroboost brake systems with the engine off. Might be way off on that one though. Lol

Sent from my SM-G892A using Tapatalk

 

[greyford1979]

Did you check to make sure none of the calipers aren't swapped onto the wrong side? If the bleeder screw is below the brake line hookup you'll never get all the air out and will cause this. Just a thought, not that I've ever accidentally done that. :lookaround: LOL

 

[rusty1161]

Is the master cylinder new? Any way to confirm the bore size?

Rusty

 

[6.0 Tech]

The power steering lines at the booster may be swapped. Did that on my first 6.4 body off job, made for a fun ride....

 

[Peroni]

RABS valve shouldn't have much to do with it. You should still get decent braking, at least from the front.
What about the pushrod between the booster and master? Maybe you need to adjust it?
Some reason I seem to recall needing to bleed hydroboost brake systems with the engine off. Might be way off on that one though. Lol

I don't know about the pushrod, didn't think they were adjustable? If it were too long I'd assume the brakes would drag when pedal was up, and too short would result in a larger pedal travel?

Bleed proceadure per Ford is done with the front end jacked up and engine running. Turn wheel lock to lock several times and pump brakes all while maintaining vacuum on reservoir. I did this with no improvement.

Did you check to make sure none of the calipers aren't swapped onto the wrong side? If the bleeder screw is below the brake line hookup you'll never get all the air out and will cause this.

Yes I checked them all and bled them again, all are in the right location and orientation.

Is the master cylinder new? Any way to confirm the bore size?

Yes it is a new manufacture Raybestos part # MC390158. I did not take it apart to measure but just comparing it to the Ford part on my truck it does indeed match the larger 1.312 bore F Superduty master.

The power steering lines at the booster may be swapped.

Wish it were that simple, lines are connected up in the right order.

 

[Peroni]

I checked the pushrod on my spare hydroboost unit and these are not adjustable. Did a bit of digging online and found a Ford publication stating adjustable pushrod is for vacuum boosted vehicles only.

 

[mandkole]

Just thoughts...

Does it always, or randomly, stop poorly?
Can you get better stops by pumping the pedal?
Did you replace the rear axle jumper line also?
Did you look for kinks in the tubing?
Have you put a pressure gauge in the system (to determine if it's a hydraulic or a mechanical issue)?

 

[Peroni]

Just thoughts...

Does it always, or randomly, stop poorly?
Can you get better stops by pumping the pedal?
Did you replace the rear axle jumper line also?
Did you look for kinks in the tubing?
Have you put a pressure gauge in the system (to determine if it's a hydraulic or a mechanical issue)?

I spent a little more time with the truck today.

Yes it always stops poorly, doesn't matter if brakes are cold or hot.

Pumping the pedal does give better stops.

Rear axle line was replaced. I found out today the owner replaced all the hard lines as well as flex lines.

Checked again but no kinks, pinch points or leaks to be found anywhere. Owner did a nice clean job putting all this stuff in.

I've not put a pressure gauge on the system yet. Have one specifically for checking brake line pressure but it's eluding me at the moment. I did plan to check this once I find my gauge.

 

[Denver]

From the first post you have like a half of dozen different brands mixed together for the brake setup. Stick with one brand. The motorcraft pad may not be a good match to the rotors that are on the truck. My 02 I bought used didn't stop like the other superdutys I have driven. Turns out autozone pads on motorcraft rotors wasn't a good match. Put motorcraft pads on and was night and day difference.

 

[Peroni]

I finally got back to this today. Using a pressure gauge in place of the bleeder we got a very ever pressure reading on all 4 corners. Did find out something interesting. Using "normal" foot pressure on the pedal was only generating 400psi at the caliper. Pumped the pedal 3 times, first was 400, second 1200, 3rd 2000psi. This seems to make sense as the truck stops better pumping the pedal. Would this point to a problem with the master cylinder even though it has no fluid loss or external leaks? Stomping the pedal gets 2000+ but results in more travel than if it is pumped.

 

[mandkole]

It's possible the piston seal is failing, or could have air in the master. After pumping, does the pedal stay up or does it fall away?

 

[Peroni]

It stays up, never falls away. The owner bench bled the master before initial install. I was going to suggest to him that he spend the money and get a genuine Motorcraft part instead of the aftermarket he has now.
​

 

[79jasper]

Well... he said he bench bled it.
Do you feel he knows enough about what he's doing to make sure it was fully bled?
Or maybe just did a half arsed job?

Sent from my SM-G892A using Tapatalk

 

[Peroni]

The owner is not a professional mechanic but all the work he has completed has been neat, clean and well done. He has the correct Ford service book and I see where he made notes and highlighted torque specs. His tools and workspace are clean and organized. Certainly doesn't look like some half ass shade tree mechanic with parts scattered in the dirt.



I trust that if he said he bench bled the master then he took his time and did it carefully. Although it probably wouldn't hurt to take it out to do it again and I'll be there to double check there is no air in it. Certainly does not feel like there is any air in the system but something just isn't working right.:shrug:

 

[Garbage_Mechanic]

Peroni,

I did my 91 one weekend and it was good to go from the first moment. Not much fuss bleeding brakes or PS system. It does not have rear discs and has the OBS SD master. Actually thinking about going back to 1.250 master with drums. It has 2x the stock brakes but is almost too much with the 1.375 M.C.

My point is in my years of experience it is seldom the bleeding and such.
Likely the booster has an issue. Put the pressure gauge on your truck and let us know the difference. I'll be there is one.

One more thing. Where to get such a gauge? I have needed it before and didn't know of the bleeder port set up for a gauge!

 

[Peroni]

Just to update this I got the owner to pony up for a genuine Motorcraft master cylinder and that fixed the problem. I generally believe Raybestos to make a good product but something was obviously not right with the one he had previously purchased new.



Garbage Mechanic I got the gauge and adapters as a kit off Ebay years ago, it was under $40.

 

[ghohouston]

I have been wondering about my obs. There are times the brakes work good, and there are times they SUCK, and i have to downshift like a 17 year old honda civic driver to be able to stop. Motorcraft hydroboost unit i bought new and installed back in 2015. Has probably 15-20k miles on it max. Never did relocate the pedal pin where it needs to be though. Wondering if thats my issue. Im not exactly a brake expert. There was one time i hit the brakes what i would consider semi hard, and they locked up, and truck actually skid a bit. Has not happened since. I am definitely not satisfied for the amount of money i spent on a new Ford hydroboost.

 

[old man dave]

Relocating the brake pedal pin greatly increases the leverage applied to the hydroboost. That's why the F-SuperDuty pedal had the relocated pin. There has been a lot of posts by people who installed the hydroboost and complained about very high pedal pressure. They then relocated the pin and the brakes worked.

 

[ghohouston]

Yeah, im gonna give that a try, like i said, i just never got around to it when i installed the new unit. Hoping with the lack of mileage on the hydroboost, there isn't an actual problem with it.