No Brakes!

[mdvberg]

Last weekend I took the '56 FFPW out for a drive and the brakes seemed a bit mushy. Usually the brakes work very well, with no pumping required, but this time they seemed a bit soft, but firmed up with a pump or two. I made it to Lowes with a pump or two on the brakes, but no big deal. On the way back, coming to a red light, I tapped the brakes and NOTHING...the pedal went all the way to the floor. Downshifted, and pumped the brakes and still nothing! Did some panic pumping and finally went for the nuclear option of reaching for the emergency brake. Fortunately this is well adjusted.......If I'd been a bit gentler with the e-brake I might have come to a gentle stop, but being in a panicky state of mind, I just yanked it back as hard as I could and it locked up the back tires resulting in a tire howling stop that nearly gave me and everyone else in the intersection a coronary!

So the good news is that I managed to make it home without crushing any Honda Civics, but the bad news is that I can't figure out what is wrong!

Here's the state of affairs as best I can figure them.

1) This is a 1956 FFPW with factory Hydro-Vac power assist.



2) The brake shoes in good shape, and are well adjusted
3) All new wheel cylinders, and none of them are leaking.
4) I removed the master cylinder and bench tested it, and it seemed to work under bench test conditions. I disassembled it, and it has either been rebuilt, or has been replaced in the past couple years. At least when bench testing, it seemed to build up pressure, and would hold it without any evidence of leaking past the piston.
5) I put the master cylinder back on the truck.
6) I have bled the brakes using the garden pressure sprayer method, including the bleed valve at the hydro-vac booster. (I have a remote reservoir hooked and and just tapped the garden sprayer into the line that goes from the reservoir to the master cylinder)




7) Brake fluid is completely clear with no rust evident anywhere.

After all this the brake pedal still drops to the floor. Here's the weird part...with the garden sprayer hooked up to the master cylinder and pressurized, the brakes work great. Take the pressure off the garden sprayer and they flat out don't work at all.

I'm stumped...but thinking that maybe the hydro vac is busted?

I've read that upgrading to a dual reservoir master cylinder is not a difficult job, but I don't know if the master cylinder listed there (NAPA, #4736308) would be compatible with my hydro vac assist.
http://mysite.verizon.net/kkull99/Fr...les_brakes.htm

Any help would be appreciated!

Mike

[Charles Talbert]

Well, if everything else in the system is up to par like you've stated, I'd say the issue is definitely hydraulic. If the booster has never been gone through, that is a really good place to start. In fact with a brake system this is my mindset. All the components are resonably priced as new parts. A brake system is definitely not the place to put the trial and error method to the test as you have already found out, you don't want them failing in traffic. If you have not been through the system personally to know exactly what has been done, replacing all hydraulic components is without a doubt the best idea. Both boosters and master cylinders are prone to internal leaks that you will never detect visually until issues develop making it obvious something is going on. Boosters will leak internally causing the problem you have, the escaping fluid remains internal, and is pulled into the engine intake via the vacuum line. You never see a thing to make you suspicious until the surprise comes up, sometimes with no warning at all. At least you did have a slight chance to get suspicious before complete failure occured. You might can get a replacement booster at NAPA or equivilent parts store; if not available as a rebuilt unit, they can send yours in for rebuilding and get your same one back in a few days.

If you prefer to do the dual line set up like you mentioned, it is the safest way. That way if a leak develops on the rear for instance, you still have good brakes on the front axle. But, bear in mind that if a master cylinder or booster issue develops even in a dual line system, the whole system can be effected. The biggest safety net with a dual system applies mainly in off road application in the event a line or hose got damaged and began to lose fluid, only that portion of the system would fail. With that being said, it still is a good option as any brake system improvement is a big plus.

To answer your question about your current booster being one that will work with a dual line system, basically speaking, the answer is no. The only way this type of booster will work with dual line is to have 2 boosters in the system, 1 for each line. Doing it this way works well, but an adjustable proportioning valve in the rear circuit is a must. Other options are to mount the vacuum booster on the firewall with the dual reservoir master cylinder piggybacked onto it. A single booster will serve the whole system with this type. You would need to convert to a hanging style brake pedal with this however. One other option is to use a hydraulic booster with the master cylinder piggybacked, these are available in a small enough package to fit in the original M/C mounting position with some minor modifications. The worst draw back to this method is an engine mounted hydraulic pump becomes necessary to power the booster. All this doesn't make this a really attractive option as vacuum is much more simple to design, install, and is far less expensive. Some who are wanting to install power steering use this option since a hydraulic pump is needed for the steering and it's simple enough to plumb a priority valve into the circuit for booster power. An even better hydraulic option is to spend a little more on the pump for a unit that has a primary and secondary pressure flow port, primary for steering and secondary for the brake booster.

A lot of possibilities, depending on how far you desire to go. At the very least, I would certainly recommend installing all new hydraulic components into the original system. It's a really cheap price for peace of mind and dependable brakes.

[mdvberg]

Thanks for the reply Charles. There is a lot to digest there! Since I've been through the wheel cylinders and brakes personally, and am satisfied that they are in good repair, I think at the very least a new MC, rebuilt or replaced booster, and new brake lines would give me some confidence.

Thanks again for your expertise,

Mike

[jackw19]

Dual Hydrovacs

A whole, long-winded reply just vanished into the bit-bucket. If it turns out I'm repeating myself--sorry.

My lifetime total hydraulic brake failure count stands at three, so I'm fitting the 57 PG W200 with a dual M/C and dual HydroVacs.

Didn't want to go the hanging pedal route.

If you've already got power steering in place, the HydroBoost (power steering based boost system) is certainly worth considering.

If you decide to have at it, pls let me suggest a really good hydraulic flaring tool. Sure, it'll cost $300, but you'll be spending lots anyway. And making lots of flares.

Copper-nickel alloy tubing is supposed be easier to work with--it's tuff enuff for Porche and Volvo. (This is not the Home Depot stuff.) I haven't used it myself.

I decided to use -4 (1/4") stainless and 37 degree fittings. That's the tubing size that was on the truck, and I had a bunch of 37 degree leftovers from other projects. Stainless is forever, sort of, especially if the alloy is suited to the job.

There're many online resources that discuss 45 degree double flares vs 37 degree single flares + AN tube sleeves. I'm not a professional engineer, so I won't weigh in.

If you've got a 1-1/4" M/C, the 71-74 GMC Step Van P20-P30-G30 might be a possibility. It turned out to have fitting locations, fluid capacity and general dimensions that satisfied my constraints.

Don't forget: i) Residual pressure valves, external if reqd. (Verify whether the M/C you're using already has them and how many lbs.) ii) Check valves and air filters for the HydroVac's iii) Proportioning valve, including the road test and dial-in steps. iv) Don't use just any OEM "proportioning valve"--many are multi-function units that may or may not be suitable.

There are some rat-rod suppliers now who make boosted M/C units for floor installation. Could turn out to be easier to fabricate a set of brackets for this kind of system than messing w/ HydroVac or HydroBoost.

I chose HydroVacs based on their originality, and because I thought they'd be cheaper. That was when I thought I could get away with just installing HydroVac on the fronts. Now that I've got two units on the dining room table, I'm not so sure now about the cheaper part. A previous owner had already grafted Saginaw power steering on my truck and if I was doing this again, I'd take a second look at HydroBoost.

I did have a space problem w/ certain HydroBoost parts. There was some boost unit or pressure accumulator that was reasonably priced if attached to the M/C, but significantly more if mounted remotely. I was about 1/2" short.

Good luck.

NB I got some parts and some excellent advice from Portland Brake Systems. I don't live in Portland, but these guys are good.

[Matthew Ziegler]

brake booster

Speedway motors sells an electric brake booster. I haven't bought one since my m37 is still 24 volts, however it appears to be easy to adapt to almost any vehicle, you might consider giving them a call, I've gotten some really good tech support from them in the past.

[Charles Talbert]

new system in the works

We are currently designing a new hydroMax system for M37 and Power Wagon. The cost of good vacuum boosters has gone so outrageous, and remote mount boosters are becoming scarce. I think it is just as cost effective for us to go hydraulic, also easy since almost all our trucks get power steering anyway. The system is compact enough to fit under the cab on the frame rail, so a hanging pedal assembly is not required.

[Bob2]

We are currently designing a new hydroMax system for M37 and Power Wagon. The cost of good vacuum boosters has gone so outrageous, and remote mount boosters are becoming scarce. I think it is just as cost effective for us to go hydraulic, also easy since almost all our trucks get power steering anyway. The system is compact enough to fit under the cab on the frame rail, so a hanging pedal assembly is not required.

Charles,
Keep us posted on the development, I am interested in one for my 66 WM300.

Bob H

[Charles Talbert]

Charles,
Keep us posted on the development, I am interested in one for my 66 WM300.

Bob H

It is nearly completed; I'll let you know.

[Bob2]

It is nearly completed; I'll let you know.

Charles,
Thanks.
Bob H.

[CSCameron]

It is nearly completed; I'll let you know.

I'm very interested also! Look forward to updates...