2nd Gen Non-Engine/Transmission 95 Brakes

[Balzac]

Looking for ideas to improve my brakes.

I have followed my service manual with all the checks.

All componnants have been replaced except the RWAL parts and the Proportioning valve.

Vacuum is , idle---15 in.

2000 RPM----------25 in.

No vacuum leaks. vac. valve at booster is OK.

Pedal is hard, at 35mph, hit the brakes hard and the rears chirp, then the RWAL cuts back and the truck comes to a stop with no front lockup, but not all that fast.

Put a pressure guage on the caliper, @ 20 in. vac. 1000 psi.

letting the engine idle, release pedal and apply again, only 400 psi @ 10-12 in. vac.

I believe I am short of pressure, therefore not getting sufficient braking. (possibly a vacuum problem, although I read that this vacuum system is not the greatest. )

Replaced in last 2 years, Discs, drums, calipers, vac. booster, 3500 rear cyl's. , & shoes from Raybestos. Pads- Performance Friction. DOT-3 fluid changed twice.

Tomorrow I will check pressure at rear cyl. to see if there is any problem with valves.

I have talked to Glen @ EGR about shoes and pads. I think there is another problem, and until I either find it, or are convinced there is not, I am looking for help.

Any suggestions welcome.



Jim

 

[BillGotthelf]

Your signature does not indicate a 2500 or 3500. If it is a 3500 talk to EGR about the bigger rear cylinders and the carbon kevlar shoes. I put them on my 96 3500-big difference.

 

[Joe G.]

Have you changed the brake hoses?

 

[Balzac]

Joe



I have decided to replace the hoses, but don't think that is my problem. If a hose expands, the pressure is still the same, and as I feel it is a hydraulic low pressure problem, I believe Sam Peterson said to expect around 1800 p. s. i. , so I am suspecting the vac. booster, even though I did replace it. With the vacuum within specs. , and if I get the same pressure reading at the rear(going out to check this in a few minutes), doesn't leave much else. Thanks for your response, I changed my sig. to indicate I have a 2500.

Thanks

Jim

 

[Joe G.]

I was thinking the old hoses may be coming apart inside and blocking fluid flow. If you have checked everything else then it's time to start considering unusual things.

 

[illflem]

Bad hoses are a quite common "trick" problem with no indication from the outside of the hose. What happens is the hose plys may separate inside and cause the hose to turn into a check (one way) valve.

 

[Balzac]

Thanks for the reply's.

Do you think that pressure in a static system can be influenced by anything in the hose?

My idea is that static pressure is the same whether in a 1/2" hose or a pinhole size hose. If there is flow, then a restriction will affect quantity but not pressure.

The only flow is when the pedal is moving unless there is a large restriction, then as the fluid flows past the restriction, and the pistons reach the end of travel, the pressure stabilizers at static pressure.

My rear pressure is the same as front, 1000 psi. My memory is bad, but I believe the last time I checked them, after I changed all the parts, the readings were 1800psi. or more.

So now I might take off the booster and see if I can get it tested.



Jim

 

[Balzac]

Thanks all for your help.

After all the reading on this site and others, talking to the vendors, and assessing and weighing others results for $ spent, I have come to the following conclusions;

First of all, my brake problem that bothers me the most is poor stopping distance while empty( not hooked to fifth wheel). Most of my driving is on the hi-way at 50-75 mph. When towing (12,000 lbs), My trailer brakes, Pac-Brake, and Smart controller work great.

1. I talked to Glen at EGR, he suggested his Carbon Kevlar shoes and pads.

2. I considered rear discs, and after talking to someone that was very knowledgeable on these calipers (EGR kit), discounted this option.

If at some point I feel this is the answer, I will wait until the guys at Piers Diesel have time to put out their kit(rear discs) or do my own from 2002 OEM parts.

3. Talked to Sam Petersen, he suggested replacing my Performance Friction pads with his Carbomets. He feels it is not worth the money to do the carbon Kevlar shoes .

So I ordered the Carbomets from Sam as he says they are much better when cold than the Per. Friction pads I am using now, and almost all of the time my brakes are cold when not towing.

I did have the vac. booster checked and was OK.

I have 1000 #'s at the master cylinder, Sam says I should get around 1800#'s. Maybe my gauge is off.

I will replace my hoses (which do not affect the pressure) next week and that is it for a while.

Jim

 

[Clinton]

What about the booster's check valve

Hey Balzac,

With all your research, can you inform me of the booster's check valve role in the system's performance. It is supposedly the only serviceable part of the booster. Older ones were a different style (flapper) and I think you can swap in a newer one (spring loaded). I have suspected mine is faulty, but I'm not sure. How would you troubleshoot it? Thanks.

 

[Timinator]

I would just replace the check valve. They are less than $10. I purchased one last week.

 

[sam peterson]

The purpose of the check valve is to hold vacuum in the booster to give you power assist if the motor quits. It only last for a couple of pumps. As long as th motor is running it doesn't serve much purpose. ---Sam

 

[Balzac]

Clinton



As Sam said. To test you must have a hand operated vacuum pump, or run engine, shut off, wait 2 minutes, apply brakes, vacuum should last for 2 pumps of pedal.

Jim

 

[Clinton]

Thanks

My check valve is fine.