Ser# CMP570D-01289590KF. Over the past year and a half the dealer has put in 2 master cylinders and a set of wheel cylinders and we continue to have the same problem: With engine off there is brake pedal pressure but as soon as the engine is running you lose all pedal pressure and the pedal goes to the floor. Any ideas would be much appreciated.
Showing items 1 - 18 of 18 results.
Joe- checked out booster- looks like it's a MICO unit- google their website & see if the booster there looks familiar.
Their boosters are all rated at between 0-2000 psi & between 3-10 GPM. Perhaps your challenge is flow- not pressure.
If your raise the engine rpm- does that change the symptoms?
If you hold the brake pedal to the floor (without pumping) will the pedal begin to rise on it's own at some point?
Hope this helps
In studying the schematic & checking out the only manual I have on this type booster assy (it's on a Hyster- not sure how it relates to yours) I have a few concerns:
1)- from the schematic it looks like the front of the booster is a sliding valve assy. It's hard to tell but it looks like the hydraulic system doesn't hold pressure unless that plunger is depressed- is that correct- when does the hyd. portion have max. pressure?
2) From my Hyster book (yours may be different) there's an adjustment screw on the front mounting plate of the booster ( it would be covered when mounted), have you seen/adjusted this screw. It sets the pressure of by-pass.
I wish I could be of more help- without a picture of the master cyl/booster assy I'm out of ideas. List the part # of them & I'll get a breakdown from my vendor
I saw you have a schematic of the brake system- does this include the paths thru the master cyl & booster? Could you email or fax it to me?
Can you get the specifications of the wheel cyl's, master cyl & booster (as far as bore diameter)? Sounds like you have a volume issue.
Oh yeah, bbforks, there's no mfg. stamp in the casting of the booster but it's a clark oem part ordered from the local dealer.
@ bbforks, the brakes haven't been perfect since day one. I've been taking care of it 5 of it's 9 years. I try to do most of the wrench turning around here even though I'm stuck managing maint. for 3 warehouses but when I get a time consuming break down (enter pain in the a**) I will contract out to one of my local dealers and a brake job on this dual hub, solid tire POS fits the category.
After the dealer tech did the brake job the last time he didn't get the lug nuts tight enough and while I was on vacation a couple of them just rolled off the lift. The area supv. called the tire company we use and they came out and torqued em down with a 3/4 impact. A couple of weeks later the brakes locked up...the backing of 2 of the studs had broken off and lodged in the left hand adjuster and wiped out the wheel cylinder, adjuster, hub and shoes. The truck was down almost 3 months waiting for replacement lug studs (all the ones available) that were coming from Japan by boat. That was late last year. I'm seriously thinking about testing out our fire insurance.
@Mrfixit, they did away with the inching cylinder (2 as a matter of fact) with the Group 23 brake system. This truck has a Group 29/30 and no inching cylinder. Both pedals work the same brake booster/master cylinder with a switch on the back of the inching brake that activates a solenoid to disengage the trans. A convoluted POS!
What make are the master cyl & power booster?
You say that the wheel & master cyl's were replaced about 13 months ago & afterward everything worked fine. What are the symptoms you get that let you know the system needs service?
In your original post you say that the dealer has replaced the master cyl twice- does this usually put the systems to bed (for a while at least)?
Do you personally have a history with this unit or did you get stuck with someone else's ****? If you have a history, Has this unit always had a brake issue or is this something new?
How does the inching work on that bad boy? Doesn't it have a slave cylinder hooked to the brake system? Is that bleed?
There is no vaccum lines to the booster. The wheel cylinders engage. With the engine off you can feel them quite well and with the engine running you can if you pump the brake pedal. the wheel cylinders and master cylinder were all changed apprx. 13 months ago and the brakes worked fine afterwards. I've tried regular bleeding, a vaccum bleeder (from the wheel cylinder bleed screws) and a pressure bleeder (at the resevoir) to make sure there is no air in the system and in all cases when the bleed screw is opened the flow pressure of the brake fluid coming out is normal.
did you verify the new pumps pressure?
are the wheels adjusted up correctly?
check the wheels to verify that you are getting some reaction at the wheels.
are you absolutely sure you have all the air out of the lines?
pressure blead the system?
just some thoughts that come to mind
Now that I've invented numerous new cuss words in a variety of languages I'm out of ideas. The boost runs off a seperate aux pump on the side of the engine. After contacting the factory I was told to check output pressure from the aux pump and it was a little low so I changed the pump with the same result: no brakes with engine running. The master cyl and boost are an assy and short of disconnecting and plugging the hyd line that goes directly from the pump to the boost (which could damage the pump) there's no way to bypass the boost. There is no relief or pressure ports in this system that I can find visually or by schematic. We tried adjusting the cyl. stroke plus and minus to no effect. We even double checked the prime on the pump to 600rpm and tried bleeding the brakes with the engine running...still no air coming out from the cylinders and no brakes. If anybody has ANY ideas please help as the dealer, factory and I am out of ideas.
To bbforks: The master cyl/booster comes as an assy and yes, it was changed out 2 days ago. 2 pedals, both operating off the same master cyl. with a switch on the inching pedal to disengage the trans. w/ a 1/4" free play on both pedals.
I think I got it with some helpfull info from the factory. This machine has the group 30 brake system. The hydraulic portion of the brake booster/master cyl is powered by a small aux pump on the right side of the engine. The specs state rated pressure of 3500 psi. With engine running I'm getting 1500 psi. There's no adjustment and the lines run directly to the booster so I'm thinking it's not enough pressure to run the booster so I ordered a new pump.
I'm assuming the master cylinder & booster are new? With engine off- how high is the brake pedal & is it firm? How much free play is there in the master cylinder input rod? Does the brake pedal have an adjustment for height? Does unit have 1 or 2 brake pedals? A picture of the master cyl, brake pedal adjustments & booster to my email would be helpful.
Ok, while I wait to see if this POS has fire insurance...I changed out the booster/master cyl assy., bled the brakes thoroughly and have the same issue: with engine off there is back pressure on the pedals but after you start the engine (when you can get it started...the starter is trying to go out now) you loose all brakes. Does anyone have a hydraulic schematic on this thing. My addy is in my profile. Thanks in advance.
Check the power assist valve. It should be mounted on the front of the mc. I believe there is a rb kit avaailable for it.
this a diesel truck?
see if there is a vacum booster on the master cylinder and also check for a vacum pump on the engine somewhere, usually mounted on the rear of the alternator/generator. check any lines in those systems and the operation of the components themselves.
do the basics first though, make sure the master cyl rod freeplay is properly adjusted, and the wheel adjusters are adjusted up correctly on both drive wheels. once this is correct if problem still exists then check the brake vacum assist for problems.
Hi,I'm not familiar with this machine,but it sounds like you have a problem with whatever brake assist system its running.Be it servo or pressure boost.Can you disconnect assist system & see if you then keep pedal pressure.
Forkliftaction accepts no responsibility for forum content and requires forum participants to adhere to our rules of conduct. Click here for more information.
If you are having trouble using the Discussion Forums, please contact us for help.