CAT 621B Scraper Brakes. How to Disconnect Air Supply.

I have a continuous air leak on my 621B (2DB Army Model) and would like to totally remove the air supply to the braking system. I am open to suggestions on how to best accomplish this task. Where should I cap off the air supply, and do all of the brake actuators need to be Caged, (none of the brakes actually work) Not Sure if the pads are worn from the Army's use or what the problem might be. Thanks for you expertise.

What are you planning on doing with the brakes going forward.? Do you have a service manual.? A machine Serial Number might help with information.

Yes, the serial number 2DB00550 (US Army Model) . I do have a service manual and a parts manual that are for the 45P series machines that are of the same vintage. I have been operating the scraper on steep mountainous terrain, so I need the Retarder going down 20 percent grades. The machine currently has no functional brakes which I can live with, but the loss of air pressure for transmission controls, and the Retarder is necessary. So, I want to eliminate the air loss in the brake system by capping it off. I am trying to figure out the best method or location to cap off that system. Thanks for your advice.

What is so advantageous about circumventing a known safety feature? As a mechanic, I don't get it. I had an owner tell me we didn't need brakes on the scrapers. A month or two later, I watched a TS14B roll off a brand new Talbert de-tatchable bending seven cross members with the apron cable block because the operator couldn't raise the bowl fast enough when it started rolling. I never heard another comment from him about brakes. He was all about cutting corners and saving the last penny. I hope no one gets injured around that machine while being operated in that condition. The OSHA investigation will end your retirement.

Yes, that is certainly another concern. But, the parts necessary to fully restore the braking system on this 1986 vintage scraper are obsolete from Caterpillar and are difficult to find in a usable condition from other salvage yards. My main concern is to keep the Retarder and other transmission functions that rely on the air system to be fully operational. The major air leak is in the braking system, and I interested in where would be the best location to cap off that component. Thanks for your concern.

Do you realize that by circumventing a factory installed safety system that you are putting yourself at serious risk of prosecution, both civil and criminal, should someone get hurt? The days of cutting a fat hog by running junk are rapidly fading into the past. What it takes to do what you are proposing is not difficult to figure out. The fact that you are asking for advice here points to your inexperience or ignorance of the consequences or your actions.

The same thoughts as posted above crossed my mind. Have you identified exactly what’s leaking.?

I would be surprised if you could find very many of these old US ARMY 621 scrapers that still had operational brakes. The lack of parts and the age of these machines is certainly a problem for most operators. I am 82 years old and I certainly would not let my Grandkids or anyone else operate this machine. In the mid 1980s the military somehow purchased about 2000 of these machines. I'm not sure if they planned to make the earth flat or it was some kind of stimulus program for Caterpillar. Many of them sat unused for more than 30 years, and then the military transferred them to other agencies, such as county government, many are now appearing on the auction market. Due to their age many of the rubber seals and hoses have deteriorated. The compressor will still build 150 psi when it is isolated, but 40 psi is about all it can do when connected to the entire system. After shutting the machine off, the 40 psi escapes in about 5 minutes and the rush of air through the tanks, makes it difficult to locate the exact leak. I have a separate 80 gallon air tank, that I connected to the scraper compressor line, and located this tank 50 foot from the scraper, so it would not generate any noise during my testing. I pumped this tank up to 150psi with the scraper compressor, and then shut off the scraper engine. Now I can hear air flowing directly to the scraper air system. I also bypassed the scraper air tanks which were making noise as air flowed through them. I still haven't found the air leak.

You say there are no parts available but you haven't identified what type of brakes the machine has. Are they air over hydraulic or S cam. Parts are available at most auto parts houses and truck repair parts places for either. It doesn't have to say Cat on the label to work. I have found parts for old stuff like that from 6 Robblees many times. Possibly you have an air dryer on the machine that is stuck open. Maybe a quick release valve. Most valves that haven't been used acquire junk that is stuck on the pistons or maybe there is a broken diaphragm. Consider how much you paid for the machine and just figure this into the overall cost. I know they aren't much when they work properly. There are times when rolling a couple of feet unintentionally can get someone hurt.

You didn't share what is leaking. The rotochamber seal kits are still available, as is the treadle valve.

John C. said: You say there are no parts available but you haven't identified what type of brakes the machine has. Are they air over hydraulic or S cam. Parts are available at most auto parts houses and truck repair parts places for either. It doesn't have to say Cat on the label to work. I have found parts for old stuff like that from 6 Robblees many times. Possibly you have an air dryer on the machine that is stuck open. Maybe a quick release valve. Most valves that haven't been used acquire junk that is stuck on the pistons or maybe there is a broken diaphragm. Consider how much you paid for the machine and just figure this into the overall cost. I know they aren't much when they work properly. There are times when rolling a couple of feet unintentionally can get someone hurt. Click to expand... Yes, I need to locate the exact item that is leaking. I will try to get one of the Grandkids that can still hear help to find the leak.

heymccall said: You didn't share what is leaking. The rotochamber seal kits are still available, as is the treadle valve. Click to expand... Yes, I need to locate the exact item that is leaking. I will try to get one of the Grandkids that can still hear help to find the leak.

A spray or squirt bottle of soapy water is the most highly desired tool for your troubleshooting. If you release the brakes and there is heavy air leaking from a brake chamber, most likely the parking brake spring broke in the chamber and punctured the rubber pancake. Any decent truck mechanic could quickly solve 90% of your leaks and overall air system performance within a few hours. The expensive rotochambers can be economically replaced with 36-36 maxi's. The 36-36s have the same parking brake force as the original rotochambers.

Questionable wizard said: A spray or squirt bottle of soapy water is the most highly desired tool for your troubleshooting. If you release the brakes and there is heavy air leaking from a brake chamber, most likely the parking brake spring broke in the chamber and punctured the rubber pancake. Any decent truck mechanic could quickly solve 90% of your leaks and overall air system performance within a few hours. The expensive rotochambers can be economically replaced with 36-36 maxi's. The 36-36s have the same parking brake force as the original rotochambers. Click to expand... That is good information to know. Thank you. I think I will use my separate 80 gallon tank with 150 psi so I have more time to check out all 4 brake actuators. I still think the brakes are pretty much shot, because last year when I move a thousand yards of material down the 20 percent mountain grade, and the air system was building up to normal limits, I still had no brakes. The Retarder worked great though.

Most likely the slack adjusters need adjusted. Just like a truck.

Questionable wizard said: Most likely the slack adjusters need adjusted. Just like a truck. Click to expand... Thank you. I need to take a better look at how much damage was done to the brake system by the Army or the previous owner..

The brakes weren't meant for stopping or even slowing the machine down. They were designed to stop or hold the machine when moving slowly in tight places. Does this machine have S cam type brakes?

I'll take a look at cam arrangement, but I suspect it is the S type. I'm sure the Army was pretty rough on the brakes even though the machine only had a couple of thousand hours of use.

John C. said: Does this machine have S cam type brakes? Click to expand... See the attachment. According to the Commonality Chart any 2DB-prefix military machine is the equivalent of civilian S/N 45P3594.

Nige said: See the attachment. According to the Commonality Chart any 2DB-prefix military machine is the equivalent of civilian S/N 45P3594. View attachment 365908 Click to expand... Very Good. I have the CAT parts Manual for the 45P2712 and last Last Built