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It seems we may have found the answer. The slack adjusters were wore out and backing off by themselves. So, immediately after tightening up the brakes, they would back off to their lack luster performance level. We have new adjusters and much better brakes now. Thank you all for your input. Now I have a new valve/lifter issue I will post in engines. Thanks again!!

Congratulations, that sounds like a great combination. We just ordered a new axle back 60" midrise. 445C engine, Maxitorque 13 speed, 3:11 Mack rears, twin Y suspension. Over the road hopper bottom. I spent almost 6 months specing new trucks before we ordered this one last week. We are a small business and a 130K investment has to be spot on. I feel pretty good about our purchase. I liked everything I could find about the Mack drivetrain and the price was slightly better. We seriously considered the M-drive but decided against it at the last minute. We went with high speed rears to try to create the M-drive like rpms at cruise speed in top gear (1206 rpm@64 mph). This keeps 12th very usable (1440 rpm@64 mph) for cruising the hills. The deciding factor on the Maxitorque vs Eaton was the standard (not extended) warranty. Mack offers 750K warranty while Eaton was only 500K. We have had good luck with our Eatons but wanted to try the Gold Bulldog on for size.

Thank you all. We bring the truck in on Thursday go over the brakes with a comb. I will let you know. Thanks again.

Yah, it definitely has the 44K rears.

All, Thank you all for the input. There is much here at which I need to look closer. At first glance I think I need to look closer at the locking collars on the manual adjusters. I think they may be sticking in the depressed position meaning the breaks could back off. I will check this while I look at the shoes and drums again. If we still can't find anything we will look into putting a pressure gauge at the brake can. Thank you all!

You are right Superdog, we have twins--I don't think flat "hotrod" black was a factory color in '78 but maybe. As for the camelback I don't know if it is a 34 or 44K, how would I know? I don't know what rear ends it has other than LOW. At 2100 rpm it does 60 mph. We deliver on all two lanes and gravel roads so it works well (no speeding...). It has the Maxitorque twin stick 6 speed and an ENDT 676 rated at 283 hp. At some point in its life someone combined it with a glider so the only VIN type number we have is RD3307KIT which makes parts guys crazy. We have been running it long enough now that I know some of the right keywords to mention when getting parts so the parts man doesn't implode trying to look up my VIN. If anyone has any more info about tracking a glider VIN it would be helpful. I just bought a kit from quiet ride and some new window/door seals. I will install it this fall in an effort to retain feeling in my toes and fingers this winter. It took until June to get the feeling back after last winter.

I am not sure what proper slack adjusters would be or if they are installed at the correct angle. I would like to find out though. Where would I look? Thanks.

how do you adjust the brake ? I tighten the (don't know what they are called) nut with the lock collar until the shoes are barely touching the drums and even all the way around how about oil leaks around the axle ? Good point, I will look. We had a wheel seal out and changed. I wonder if some oil has that drum and shoes slicked up. Can oil ruin the shoes? is the shoes the right radius for the drum some times shoes have to ground to suit the drum if it is worn ? I don't know, but it seems the shoes fit the drum well. is there air leaking out when you apply the brakes ? No. do you have enough air pressure at the maxi chambers on the axle ? I don't know, how would I check? Tee-in a guage at the chamber? What is the Maxi chamber? Is that the canisters? I will have to look. How much should I have? As for 30x30 chambers, will that make the brakes more powerful if I switch to them? As for the service relay valve, I don't think that is the problem. The red and yellow buttons are inoperable and permanently pressed "in" on this truck. We only use the blue valve. We don't pull a trailer with air brakes. Could there still be a problem with the red or yellow buttons? Thank you all!

Greetings, We run a small agricultural supply business in Iowa and one of our trucks is a 1978 RD600. We've added a Red Dot AC and paint but other than that is is fairly stock (I won't say original...) It does about 400 miles a week loaded at 50K delivering products to farms. We love the truck because of the almost non-existent cost of ownership compared to our newer trucks. The camelback suspension performs well on the soft and uneven ground we deliver to. We do most maintenance ourselves but it is obvious we sometimes need advice and unfortunately old Mack mechanics are harder to come by. Truck mechanics do/tell me the same things I find out by myself or know all ready (not much). So, I wanted to join your forum and hopefully keep our truck on the road for many years. I did just post a topic concerning brakes in the air and brakes forum--please check it out. I am interested in any old manuals or service check lists that someone may have for these old trucks--again most mechanics look at us funny and tell us to buy a new truck. But I like this one and hope to keep it going--it always gets nods of approval (and usually a story or two) from our customers. And when you drive it----you are definitely never confused about what you are driving. It has personality all its own. Thanks in advance to everyone. Ross

Hello All, I have found much helpful information on this site--thank you all, but I haven't found exactly what I am looking for concerning brakes. I have a 1978 RD600 that does about 400 miles a week delivering products (usually loaded at GVW 50000 lbs) to farms. It has what I consider "regular" brakes, that is they look and adjust like any other brakes we use. I think they have Bendix 20/24 canister or similar. The brake are barely adequate. We have put on new liners, the drums are not wore out. I keep them adjusted as tight at I dare. Does anyone have any ideas to make them better? Like I said, they are adequate but if you have to stop in a hurry is where there effectiveness runs short. Are there upgrades? Its like I wish they had a power assist--is there such a thing? Can I add it? We love the truck (almost no maintenance cost compared to our newer trucks) but I wish it had better brakes. Any insight is appreciated. Thanks Ross