rmuhlbar Posted September 18, 2014 Share Posted September 18, 2014 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. ThanksRoss 2 Quote Link to comment Share on other sites More sharing options...
mrsmackpaul Posted September 18, 2014 Share Posted September 18, 2014 first welcome aboard I would have thought the brakes should pull it fine I suppose first things first how do you adjust the brake ?how about oil leaks around the axle ?is the shoes the right radius for the drum some times shoes have to ground to suit the drum if it is worn ?is there air leaking out when you apply the brakes ? do you have enough air pressure at the maxi chambers on the axle ?Paul Quote Link to comment Share on other sites More sharing options...
Popular Post maint1 Posted September 18, 2014 Popular Post Share Posted September 18, 2014 Everything Paul said, also the truck should have 30X30 chambers on it. Also check the service relay valve, some of the newer valves were designed to put out more air if the trailer valve is released. I don't know if it ever pulled a trailer or not, but if it has that type of valve it will have an extra line from the emergency relay valve or the quick release valve. You can check by blocking the trailer output and try driving with both tractor and trailer buttons released, if equipped with both. I use a fifth wheel tow unit a lot and have the problem you describe, if I don't do that. 3 Quote Link to comment Share on other sites More sharing options...
Freightrain Posted September 18, 2014 Share Posted September 18, 2014 I'm thinking Trent had the same issues years back with his R700?Does it have the proper slack adjusters on it? The installed angle proper? 1 Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment Share on other sites More sharing options...
rmuhlbar Posted September 18, 2014 Author Share Posted September 18, 2014 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! Quote Link to comment Share on other sites More sharing options...
rmuhlbar Posted September 18, 2014 Author Share Posted September 18, 2014 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. Quote Link to comment Share on other sites More sharing options...
Freightrain Posted September 18, 2014 Share Posted September 18, 2014 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!I can't say for sure, but this sounds fishy. Not sure how the three button control valve works, but something might be amiss with this set up and causing problems.Typically the "Slack adjuster" needs to be within a specific angle to the brake chamber rod for proper leverage.I'm sure someone more in the know, but I would assume that 30/30 chambers would apply more brakes then 20/20's? 2 Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment Share on other sites More sharing options...
thomastractorsvc Posted September 18, 2014 Share Posted September 18, 2014 Take some pictures of the brake set up so we can see what type of slack adjusters you have and find out if they are all the same. If they are manual adjusters there is way to adjust them that is different then automatic/self adjusters. When you adjusted them was the brakes released or set? What position on the truck? Does the axels have the dust cover backing plate protecting the shoes? can you see the shoes or wetness in the drum? When you replaced the brake shoes how did you determine the drums were still good? Was the drum cleaned of the old oil from the leaking seal? The cost of brakes and drums is not much more than it would cost for your car, typically if you replace the shoes most replace the drums too because of heat checking and possible out of round and grooves and such and they are cheap. Was the hardware kit replaced with the shoes? Is the S-cam free and turn easily when you had the drums off? Are they greased? 1 Quote Robert"I reject your reality and substitute my own." Link to comment Share on other sites More sharing options...
Popular Post gearhead204 Posted September 18, 2014 Popular Post Share Posted September 18, 2014 we had 2 rd688s with 24x30 maxis 30x30 would hit the drums. any how one truck stopped fine the other stopped with the trailer, these were sister trucks 1 vin # apart . turned out that the application relay valve was bad. 38.00 dollars fixed it. to test do as said before install a 150 psi - 300 psi gauge into the application port of the brake can. apply 10-20-30-40-50-60 lbs. in increments to the brake pedal and then observe the gauge and make sure it pressure follows closely to what the foot pedal does. 3 Quote Link to comment Share on other sites More sharing options...
Bobby j Posted September 18, 2014 Share Posted September 18, 2014 How often do you have to adjust your brakes........could be stripped slack adjusters..........my two cent .......bobby j. Quote Link to comment Share on other sites More sharing options...
mrsmackpaul Posted September 18, 2014 Share Posted September 18, 2014 thought this might helphttp://flxibleowners.org/article-the-brake-system-adding-spring-brakes/http://www.youtube.com/watch?v=QVJSFlp8Pwshttp://www.youtube.com/watch?v=4rqvO_IwHbMI didnt watch it all but they explain how the brakes are meant to work as they a picture is worth a thousand words I hope this helpsPaul Quote Link to comment Share on other sites More sharing options...
b61mack Posted September 18, 2014 Share Posted September 18, 2014 I tighten the slack ajuster tight then back off 1/4 of a turn, and make sure the collar cons back up to lock it. it the collar doesn't come back up the brakes could back off. 2 Quote Link to comment Share on other sites More sharing options...
rmuhlbar Posted September 22, 2014 Author Share Posted September 22, 2014 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! Quote Link to comment Share on other sites More sharing options...
MACKS Posted September 22, 2014 Share Posted September 22, 2014 This might sound funny but on a truck that old check the floor boards for rust and weakness make sure the brake pedal mount and floor boards don't move when brake is applied, you would be surprised what a difference it will make..good luck 1 Quote Link to comment Share on other sites More sharing options...
MACKS Posted September 22, 2014 Share Posted September 22, 2014 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!if the collars are sticking don't hit the adj nut with a hammer like a lot of guys instead grab the collar with a pair of vice grips and twist side to side while puilling up also clean it up good with a wire brush and air pressure.. Quote Link to comment Share on other sites More sharing options...
Freightrain Posted September 22, 2014 Share Posted September 22, 2014 Put some grease into the slack. There should be a fitting on the one side. Then carefully pry the lock collar up. Use a screwdriver? maybe pliers? You may need to turn the adjuster to get it to line up enough to pop up. Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment Share on other sites More sharing options...
thomastractorsvc Posted September 22, 2014 Share Posted September 22, 2014 Or buy new ones-they are only about $15 http://www.truckspring.com/products/Slack-Adjuster-16-inch-37-Spline-6-inch-Span__GS6020013715.aspx?gclid=CjwKEAjwkf-gBRCd-b2m2aOo0EQSJABMeQDk-tvnAF8-NNjhcrpYyRrjOIudHur7uYXvLBEUwXyFXBoCXujw_wcB 1 Quote Robert"I reject your reality and substitute my own." Link to comment Share on other sites More sharing options...
RowdyRebel Posted September 22, 2014 Share Posted September 22, 2014 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 around1) Chock the wheels so the truck won't roll.2) Make sure the truck is aired up.3) Release the brakes.4) Tighten the adjuster good & snug.5) Back it off 1/4 to 1/2 turn. I usually go 1/4 turn and tap the drum. If it rings like a bell, I know the shoes aren't dragging on the drums. If it sounds muted, I'll try backing it off another 1/8 and try again. Don't go past 1/2 turn, though, or you risk getting into the "out of adjustment" territory. If the shoes are dragging on the drums, it is going to hurt fuel economy, make a lot of heat, and wear the shoes and drum out prematurely...so it's best NOT to leave them dragging if you can avoid it.One of the possible causes of the problem you are having might be caused by the way you are adjusting the brakes. The constant light pressure between the shoes and drums will polish them both up real good, decreasing the friction they are capable of making when you apply the brakes, causing your brakes to suck. To solve that, you'll want to scuff up the shoes and inside of the drums with a piece of sand paper to get rid of the polished surface....and then properly adjust the brakes so that they aren't constantly dragging. Quote When approaching a 4-way stop, the vehicle with the biggest tires has the right of way! Link to comment Share on other sites More sharing options...
rmuhlbar Posted September 24, 2014 Author Share Posted September 24, 2014 Thank you all. We bring the truck in on Thursday go over the brakes with a comb. I will let you know. Thanks again. Quote Link to comment Share on other sites More sharing options...
scjpll1 Posted September 28, 2014 Share Posted September 28, 2014 check the drums thay might be glased over.. the angle of the slacks are very inportan. If the slack goes over 90 it will affect the stopping... one more thing.. how does the pedal feel. if it is like stepping on a brick it is bad... 1 Quote Link to comment Share on other sites More sharing options...
Popular Post rmuhlbar Posted October 14, 2014 Author Popular Post Share Posted October 14, 2014 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!! 4 Quote Link to comment Share on other sites More sharing options...
RowdyRebel Posted October 14, 2014 Share Posted October 14, 2014 Glad you got 'er figgered out. Quote When approaching a 4-way stop, the vehicle with the biggest tires has the right of way! Link to comment Share on other sites More sharing options...
Lmackattack Posted October 18, 2014 Share Posted October 18, 2014 I'm thinking Trent had the same issues years back with his R700?Does it have the proper slack adjusters on it? The installed angle proper?Larry i Have the same issues still. I replaced the foot valve,slacks,cans,s cams,shoes, all hard ware. Removed the anti lock air valve.Truck will still not stop like it should. I checked air pressed at the chambers and it's correct. I gave up as its jist a parade truck now. Quote Link to comment Share on other sites More sharing options...
carlotpilot Posted October 19, 2014 Share Posted October 19, 2014 before you give up completely check the inner bore of the brake drums could be that they have been turned to oversize dimentions if so even new shoes would not give proper stopping power 1 Quote Link to comment Share on other sites More sharing options...
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