Semi brake question

notjustair · Nov 15, 2013

97 Freightliner and Dakota hopper bottom grain trailer (700 bushel tandem axle).

When I get to the elevator I can smell trailer brakes. They are all equally warm and maybe a little too warm. It is in the 40's outside at the highest. It seems to be getting worse. I could barely detect it two days ago but tonight when I was waiting in line it was smelling enough that the boy behind me noticed it. They are not dragging at all (it rolls just as soon as you let off the brakes). The tractor isn't hanging up anywhere. All of the releases are working etc. The actuator on the column is all of the way up.

Is there any way the slack adjusters could be setting too tight on all 4 equally (trailer wheels)? I'm wondering if the trailer is stopping the rig. I haven't ever had them lock on the gravel road, though. I drove home from the elvator at 30 mph and only tapped the brakes three times. Still pretty warm but no smell. This is the first time I have ever smelled brakes on this trailer (this bean harvest).

I'm puzzled and really don't need a breakdown! Both of the elevators close by were full by 5:00 today. Grrrrr.

schriffs · Nov 15, 2013

Could the s cam shaft bushings be too dry? I see a lot of trailers that don't get used much where the grease will dry up and they wont release completely. If it was sitting for an extended period like many farm grain trailers, just shooting some grease in won't loosen it up enough because it can't push the dried grease out. They have to be worked back and forth a bunch, maybe back them off first so they get more movement and then reset them after it's loosened up.

fixerupper · Nov 15, 2013

It would seem to me if they're hot enough to smell they would be more than just a little warm. Do you have a leaky wheel seal? When the brake warms up that 90WT it starts smelling. Just an idea. Jim

todd hamilton · Nov 15, 2013

Cousin's 750 bushel wet hoist would smell just a little when arriving at elevator, but we drove pretty hard to keep up with combine. How is your overall pressure when going down the road? Is she holding steady at 120 lbs plus?

moresmoke · Nov 15, 2013

Also check that the clevis pins are loose. Some
times they hang enough to not let the rod back into
the can and keep some pressure on the brakes. More
common on trailers that sit a lot.

Mark-Mi · Nov 15, 2013

The clevis pins in the slack adjusters may be seized and not allowing the brakes to return fully.
I have seen this to be the problem a number of times with trailers that sit through the off season.

Anonymous-0 · Nov 15, 2013

i havent worked on semi s but have worked on triaxles.i have fixed many brake pedals that dont retract all the way.if the trailer brakes apply first [dont know]thy may drag alittle.normally brake light stay on.may be air leak on maxy air line.bad glad hand.brake adjustment tighten down ,1/4 to 1/2 turn out

notjustair · Nov 15, 2013

Yup, it has no problem holding pressure. I can't hear anything out of the ordinary.

jm. · Nov 15, 2013

Season use grain trailer , I would agree with the others your brakes are not fully releasing . WD40, pipe wrench, grease gun and about an hour. Going to have to free up all that linkage. Grease the cam rollers and shaft and work them back and forth.

jon f mn · Nov 15, 2013

All these responses are good, but it is not uncommon to get brake smell. Especially if there is a down hill as you come into town. Do you get the smell if it's empty? That would be the tell.

showcrop · Nov 15, 2013

As Jon says it is not uncommon. In fact I would say that it is directly proportional to the direction that the wind is moving as you come to a stop. In other words if there is a little bit of tail wind, when you come to a stop the smell is right there. Going into or side to the air movement it will go right away from you, so I wouldn't worry about it. Especially since you are rolling good,

the tractor vet · Nov 15, 2013

With out looking at it myself i am guess ta mating here . (1) could be that the cams are starting to seeze up due to lack of greasing (2) could be that the return springs are not pulling the shoes off the drums (3) could be the pin that goes thru the clevises on the slack adjusters are seezen up and not allowing the brakes to come all the way off . Seen this many times on trucks and trailers that are only used once in a while . When doing a brake job on big tonka toys remember that NEVER SEEZE is your best friend . I also have seen trailer valves that will not let all the air off or leak a little and hold the brakes on just a wee bit . So for shuts and giggles get yourself a three or four pound hammer and a can of your favort panther pee and your coveralls and a pair of vice grips and check them pins first off and make sure that the turn free . Next grease the hello out of the cam bushings.

James Williams · Nov 15, 2013

Ive heard of trucks and trailers that sit alot,that the brake shoes would start seperating and the shoes would rub the wheels

jimmy

Fullthrottle · Nov 15, 2013

A quick and easy test to see if it's air related. Block the wheels and release the brakes. Pull the service (blue) line off the trailer and see if any air pressure is present at either truck or trailer. If so then you got a problem.

Anonymous-0 · Nov 16, 2013

Don't know where your from or how cold it is there. But round here I know I be checking for ICE in the air lines and air tanks.

larryanderson · Nov 16, 2013

Having had semis for a long even with new trailers there are many things that can cause brake smell[most have been covered].Many times it is caused by operator just slowly down to quickly, not using jake brake, or shifting down properly. I have seen many inexperienced and experienced drivers that think it is the same as their pickup or car and it usually weighs 10X more than a pickup.

Trkr · Nov 16, 2013

One thing I carry in my truck is one of those temperature guns.After you stop,just walk around your rig and check the temps on your brake drums,will tell you quickly if you have a brake dragging.Can also tell if you've got a low tire if you get them warm.

ericlb · Nov 16, 2013

does the trailer have automatic slack adjusters? one thing that is possible, and i have to watch this with my end dump is if you unload by using the hand trolley to hold the trailer, which must be done to unload a end dump, is automatic slack adjusters can get a notch up on the tractor if you use more than 30 to 35 psi to hold the trailer, this will make the trailer do more braking than the tractor under normal brake aplication, mine will actually slide the tires when running empty when this happens to it, then i have to get under it and fix it , but that will only happen if you have automatic slacks and hold the trailer with the hand lever

john in la · Nov 16, 2013

Some good answers but most are dealing with brakes to tight or stuck pieces.
And yes it is true that if one brake is sticking it will smell. Most times if it is bad enough to smell it will smoke also on longer distances.

Your truck could also not be proportioning the air supply equally between the truck and trailer causing on to be doing most of the stopping.

With all that said it could be just a simple adjustment problem. We had a trailer that if you used the foot valve the rig did not seem to be stopping well. On the other hand if you cranked down on the hand valve the trailer brakes would smell and smoke would pour out. The trailer brakes were out of adjustment and the throw of the chamber was not allowing them to apply fully. So while the trailer brakes would apply hard enough to heat up they were not applying hard enough to cause any real stopping power.
Same thing happens to a truck going down a mountain. The brakes that are not adjusted tight enough are the first ones to smoke.

So we got to ask.
How much throw do you have on the shaft where it comes out of the chamber.

D7fever · Nov 16, 2013

You probably have a maxi-can going bad. it is possible that one of the air valves is malfunctioning

RodinNS · Nov 16, 2013

Could be a lot of things... stuck clevis pins, broken/weak shoe return springs, a maxi can going bad and won't retract or automatic slacks that are not correctly adjusted. I often wonder how many people on these forums actually take the time to correctly adjust the rod/clevis for the correct slack angles when they replace a can... I'm guessing not too many... and that angle is critical. If the rod is too short the slack will overadjust. If it's too long it won't adjust at all... and the sweet spot is pretty small. If you've changed any can lately, that's probably the first place I'd look.
Beyond that... without being there... what you smell might very well be normal. One good application is all it takes to make a good stink for 5 min.

Rod

Frank 41 · Nov 16, 2013

I would say like the others that you have a rusted pin. Get some WD40 or if it is real bad the torch.

kevinj54 · Nov 16, 2013

(quoted from post at 00:33:39 11/16/13) With out looking at it myself i am guess ta mating here . (1) could be that the cams are starting to seeze up due to lack of greasing (2) could be that the return springs are not pulling the shoes off the drums (3) could be the pin that goes thru the clevises on the slack adjusters are seezen up and not allowing the brakes to come all the way off . Seen this many times on trucks and trailers that are only used once in a while . When doing a brake job on big tonka toys remember that NEVER SEEZE is your best friend . I also have seen trailer valves that will not let all the air off or leak a little and hold the brakes on just a wee bit . So for shuts and giggles get yourself a three or four pound hammer and a can of your favort panther pee and your coveralls and a pair of vice grips and check them pins first off and make sure that the turn free . Next grease the hello out of the cam bushings.

And don't forget them 2 big pins that hold the shoes to the axle, I have had them freeze up also.

Tim in OR · Nov 18, 2013

How about dirt under the brake pedal? I have seen that happen. On the truck I currently drive, the floor mat slid forward during a hard stop, causing a similar problem.
Tim in OR

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