Tractor trailer brake adjustment

[Csm Davis]

On a M939 series is there any way to adjust the brakes on a trailer to not engage so quickly when empty vs loaded?

 

[73m819]

NO

 

[Csm Davis]

What about adjusting the valve at the back of the cab would that slow the application of the trailer brakes? It should affect it some, because right now on empty trailer I just unhook the service gladhand and I would like to find a better way to keep my trailer from flat spotting my tires.

 

[hklvette]

What about adjusting the valve at the back of the cab would that slow the application of the trailer brakes? It should affect it some, because right now on empty trailer I just unhook the service gladhand and I would like to find a better way to keep my trailer from flat spotting my tires.

Partially closing the valve would not only slow the application, but it would slow the release as well. I think I recall reading on here that the biggest problem is the difference in behavior between S-cam brakes (on the trailer) and wedge brakes (on the truck). Not sure if there's a way around that...

 

[frank8003]

Is that why DOT inspections catch so many truckers with disconnected front brakes?

 

[Csm Davis]

Is that why DOT inspections catch so many truckers with disconnected front brakes?

I don't know but that's nuts! And I don't think that would stop the rear trailer tires from locking up.

 

[73m819]

About the only way is to back off the trailer brake adjustment, but the DOT frowns on that to. Does anybody know if there is such a thing as a load compensating valve tied to the rear trailer suspension, sorta like the air bag level valve.

 

[Csm Davis]

About the way is to back off the trailer brake adjustment, but the DOT frowns on that to. Does anybody know if there is such a thing as a load compensating valve tied to the rear trailer suspension, sorta like the air bag level valve.

Like on the back of a M1008! Great idea Ron but doubt it can be rigged up.

 

[frank8003]

This is one of the oh so many hits when I searched for "tractor trailer load compensating valve".

http://www.fwi.co.uk/machinery/guide-to-fitting-a-load-sensing-trailer-brake-valve.htm

this was interesting too
http://www.gonefcon.com/trucktcom/brakes_bobtail_valves.htm

 

[juanprado]

I would recommend talking to the tech folks at Haldex. They are a market leader and manufacture or rebuild anything with air brakes.

http://www.haldex.com/en/North-America/Tech-Support/Live-Support/

 

[1 Patriot-of-many]

Is that why DOT inspections catch so many truckers with disconnected front brakes?

Never heard of that. Front brakes on tractors have half the braking power rear axles do for a reason.

 

[m16ty]

Is that why DOT inspections catch so many truckers with disconnected front brakes?

For years big trucks didn't even have front brakes. After that they had them but there was a switch on the dash where you could turn them off. The thinking at that time was that the use of front brakes on wet roads and other slick conditions would cause the truck to skid out of control. Modern brake proportioning took care of that issue.

I'm assuming the people that disconnect their front brakes are still operating under that old way of thinking.

 

[73m819]

For years big trucks didn't even have front brakes. After that they had them but there was a switch on the dash where you could turn them off. The thinking at them time was that the use of front brakes on wet roads and other slick conditions would cause the truck to skid out of control. Modern brake proportioning took care of that issue.

I'm assuming the people that disconnect their front brakes are still operating under that old way of thinking.

Or do not have ABS

 

[zebedee]

Hmmm, silly question...

Jeff, would it be easier to put a lift cylinder on one of the trailer axles? (Assuming you have a double axle trailer) That way you would be more than doubling the load on the non-lifted axle which may be just enough to stop it skidding, plus you'd get the benefits of running a single axle when empty.


..to all the neigh sayers. I did start out with "silly question"!!!

 

[Csm Davis]

Good idea but I have multiple different trailers.

 

[R Racing]

How about a small restictor and a parrelel 1 way check valve? That way you are filling the system a little slower but releasing faster?

 

[Warden]

I first change clevis location , and if no help then I change chamber size , this is on my over the road & custom made trailers , non military ! There is no other safe way that I'm aware of to balance your trailer brakes ! All your testing can be done with your hand brake and your current set up , if u can't stop your rig on just the trailer with relative ease and no lock up then the system has a mis match in it ! Cans are dirt cheap , once I proved to myself restrictors and valve don't work , all my trailers stop like a dream , no lock , and plenty of progression , loaded and empty