GMC 4107 Brake Question

[Christyhicks]

Does anyone have a diagram or picture of the front brake setup for a 4107?  Ours is a 1966 model.

You see, we're getting ready for the big road trip and while adjusting our brakes, Larry found something "hanging" under there that concerns us.    What looks to be the "return spring" for the passenger side front . . .well, there is a broken one that was just kind of hanging under there.  There is a good one installed, but I'm wondering if there were supposed to be two, or if when they installed and new one, someone "forgot" to remove the old one totally.    It was rusted and the spring broken off one end.  Anyway, sure would be nice BEFORE WE LEAVE  to find out for sure that there's not supposed to be two, and if there is, exactly where the second one attaches.

We appreciate any help, Christy & Larry Hicks

[Ncbob]

Christy, can't imagine that it would be a return spring because they're inside of the drum.  If this is one you should name it "Houdini" for being able to pass through the drum without making a hole in it.

Hoping to see you and Larry at Arcadia next week and a Merry Christmas to you!

Jackie & NCbob

[Christyhicks]

Larry said it was 1/2 hanging out of the backside of the drum.  That's what has us baffled.  The drum has holes in it, and he managed to work it out through one of the holes. . . and you can see pretty well inside the drum with a flashlight, so he could see a good return spring installed. 

He hasn't brought any of the large tools over from his other shop, so he didn't have anything big enough to remove the drum.  That's why he needs to know if there were originally two, since he can see one good one in place by looking through those holes.

Yeah, we're not really excited about having to cover so many miles in only a  few days, but as long as we can leave as planned on Christmas Day and his back takes it, we'll be there by Friday evening.  If we need parts for this brake, well, then we won't be leaving before Tuesday afternoon, so that might throw a bit of a crimp in our plans, but safety has to come first.  That's why I got on quickly to see if anyone has anything to tell us. 

We definitely are leaving home, one way or another, as we deserve a few weeks alone together.  It's been a heck of a year. . . sales up 30% over last year, with less help in the office, so this will be a much appreciated and needed break from that darn ole grindstone!  It'll be nice to be able to actually TALK to each other without someone else  demanding our attention! 

We'll talk to you soon, Christy

[Runcutter]

Christy, I responded here, posting scans from my maintenance manual, but something ate my response.  I just emailed you 3 scanned pages from the maintenance manual. 

There was a change at serial 1067 (our 4107 is serial 1180,1968) - however I would not expect any changes in the brakes.  Interestingly, the maintenance manual doesn't show the front brakes from the inside, but it does show the rears - so I sent two illustrations from the front, one from the rear brakes - it may help identify the part.  My parts manual doesn't have an exploded picture of brakes, either fronts or rears, but I'm suspicious that we're missing pages from our parts manual.

Good luck, hope this helps.

Arthur Gaudet   Carrollton, TX

[larryh]

Christy &  Larry

Each front brake should have two spring's one ea at front and rear of shoes please check it as it can leave a brake shoe rubbing on drum as these are return springs.

LarryH

[Christyhicks]

Yeah, our maintenance manual doesn't show a breakdown or a decent picture of the front either.  That's why I was hoping someone knew for sure more about it.

Larry went ahead and jacked up the wheel and the break is pulling away from the drum, he can tell that also.  A closer look at the spring pretty much indicates that it has been broken for some time, and the one that is easily visible is in good shape, at least from appearances.

Thanks for your response LarryH.  We'll look more into it and decide what to do.  Christy

[larryh]

If the shoe is pulling back from the drum enjoy your break as you two deserve it and go for it and don't talk his leg off LOL.

Merry christmas and a happy new year.

LarryH

[NJT 5573]

when you drive it, if the spring is broken, you can hear the shoe riding the drum. even in this condition I cant believe that it will create enough heat to cause a problem. mine never did. the situation you have to be very carefull with is with maxi brakes. if the diaphram on the service side wears out or blows, it will alow the spring brake to activate as the system looses air. the spring brake will activate the shoes and burn your rig to the ground before you know it. since maxi cans are normally only found on the drive axel, I think you are ok. regular maint on a bus should include changing maxi diaphrams out every couple years. on a truck when one fails a lot of air goes over the drum and you usually get a second chance. not so with a bus. a diaphram costs less than 5.00 and is easy to install. Just put the key in the hole of the maxi and take it apart at the clamp that is leaking. If you find a leaker, use the key, back the brake off with the key, leave the key in and carefully get off the road and replace the diaphram.

[buswarrior]

Hello Christy.

when you pull it apart, replace both of them, and better check the rest of them on the coach, especially the other front.

Good preventive maintenance, that the previous owner obviously didn't bother with.

Spending money on brakes, spending a lot of money on brakes, should give all of us a warm fuzzy feeling.

NEVER cheap out on brake work. Change it all, and feel good about the update.

happy coaching!
buswarrior

[TomC]

Christy- sounds like a prime time to have the brakes replaced in the front.  Most shops will either take your old linings in trade or just reline your backing plates.  Unknown to most there are numerous types of linings you can use.  With the advent of these many types of specialized lining, this is one of the main reasons we still haven't standardized on disc brakes for trucks and buses.  Just to give you an idea, most new trucks comes with a standard gray block which is a good middle of the road lining that will do the trick for most.  Some of the specialized linings made- semi metallic for transit buses that actually work better when hot; lining that is tough to dirt for logging and off road use; softer linings for cross country trucks that spend most of their time on the road and have to have brakes that work well when cold (this would be my choice for replacement); slightly softer than semi metallic for trash trucks that makes several stops daily but not the severity of transit coach, etc.

Quite possibly the spring piece you see maybe the outer spring.  Some spring kits for brakes use double (inside/outside) springs for exactly this senerio of outside broken spring.  If you get the brakes redone, make sure to completely inspect the drums for serious cracks (will most likely have small heat cracks which is normal) and possibly turn them or just get new ones ($150 ea).  Good Luck, TomC