GMC Rear Brakes

[Mrbill4108]

Have a question for all those GM bus owners out there. 
Has anyone ever converted their rear brakes to the bigger 4905 brakes? 
I have a 4108 and am considering upgrading to the larger 4905 brakes and would like to know if you think it was worth it, also what problems did you have doing the conversion?   From what I can see & find out with the parts book looks like everything is the same less drums, shoes, and slack adjusters.   
One thing that bugs me is the book calls out 2 different axle housings, one for a 4108 and one for the 4905.   
So if you've done the conversion or know someone that has, what are your opinions/ problems incurred doing this.

Thanks,
MrBill4108

[pvcces]

It might be related to the axle ratios.

As I recall, the 35s take a 4.125:1 and the 40s take a 4.375:1 ring and pinion. I remember that Fast Fred replaced his differential and wound up with a 40 in his 35. I think that he wasn't too happy with it.

For what it's worth.

Tom Caffrey

[RJ]

Mr Bill -

Why don't you give Luke a call and ask him?  He's probably forgotten more about these GMCs than all the collective wisdom on this and BNO combined!  1-888-262-2434 is his number, M-F, 9-5 Eastern.

Tom's right about the axle ratios, btw.

FWIW & HTH. . .

[TomC]

You'd do better to investigate using different brake linings.  There are about 2 dozen different linings made today for various different applications.  What you want is a softer lining that works best when cold.  You might have metallic linings that are typical for many bus applications.  While they work the best when hot, since they are very hard, don't make for the best stopping power.  Call Meritor and discuss with them brake linings.  Believe me-brake linings in the last few years have gotton to be down right scientific compared to when the buses were first built. 

On big rigs, the next step is to go with bigger drums also.  Currently, the common sized drums are 15 x 4 on the front and 16.5 x 7 on the rear.  By 2012, those will go up to 16.5 x 5 in the front and 16.5 x 8.625 in the rear for better stopping distances.  If those don't do it, then changing to air discs will. I called Bendix to see if I could convert my truck to air discs, and currently they do not make a conversion kit-yet.  When they do-I am changing mine to air discs-problems solved.  Good Luck, TomC

[zubzub]

Hey Tom, is that air discs for the rear or just the front? 

[Mrbill4108]

All I'm trying to do is a simple bolt on conversion.   The 4903/4905 models have 10" brakes and the 4107/4108 models have 8" rear brakes.  So converting to the 4905 rear brakes would result in 25% more rear braking then what I have now.  As I said the only differences I can see so far from the parts manuals are the drums, shoes & slack adjusters.  Along with axle housings having different numbers but I'm thinking (hoping) that is because it maybe a beefier housing for the extra weight of the 4905's. 
The part numbers for the housing has nothing to do with the axle ratio as the housing comes empty. 
Just looking to see if anyone has done this mod, as it seems like it would be a simple bolt on mod for improved braking.
Thanks,
Mrbill4108

[TomC]

Zubzub- yes that is for disc brakes at all corners-including the trailer, if you want.  On a 3 axle tractor it adds about $1,500.00 to the initial price of the truck.  Good Luck, TomC

[zubzub]

cool, I was wondering when they would make that an affordable option.

[DaveG]

Okay Mr Bill, I am no GM guy...in fact I'm not even a bus guy...but in the HD truck industry, the brake spider (that generally bolts to the rear end housing at the wheel ends and holds the brake shoes, S cam, etc) is different with different width shoes. That being said, some shoes are off-set from center, so add that to the mix.

Just didn't want you to get into the project and not be able to get the drum on...don't ask me how I learned that one.

Tom has a good point with regards to brake lining. Why not try a new set of brake shoes (with your application specific grade of lining) and see how they work?