How to adjust tag brake pressure

Scott & Heather · October 30, 2020, 04:19:29 AM

Long story short, my bus brakes have been terrible from the time I bought it. I took it to several shops including WW Williams and spent $3000 easily to have the brakes adjusted, new slack adjusters, new shoes etc all to no avail and the shops would all tell me it was braking as it should. I never believed them. And then I took it to the brother of Jonathan Leid (leid diesel rebuilt my 8v92 this spring). His brother runs an outfit in new Berlin PA and kept the bus for 5 days and figured out that the push rod from the pedal to the treadle valve was out of adjustment. This was allowing about 52 psi to the brakes on full pedal depression. They readjusted it, and I'm now getting 110 psi to the brakes. And now my bus STOPS. NOW. It's amazing. Literally NIGHT AND DAY.

Ok, so I'm thrilled beyond thrilled for this. Seriously it's changed my confidence level in driving the coach completely. But they mentioned to me that I was only getting about 25 psi or so to my tag axle brakes. We were needing to retrieve the bus from their shop immediately so they didn't have time to remedy this but he mentioned I might be able to adjust a regulator to the tag brake air and raise the pressure just high enough that I get braking assistance from the tags but not skidding. Can anyone point me in the direction of these regulators for tag brakes if they exist? 1992 102C3

sledhead · October 30, 2020, 04:53:50 AM

can't help you with the tag brakes but nice to see that the Leids guys have helped you out . I miss seeing them as when I had the M C I they were great with it and did lots of engine work on it as well as the out of frame rebuild . with the cat I have no need for repairs other then regular preventative maintenance and oil changes .
nice guys and nice area they live in and I miss the visits

dave

luvrbus · October 30, 2020, 05:14:17 AM

Never saw a regulator for tag air brakes on a bus,the tag and drivers work off the same brake relay they just use smaller brake chambers on the tags to regulate the brakes pressure if you do have a regulator it would need to be past the rear brake relay

blue_goose · October 30, 2020, 05:43:19 AM

There are pressure adjusters on each side behind the tag wheel.
Jack

chessie4905 · October 30, 2020, 08:27:34 AM

leids dont work on Cats- allergic.😅

Jim Blackwood · October 30, 2020, 08:49:06 AM

Speaking of Cats and cat allergies, I saw a nice little cat 4 cylinder at the scrap yard yesterday mounted on a skid. Looked like something about generator sized. I'm sure they would sell it really cheap. Had fresh paint and filter but the exhaust was off and it had clearly been run. David Hirschbergs in Cincinnati if anyone is interested.

Jim

Scott & Heather · October 30, 2020, 09:57:20 AM

Quote from: blue_goose on October 30, 2020, 05:43:19 AM
There are pressure adjusters on each side behind the tag wheel.
Jack

HEY JACK,

Where? Not on the fenders right? I have pressure valves for the tag airbags but haven't seen ones for the tag brakes.

buswarrior · October 30, 2020, 10:19:06 AM

I would do more diagnosis, since the info you have so far is incomplete.

Measure the air deliverd to the chambers, front, drive and tag, by loosening a hose and affixing a proper gauge.

This is a huge problem in north america, nobody looks any further than the mechanicals, and blindly trust the air delivery is what it should be, when that is where some complaints, the diagnosis should start.

Relay valves, new in the box, with wildly varying cracking pressures and delivery pressures.... How would you know?

Happy coaching!
Buswarrior

blue_goose · October 31, 2020, 07:15:51 AM

Quote from: Scott & Heather on October 30, 2020, 09:57:20 AM
HEY JACK,

Where? Not on the fenders right? I have pressure valves for the tag airbags but haven't seen ones for the tag brakes.

Sorry my bad thinking about air bags
More than likely you will have to go with larger brake cans to get more power to the tags.
Jack

buswarrior · October 31, 2020, 07:28:42 AM

Long ago... i don't think there is a regulator.

We would have found it and beat it to death for letting us slide the tag tires, flat spotting them. (That problem was the not enough weight on the tags, suspension regulator required adjustment.)

Be careful what you wish for, so long as they are dragging, don't encourage a tag brake to do more. If you have never driven a thump thump thump flat spotted tag tire... you don't want to.

I think you will find the tag brakes plumbed off the drives, my manuals are buried somewhere...

Happy coaching!
Buswarrior

lovetofix · October 31, 2020, 08:16:30 AM

I don't know anything about a 102C3 but my MC9 definitely has pressure regulators on the tag brakes.
They are just on the inside of the inner wheel well, one for each side. One of them was bad and letting full pressure to that side and was sliding with normal braking. I backed off the slack adjuster to get it home and am working on rebuilding or replacing every component in the braking system.

Jim Eh. · November 01, 2020, 01:14:25 AM

My MC12(MC9)
Type 24 pots and 15x4 shoes should be matched to that tag axle application. And since the weight transfer "tag dump" system should only be used for times starting from parked with less than optimal traction and not highway driving, I can't really see a need to have adjustable pressure valves.
In my generic parts list there is only (like Cliff says) a single (R12) relay valve. I have not physically looked on the bus tho.

chessie4905 · November 01, 2020, 03:59:16 AM

The only other concern could be the friction rating of lining installed, although it may only be available in one rating. If someone has a brake system diagram for that model, should show whether there is a pressure reduction valve, and adjustable or not for that axle after relay valve. Or description of operation in brake system service section.

blue_goose · November 01, 2020, 05:07:14 AM

This may help.
Jack

chessie4905 · November 01, 2020, 05:20:18 AM

#86. Trailing wheel pressure regulator. Should be specs in your service manual.