MCI Brake Valve...has anyone ever changed theirs?

[Ncbob]

Just having read Dreamscapes' "First accident in 40 years...." it once again brings a question to my mind: the MCI brake valve for DD3's seems to have been engineered for the comfort of the passengers...not the driver.

And well I understand that the revenue bus companies spent a lot of money training their drivers 'their way'...that doesn't apply to us. There are times when I wished my brake valve had been a little more aggressive, I might not have had to change my shorts, to be comfortable in a given situation.

Yes, I keep more than a comfortable interval between me and vehicles ahead of me and yes I 'cover' the brake pedal any time in doubt and I keep my slack adjusters properly adjusted.

I slow down for a long green light expecting it to turn amber but sometimes get caught with my britches at half mast. Scary!

and I don't really want to 're-manufacture' my bus..just want to be a bit more safe.

Any suggestions?

NCbob

[JackConrad]

Bob,
   I seem to recall an E1 and E3 brake valve.  I don't remember which was which, but one limited brarke application presure to around 65-75 PSI and the other one allowed full PSI. 
   I installed a brake application pressure gauge on our bus and found that a "ok, I see brake lights up the road" application is about 15-20 PSI, a "Oops, the light just changed" application rarely exceeds 40 PSI, and an "Oh S^&t", grab the steering wheel and push for all I am worth gives a 65-80 PSI application. I can tell the difference bewteen freshly adjusted brakes and brakes that should be adjusted.  Jack

PS: My son and I were in Bryson City a couple weeks ago, but were on rivers (Oconoluftee, Tuckaseegee, Nantahale, and French Broad) every day, no time to stop by to visit.

[bevans6]

I never had a feeling that I couldn't get a decent brake application if I wanted it, as long as the slacks were adjusted.  I don't think I can lock the front wheels on dry pavement, but I can sure need seatbelts if I apply full pressure.  I think this bears talking about!  Nothing any anything I have read suggests the MCI spec brake application valve limits pressure, so I am very interested in this.

Brian

[buswarrior]

We've got a problem...

well, a few actually.

Are we getting the air pressure we desire, applied AT THE WHEELS?
The treadle valve and the relay valve may be performing according to design, or may be performing as deteriorated. To be sure, we need to measure the air pressure as delivered at the brake chambers.
I am told that this is part of PM in some European countries, with fittings installed for the purpose.

You might be shocked at how a test of brand new valves does with this...never mind our old and tired relay valves.

What are we getting for friction out of the brake linings?  How old are they? What condition are they in?
This one is way more difficult to decide, and there are precious few people on the continent with the background and credentials to offer advice. Fresh linings is one sure way to reset the counter to zero.

Then the state of adjustment, the wear or not in the cam bushings, previous contamination by bearing lubricant...

Lots of variables, some of them very significant to the outcome, yet, not routinely measured.

happy coaching!
buswarrior

[Ncbob]

I was going to add to this thread with some more information last night it got too late. The last time I had the brakes adjusted it was at the truck shop which replaced the transmission. An afterthought caused me to think that the mechanics are used to spring brakes, not DD3's, and they might have just thought they released the parking brakes by pushing in the PB valve. We know better.

I'm going to make it a point to stop on my way south and put the bus over their pit, plug in their compressor to keep the brakes off and ask them to adjust them again. Perhaps that will give me a more definitive answer.

NCbob

[bevans6]

Why do you need to plug  in a compressor to keep the brakes off?  As long as you have over 30 - 40 PSI in the emergency tank they will not apply automatically.  Anyway it's impossible to adjust the rear DD3 brakes if the parking brake is applied.  There is around 2200 lbs of force on the pushrod if the parking brakes are applied  correctly.  Ain't nobody adjusting nothing with that force on the pushrod.

Brian

[dougyes]

After many years of mushy MCI brakes and no shop able to make them better we replaced the can diaphragms. Mucho better now. 

[Cary and Don]

We have found that often these mushy breaks are air leaks.  Add up a few small leaks and it is like a big leak. You can't always hear them. If you can't pass the DOT air break test,  you have some medium to big air leaks.

Don and Cary
1973 05 Eagle
GMC 4107
Neoplan AN340

[Ncbob]

Don & Cary, I know I have a problem with the RF air beam (leaks) and have the block-off plates to correct it...but at 75 am not quite up to it.

I guess it's just a question of time as to which one wins...the bus or the Grim Reaper.

Thanks for you input.

NCbob

[Cary and Don]

Know what you mean.  We don't match your 75 years yet,  but bad backs are a pain too.  We started with brakes that had 70lbs of application and mushy.  The air drained to zero in about four hours of sitting.  Now we have the full pressure for application and 80lbs still on the gauge 24 hours after shut down. We know there is at least one small leak left. Someday,  maybe it will have no leaks. Wishful thinking.

Don and Cary
1973 05 Eagle
GMC 4107
Neoplan AN340

[belfert]

I know from experience that worn drums, shoes, and chambers can cause brakes to perform poorly.  I had my brakes checked out at a repair shop and I ended up with all new drums, shoes, and at least one chamber.

After the repairs I nearly put myself through the windshield when I stopped at the end of the first block.  The braking performance was night and day difference.