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Author Topic: Another Brake Relay Valve - Updated again  (Read 3066 times)
Tenor
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« on: May 10, 2010, 02:44:20 PM »

I just replaced the brake relay valve with a new one from Luke, and it's blowing out air like crazy when I apply the service brake!  I hadn't even taken it around the block!  I put it in the same way the old one came out.  Is there a way to mis-plumb it?  In fact, once I was finished installing it, I aired it up, applied the brake, and there was no pressure loss.  Now it blows like a whale.  Of course I'll call Luke in the morning - I know it's not his fault!

Glenn
« Last Edit: May 25, 2010, 01:34:52 PM by Tenor » Logged

Glenn Williams
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1968 MCI 7 Ser. No. 7476 Unit No. 10056
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NCbob
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« Reply #1 on: May 10, 2010, 03:26:23 PM »

Glenn, believe it or not but that relay valve is available from your local NAPA store. I have one as a spare...they're not that expensive.

Good Luck,

NCbob
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junkman42
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« Reply #2 on: May 10, 2010, 03:51:31 PM »

Ncbob, do You have the napa part number for the relay valve?  Sorry to break in but I would like to have a spare.  John L
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« Reply #3 on: May 10, 2010, 06:34:12 PM »

At this time my bus is sitting in the shop yearning for a replacement 4 speed Spicer transmission and it's 14 miles away. I'd need to look in my spares bin to get you the number. I will write your request on my list of things to do
(which is eons away from my wifes' 'Honeydo List" and post the info as soon as I can.

After all, isn't this what this Board is all about?

NCbob
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Barn Owl
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« Reply #4 on: May 10, 2010, 09:23:52 PM »

If I remember correctly, they can do that if they get trash in them from the brake system. They are easy to clean.
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« Reply #5 on: May 11, 2010, 06:29:45 AM »

See my other post and related thread here about relay and inversion valve. I had air exhausting from the relay valve and it turns out one of the parking brake diaphrams was torn and the air for the parking diaphram was leaking into the service diaphram; out the air line (backwards) and back to the relay valve exhaust.
Fred
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Fred Thomson
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« Reply #6 on: May 11, 2010, 07:01:44 AM »

Glen,
   Clamp off the service brake lines to the DD3s, one line at a time. Then apply the service brakes, if the leak stops you know you have a bad diaphram.  Jack
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« Reply #7 on: May 23, 2010, 07:30:41 PM »

Well, here's an update. 
I used Jack's method, (confirmed by Bill at US Coach) and blocked off the air lines one at a time (using a pair of wide gripping surface welding vice grips - no teeth) and applied the brakes each time.  Air continued to dump from the relay valve.  So, I figured that I had a dud new relay valve.  Got a new one from Luke (Thanks!) Put it in, and it does the same thing!  Is there a better way to to test this?  Take one line off at a time?  From the brake can?  Which ones and in any particular order?  Do I need to block a corresponding line at the same time?  I hate to think I am being outsmarted here!  Thanks everyone!  Oh, of course, I need to get this done by Friday!

Glenn
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Glenn Williams
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1968 MCI 7 Ser. No. 7476 Unit No. 10056
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« Reply #8 on: May 23, 2010, 08:01:42 PM »

While you/re having fun down there maybe just pinch off all the lines, trouble shooting will be faster.  I have had good luck using cloth covered vice grips, wood clamps etc..
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« Reply #9 on: May 25, 2010, 01:37:56 PM »

OK everyone,
I've repeated the process of clamping off each line to the DD3 cans, one at a time, applying the service brake while the parking brake is set and when it is not, and it continues to dump air when you apply the service brake.  It does not leak at any other time.  Could the inversion valve be causing a feedback?  I'm reaching here. Huh  BW?  Any ideas?  please.... Undecided

Glenn
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Glenn Williams
Lansing, MI
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1968 MCI 7 Ser. No. 7476 Unit No. 10056
8v71
4 speed Spicer
robertglines1
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« Reply #10 on: May 25, 2010, 01:41:33 PM »

could you have mixed sup and del hoses up or maybe new valve has them in different location..compare old and new.As Fred  said it could be a bad diaphram feeding back...Good luck Bob
« Last Edit: May 25, 2010, 01:47:56 PM by robertglines1 » Logged

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Tenor
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« Reply #11 on: May 25, 2010, 02:14:20 PM »

Bob - Thanks!  I just double checked, and everything is plumbed properly.  The relays are the same, except for another drain option on the original valve that is not cast into the new ones.  I'd be shocked if this one is bad too.  Two faulty ones in a row? 

I also decided to do a different test.  I used 2 C-clamps at a time - one for each can, on the corresponding air line.  IE, I blocked the service brake air signal to both cans, then hit the brake pedal with the parking brakes on and off, and the brake relay valve continued to discharge.  I repeated this test for the parking brake lines and had the same results. 

Glenn
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Glenn Williams
Lansing, MI
www.threemenandatenor.com
1968 MCI 7 Ser. No. 7476 Unit No. 10056
8v71
4 speed Spicer
JackConrad
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« Reply #12 on: May 25, 2010, 02:29:03 PM »

Glen,
    I would clamp off all lines (including parking release lines) and see what happens. If no leak, release lines one at a time until you find the source. If you still have a leak with all lines clamped, at least you know where the problem is not.  Jack
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« Reply #13 on: May 25, 2010, 03:29:58 PM »

Thanks Jack!  I'll try that now!

Glenn
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Glenn Williams
Lansing, MI
www.threemenandatenor.com
1968 MCI 7 Ser. No. 7476 Unit No. 10056
8v71
4 speed Spicer
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« Reply #14 on: May 25, 2010, 04:04:47 PM »

 Shocked Shocked Shocked
While you/re having fun down there maybe just pinch off all the lines, trouble shooting will be faster.  I have had good luck using cloth covered vice grips, wood clamps etc..
  Shocked Shocked Shocked
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