View Full Version : Drive axle brake chambers

05-15-2014, 11:46 AM
http://prevostcommunity.com/forum/UserPics/IMG_0352_1.jpgBrake chamber photoshttp://prevostcommunity.com/forum/UserPics/IMG_0345_3.jpg
This time I've really made an expensive screw-up. Over a year ago, I ordered eight brake chambers from various sources (6 wheels and 2 tag lifts). I installed all but the drives before running out of time. Now, when I'm ready to finish the job after a lengthy delay, I find I've got the wrong chambers. The right photo (oops, upside down) is the left drive chamber on my disk brake equipped H3. Note the wedge-shaped outboard end. The left photo is the replacement a local truck center sold me. Both are 24/24 chambers, but the new one not only has a flat end, but appears to have more travel as well (I assumed all 24/24's had the same travel). I'm guessing that means I can't even swap ends on the new ones and use them. Because of the time involved and the fact that that chamber is not a regularly stocked item, they will not exchange them or take them back. A truck center where I am now tells me that because Prevost calls for a left and a right chamber, they are unique to my coach and he wouldn't even be able to order them from his supplier. The cost difference, $321 from Prevost versus $110 from the truck center seemed like a bargain at the time. Now it appears I'm out $220 and am faced with paying Prevost $642 for the correct ones. Any chance of an encouraging word or cheaper solution from you folks out there who are wiser than I?

Joe Camper
05-15-2014, 01:28 PM
U have problems for sure.

First that top photo is not a 24/24 it is a 30/30 and a good price on a 30/30 is 50 bucks. (never heard of a 24/24)

IF your bus had Rockwell disc (IT DOES NOT) that style chamber would fit, but, STILL would be incorrect because we have 30/36s not 30/30. Truck guys and less than safe bus owners can and do use THE 30/30 anyway.

Also if Rockwell disc the tag chambers would be 16/24s.

There is no 24/24 anywhere on a prevo.

Prevo does in fact call left and right different but really they R NOT. They do clamp the 2 halves togeather so that the ports R pointed in the right direction. They precut the pushrod to the correct length and put the fittings in it. ALL these things an off the shelf 30/36 would need to have to have done to it after the purchase probably not an hours time.

So for the novice the extra prevo wants for the chambers is warranted for me not. Again this all pertains to Rockwell disc that U do not have.

Now on to what U DO have.

Knore Bremse. That bottom photo is a drive axle maxi (parking brake chamber) for knore bremse.

Why R U changing that. How have u determined its leaking or is this a proactive service?

I have never seen another vehicle with knore bremse disc brakes besides the Prevo and would not be trying to get parts for that anywhere but Prevo because of that fact.

Take the 30/30 back and tell them they sold u the wrong stuff. THE Prevo with Rockwell disc need 30/36s not 30/30 so those were wrong even if u did have rockwell. Maybe that might get some traction for U otherwise chalk it up as a learning experience.

Be carful seems to me U r treading deep water.

Joe Camper
05-15-2014, 01:42 PM
If they will not take the 30/30 back I will give U 75 for the pair U pay the shipping and we will use them on uncle Harrys Pete. I can get 2 new locally for right around 100 bucks.

Good luck

05-15-2014, 02:14 PM
Hey, Joe, thanks for jumping in here. The 24/24 I got in my head came from the Prevost parts manual where they list the part as "641432 BRAKE CHAMBER ASSY L.H. & R.H. / TYPE 24/24." If they're listing it wrong, they're not helping educate us newbies at all. I am indeed in over my head and easily misled. Since I don't want to take any chances on installing something that isn't right, I was leaning toward just biting the bullet and ordering them from Prevost Parts. You've helped me make up my mind to do just that. Thanks.

You are most gracious in offering to take the 30/30's off my hands. I'll get them to you later. Thank you again.

05-15-2014, 02:23 PM
Oops! I failed to answer a question. Since the coach was built in 1997 and I am assuming all parts are original, I'm just replacing everything to establish a baseline for myself. It's time to do it and consider myself lucky I haven't had a failure that would stop me beside the highway.

Joe Camper
05-15-2014, 02:49 PM
The failure rate on the maxis on the knore bremse that I have seen has been slim to none. Ive only seen 3 or 4 new chambers over the course of time. What I would do if I had knore bremse brakes if I were doing proactive service with factoring in costs.

Id buy a chamber new. Just 1. I'd make it a spare. I would combine that with a strict regiment of doing a pretrip brake inspections every time I started cold and got aired up.

As the bus builds air release the parking brake before the dryer sneezes and stops building pressure. When the dryer does go off turn the bus off with the brakes released (enduring the warning buzzer) (flat ground wheels chocked). Walk back to the rear and listen very close. U want 0 air loss brakes released engine off. If the bus already has brake tank air loss and if u try 2 watch the gauges u need to take this into consideration too . U will be wanting no greater loss than already present when conducting this emergency air test.

This habbit will keep you from "a problem on the road" just the same as putting 4 new chambers in now that may not be nessessary for a long time to come.

When a maxi starts to fail its not "boom" and its done. Its starts leaking slowly and over time gradually gets worse. I had a thread about this somewhere recently.

So say one morning U r conducting this test and shazam u hear a leak starting. U r still not "screwed" U can drive a small leak early on to a service center for repair and hand him your spare.

We R all suppose to be conducting this pre trip brake test anyway. Right? Ya right. Well here is more good reason in addition to safety......money.

Im not sure if the tag axle has the same chamber or not if it did that would be even better.

U have 6 rubber lines on the rear 4 to chambers 2 coming off the carriage. 1/2 in rubber change those.

make sure all the caliper slide pin boots r good replace all those. ( always see the boots bad many rusted slide pins)

Make sure the rubber linkages for the ride height valves r not sloppy or bent over.

Monroe matic shocks.

Weather u r changing pads or not id ratchet the calipers all the way back like U were, just to exercise the ratchets. The ratchets fail, the caliper is junk. I think doing this may help.

Take a good look around, clean paint.

05-15-2014, 11:29 PM
Joe, thanks for all the smart tips you pass on. They're super valuable stuff! Makes good sense to me!

Do you buy hoses from Prevost or have them made up at your local hose shop?

Joe Camper
05-16-2014, 07:18 AM

Some of the chassis have rubber brake hose with aeroquip 2-piece reusable hose ends. If this is the case a 25 ft box of 1/2 in rubber is around 50 bucks and it will be enough to do all of them and have some spare left over.

Some chassis do not have reusable ends and U will either have to buy complete hose assemblies OR get the aeroquip fittings to make the hoses repairable with just the rubber portion.

Recently aeroquip fittings have gotten very expensive 75bucks a piece. Velvac has a brass 2 piece reusable end with swivels for about 1/2 that and serves the same purpose of aeroquip making the repair doable on the side of the road without the necessity of finding a hose shop to make them up.

SO if u have reusable ends (u should on that year)your golden. If not make it so. That's what I do.

If u go to a truck supply trucks R 3/8 hose don't use it. We have 1/2in and the hose ends R 1/2 by 1/2 pipe as well. Keep it that way.

05-16-2014, 12:51 PM
Joe, as usual, you're a wealth of information. Thank you for again contributing to our education.

Joe Camper
05-26-2014, 09:01 AM
Now that Prevo has recently increased prices on the 30/36 drive axle parking brake chambers to 350+ and almost the same for the 16/24s on the tag axle on chassis with Rockwell disc I expect to be doing more and more replacements with 'piggyback" chambers from local suppliers.

A piggyback chamber utilizes the existing original portion of the component with the mounting studs and push rod and smaller service brake return spring that quite regularly does not need replacing saving cost on the parts. We found all 4 for 600 bucks total. They will also save u labor taking slightly longer than 1/2 the time to pull the entire thing.


The bottom chamber is a complete one the top is what u get if U buy a piggyback.


This is what is retained from the old component that remains on the bus when u go piggyback. The only time u would need to replace this is if it is rusted or rotten or the smaller return spring is broken. Sometimes on trucks ive seen these rot out. They sometimes without proper service rot completely out at the studs and fall completely off hanging from the air line. That is on truck chassis that have seen very hard service with very little maintenance. I have NEVER seen anything close to that on one of our motorhomes so this is a great way to keep costs down when doing maintenance in this area.

Ron how did your job turn out??

Joe Camper
05-26-2014, 09:10 AM
Here is another tip.

When removing brass 90s and 45s that r in very tight.


Put a plug into the threads before U exert a great deal of force attempting to loosen it. If its real tight and u don't U will bend and twist and ruin it.

05-26-2014, 03:14 PM
More good info... thanks, Joe!

Joe Camper
05-26-2014, 07:23 PM
Ron I have encountered another air system with very similar woes. 96 chassis
I have a regulator that doesn't respond adjustment consistently but rather is very erratic. I have an exhaust port on the dryer hissing air and also after its turned off too slowly and gradually is goes away. Takes about a minute or so. If u adjust the reg 1 pound over 120 the dryer never sneezes off. The pressure stops building but no sneeze just the hiss of air constantly leaking out the exhaust port on the dryer.

Here's the kicker its recently had a shop replace the regulator and put a new discharge valve in the base and checked the limit valve in the head of the compressor.

Went to my go to guy. He thinks I have multiple problems (I agree) 1 of being the check valves on either the primary or secondary air tanks. Uncle Uncle

The one in the back is not too hard to get at.

The front one I don't know didn't look while the tires were off up there.

Here is what gets me how is it that it can stop itself eventually that doesn't add up for me. Running it will continue to hiss out the dryer not stopping.

Shut it off and gradually after a min. or so sealed up tight?

Splain that.

Someone smarter than I willed to explain that to me. We have 2 valves coming. As for the base of the air dryer. When the other shop rebuilt it, it was not in right and it shot out as air built up they stuck it back in.

These spin on dryers that were suppose to make things easier for service and more cost effective have done just the opposite.

Multiple problems plus potentially someone else's mess. I just don't know

Did u ever get a price on a complete new base or rebuilt on exchange or no.

05-26-2014, 10:10 PM
I had a similar issue with hissing for a couple minutes after shutting the coach off. It was the turbo inlet valve leaking.

Joe Camper
05-27-2014, 07:53 AM
How did u identify that where is it located and how much was it.

05-27-2014, 12:21 PM
Identifying it was easy. I put my hand under the valve and felt the air. It's right next the purge valve. I had my local CAT dealer do the work, so I'm sure the prices were high. The Turbo valve kit was $57.95. If you pull it, it makes no sense to not replace the purge valve, dryer cartridge, and check valve, if it has one. The purge valve kit was $57.74. Both were easily installed. I didn't have the check valve replaced, as I didn't know there was one, if I do I have one. They charged 3 hours for troubleshooting and repair. The actual work didn't take an hour once the dryer was out.

05-27-2014, 09:49 PM
Joe, like you, I have multiple problems. I put the two kits in the air dryer last time. To be sure I didn't contribute to my problems with a less-than-perfect rebuild this time, I swallowed hard and bought a brand new AD-9 from NAPA for $347.91. That stopped most of the singing in the area of the drive wheels, but not all. Close investigation with a medical stethoscope revealed a brake relay on the driver's side has a steady whine at the bottom of it. Discovering that may be the "aha" moment I've been looking for. Since I've mounted my 8D AGM's in front of it, it's gonna be a hassle to change it, but I'll do what I've gotta do.
I've got one small success to celebrate today. I repaired my badly leaking ISRI seat height adjust valve with a generous application of JB Weld. At well over $100, that valve is more valuable per ounce than gold!

Joe Camper
05-28-2014, 07:48 AM
That really amazing Ron. We too had a R14 brake relay on the drive axle leaking out the exhaust port when the parking brake is released also.

We too had bad lines going to the ISRI seat controls.

They (ISRI) sent this "new and improved" rubber line to replace the 1/8 in plastic. This new rubber line is suppose to work without clamps and it does not. There r 2 different sized barbs coming off those switches and that new rubber line will not stay put on the smaller barbs. I thought about putting crazy glue on the rubber hose going on the smaller barbs for now the very small zip ties R on them and time will tell if that will be a lasting fix.

On a side note if we shut off the seat the auxiliary air pressure loss goes down to less than 2psi per hr and that is a tremendously slow rate of loss for aux air.

Just to clarify U no longer loosing ANY air out the base of the dryer accept when it discharges and the discharge is now a quick "sneeze" without any air loss leading up to or continuing after it??

05-29-2014, 12:55 AM
Joe, the clamps on my seat hoses are collars that are slid over the tubes once they're on the smaller barbs. If the collars are missing, I'd use an old trick that works using safety wire. Bend a long flat "S" in the wire, lay it parallel against the tube, then wrap tightly around it and the tube. When done, put the end of the wire through the exposed loop and pull it back under the wrapping so you wind up with each end under the wrap and cut off on the other side. I hope that makes sense. It makes a tight clamp for any size tubing.

After installing the new air dryer, I sprayed soapy water on all connections and replaced the leaking 1/4" push connection with a compression fitting to stop that leak. I get a quick "sneeze" with no more singing before or after and heard no leaks with a stethoscope, however, I stopped short of really soaping up the main exhaust and looking for bubbles there. I'll do that the next time I'm under there, but it appears the dryer is not leaking ANY air before or after the "sneeze."

Joe Camper
06-02-2014, 04:47 PM
Well we just put in the replacement Wabco spin on air dryer base on a chassis that we were told to be a litany of different potential problems. SO before replacing anything else we did that first and U guessed it.
Everything is working perfectly.

The entire thing was 270 bucks that was with tax and shipping. There was a core charge no big deal there.

If your base is original get it out of there if for no other reason than to break free the swivel on the stainless braided line coming from the compressor before it gets so deteriorated U done ever get it loose. I was just barley able to get it loose and get the swivel free without ruining it.

From now on Im suggesting replacing these every 4th or 5th service interval get the entire thing and start a new.

Joe Camper
06-08-2014, 06:38 PM
Sometimes I get e-mail that friends cut and past from other internet forums and this one im going to respond to because I know lots of other pogers participate there, this is a common problem in fact I just straightened out a beautiful Marathon with the same mistake.

Whoever belongs to this bus in the photo someone should get him my number.

Here is the photo and the additional input I think could be very informative for all of us.


Here r some of my observations.

This set of spool valves R on the driver side of the bus. See the line coming up from below on the right valve that is coming up from the rear drive bag drivers side. the line coming out the top of the right valve is going to the drivers tag bag.

This chassis is a 96 so that right valve needs signal air into the end where the small 1/4 in line goes and that means that that right valve is almost plumbed right. Shouldn't have a plug in it. That's all that's configured wrong there.

FOr the record if u have a newer chassis that the tag is configured "logically" the ONLY difference is the bottom 2 lines would be switched.

That left valve is not a Norgren it is a Burkert nobody else seemed to notice that. That is where air is supplied and released for the tag "lift chamber" on the same side. It works the same way and needs the plug removed.

Let me try to shed some light on how this could very easily potentially happen.

Take a closer look at the left Burkert valve and how it is configured very similar to the norgren. 2 ports out the bottom 1 port out the top (look close its hiding some in this pic) and the signal line in the side.

Some, quite a few chassis, r plumbed with a combination of spool valves like this.

The Burkert valves r configured 2 different ways and sometimes prevo will send a replacement that is a burkert for a burkert BUT BUT BUT not the exact same valve. A burket that is configured quite a bit differently. Then guys who usually don't work on prevo get confused and put them in wrong.


Here is the Burkert valve that I think originally came on this bus. It is a 2 position valve just like the top left valve in the first photo and will provide the exact same function.

U see this original valve in this pic directly above has the same small signal line but only 2 bigger ports with threads NOT 3. That's where the rookies get very confused.


The THIRD port on the original 2 position Burkert is a porous stone that is built right into the body of the valve INSTEAD of the 3rd threaded port like prevo often likes to send as replacements. See where im pointing that's port #3 on this spool

Soooooooo schnooks see that "extra" port on the slightly different replacement with the 3 threaded ports and get scared or something and plug it. The original with the porous stone can get real dirty and some may not even notice it while others do but do not figure out what gives.

Another thing about the top photo look at the abomination of fittings on the norgren on the right. Norgrens have 3/8 ports way bigger than the 1/4 in ports on the burkerts. Some nipplehead has reduced down the T from 3/8 to 1/4 in pipe. LOL They have 5 pieces of brass out the bottom left port on the norgren that is duplicating a VERY COMMON 1 piece fitting 3/8 pipe to 3/8 compression branch T.

If the pass side is still 3/8 whats that gonna do to the performance Hmmmmmmmmmmmmmm.

I brought this up more than a few times before about the mix and match spools. About the advantage of going to all norgren when its time to do things in that area. The fact that Burket spools have plastic bodys and 1/4 in ports instead of a block of aluminum with 3/8 ports the norgrens have.

The attaching air lines r short and fastened securely but the conversion is still possible without the necessity of letting everything just hang from the lines like we see in that first illustration.

So in conclusion when U have a chassis with the burkert 2 position valves and have some new ones coming prevo could potentially send u 3 different valves that all will work if installed correctly. A Burket with 2 threaded big ports and a porous stone just like the original. A different burkert with 3 threaded bigger ports or an upgrade to a Norgren 2 position

I know there r enough guys out there that have this stuff have the ability to do repairs and WILL encounter exactly what I have just described SO now u have "the rest of the story"

When the parts come from prevo and the 2 position valve is different U will know just what to do.. call me.

I love U all

Be carful out there boys and girls.

Joe Camper
06-08-2014, 07:31 PM
More tidbits

Here is a "5 port" 3 position norgren. For sake of understanding forget the "5 port" designation. View it rather as a 3 position in relation to the 2 position iIMO its easier to get a handle on this way for the beginner. Another reason for this suggestion is because ALL the 3 position valves have ALWAYS have plugs in port 4 and 5. ALWAYS


Here is how our 3 positions norgrens lay out.

2 small 1/4 in plastic signal lines going in left and right. LEFT is the signal for driving mode when it gets pressure it opens up the bottom left port coming from the ride height valve and flows out the top to the air bags on its corresponding corner.

Right end 1/4 in signal gets its signal when U select that position for level low. It gets air when u either hit the up or down button and it opens the bottom center port coming from the auxiliary air tank and flows up to the top fitting going to the bags.

This configuration of 3 position is the same on everybody and U don't get to say that very often about things on these chassis.

No need for seminars or articles. Threads r just swell

06-08-2014, 08:38 PM
Joe, I follow several forums. In all the posts I've read it is evident to me that when Joe says something about Prevost air systems, it is not only correct but includes the best descriptions I've read anywhere.

Thanks Joe!

Joe Camper
06-09-2014, 08:02 AM
Appreciate that Gill unfortunately there R those who don't feel the same.

A quote from the same page from another fellow.

"There is a guy on another forum that everyone idolizes but over the years he has gotten creative and has not been afraid to modify someone's coach"

An insult like that I can handle I have thick skin


That's either an outright lie or a totally ignorant statement. I have NEVER changed or altered suspension or air components on any bus. For someone to accuse me of doing work like this is an outright lie and defamation of character.

I see it as very rude when it happens and if I were a lesser man also be insulting.

Just took another look at the picture and description of the 3 position I tried to explain. I need to edit that post. I have the dern valve pictured backside out and has everything flip flopped and would be really confusing and difficult to be of help if need be. I can do much better No time now later.

06-09-2014, 09:17 AM
Joe, just consider the source......your post's are very informative....keep up the good work!

06-09-2014, 10:09 AM
Joe, keep the posts coming and don't let the others get to you . You are a valuable asset to POG.

Joe Camper
11-03-2015, 03:08 PM
Did u know.When u r replacing emergency brake chambers and u get them from prevo they r superior to the compatition in 1 way and for the person manning the spanners it's a great big gift.

Let's see who knows what this is difference is? I'll be the judge.