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Old 08-20-2011, 11:38 PM   #1
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Meritor Braking Improvement

There are several posts about Meritor Brakes. I used the Chevron Syn fluid in the hydraulic system . I flushed the brake fluid and put in DOT 3 and could notice no difference. Then I looked at the length of rubber brake hose WRV installed. There was a total of 13 feet on the front and rear. That is lot of hose to expand every time you step on the brake. I didn't like the way front hoses were on top of the king pins either. I decided to replace them stainless steel braid teflon hose.

I did find a quote from a hydraulic engineer that explains this very well.

"While the steel (or other material) braided over a hose liner does serve to protect the liner, its primary function is to _reinforce_ the liner. A plain Teflon tube will only take a small amount of pressure, and tends to kink very easily when flexed. Adding braid creates a hose capable of handling very high pressures, and actually improves flexibility somewhat.

The hose wears out when the braid wires fatigue or corrode, or if it is damaged. The Teflon doesn't age, and is unaffected by brake fluid (and just about everything else). The Teflon hoses are favored in high-performance applications because (a) they have an effectively infinite working life, if the proper hose is properly installed, and (b) the Teflon liner doesn't "give" under pressure like a rubber liner does, so hydraulic systems function more crisply and efficiently.

In racing, military, aircraft, etc. applications, hydraulic hoses and systems get pressure-tested, typically to 1.5 x working pressure, on a regular basis to find bad components before they fail in service.

The pressure-testing on your Bus happens every time you step on the brake pedal... and the consequences of failure could be dire. DOT certification gives peace of mind for a couple of reasons: you can be sure that the hose has the correct pressure rating for your vehicle, and is sufficiently high that failure is extremely unlikely; the manufacturer proof-tests the hoses to verify that they will take pressures well in excess of what they will see in your vehicle; and if there's a failure and an accident results, the manufacturer has liability insurance.

If you want to specify a Teflon / SS hose assembly to use for your brake lines, then by all means be sure that you get them from a reputable supplier, and that they are tested at proof pressure. There are plenty of little shops around that will slap together hose assemblies of very poor quality, and I'm sure you'd agree that it's not worth taking chances with your brake lines. Teflon hose assemblies are quite a bit trickier to build than are rubber hoses."

I did have a DOT certified hose supplier make and test them. I did blow them out good before I installed them. All hose and fitting were new except they reused the banjo that bolts to the Caliper. There are two thick copper washers on each side of the banjo that I couldn't find at all the major brake supply houses. I did check with Meritor and they didn't supply them to WRV. Just save them and reuse them. Had to make a couple brackets to keep plenty space from the wheel. The front ones I made about the same length since these Alpine's do turn sharp. I did check the turning when I was finished. The rear lines where they come off the frame were a little hard to get to because of the Aqua Hot exhaust. Cost of the lines was over $300 for the material.

I did this 1 1/2 years ago and this greatly improved my braking. I did get a chance to give it a severe test on I-5 in Seattle. I was in the right lane and there was a car stopped on the shoulder. Without signaling or a accelerating pulled out directly in front of me!!!! All I could see is a white roof. I stood on the brake pedal and I was surprised how quick I stopped and I didn't hit the
idiot. In the rear closet with the 6 foot rod across the the back, it threw all the hangers with clothes off the rod against the doors. The front sliding windows which weren't locked slammed all the way open. Can't remember what else flew ahead. For me stainless/teflon lines greatly improved my braking!
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Old 08-20-2011, 11:41 PM   #2
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Old 08-21-2011, 02:47 AM   #3
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Since we've just been 'Round the Horn on Jake Brake, this is the perfect topic to come next.

Kraig- what shop made up your no-longer-new brake lines, and how did they reuse the banjo (it looks to me like its crimped on the hose end)? Sounds like a worthwhile mod.

I know of two Apliner's who have modified their bell-crank that sets between the brake pedal and the Hydro-Max. One moved the lower pin closer on its original offset plate to the vertical spindle pipe by about 5/8" changing the bell-crank from a 1:1 (top offset from the brake pedal to spindle, lower offset from the spindle driving the HydroMax), to a ~1.3:1 or maybe 1.5:1 leverage. Bada-Bing, improved brake response. He angled the HydroMax to maintain the correct actuator geometry, accomplished by shimming out the forward two bolts holding the hydromax to its bracket w/about 1/4" of stacked washers.
The other bell-crank modifier IIRC ground off the OEM lower offset plate, and welded on a new one w/the actuator pin located about the same shorter offset from the spindle as the first guy (~5/8"), and then ovaled the HydroMax mounting holes to slide the master cylinder forward the 5/8" on its mounts (no shimming required) to maintain actuator geometry.
Both drivers report satisfactory brakes after long frustrations of inadequacy.

Just heard a couple days ago from another Alpine hot-rodder who can't leave OEM stuff alone. His brake frustrations took him to a truck shop in San Diego area w/a sort of Yoda-like brake sage. The sage's advice- "You've got the wrong master cylinder sonny. You've got the 2" bore HMax (you can see the bore diameter cast on the steel cylinder, it says 50.80 which is 25.4mm x 2 or 2" for us dummies which they could have cast on the cylinder so I don't have to do higher math), and you should git yerself the 1.75" cylinder." Preliminary tests and the driver reports about 30% better brake response out of the box (which corresponds directly to the ratio of 2" cylinder area to 1.75" cylinder area). The actual master cylinder portion of the HMax is the right-hand (for under the gen cap HMax rigs, and forward facing for under the drivers floor boards rigs) black painted portion w/4 bolts holding it to the aluminum housing of the boost section of the HMax assembly. On the 04+ M.Y. rigs it has the Dot3 tank on top of it. The driver changed it out himself, then bled all 4 corners inside & outside bleed screws. He reported the bleed process took a long time, but Voila! better brakes.

My theory takes us back. Way back, to maybe 1997-ish. In my collection of trash bequeathed to me from Cummins NorthWest is a stained, partially illegible, hand drawn partial hydraulic schematic. I asked Mike Young what that was all about. CNW participated in a recalibration of the hydraulic system somewhere in those earlier years with WRV personnel, necessitated by early death of some air compressors. Seems too-high strain on the compressor shafts from the hydraulic pump (which is mounted on the forward, for us (rearward for Cummins since the engine in a pusher is mounted backward according to them) making unnecessarily high pressure. Fix was to put the rig in the shop and tune the pump output down by shimming, which relieved strain on the compressor's shaft. Future pumps were supposedly ordered pre-shimmed to make the correct, somewhat lower pressure.
Fast forward to 2007, Cedar41 had a brake problem where when he started the engine & the brake pedal depressed 1/2" partially applying the brakes (and overheating his fronts after not very long down the road, and probably using up a lot more fuel). Turns out his hydraulic pump was over-pressuring the system and auto-applying the brakes; new pump and Voila! back to good again.
Fast-forward some more to 2011, I'm test driving the heck out of some Jake Brake issues, and I notice the hiss coming from my steering gear at idle RPMs, which goes away w/even very slight rise in RPM. So I put 2+2+2+2 together to make 4, and codger up a theory. Hydraulic pumps are not all sent out of the factory the same. As you can see, its a pretty complicated theory, which explains why it took me 4 years to codger it up. My pump is mounted on a PTO off the transmission (I think all ULSD-Only engines received this new setup), so for it to be different in output than the compressor shaft mounts is easy to surmise. But the earliest units (which were likely all the same pump model) needed tuning, so maybe mine does also.

Sooooooooooooo, my bottom line is I think my rig isn't making enough hydraulic pressure to properly boost the 2" cylinder, and maybe that's the trouble w/the various, random Alpines that report hard-to-operate brakes. I have some hydraulic pressure gauges, but I may need a flow gauge also. I have the R.H.Shepperd steering gear spec (2175 psi max, 3-5gph) and the HydroMax spec for input some place (1000psi and some flow er other IIRC). Placing one gauge before the steering and one after should tell me if the HMax is getting correct feed and steering also. Just need to hunt down the equipment and get some hydraulic fluid all over myself to run the test.
Motorhomes are great!
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Old 08-21-2011, 11:46 AM   #4
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Thanks guys for the very interesting modification work on the brake system!

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Old 08-21-2011, 12:56 PM   #5
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Yes, I agree with Beagle, please post the manufacturer of the brake lines for us, so we can get those in my database of parts places.
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Old 08-21-2011, 03:09 PM   #6
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Mike, thanks for all the info.
Premier Rubber and Supply
9841 N Vancouver Way
Portland, OR
503 285 4697
I don't store my M/H here to look at it. As I remember the fitting was brazed to the banjo and then crimped to the hose. After I installed and bled the brakes, I constantly checked all the connections for leaks and checked my master cylinder to make sure it was full. No leaks at all.

I have the same PTO driven pump, but I don't notice any noise, but then again I don't hear well.

Might as well post that I had to replace the the what they call the brake pump and motor only because it had a slight leak. It is a Haldex brake pump and motor. You can get them new or Rebuilt which is $75 cheaper. Rebuilt #RV2771494X for $257.Only problem was it seals with 2 o rings which were the wrong size in a sealed box. Made no difference in the braking.
Brake Systems Inc
2221 NE Hoyt
Portland OR
503 236 2116

Only other thing I didn't post was rubber brake hoses are supposed to absorb moisture, but I haven't checked it out.
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Old 08-21-2011, 05:47 PM   #7
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Kraig- is that the 12V pump mounted below the HMax assembly?
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Old 08-22-2011, 03:14 PM   #8
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Mike-Yes, that is the 12 volt pump you hear when step on the brakes with the key off and is the back up pump to give you brakes, if you loose your hydrauic pressure.
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Old 08-22-2011, 10:18 PM   #9
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OK, so what if you don't hear anything when the key is OFF and you step on the brake pedal? All I get it about a inch push on the pedal and nothing else. With key ON, I get the motor sound and the pedal goes down further.
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Old 08-22-2011, 11:01 PM   #10
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David- Let me check the key position again.
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Old 08-25-2011, 06:10 PM   #11
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David- I just checked mine and brake aux-boost growls w/key-OFF or key-ON-engine-OFF. Yours should do likewise. IIWMI'd get the brake's electrical feed rewired to come off unswitched 12V.
As soon as there is hydraulic fluid flowing (flow switch on HMax senses that), the relay cuts the small pump out of the loop, so either way your brakes should act normally. Right now if you dog should jump on the Haldex parking brake release and pop it down (off), coach would roll and you would have limited braking. That's the reason it should be wired off non-switched 12V source. Should be easy to do as unswitched 12V is readily available up front.
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Old 08-25-2011, 06:57 PM   #12
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Soooooo, I had hydraulics tested at Berendsen Fluid Power's West Sacramento, CA shop this morning. It didn't test well. Instead it tested so incredibly close to spec, I was amazed!!! Ran steady at 5gpm flow, valved nearly off it releases at 2000psi (steering max is 2175), and stepping (damn hard) on brake drives it up to 1050psi or so on a 1000psi gauge (HMax spec is 1000psi). Test took 1 hour shop time, $90. Lost maybe two tablespoons of fluid.

Conclusion- hard pedal is no fault of hydraulic setup, its all in the linkage & master cylinder itself, plus losses in lines as discussed above. I.e. its all brake system components. I'm making an 08+ hydraulic schematic that should help others down the road as a result of the info I've collected.

So I'm thinking through the next steps:
~ changing master cylinder takes a full system bleed
~ changing brake line flex jumpers takes a full system bleed
~ monkeying w/the linkage lever arms takes some de-machining, machining, and welding

Here's the result of one brave soul's brake pivot alteration:

View is looking east from northwest corner of coach, along HMax centerline (black pleated boot is the rubber boot over HMax actuator arm, that applies the push to brakes. Pivot in fore ground is the bottom pin on the vertical pivot assembly; upper pin comes off brake pedal. The hole is where the pin was previously. Owner slotted the mounting holes for the HMax to slide it forward on mount (leftward in this photo) to keep the push-geometry linear. IIRC it was about 5/8" on a 2-9/16" overall (I just measured that last), for an increase in leverage of 24%.
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Old 08-25-2011, 08:02 PM   #13
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Here is a photo of the 1.75" Hydromax Master Cylinder vs. the stock 2":

the 1.75" came w/two fluid compartments that are separated, so you have to deal w/two tanks (one for front, one for rear). The OEM 2" has a single tank for front & rear. You can see the casting on top of the 2" (left top of right hand unit) where the second cap would go if similarly finished off. And you can see the difference in the casting diameter of the cylinder.
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Old 08-25-2011, 11:42 PM   #14
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David- Mine is wired the same as Mike's.
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