msham87 Report post Posted March 31, 2014 I have a 2000 Forest River Reflection Class A motorhome with a Spartan chassis and air over hydraulic brakes. When engaging the parking brake (by pulling the yellow dash button), I hear air being discharged which seems to indicate the engagement of the brakes. However, the brakes do not seem to fully engage and on a slope, will not hold the motorhome. The brakes on the motorhome were replaced less than 5,000 miles ago and have only been used on long distance travel. Any suggestions? Share this post Link to post Share on other sites
dickandlois Report post Posted March 31, 2014 msham87, Welcome to the FMCA forum! Air over hydraulic brakes use compressed air to increase braking. Have you noticed any decrease in your road braking? An increase in the fluctuation of the air gauges? The parking brake valve applies air pressure to the booster cylinder, this applies the brakes. Much the same way as when you press the brake pedal. Any air leaks or a compromised / failed booster cylinder would directly result in a loose of park brake holding power. Rich. Share this post Link to post Share on other sites
msham87 Report post Posted March 31, 2014 Thanks for your reply. In-motion braking has been fine and air pressure readings have been consistent. Both front and rear pressure gauges drop by 5-10 psi when brakes are apply but quickly return to normal range of 120-125 psi in the normal recovery time of 20-30 seconds. Your suggestion about a compromised or failing booster cylinder might help. Am I correct that this cylinder comes into play when using the parking brakes but not when using the in-motion brakes? Share this post Link to post Share on other sites
dickandlois Report post Posted March 31, 2014 Correct. This is a link to some common system layouts that might help. They are generic in nature. https://www.google.com/search?q=Air+over+Hydraulic+parking+brake+system&tbm=isch&imgil=_ULBNQZg_izFOM%253A%253Bhttps%253A%252F%252Fencrypted-tbn1.gstatic.com%252Fimages%253Fq%253Dtbn%253AANd9GcQGCPdnqKbPczyW9q8dr9uR8oii4J_y01sprDrbKnmOvbJ3uo5dcA%253B313%253B199%253BPS0bmaN-7NhoEM%253Bhttp%25253A%25252F%25252Fenginemechanics.tpub.com%25252F14081%25252Fcss%25252F14081_90.htm&source=iu&usg=__G2zGZYwQJG9fSEkqmRj3znQfY-0%3D&sa=X&ei=gtM4U9GLEunR2wW7t4CwDQ&ved=0CCkQ9QEwAA&biw=1366&bih=598#facrc=_&imgdii=_&imgrc=cHXxy7kqKusTfM%253A%3BPS0bmaN-7NhoEM%3Bhttp%253A%252F%252Fenginemechanics.tpub.com%252F14081%252Fimg%252F14081_90_3.jpg%3Bhttp%253A%252F%252Fenginemechanics.tpub.com%252F14081%252Fcss%252F14081_90.htm%3B647%3B358 Rich. Share this post Link to post Share on other sites
dickandlois Report post Posted March 31, 2014 msham87, This link might help if you have disk brakes. http://www.axletech.com/resources/service_manuals/pdf/MM_9902.pdf From your information your coach has hydraulic brakes with air assist / air cylinder that locks the brakes until you release them. To do this there are two separate cylinders, one for the boost and one for the park brake. They can be one assembly or 2 units located in different areas but connected to the common hydraulic master cylinder. Rich. Share this post Link to post Share on other sites
dickandlois Report post Posted March 31, 2014 msham87, After you read the information, think you will better understand why I as if the brake pedal system was stopping the coach properly. The manual will give you a list of tests to check the entire system. Chassis manual - covers Air brakes on page 5. for most of it. http://hmcmotorhomes.homestead.com/files/2011_Manuals/Spartan_Manuals/Spartan_Manual.pdf You will see that the proper operation of the Park, Emergency and foot operated brakes are all dependent on the adjustment of the wheel brakes and how the braking system(s) are integrated. Still looking for the air line plumbing drawings for the Spartan Chassis. Rich Share this post Link to post Share on other sites
dickandlois Report post Posted March 31, 2014 msham87, You mentioned a 2000 Spartan Chassis. This is a link to the parts list and plumbing for the air brakes on the 2000 EC and WC series chassis for 2000. This might not match perfectly, but should get you into the ballpark. Page 24 PDF file-pictures the Plumbing and a parts list of both the Hydraulic and Air cylinders and there apx. locations. SECTION 3 Page 4 in the manual http://truckroadservice.com/barth_attachments/EC-2242-Maint-Manual.pdf Rich. Share this post Link to post Share on other sites
bcdoghunter Report post Posted July 29, 2015 Had to reply to this one . I had this problem on a 2000 Reflection . I found the bracket on the transmission that holds the parking brake "works" had loose mounting bolts. Tightening those fixed the brake and a transmission leak. Share this post Link to post Share on other sites
desertdeals69 Report post Posted July 30, 2015 Is the park brake on the end of the transmission? If it is the air releases the brake and it is activated by a spring not air. Share this post Link to post Share on other sites
obedb Report post Posted July 30, 2015 Air over hydraulic? Gotta be kidding me. Really?? Sorry but who thought that up? My apologies to the poster having the problem, but the motorhome industry never ceases to amaze me. Share this post Link to post Share on other sites
desertdeals69 Report post Posted July 30, 2015 Air over hydraulic? Gotta be kidding me. Really?? Sorry but who thought that up? My apologies to the poster having the problem, but the motorhome industry never ceases to amaze me. My Spartan chassis had air over hydraulic brakes originally, which is not that uncommon. I have since changed my suspension to air bags and brakes to full air brakes. Since I removed both the air actuated master cylinders I have repurposed one of them to my tow dolly and got rid of the surge master cylinder so I don't have the continual brake on going down a long hill. Share this post Link to post Share on other sites
obedb Report post Posted July 30, 2015 Desert Deals/ You must be quite the wrench. Wish that I had those skills. I think of myself as a better than average shade tree mechanic (amateur). Won't bore you with some of the stuff I have done over the years, but the body is not as willing as in years past. I really have not heard of air over hydraulic. We had big 4 wheel hydraulic disc brakes on our Oshkosh chassis, and managed the Rockies OK. I am really happy to have full air drum brakes now. Share this post Link to post Share on other sites
bcdoghunter Report post Posted July 30, 2015 The parking brake is on the transmission output . Pulling the yellow dash knob dumps the air from an actuator , allowing a spring to set the brake. Share this post Link to post Share on other sites
bcdoghunter Report post Posted July 30, 2015 I would add that the 4 wheel disc air over hydraulic work fine. They just use air pressure instead of vacuum because of the diesel engines lack of engine vacuum. Share this post Link to post Share on other sites
obedb Report post Posted July 31, 2015 Well, if it is just the parking brake, than I see the value of that. Air pressure releases the parking brake. Makes sense. That way a loss of air pressure will not allow the unit to roll if parked. There have been air pressure released spring brakes, on trucks for many many years and also on air braked vehicles of other sorts including DPs. The change over to air released spring brakes on 18 wheelers started in the sixties. It is a much safer system. I remember 18s without them/ scary when I look back. Share this post Link to post Share on other sites
