Drum Parking Brake Improvements - Bdub.net

GMC Motorhome Parking BrakeDeficiencies and Improvements25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 1

Objective• Why the OEM park brake system waspossibly designed the way it was ?• Let us look at the OEM park brakeassembly and its various components• Discuss each of the components andhow they might be improved upon25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 2

Lowes / Home Depot type Parking BrakeThe “ Good Samaritan” from Ohio sent this photo !25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 3

“Favorite Wife” Wheel Chock !$14.95 at Camping World and $16.95 “ With Rope Handles”25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 4

Why the OEM park brake system waspossibly designed the way it was ? Although safety was important andsafety improvements were constantlybeing implemented, they werealways done with an acute eye toeconomics.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 6

Why the OEM park brake system waspossibly designed the way it was ?If the GMC Motorhome were to have thevery best of everything that was availableto the automotive industry when it wasbeing built , GM would have probablyhave canned it in ‘75 or ‘76 instead of1978. The overall cost would beenprohibitive .25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 7

Why the OEM park brake system waspossibly designed the way it was ?Corrosion proof components were simplytoo expensive or not available at all . Alsothe automotive market does rely on asignificant ifi portion of their revenuessupplying replacement parts.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 8

Why the OEM park brake system waspossibly designed the way it was ?We GMC’ers are in a unique position inthat we own and drive a vehicle thatstatistically is three lifetimes old, we lookfor the best products available forreplacements and quite often if there is apermanent fix, we’re all for it as long as itis a good value.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 9

Why the OEM Park Brake System WasPossibly Designed the Way It Was ? Warranties and competition back thenwasn’t what they are today. The pursuit ofexcellence in design and materials did notbode well for the bottom line of the “ BigThree”25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 10

Why the OEM park brake system waspossibly designed the way it was ?With regards to our parking brake, it mayhave been designed on a Friday afternoonor Monday morning.However, rumor has it that the handlelocation was chosen by a hung-overengineer working overtime on New Yearsday in 1972.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 11

Why the OEM Park Brake System WasPossibly Designed the Way It Was ? BOTTOM LINE :Our parking brake system is not of substandard materials or design . In fact itfunctioned well when it was new. If allnew OEM components were installed andadjusted properly it would be quiteacceptable even now. Although newerand higher tech equipment exists today atan affordable cost.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 12

From what information I have been able to gatherin the last 5 years, I have basically concluded thatthe OEM parking brake for the GMC currentlysuffers from the following deficiencies:1/ Sufficient force could not be applied to 4 rearbrake shoe sets to ensure a positive braking effect onsay a 6 to 10 percent grade, forward or backward.2/ Due to the ergonomics of the parking brakehandle, or lack thereof it becomes increasinglydifficult for some of us to generate the force requiredto"set" the parking brake properly so it can do itsjob.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 13

Why the OEM park brake system waspossibly designed the way it was ?25/05/20113/ Due to insufficient force being appliedto the 4 rear shoe sets, many GMC'erscomplained that they "drove away" withthe parking brake engaged, perhapstheir "tell tale" lamp was burned out ,or missed! Or the switch failed. This ofcourse leads to all sorts of nastyconsequences regarding brake shoes,drums and bearings.HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 14

Why the OEM Park Brake System WasPossibly Designed the Way It Was ?4/ Even though the OEM park brakeassembly would meet the requirementsof GM and the US DOT in the 70'swhen the assemblies were new, ,properlyp adjusted and "set", it wasn't longbefore corrosion and old age took theirtoll on the system.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 15

Why the OEM park brake system waspossibly designed the way it was ?5/ Because of corrosion issues andaccompanying " oxide jacking" inside thespiral "bowden" conduits, the core cablesgradually became tighter and tighter andeventually seized inside the conduits. This ofcourse caused the brakes not to release andcaused all sorts of headaches for the coachoperator.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 16

Why the OEM park brake system waspossibly designed the way it was ?6/ Since the cost of replacing the originalOEM park brake system with a new OEMsystem is approx. $300.00 , many GMC'ersconcluded " why bother ? ", in 3 or 4 yearswe'll have the same problem with corrosion os oand huge friction issues and have a parkbrake system that we can't trust. Also thewarranty has long expired , typically lasting90 days to 6 months from date of purchase.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 17

Let us look at the OEM park brakeassembly and its various componentsBrake drums and shoesParkbrake levers and strutsShoe bearing padsAuto adjustersBacking plate spring hardwareBacking plate wheel cylinders25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 18

OEM Park Brake Assembly and Its VariousComponentsBrake Shoes :Two differenttypes and twodifferent widthsas well asassorted frictionmaterials.25/05/2011Photo courtesy of Bill BrownHOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 19

Backing plate wear pads:Over time these shoe wear pads takequite a beating, when installing newshoes carefully clean and inspectthese pads, using a zirconia flap discone can generally buff out the worstof the wear damage in severe casesthe pads have been built up usingbrazing rod and buffed flat after ,due to a new backing plate not beingreadily edyavailable. be. Ensure suethese esepds padsare sparingly lubricated with never –seize or a similar compound .Blank backing plate25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 20

Brake shoes• Disregarding friction materials, there were two basicshoe configurations. The 1973 and ’74 GMC used ashoe set originally designed for the 1969 PontiacBonneville S.W. , commonly referred to as a #272 ,The park brake lever hole was very high up on the shoeweb compared to the later and current shoe used onthe 1975 thru ’78 GMC’s ; the #462 shoe was designedfor the 1972 and ’73 Pontiac S.W.• GM essentially recalled all the 1973, ’74 and a limitednumber of ’75 rear brake assemblies and reissuedcompletely loaded backing plates of the newer Pontiacvintage, ie. The #462 shoe set.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 21

Brake shoe• Current shoe type #462 ( Low hole )Note : bottom of parkbrake lever hole in linewith top of piston pushrodnotch25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 22

Brake shoe• Current shoe type #462 ( Low Hole )Note how tang on brakeshoe aligns correctly withthe notch in the park brakelever and that thehorizontal strut is centeredand level. This is a correctconfiguration25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 23

Brake shoe• This is a pre 1975shoe ie. #272 with apost 1975 park brakelever, note the severemisalignment due tothe high hole on the#272 shoe . Thisusually occurs when anew owner doesn’trealize that GM recalledthese assemblies in1975.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 24

Brake shoeThis is a post 1975 shoe ie.#462 with a pre 1975 parkbrake lever, again severemisalignment due to thelower hole on the shoe anda lever that’s too long . Thisscenario would be very raredue to the recall on the oldpark brake levers and theinability to purchase newones.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 25

Brake Shoe / Park Brake Lever Mismatch• The pre ’75 shoe and the current parkbrake lever is by far the most commonmismatch. This type of mismatch willcause severe binding between the crossstrut, the park brake lever and shoe.This will impair parking brake operationand to a lesser extent the operation ofthe service brake as well25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 26

Park BrakeStrut:• Over time the cross strut will wear at both endsleading to excessive play in relation to the PB leverand brake shoe. This will translate t to lost motion inthe PB cable system. With the total handle traveldistance limited to 2.375” , lost motion must be keptto a minimum. With the brakes properly adjusted ;the end play of the PB strut should not exceed1/32” , replacement or building up the worn areas inthe notches will be necessary if wear is excessive.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 27

Auto Adjusters:• The auto adjusters will work if the coach isbacked up with sufficient i conviction i and thebrakes are sharply applied. However the“significant other” will be less than impressedwith the rearrangement of the cupboard andfridge contents. ts THUS: Manual adjustment t isstrongly advised whenever the brake pedal travelapproaches halfway.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 28

Backing plate spring hardware• The backing plate springs are normallyregarded d as passive devices, ie. If theyare there and in one piece, then all iswell. Even if the springs still have thepaint on them, they only have a limitedlifetime due to constant t cycling andheat. They should be replaced at leaston every second shoe change.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 29

Backing plate wheelcylinders• Check for any signs of fluid leakage ,rubber boot damage and excessiveewear of cylinder push rods.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 30

Park Brake Conduits and cables• The OEM conduits are of a “spiralbowden” design, essentially a closedflat wire spring with attachment fittingsat tthe ends. The OEM conduit ithad noouter covering , this is beneficial in thatthe conduit / cable assembly could dryout after being wetted thus helping tolessen corrosion problems.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 31

Park Brake Conduits and cables• The inner cable or “ strand” is a 1 x 19steel cable , 1/8” diameter. Sometimesgalvanized , sometimes not. Thisresulted in a steel on steel assemblyand friction increases mounted quicklyas a function of degrees of bends in thecable system and accompanyingcorrosion .25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 32

Park Brake Conduits and cables• Cable pull friction is a function of thefollowing:1/ Materials being used, ie. Steel onsteel, galvanized cable being rougherthan plain steel .2/ Total number of degrees of bends inthe system.3/ Total load ( pull force ) the cablesystem has to exert.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 33

Park Brake Conduits and cables• Except in very special cases and at therecommendation of the manufacturer ,conduit / cable assemblies are never tobe lubricated. This will only be a shortterm fix and due to dirt and metallicparticles with accompanying loss ofvolatiles in the lubricant, friction issueswill reappear and be worse than beforelubrication.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 34

Park Brake Conduits and cables• New metal to metalconduit / cable assemblyVs. plastic lined conduitsand galv. steel cables.Polished stainless steelcables with teflon linedconduits will performapprox. 50 to 70 %better than evengalv. / plastic25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 35

Park Brake Conduits and cables• Braided stainless steel conduits with teflonliners and polished stainless cables arevirtually “bullet proof” they will last a life timeprovided they are not physically crushed andthat their loading is limited to approx. 600lbs. , ie. A 3.5 to 1 safety factor.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 36

Park Brake Conduits and cables• Front bogie cable guide:OEM guide is extremely restrictive to the frontbogie conduit movement. It should be modified toa similar configuration as seen in the photo on theright or removed completely.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 37

Photo of homemade conduit guide25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 38

Dual Conduit Cable Equalizer• Brake cable equalizer and adjuster for rear andintermediate axle brake cables. One on each sideof the coach, outside the frame rails.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 39

Dual Conduit Cable Equalizer• The dual conduit cable equalizer / adjusterturns the rear most cable 180 degrees andallows it to be connected to the front cable viaa cable connector.• After a number of years the cable will take amore or less permanent set in the equalizerand corrosion between the cable and theequalizer and between the cable strandsthemselves will essentially prevent theequalizer from doing its job of balancing theforces applied to the two joined brake cables.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 40

Dual Conduit Cable Equalizer• To help prevent this problem a number ofpeople have replaced the OEM equalizer witha suitable pulley and yoke assembly. Thereare a number of folk in the GMC communitythat sell these pulleys. One pulley possibilityis the Stanley ygarage g door pulley, it’s aboutthe right diameter. Just seal the small bearingagainst water and dirt.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 41

Dual Conduit Cable Equalizer• Note the stainless return springattached to the pulley yoke.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 42

Dual Conduit Cable Equalizer• The intermediate cable retract springsavoid having to rely on the individualid conduit springs to help pull back theintermediate t and brake handle cable,thus ensuring positive release of brakeshoe tension when the PB handle isreleased. Together the two stainlesssprings apply about 35 lbs. pull backforce on the above cables.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 43

Thru – Frame Routing PulleyOne of these pulleyson each side of thecoach to replacethe old “S” hooks.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 44

Thru – Frame Routing Pulley• Pulley isReplacement forthe OEM S-hook,pulley mainlyadded forstrength25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 45

Thru – Frame Routing Pulley• The keyhole slot inthe frame is toprovide clearancefor the union on theintermediate cable.The OEM slot isapprox. 3/8” inheight , whereas thenew slot is 9/16” inheight.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 46

Thru – Frame Routing Pulley• This union is not to be taken apart. Astainless steel cylinder has been swaged ontothe cable inside the union to supplement thestrength of the two ¼” Allen set screws.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 47

Thru – Frame Routing Pulleyul Warfield 037r1.j• But all is notlost ! When youbuy a new framefrom the “ FrameDoctor” the enlargedslots are includedabsolutely free ofcharge !25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 48

Intermediate Cable• The OEM intermediate cable was supplied in twolengths , to accommodate the 260’s and the 230coaches as well. Presently there is only onelength available to the best of my knowledge. Ifyou own a 230 coach be prepared to tie a fewknots in the cable to shorten it up by therequired 40 inches. However the new stainlesssteel intermediate cables come in both lengths !IntermediateCable union25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 49

Intermediate Cable• OEM equalizer to connect intermediatecable to park brake handle cable25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 50

Intermediate Cable• This is the wrong equalizer to use underthe coach where the PB handle cableconnects to the intermediate cable25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 51

Intermediate Cable• In the previous slide the equalizer bar isfor the dual conduit cables on the sideof the coach. With the angles formedby the cable routing , one would have afixed point equalizer. One canexperience differences of 300 to 400 %in pull forces between the two sides ofthe coach if the cable is old andsomewhat corroded.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 52

Intermediate Cable25/05/2011Premium OEM The “absolutelyEqualizerEqualizernot” equalizerHOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 53

Intermediate CableWill balance left and right pull forces to less than10 % , a 2 to 3 times improvement over OEM Eq.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 54

Park brake lever25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 55

Park brake lever• Due to State and Provincial DOT regulations andcivil litigation issues it would appear that we arestuck with the OEM park brake handle and itslocation forever. I have spent days talking tovarious state and provincial DOT authorities andthe vagueness of their answers was onlysurpassed by their number of times theyrequested “ please leave a voice message” theirgeneral response would make most politiciansiproud.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 56

Park brake lever• To “set” the parking brake properly and toachieve the most effectiveness, one shouldobserve the following:1/ Step firmly on the service brake pedal2/ Attempt to rock the coach slightly ahead orback in “D” or “R” depending whether thecoach is descending or ascending a grade.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 57

Park brake leverDon’t underestimate the effectiveness of theBendix duo servo brake system! Make itwork for you . It’s “all in the technique” as Iwas reminded by an experienced GMC’er whoobserved me slamming my coach door.3/ Apply the park brake and try to move thecoach under moderate power. It should notmove.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 58

Park brake lever• One should attempt to keep a ¼”adjustment t remaining i on the PB handleadjustment knob. If less than thisamount of travel is remaining, i then oneshould readjust the cables at theequalizers on the side of the coach.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 59

Park brake lever• Relating to our original objectives in summary:1/ The mechanical aspects of the brakedrum and shoe assembly must be addressed.2/ The cables and conduits must operate freelyand be free of corrosion.3/ The correct technique must be used in applyingthe park brake.25/05/2011HOW ABOUT A GMC PARKINGAND EMERGENCY BRAKE ? 60