got to my place of work thursday morning ,hoping to start working on a dennis dart bus i was carrying out safety inspection on and preparing for Mot and rectifying defect found,when i notice the allison automatic gearbox leaking fluid through the seal by the gearbox pump and torgue converter. anyway i was just about to start my day when the enginner manager told me one of the buses under my care to maintain is faulty that the compressor is not building up .
took some tools with me,start the engine,build up the air pressure but the warning light in the dash is still on, and the rear brakes is bind.the bus was a mercedes vario 814dmodel,engine type om904la.
undone compressor main pipe,start engine again,compressor building air pressure of about 165bar,which is very good to fill up the air reservoir and activate every air valve or unit in the vehicle.anyway i notice the binding was only on handbrakes,there was no air going to handbrakes system of the vehicle,and the passenger entrance door,which i know always operate with the handbrake on most occasions is not working either.
did replace the quick release 4way valve,but the problem was still there , i knew it was not electrical fault so i didnt go there at all,check the handbrake control valve pipes there was no air there,check the main pipe to the air dryer valve or unit ,then i notice there is enough pressure going in but not enough going out to feed other part of the system,especially the pressure regulator valve that control the part of the handbrake chamber ,air going into the regulator is not coming out from the other part to feed to the chambers.
so i had to replace the air dryer valve or unit.
defect rectify, drive the bus onto a ramp to complete my work. Anyway back to my previous work of the day , vehicle alright on a ramp, disconnect the battery,drain the coolant,took the coolant pipe off completely from the radiator and cooler,because it run behind the gearbox to the cooler.undone exhaust manfold down pipe to create more room,disconnect starter motor lead/wires and undone bolts,place on the floor,disconnect the speedo cable,gear selector linkage and cable, secure it to the chassis cross member,undone fuel return and main pipes that run on top of the gearbox, because it can be easily be broken,unplug the reverse gear switch,undone propshaft bolt,secure it to cross member.return a cover by the starter motor housing on the engine offside, undone the torgue converter bolts on the flywheel backplate but be careful not to drop any bolt because it will fall behind the flywheel and you end up remove the flywheel just to retrieve it.Anyway undone gearbox box and mounting bracket bolt,position hydraulic jack,gearboxsecure,pull gearbox backward fully , torgue converter came out easy with gearbox, lower hydraulic jack down ,move out to good place to work on, seperate torgue converter from gearbox,inspect it ,found that the bearings inside has collapsed and have fool the oil seal on the gearbox , get a reconditional torgue converter from the part store, replace the oil seal on the gearbox without taking the pump apart.
refitted converter to gearbox and mounting of gearbox to engine fasten all bolt and converter bolts and all other parts was refitted and added coolant,start engine refill and top up gearbox with ATF fluid,leave engine running to raise the gearbox ATF fluid temperature,top again, road time bus , no leak was found.
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