TideLog Posts Tagged “fixes”

I recently had to overhaul the steering system on Rikku’s B7R coach after it hit a very bad pothole, shattering the track rod & link rod balljoint cups. Here’s an article on my most common steering problems, causes and remedies. This article covers all Volvo coaches and buses with recent power steering systems, such as the B7R, B7RLE, B9TL, etc.

NOTE: If balljoints, joint cups or sealing rings are damaged the system should have parts replaced. NEVER repair damaged balljoint systems, as they will simply fracture again. Never re-use or repair gaskets, they are single use only. When inspecting, ideally you should steam clean or wash the steering system completely and use an infrared detector and magnifier to detect hairline cracks in the WHOLE system, including hubs and hub bearings as not all damage is obvious to the naked eye. Seizure of the hub shafts can result in a wheel coming off and a serious accident occuring, I have seen hubs sheared straight off due to fatigue at the hub shaft and the bus/coach has lost a wheel at speed when it finally gives way.

WARNING: This article is for EXPERIENCED mechanics familiar with bus steering systems and Volvo Impact software. You MUST ALWAYS follow Volvo’s guidelines for repair, bolt tightening torques, and always use GENUINE parts. Vehicle and passenger/driver safety can be compromised otherwise as the steering is a critical function of the bus that should have its safety and reliability maintained.

The steering and suspension of a bus comes under EXTREME stress under load at normal use due to bumps and uneven surfaces, NEVER overlook things that don’t feel right in terms of handling. This article only gives general guidelines, it is up to your judgement and professionalism as a mechanic to carry out the work.

Steering stiff in both directions

Cause Remedial actions
Oil level too low, or drops continuously when filled. Check and find any leakage in system and hoses/attaching bolts.Fill with oil and check the level of the reservoir. If the oil level continues dropping after being filled this is certainly a leak.
Air in hydraulic system. Check the reason and bleed the system.
Oil pump control valve sticks or oil drilling clogged. Disassemble and clean the valve and replace if necessary.
The filter is clogged. Ducts are obstructed. Change the oil filter and clean the ducts.
Universal joint hard to move. Check for interference.
Valve plunger stays open or leaks. Remove the plunger from the valve. Replace the plunger set.
The sealing ring at bottom of plunger not sealing. Replace. DO NOT attempt re-use or repair!
Plunger sealing ring damaged. Replace. DO NOT attempt re-use or repair!

Steering stiff in one direction

Cause Remedial action
Pressure limiting valves leaking. Replace the valves. For safety DON’T attempt repair, they are designed to be replaced.
Pressure limiting valves open too early. Check adjustment and adjust as necessary. Refer to Volvo Impact software for procedure.
Plunger sealing rings damaged. Replace. DO NOT attempt re-use or repair!
Cylinder lower chamber without pressure. Replace all sealing rings. DO NOT attempt re-use or repair!
Cylinder upper chamber without pressure. Replace all sealing rings. DO NOT attempt re-use or repair!

Steering heavy with rapid steering wheel turns

Cause Remedial action
Air in the hydraulic system. Check the reason and bleed the system.
Oil pump control valve sticks or has the oil drilling clogged. Disassemble, clean and make sure the valve works freely.
Servo pump oil flow low. Repair or replace the pump. Replace any sealing rings or gaskets. DO NOT attempt to repair rings or gaskets, they are single use only!

Stiff steering return

Cause Remedial action
Steering column shaft not lubricated or damaged. Lubricate, and if damaged with scratches or pits, replace the column shaft assembly.
Steering column not fixed properly. Check attachment and fixings, tightening as necessary.
Interference between spindles on fixing sleeve. Adjust.
Pressure point set too hard Check adjustment

Difficult to hold straight course

Cause Remedial action
Oil level too low. Check for leakage, top up the reservoir with oil.
Air in hydraulic system. Check for leakage and bleed the system.
Looseness in steering system Tighten the loose parts to correct torque settings given in Impact software.
Ball joint with excessive play. Replace. DO NOT REPAIR OR RE-USE DAMAGED BALLJOINTS, this is CRUCIAL for safety!!
Loosened connecting sleeve. Tighten the sleeve.

Impact felt in steering wheel

Cause Remedial action
Oil level too low. Check for leakage, top up the reservoir with oil.
Air in hydraulic system. Check for leakage and bleed the system.
Excessive play between worm shaft and piston. Check and adjust the worm shaft. If damaged with scratches, replace it.
Excessive play between sector shaft and piston Check and adjust pressure point.

Steering wheel vibration (Shimmy)

Cause Remedial action
Wheels unbalanced. Balance the wheels according to type of tyre and wheel manufacturer’s guidelines. This MUST be done correctly, as an unbalanced wheel puts stress on the wheel hub and shaft, possibly resulting in it shearing clean off with the wheel on prolonged use.
Steering out of alignment. Disassemble, clean and reassemble the steering using Impact software guidelines. Check it works freely and test extensively.

Steering wheel independently goes to either side (pulls)

Cause Remedial action
Oil level too low. Check for leakages, top up the reservoir with oil.
Air in hydraulic system Check the reason and bleed the system.

Oil leakage

Cause Remedial action
Reservoir cap loose Fix the cap or replace if worn/damaged.
Servo pump shaft sealing ring leaking. Replace the sealing ring. DO NOT attempt re-use or repair!
External leakage in power steering Replace sealing rings. DO NOT attempt re-use or repair!

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