Power-assisted steering, Control Valve
The power assistance of steering (hereafter, PAS) is operated by the oil pressure of hydraulic system. The flow distributor (hereafter, FD) supplies the oil pressure to the PAS system as long as main suspension and braking system hydraulic circuit works with certain oil pressure. If the oil pressure to the latter circuit goes down by some reason, the FD stops to provide the oil pressure to the PAS hydraulic circuit. It brings on "non power-assisted steering". The hydraulic system of the BX gives priority to the braking and suspension system.
When the main system and FD function normally, the oil pressure from FD is distributed from the steering pinion gear and control valve (= pinion valve) to two chambers of the power cylinder. The power cylinder is operated by the oil pressure right and left at the steer, and the steer power is assisted.
Pinion valve is divided into 3 rooms with 5 oil sealings and distributed hydraulic oil passes through each room. If the 3 sealings inside of them are deteriorated, those 3 rooms will not be divided well. Consequently, feeling of steering becomes very heavy as if it were freezed. It comes on the one side; we have some user's reports on the left side. Last symptom is typical model caused by deteriorated sealings.
When you feel steering heavy anytime, it is not easy to specify the cause. It happens by the deteriorated flow distributor, the power cylinder, steering gear...etc.
If the oil sealings which are at the top and bottom of the pinion valve become worse, LHM oil will leak from there. Concerning the top side, you can check the leakage by eyesight. However, leakage from the bottom side occur in the rack. In this case, LHM oil may leak from the steering rack gaitors.
Reconditioning of the pinion valve
Following is how to break up a pinion valve and replace oil sealings. It seems impossible to recondition the metal parts except bealings.
- Pinion valve repair kit
Repair part No. 95 669 033
silicon grease, snap ring pliers, vinyl tape, polypropylene plate(70x100x1 mm),
hose clamp(35 mm), plastic hammer ...etc
- Remove the valve body from its housing. Put it on the vice indicated in the figures. Strike the shaft by plastic hammer. The valve body will come off.
- Remove the snap ring and the oil sealing which are on the top of housing.
- Remove the oil sealing of steering rack side. There is no snap ring this side. Flat side faces outside. Do not forget it when reassembling.
- Remove 3 pieces of sealings from the valve body. Although there are 4 diches, oil sealings must be fitted into 3 of them as indicated in the figure. Pay attention to it.
Make clean the valve with part-cleaner after sealings are detached.
- Grease new sealings and the valve with silicon grease. Assemble them with a pick-up tool.
Note that this sealing is fragile and hard to restore to the original state.
It is quite different from usual O-rings. It seems to be made of carbon rubber. Please handle the sealing gently in order not to damage.
After you assemble the sealings, they must be expanded as indicated in the figure; it is inevitable. They will not be restored to the original state if you wait. You have to shrink them to let the valve
insert into the housing.
Following is the method we took.
- Bind up the sealing tightly with vinyl tape about 3 rounds. We used transparent vinyl tape in oeder to make observation easy.
Wrap the valve with polypropylene plate. Fix it with with a hose clamp. Do not fix it too stlongly to avoid the sealings transform where hose clamp is piled up. Note that the sealings will be swelled up at the gap where the hose clamp is piled up.
Turn the clamp half round per about half a day. The sealings will shrink almost enough in about a day.
- Remove the plate and vinyl tape and grease the sealings with cilicon grease. Insert
the valve into the housing till the bearing attaches to the entrance and leave it about an hour.
- Remove the valve from the housing again.
- Install oil sealing into the bottom of housing. Push it with a suitable socket etc.
- Install upper oil seal and the snap ring into the housing.
Silicon grease will make this work easy.
- Before assembling the valve, stuff molybdenum grease from the housing side of the bearings and make get to fit it by rotating the bearings.
- Re-assemble the valve body into the housing using plastic hammer.
Stuff molybdenum grease from the rack side of bearings after assembling.
- Attach the shaft cover at the top of valve.
Refer to this section about the removal of the pinion valve.
(C) Yohsuke NARABAYASHI
Translate: Tomio NOGUCHI