Power steering slack/adjustment on BMW E28, E34, E38
If you like the steering of your 535i but it has that large amount of play in the center, it is very easy to correct and adjust.
The image above shows the type of play we are talking about.
First understand how the steering works.
The screw on top of the steering box is for adjustment and the smaller screw at the end of the steering wheel shaft is a drain plug.
See image above. When you turn the adjustment screw clockwise it pushes the tapered gear (arrows in red) closer to the nut. This reduces the play in the steering. The steering in the BMW 535i E28 is very good and it should have zero play if all parts are in good condition. It is still one of my favorites set ups but it requires minor adjustment probably every 50000 klms because it is very sensitive to tolerances. Every other part inside the steering box is mounted on bearings and has virtually no wear and offers zero friction and great feel if the hydraulic seals are good.
To adjust the play: lift the front wheels from the ground so that there is no weight on the steering and it can be turned while the engine is off with the tip of your fingers.
Turn Adjustment screw clock wise a small amount at the time then turn steering wheel from lock to lock until there is no play in the center position of the steering. It is that simple but there is things you must know and they are very important to understand. If you turn the adjustment screw too much and the steering feels tight at the center position. The forces inside the steering box multiply and are huge. They can wear the components that otherwise never wear out. Or in a bad case scenario it can break the parts inside the steering box (from mechanical fatigue). That is why it is necessary to lift the wheels from the ground and turn the steering wheel (with engine off) from lock to lock and there should be absolutely zero friction (or pre load or tightness) in the steering at the center position. I use my finger tips to turn the wheel. Not my hands. There will be some play when the steering is not in the center position because it is designed and machined that way. Steering adjustments need between half a turn and two turns depending on when was the last time somebody adjusted it. What I normally do is turn the screw more than what it needs then feel the steering wheel for any tightness. And bring the adjustment screw out until there is zero preload in the center. That normally gets me zero steering play in the center. Enjoy it.
Things I have noticed:
The play in the steering box of all the E28 can be reduced to zero. 535i E34 seems to be good too. The steering box in the 540i E34 and E38 seems to have bigger tolerances in the bearings from factory and I could not get it to zero play. Also my guess is that steering geometry of the 540i is good for stability but not for feel. Pity.
Also, if the steering feels heavy and vague it could be that the hydraulic seals are worn.
You can see the seals in the image above as well as the other internal parts of the steering of a 535i. The bearings, spool valve, and other parts never wear but the seals wear relatively quickly and make the steering feel numb. I could not notice a mayor difference between new and old seals in terms of wear but it makes a big difference. It seems the system is very sensitive to seal tightness. I changed them once and it is not very difficult and with little to go wrong if you are brave. Just be gentle and make sure you do not scratch the working surfaces of the seal. They are similar to an o-ring but made of a hard plastic. I was recommended to put them in boiling water so they soften a little to make it easier to slide them in. You can buy the seals in a kit.
Brake problems in E28 and E34
The brake booster of some top of the range E28 and E34 is hydraulic and has a very common problem. It does not work from the vacuum of the engine, instead it uses the hydraulic pump from the power steering. The reason for this is a hydraulic booster feels more solid and responsive than a vacuum booster. There is a hydraulic pressure reservoir which usually looks like a ball about 100 mm in diameter. It is there so that if the engine stops, is turning too slow or if there is a large surge of fluid needed, the reservoir has a reserve of oil at high pressure. You can tell if it is working in the following way. If you drive and brake normally the brakes feel fine. But if you drive and brake hard and very suddenly the brake feels very hard and slow to respond. Also if you turn the engine off the brake pedal feels hard straight away. If the reservoir is working properly you can brake 3-4 times before the brakes lose the booster assistance and feel hard and numb. The brakes in general have good feel but when this reservoir is not working properly the brakes feel scary. To change it is a matter of screwing a new one. But you must absolutely make sure there is no accumulated hydraulic pressure in the system (because it is designed to have a high pressure reserve even if the engine is off) before you disassemble anything. Beware, an oil leak at high pressure can cut through your skin/fingers/eyes.
Electric window/sunroof problems in BMW E30 and E28
This is a tricky problem but very cheap and easy to fix.
Usually the symptoms are like this: You press the button and the windows move very slowly or erratically or not at all. Then you check the electric motor, the switch, the wiring and it all works. What happens is the contacts of the switches erode and get metal deposits. If you take the switches off and test them with a low current multi meter they appear OK. But when they are required to pass the 5-10 amps of the electric motor, the contacts can’t pass enough current and the motor appears weak.
This picture is an example of worn contacts. You can see the dark contacts have very rough and pitted surfaces whereas the one in the middle has some wear but it is shiny and still works properly. The electric window and sunroof switches on BMW E30 and E28 had the same problem. How to fix that is very easy. Open the switch put sand paper between the contacts, press contacts together and sand and clean the surface of the contacts. Chances are once the surfaces of the contacts are flat and can sit against each other better they will have enough current capacity for the electric windows and sunroof. Note they do not need to be perfect but they need to connect better. Often you will see a tiny grain of metal fused into the surface of one of the contacts (not shown). When you remove them then the contacts are able to connect well and finally the windows work perfectly again for another 10 years.
Overheating problem on BMW E30 and E28
There is two things that often confuse people.
The thermal coupling on the engine fan. (pictured)
This has a thermostat inside that produces more drag in the coupling if the temperature is above certain point. The fan always turns when the engine is running whether the thermal coupling is engaged or disengaged. If you accelerate and the coupling is engaged you a can hear the fan becomes noisy due to the air flow. If it is not engaged it continues to freewheel but there is not change in noise when you accelerate the engine because it continues to freewheel at the same speed. This only happens if the coupling is working and the radiator passes enough heat into the coupling. That is part of the trick, it only works if the radiator is also working. Now it is the radiators turn. The radiators often form a small thin amount of rust on the inside surface. This rust stays there for years without a problem at all… Until one day, The rust dries out or changes for some reason. For example you decide to put coolant, clean and flush the radiator. Or so you think, but instead you have simply annoyed the spirits within. In this example reverse flushing the radiator is not enough to remove the thin layer of rust inside the radiator. But while you were doing the job the radiator was allowed to dry and the thin and otherwise harmless layer of rust was allowed to dry. And that pisses the spirits like nothing else. I have been there. What happens is that thin layer of rust dries, cracks, flakes and lifts itself partially. All in the entire inside surface of the radiator. This partial lifting of the rust inside the radiator is enough to produce drag and reduces the flow of water inside. If you test it with a strong pump it will flow water. But when the engine is running at moderate speeds the flow of water inside the radiator is not enough and the car runs hot or overheats. Because there is not enough water flow inside the radiator, the thermal fan doesn’t get hot enough and it does not engage either. So how do you check if the radiator is flowing enough water? (I wish I could get a dollar every time I explain this then I could afford an E30 M3 or put a rotary engine in an mx5 or E30… and tell you about the tricks…) Let the engine run and warm up. Then go for a drive at 50- 70 klms/hr for 2-5 mins. This ensures good air flow trough the radiator. Then quickly stop and touch both sides of the radiator. The water inlet and the water outlet that is.
Explanation: If you have good air flow and poor water flow in the radiator, the air is enough to cool the water. In the meantime, the water takes considerably longer to go from one side of the radiator to the other and the result is the water outlet of the radiator is cold or not very warm.
If the radiator is in good condition usually you can not feel much difference in temperature from the hot side to the cooler side. Water changes temperature for example from 90 to 80 degrees centigrade. They both burn.
Sometimes people assume that because the radiator is cold on one side it is “cooling” they then go and check the thermal fan which is not engaged because it is not getting enough temperature to engage. And they change the wrong part. Sometimes twice.
Reverse flushing again is not strong enough to clean it. What usually works best is to open both sides of the radiator and all they have to do is slide the helix spirals inside the radiator tubes to loosen the rust. Then close the radiator, pressure test it and your old radiator is now exorcised and demon free. If you are going remove your radiator for a few days and is not completely rust free put it in a safe place and leave water inside. (What type of water? Send me a dollar and I will tell you which type)