1991 BMW 850i

page 5

  1. Steering box replacement
  2. Fuel tank breather
  3. Sway bar bushings
  4. Transmission oil pan filter and gasket
  5. Transmission shifter shaft seal
  6. Fuel pump check (fuel pressure)
  7. Top end rebuild
  8. Fuel filters + hoses replacement
  9. ADS interface
  10. FTP reflector


The power steering gear box was showing signs of a leak even with no fluid pressure so I picked up this replacement on Ebay for a great price (only $99). It also came from a 91 850 but what caught my eye was it has been remanufactured by ZF... I can't be sure when but it is nice and tight.


Getting the steering box out was a fairly straight forward.....

  1. Drain the Power Steering fluid by removing the drain plug on the pump.
  2. Remove the low pressure hose to the pump to make room to maneuver the steering box (the shiny one in the pic below).
  3. Disconnect the 2 hoses to the steering box and tie them out of the way (19 and 22mm banjo bolts).
  4. Remove the bolt on swivel joint at the steering box and push the steering shaft up into the firewall (I had to use the steering column in/out adj to help with this as it is very tight).
  5. Drop the center tie rod by releasing the ball joints on each end. This is to make room to drop the steering box. I used a harbor freight ball joint separator for this with no damage to the ball joint dust covers.
  6. The steering box is held in with 2 bolts. There is just enough room to get a 19mm crows foot wrench on the nut by the engine mount. Loosen this bolt from the other end. The 2nd bolt is easy to get to and remove.


Maneuver and drop the steering box like this (below). Note this pic was taken before I dropped the center tie rod (not quite enough room to get it out).

With the center tie rod out of the way the steering box can be lowered out - it's a tight fit and not easy to maneuver due to it being very heavy and with fluid dripping out!

The ball joints in the center link and tie rod ends are all very tight which is good. There is a very slight amount of play in the idler arm at its center position - So I rotated the bushing in it to tighten this up in the center (straight ahead) position.


These are the heat shields mounted above the steering rods. Both left and right shields had a broken mounting tab which I repaired  as below (still need to drill a mounting hole in the new tab). I cleaned them up as well.


This is the fuel tank breather valve that is mounted in the rear section of the rear passenger wheel well. You must remove the inner wheel liner to get to it. I suspected a problem with mine but it turns out to be working just fine.

The valve is mounted upright as below. The top connection goes to the activated charcoal canister and the lower connection to the gas tank.

If the valve is turned on its side or upside down it closes completely - preventing a fuel spill if the car turns over.

When upright, any positive pressure in the gas tank will open the valve at a few psi allowing the gas tank to vent into the charcoal canister. This explains why you sometimes hear the pressure in the tank release when removing the gas cap. And any negative pressure (as might be created when the fuel pumps suck fuel out of the tank) is released right away - the tank breaths in through the charcoal canister.

Any gas or fumes contained within the charcoal canister are sucked into the engine when it is running via 2 valves and the vacuum created in the intake manifold.

I replaced the hose connections and used spring release clamps on these low pressure connections as they are easier to remove for future service.


10/25/15. It has been too hot to work in the garage the past few weekends but today was cooler and I finally got the new PS box installed.

The Ball joints in the steering tie rods and center drag link are all tight and in excellent condition (they were replaced by the previous owner).

I also installed the heat shields that I repaired earlier. Drivers side....

And passenger side..

Since they were only about $5 a pair (on sale), I replaced the sway bar rubber bushings as well. It is not obvious in the pic below but one of them was quite badly deformed.

Here's the next task; transmission leaking from the shifter shaft seal...

And from the pan gasket...


I dropped the transmission pan today. No surprises inside... the oil was a little dirty and some black residue on the magnets.

Here it is cleaned up and ready to be re-installed with a new gasket.

I installed a new filter transmission filter


I also removed the shifter cable and actuating arm to get to the leaking shifter shaft seal. This is the distance from the back of the clamping bolt to the end of the shifter cable (needed for exact re-assembly).

An 'S' shaped 13mm ratchet wrench makes easy work of removing the retaining nut

And here is the seal I need to replace:

Access is very tight.

The old seal was very hard. After picking away at it for several minutes most of it broke away but the metal sleeve of the seal was still firmly in place. After picking away at it for a long time I gave up!

I purchased a special tool that is specifically designed to remove this size seal but there is insufficient room to get it onto the shaft. Then I tried this tool....

There is just enough room to use it in the position shown above (it was too tight to get a picture on the transmission). First I had to grind down the lip on the tool a little (with a dremmel) so it would squeeze in the gap between the shaft and seal. With this tool the job was simple... it pulled the seal out easily.

Pushing in the new seal was easy although it took a bit of finessing to get it past the step on the shaft. A 13mm 3/8" socket is just the right size to press it in place.


Fuel system...

To check the fuel pumps I did some internal surgery on a spare fuel pump relay so I can actuate it from an external 9V battery (see red and black wires entering hole in top of blue fuel pump relay).

I installed a Harbor Freight fuel pressure gauge to the fuel supply lines (one at a time) at the engine firewall. The front fuel pump relay drives fuel to the upper fuel line (just below aux water pump and the rear fuel pump (as in my pic above) drives fuel to the lower fuel line.

I was pleasantly surprised to find both fuel pumps working perfectly. Both can easily pressurize to 90psi but it is not advisable to do so for more than a second or 2 as it puts a lot of strain on the fuel lines. At ~ 50psi the first pump/line held its pressure nicely. The 2nd line/pump was not quite as good. At the back of the car (by the fuel filters) I found out why!

These lines all appear to be original (91 date code). I will replace them all.


Installed the heater control valve, aux water pump and hoses (all new).



Essential tools for removing/installing the intake manifolds.

  1. A ground down 1/4" 10mm socket with a small magnet glued inside.
  2. Swivel and Flex extensions (need this for just a couple of hard to reach nuts).
  3. Magnetic pickup tool just incase you drop something.

Reinstalled the intake manifolds today...

11/27/15 Fuel rails installed today...

Wasn't sure if I should install the fuel injectors in the intakes first or the fuel rails; definitely attach them to the fuel rails first as the small retaining clips can be tricky to snap in place.


Here's a cheat sheet for the connections and vent valve vacuum lines at the front of the engine:


I siphoned the old gas out of the tank but it did not look or smell bad.

On the passenger side of the car about as far back as the fuel filters is a single rubber fuel hose... this is the return line from the fuel rails. By connecting a suction pump to the line below you can suck or siphon the fuel out of the gas tank. This is hose was also replaced.

I replaced the fuel filters and all of the connecting hoses. Those short pre-bent hoses are expensive (~$20 ea)!

I used a unicoil on one of the hoses that did not require such a sharp bend. These cost about $2 ea and allow use of standard bulk fuel hose. A pre-formed hose from BMW is about $30!

With the exception of the hoses at the fuel pumps I have now replaced every fuel hose on this car.... about 14 of them!


It was too cold to be working outside today so built this ADS-RS232 interface. I found this design on the web (if you recognize it, please note the pin#'s on the 20 pin con are not shown correctly on this schematic). I added a service interval reset switch too it as well. This was built using parts I had lying around. Over the years I have prototyped many circuits using this 'deadbug' style of construction, it is actually quite rugged. 

Since this is a pre OBD2 car, it uses an ADS interface and the BMW software is known not to work with a USB-RS232 adapter, you need a computer with a real serial port. I picked up a Dell 360 for $40 on Ebay and will load the BMW troubleshooting software on it.


Passenger side FTP light reflector has corroded.

I re-lined it with aluminum tape. Looks a lot better than it did but not quite oem. Chrome paint may do a better job.

And installed LED's in the DRL slots (these put out lots more light). Added a PTC across them to prevent LKM errors.

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