If you purchase an older luxury car there are two things near certain: the very first is that it will have Power seat flexible shaft, and the second is the fact that a minumum of one in the seat functions won’t work! So how hard will it be to solve a defective leccy seat? Obviously it depends a great deal of what the specific problem is and the car in question, but being a guide let’s take a look at fixing the seats within an E23 1985 BMW 735i. The seat architecture in other cars can vary, but when you don’t possess any idea where you’d even commence to fix this kind of problem, this story is certain to come in handy for you.
The leading seats from the BMW are one of the most complex that you’ll see in any older car. They already have electric adjustment for front/back travel, front in the seat up/down, rear from the seat up/down, head restraint up/down and backrest rake forwards/backwards. However, they don’t have electric lumbar adjust plus they don’t have airbags. (If the seats you are focusing on have airbags, you have to see the factory workshop manual to find out the safe procedure for working on the seats.)
The seat functions are typical controlled through this complex switchgear, that is duplicated about the passenger side of the car. As is seen here, the driver’s seat also has three position memories. Incidentally, the rear seat is additionally electric, by having an individual reclining function for each side! But in this car, the rear seat was working just great.
The driver’s seat had three problems.
The button which moved the seat rearwards didn’t work. However, the seat might be moved backwards using one of the memory keys.
The leading from the seat couldn’t be raised.
The pinnacle restraint wouldn’t move up or down, although in this case the motor could be heard whirring uselessly whenever the correct buttons were pressed.
Obtaining the Seat Out
The first step ended up being to get rid of the seat in the car to ensure that usage of all the bits could be gained. The seat was electrically moved forward and so the two rear floor-mounting bolts undone.
But exactly how was access will be gained for the front mounting bolts? Pressing the adjustment button didn’t cause the seat to move backwards, and also this stage the memory button had stopped allowing that action also! The best solution was to manually apply ability to the seat to activate the motor. All of the connecting plugs were undone and others plugs containing the heaviest cables inspected. (There will be wiring for seat position transducers and things such as that from the loom, however the motors will probably be powered by noticeably heavier cables.)
Using a durable, over-current protected, 12V power supply (that one was made very cheaply – see DIY Budget 12-volt Bench Supply), power was placed on pairs of terminals connecting towards the thick wires until the right connections were found. The seat was then powered backwards up until the front mounting bolts may be accessed. They were removed and so the Power seat switch moved forward until it sat during its tracks, making it easier to get rid of the automobile.
Fixing the pinnacle Restraint
And this is what the BMW seat appears like underneath. Four electric motors can be viewed, plus there’s a fifth in the backrest. Each motor unit connects to some sheathed, flexible drive cable that consequently connects into a reduction gearbox. When I later discovered, inside each gearbox is actually a worm that drives a plastic gearwheel, which drives a pinion operating on a rack. At this stage, though, a simple test could be created from each motor by connecting power to its wiring plug and ensuring the function worked mainly because it should. Every function nevertheless the head restraint up/down worked, so the problems aside from your head restraint showed that they have to maintain the switches, not the motors or associated drive systems. But how to correct the top restraint up/down movement?
The back trim panel from the seat came off with the simple undoing of four screws. Much like the other seat motors, the mechanism was comprised of a brush-type DC motor driving a flexible type of cable that went along to the adjust mechanism. The motor worked fine with power connected, although the head restraint didn’t move. Feeling the outside of the drive cable sheath revealed that the drive cable inside was turning, so the problem must lie from the mechanism nearest the top restraint itself.
The adjustment mechanism was kept in place with one screw, which was accessible using the leather upholstery disengaged from small metal spikes that held it into position. The legs from the head restraint clipped into plastic cups around the mechanism (the first is arrowed here) and they could actually be popped out with the careful utilization of a screwdriver.
The entire upper section of the adjustment mechanism was then capable of being lifted out of your seat back and placed next to the seat. Keep in mind that the electric motor stayed in position – it didn’t must be removed as well.
To view what was taking place within the unit, it should be pulled apart. It had been obviously never created to be repairable, and so the first disassembly step involved drilling out the rivets which held the plastic sliders into position on their own track. Using these out, the action of the pinion (a small gear) in the rack (a toothed metal strip) may be assessed. Neither looked particularly worn and applying capacity to the motor demonstrated that in fact the pinion wasn’t turning. So that meant that the issue was inside the gearbox itself.
The gearbox was held as well as four screws, each having an oddly-shaped internal socket head in which I don’t use a tool. However, realizing that I was able to always find replacement small bolts, I used a set of Vicegrips to undo them – that is certainly, it didn’t matter when they got somewhat mutilated along the way of disassembly.
Inside of the gearbox the worm drive and its associated plastic gear may be seen. Initially I was thinking that this plastic cog need to have stripped, but inspection demonstrated that this wasn’t the way it is. So why wasn’t drive getting away from the gearbox? Again I applied ability to the motor and watched what actually transpired. A Few Things I found was even though cable could be heard rotating inside its sheath, that drive wasn’t arriving at the worm. Pulling the worm gear out and inspecting the square-section drive cable revealed that the end of your cable was really a little worn and it was slipping back from the drive hole of the worm. (The slippage was occurring in the area marked through the arrow.)
The fix was dead-easy – simply pull the drive cable out of your sheath a little, crimp a spring steel washer onto it (backed with a plain washer that here has run out of sight – it’s fallen into the mouth of the sheath) after which push the drive cable down again in their sleeve. Using the crimped washer preventing the worn area of the cable from sliding back out of your square drive recess within the worm, drive was restored towards the gearbox.
The mechanism could then be reassembled. New screws were utilized to replace the Vicegripped ones, while the drilled-out rivets were also substituted for new screws and nuts (arrowed). The gearbox was re-greased before assembly plus a smear of grease was placed on the tracks the nylon sleeves run using. During the seat, the mechanism dexqpky30 checked by applying power – and worked fine.
So in this instance the fix cost nearly nothing, except a while.
Since all of the motors had now been became in working order, fixing the electric rearwards travel and front up/down motion could only be achieved with all the seat back in the car – it looked just as if it would have to be a wiring loom or switchgear problem. But even though the seat was out, it made sense to wipe over-all the tracks and exposed cogs and re-grease them.
Fixing the Rest
Within the driver’s seat can be a control Power seat switch both relays along with the seat memory facility. Close inspection from the plugs and sockets on both the system and also the associated loom indicated that some corrosion had occurred. (Perhaps at some stage a drink have been spilled upon it.) The corrosion showed itself as being a green deposit on the pins and a few tedious but careful scraping by using a small flat-bladed screwdriver removed it. Once which was done, the associated plug was inserted and pulled out 20-30 times to scrape off of the deposit within the pins in the plug, that have been otherwise impossible gain access to to clean.
At commercial rates, fixing the seat might have cost large sums of money – in both labour time and in a complete replacement head restraint up/down mechanism. No-one would have bothered repairing the gearbox drive – they’d have just replaced the whole thing. The corroded pins? That could have been cheaper, however the total bill would have still been prohibitive.