If you purchase an older luxury car there are 2 things near certain: the initial one is that it can have Power seat motor, as well as the second is the fact that a minumum of one from the seat functions won’t work! Just how hard would it be to correct a defective leccy seat? Obviously this will depend a whole lot on which the particular issue is as well as the car in question, but as being a guide let’s look into fixing the seats within an E23 1985 BMW 735i. The seat architecture in other cars will be different, however if you don’t have idea where you’d even commence to fix this type of problem, this story is sure to come in handy for you.
The front seats inside the BMW are one of the most complex that you’ll find 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. (In case the seats that you are currently taking care of have airbags, you should look at the factory workshop manual to ascertain the safe procedure for concentrating on the seats.)
The seat functions are typical controlled by this complex switchgear, which happens to be duplicated around the passenger side from the car. As can be viewed here, the driver’s seat also has three position memories. Incidentally, the back seat can also be electric, by having an individual reclining function for each side! But in this car, the back seat was working perfectly.
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 front side of the seat couldn’t be raised.
The head restraint wouldn’t move up or down, although in this case the motor may be heard whirring uselessly whenever the proper buttons were pressed.
Obtaining the Seat Out
Step one ended up being to take away the seat from your car to ensure entry to every one of the bits could possibly be gained. The seat was electrically moved forward and therefore the two rear floor-mounting bolts undone.
So how was access going to be gained to the front mounting bolts? Pressing the adjustment button didn’t cause the seat to move backwards, and by this stage the memory button had stopped allowing that action also! The answer was to manually apply capacity to the seat to activate the motor. All of the connecting plugs were undone and the ones plugs containing the heaviest cables inspected. (There will be wiring for seat position transducers and stuff like that from the loom, but the motors will probably be powered by noticeably heavier cables.)
Utilizing a heavy duty, over-current protected, 12V power source (this one was created very cheaply – see DIY Budget 12-volt Bench Supply), power was placed on pairs of terminals connecting for the thick wires before the right connections were found. The seat was then powered backwards till the front mounting bolts may be accessed. They were removed and so the Power seat switch moved forward until it sat in the center of its tracks, making it simpler to get free from the automobile.
Fixing your head Restraint
This is just what the BMW seat appears like underneath. Four electric motors is seen, plus there’s a fifth inside the backrest. Each motor unit connects into a sheathed, flexible drive cable that therefore connects into a reduction gearbox. When I later discovered, inside each gearbox can be a worm that drives a plastic gearwheel, which actually drives a pinion operating on the rack. During this period, though, a basic test may be made of each motor by connecting capability to its wiring plug and ensuring the function worked since it should. Every function although the head restraint up/down worked, and so the problems besides the top restraint showed that they must be in the switches, not the motors or associated drive systems. But how to correct your head restraint up/down movement?
The back trim panel of the seat came off through the simple undoing of four screws. As with other seat motors, the mechanism was comprised of a brush-type DC motor driving a flexible cable that went along to the adjust mechanism. The motor worked fine with power connected, however the head restraint didn’t move. Feeling the beyond the drive cable sheath revealed that the drive cable inside was turning, hence the problem must lie from the mechanism closest to the head restraint itself.
The adjustment mechanism was locked in place with one screw, which was accessible together with the leather upholstery disengaged from small metal spikes that held it into position. The legs from the head restraint clipped into plastic cups in the mechanism (the first is arrowed here) and these were able to be popped by helping cover their the careful utilization of a screwdriver.
The entire upper part of the adjustment mechanism was then capable of being lifted out of your seat back and placed near the seat. Remember that the electric motor stayed set up – it didn’t have to be removed at the same time.
To discover that which was happening within the unit, it should be pulled apart. It was actually obviously never designed to be repairable, and so the first disassembly step involved drilling out the rivets which held the plastic sliders in position on their track. With these out, the action of the pinion (a compact gear) in the rack (a toothed metal strip) could possibly be assessed. Neither looked particularly worn and applying power to the motor revealed that the truth is the pinion wasn’t turning. So that meant the issue was inside the gearbox itself.
The gearbox was held along with four screws, each with an oddly-shaped internal socket head for which I don’t use a tool. However, realizing that I was able to always find replacement small bolts, I used a pair of Vicegrips to undo them – that is, it didn’t matter should they got a lttle bit mutilated during this process of disassembly.
Inside of the gearbox the worm drive along with its associated plastic gear may be seen. Initially I thought 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 capacity to the motor and watched what actually transpired. A Few Things I found was while the cable may 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 in the cable was a little worn and it also was slipping back out of your drive hole of the worm. (The slippage was occurring within the area marked by the arrow.)
The fix was dead-easy – simply pull the drive cable out of your sheath a bit, crimp a spring steel washer onto it (backed with a plain washer that here is out of sight – it’s fallen back into the mouth from the sheath) then push the drive cable back in the sleeve. Using the crimped washer preventing the worn portion of the cable from sliding back out from the square drive recess in the worm, drive was restored for the gearbox.
The mechanism could then be reassembled. New screws were used to switch the Vicegripped ones, as the drilled-out rivets were also substituted with new screws and nuts (arrowed). The gearbox was re-greased before assembly along with a smear of grease was added to the tracks how the nylon sleeves run on. Back in the seat, the mechanism dexqpky30 checked by making use of power – and worked fine.
So in this case the fix cost nearly nothing, except a bit of time.
Since all of the motors had now been turned out to be in working order, fixing the electrical rearwards travel and front up/down motion could just be achieved with the seat during the car – it looked like it must be a wiring loom or switchgear problem. But whilst the seat was out, it made sense to wipe overall the tracks and exposed cogs and re-grease them.
Under the driver’s seat is actually a control Power seat switch both relays and the seat memory facility. Close inspection from the plugs and sockets on both the machine as well as the associated loom indicated that some corrosion had occurred. (Perhaps at some stage a drink had been spilled upon it.) The corrosion showed itself as a green deposit about the pins plus some tedious but careful scraping by using a small flat-bladed screwdriver removed it. Once which had been done, the associated plug was inserted and pulled out 20-30 times to scrape from the deposit inside of the pins of the plug, that have been otherwise impossible to get into to wash.
At commercial rates, fixing the seat would have cost a lot of money – both in labour some time and in the complete replacement head restraint up/down mechanism. No-one will have bothered repairing the gearbox drive – they’d have just replaced the whole thing. The corroded pins? That might have been cheaper, although the total bill might have still been prohibitive.