If you purchase an older luxury car there are two things near certain: the first is that this may have Power seat motor, as well as the second is the fact one or more of the seat functions won’t work! So how hard is it to solve a defective leccy seat? Obviously all depends a lot on which the actual concern is and also the car under consideration, but being a guide let’s take a look at fixing the seats inside 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 begin to fix this kind of problem, this story is certain to come in handy to you.
The front side seats inside the BMW are amongst the most complex that you’ll see in any older car. They may have electric adjustment for front/back travel, front in the seat up/down, rear of your seat up/down, head restraint up/down and backrest rake forwards/backwards. However, they don’t have electric lumbar adjust and so they don’t have airbags. (When the seats you are working on have airbags, you need to browse the factory workshop manual to find out the safe procedure for focusing on the seats.)
The seat functions are controlled by this complex switchgear, which is duplicated on the passenger side of the car. As can be viewed here, the driver’s seat also offers three position memories. Incidentally, the back seat is additionally electric, by having an individual reclining function for every single 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 front side of your seat couldn’t be raised.
Your head restraint wouldn’t move down or up, although in this instance the motor may be heard whirring uselessly whenever the best buttons were pressed.
Getting the Seat Out
The first task was to remove the seat from your car so that access to every one of the bits might be gained. The seat was electrically moved forward and then the two rear floor-mounting bolts undone.
So how was access likely to be gained towards the front mounting bolts? Pressing the adjustment button didn’t result in the seat to advance backwards, and also this stage the memory button had stopped allowing that action at the same time! The best solution would be to manually apply ability to the seat to activate the motor. All the connecting plugs were undone and others plugs containing the heaviest cables inspected. (You will see wiring for seat position transducers and stuff like that in the loom, but the motors will likely be powered by noticeably heavier cables.)
Employing a heavy-duty, over-current protected, 12V power supply (this one was created very cheaply – see DIY Budget 12-volt Bench Supply), power was placed on pairs of terminals connecting towards the thick wires before the right connections were found. The seat was then powered backwards till the front mounting bolts might be accessed. They were removed and so the Power seat flexible shaft moved forward until it sat during its tracks, making it easier to get free from the vehicle.
Fixing the top Restraint
This is just what the BMW seat looks like underneath. Four electric motors can be viewed, plus there’s a fifth in the backrest. Each electric motor connects to a sheathed, flexible drive cable that subsequently connects to a reduction gearbox. While I later discovered, inside each gearbox can be a worm that drives a plastic gearwheel, which actually drives a pinion operating with a rack. At this stage, though, a basic test may be manufactured from each motor by connecting power to its wiring plug and ensuring the function worked as it should. Every function however the head restraint up/down worked, so the problems other than the head restraint showed that they have to be in the switches, not the motors or associated drive systems. But just how to repair the head restraint up/down movement?
The back trim panel of your seat came off through the simple undoing of four screws. Similar to the other seat motors, the mechanism contained a brush-type DC motor driving a flexible cable that went to the adjust mechanism. The motor worked fine with power connected, but the head restraint didn’t move. Feeling the away from the drive cable sheath indicated that the drive cable inside was turning, so the problem must lie inside the mechanism closest to the head restraint itself.
The adjustment mechanism was locked in place with one screw, that has been accessible with all the leather upholstery disengaged from small metal spikes that held it in position. The legs of your head restraint clipped into plastic cups around the mechanism (the first is arrowed here) which had the ability to be popped by helping cover their the careful usage of a screwdriver.
The entire upper portion of the adjustment mechanism was then capable of being lifted out of your seat back and placed near the seat. Keep in mind that the electrical motor stayed in position – it didn’t have to be removed also.
To find out what was taking place within the unit, it needed to be pulled apart. It was actually obviously never made to be repairable, so the first disassembly step involved drilling out the rivets which held the plastic sliders in position on the track. With one of these out, the action of the pinion (a compact gear) about the rack (a toothed metal strip) may be assessed. Neither looked particularly worn and applying capability to the motor showed that actually the pinion wasn’t turning. To ensure meant the situation was within the gearbox itself.
The gearbox was held along with four screws, each having an oddly-shaped internal socket head for which I don’t have a tool. However, knowing that I really could always find replacement small bolts, I used a couple of Vicegrips to undo them – that is certainly, it didn’t matter should they got a lttle bit mutilated along the way of disassembly.
Inside the gearbox the worm drive and its associated plastic gear might be seen. Initially I figured that the plastic cog should have stripped, but inspection showed that this wasn’t the truth. Why wasn’t drive getting out of the gearbox? Again I applied capability to the motor and watched what happened. Things I found was even though cable might be heard rotating inside its sheath, that drive wasn’t getting to the worm. Pulling the worm gear out and inspecting the square-section drive cable demonstrated that the end of your cable was really a little worn plus it was slipping back from the drive hole of your worm. (The slippage was occurring in the area marked from the arrow.)
The fix was dead-easy – simply pull the drive cable from the sheath a little, crimp a spring steel washer on it (backed by a plain washer that here is out of sight – it’s fallen back into the mouth from the sheath) and after that push the drive cable back within its sleeve. Using the crimped washer preventing the worn part of the cable from sliding back out of your square drive recess from the worm, drive was restored for the gearbox.
The mechanism could then be reassembled. New screws were used to replace the Vicegripped ones, even though 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 put on the tracks that the nylon sleeves operate on. During the seat, the mechanism dexqpky30 checked by utilizing 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 proved to be in working order, fixing the electric rearwards travel and front up/down motion could simply be achieved with all the seat during the car – it looked just as if it must be a wiring loom or switchgear problem. But whilst the seat was out, it made sense to wipe over all the tracks and exposed cogs and re-grease them.
Within the driver’s seat can be a control Power seat switch both relays and also the seat memory facility. Close inspection of the plugs and sockets on the system and the associated loom demonstrated that some corrosion had occurred. (Perhaps at some stage a drink was spilled onto it.) The corrosion showed itself as a green deposit in the pins and some tedious but careful scraping using a small flat-bladed screwdriver removed it. Once that had been done, the associated plug was inserted and pulled out 20-30 times to scrape from the deposit inside of the pins in the plug, that have been otherwise impossible to gain access to to completely clean.
At commercial rates, fixing the seat will have cost large sums of money – in labour some time and inside a complete replacement head restraint up/down mechanism. Nobody would have bothered repairing the gearbox drive – they’d have just replaced everything. The corroded pins? That could have been cheaper, although the total bill could have still been prohibitive.