If you purchase an older luxury car there are two things near certain: the first is which it may have Power seat motor, and the second is the fact at least one in the seat functions won’t work! Just how hard will it be to correct a defective leccy seat? Obviously all depends a lot of what the exact concern is and also the car in question, but being a guide let’s look into fixing the seats inside an E23 1985 BMW 735i. The seat architecture in other cars may vary, but when you don’t have any idea where you’d even learn to fix this kind of problem, this story will certainly be useful for your needs.
The leading seats inside the BMW are amongst the most complex that you’ll find in any older car. They have electric adjustment for front/back travel, front in the seat up/down, rear of the seat up/down, head restraint up/down and backrest rake forwards/backwards. However, they don’t have electric lumbar adjust and they also don’t have airbags. (In the event the seats you are focusing on have airbags, you must look at the factory workshop manual to ascertain the safe procedure for working on the seats.)
The seat functions are controlled by this complex switchgear, which can be duplicated about the passenger side from the car. As can be seen here, the driver’s seat also provides three position memories. Incidentally, the rear seat is additionally electric, having an individual reclining function for every side! However in this car, the back seat was working all right.
The driver’s seat had three problems.
The button which moved the seat rearwards didn’t work. However, the seat may be moved backwards using one of the memory keys.
The top of the seat couldn’t be raised.
The head restraint wouldn’t move down or up, although in this case the motor may be heard whirring uselessly whenever the proper buttons were pressed.
Receiving the Seat Out
The initial step would be to remove the seat through the 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.
But just how was access likely to be gained for the front mounting bolts? Pressing the adjustment button didn’t make the seat to move backwards, and through this stage the memory button had stopped allowing that action as well! The perfect solution was to manually apply capacity to the seat to activate the motor. Every one of the connecting plugs were undone and people plugs containing the heaviest cables inspected. (There will be wiring for seat position transducers and such things as that in the loom, but the motors will likely be powered by noticeably heavier cables.)
By using a heavy duty, over-current protected, 12V power supply (that one is made very cheaply – see DIY Budget 12-volt Bench Supply), power was put on pairs of terminals connecting towards the thick wires until the right connections were found. The seat was then powered backwards until the front mounting bolts might be accessed. These were removed and therefore the Power seat motor moved forward until it sat during its tracks, making it simpler to get free from the vehicle.
Fixing the Head Restraint
This is what the BMW seat appears like underneath. Four electric motors is seen, plus there’s a fifth inside the backrest. Each electric motor connects into a sheathed, flexible drive cable that therefore connects to a reduction gearbox. Because I later discovered, inside each gearbox can be a worm that drives a plastic gearwheel, which actually drives a pinion operating with a rack. During this period, though, an easy test may be made of each motor by connecting ability to its wiring plug and ensuring that the function worked as it should. Every function however the head restraint up/down worked, and so the problems other than the pinnacle restraint showed that they must maintain the switches, not the motors or associated drive systems. But just how to fix your head restraint up/down movement?
The rear trim panel in the seat came off by the simple undoing of four screws. As with the other seat motors, the mechanism consisted of a brush-type DC motor driving an adaptable cable that went along to the adjust mechanism. The motor worked fine with power connected, but the head restraint didn’t move. Feeling the outside of the drive cable sheath revealed that the drive cable inside was turning, and so the problem must lie from the mechanism nearest to the top restraint itself.
The adjustment mechanism was kept in place with one screw, that has been accessible with the leather upholstery disengaged from small metal spikes that held it in place. The legs in the head restraint clipped into plastic cups around the mechanism (one is arrowed here) and these were able to be popped by helping cover their the careful utilization of a screwdriver.
The entire upper section of the adjustment mechanism was then able to be lifted from the seat back and placed near the seat. Remember that the electric motor stayed in place – it didn’t have to be removed too.
To find out that which was occurring within the unit, it would have to be pulled apart. It had been obviously never designed to be repairable, so the first disassembly step involved drilling out of the rivets which held the plastic sliders in position on his or her track. With one of these out, the act of the pinion (a small gear) in the rack (a toothed metal strip) could be assessed. Neither looked particularly worn and applying capability to the motor indicated that in fact the pinion wasn’t turning. To ensure meant the issue was inside of the gearbox itself.
The gearbox was held combined with four screws, each by having an oddly-shaped internal socket head where I don’t have a tool. However, knowing that I could possibly always find replacement small bolts, I used a set of Vicegrips to undo them – which is, it didn’t matter if they got a little mutilated in the process of disassembly.
In the gearbox the worm drive along with its associated plastic gear may be seen. Initially I figured that the plastic cog will need to have stripped, but inspection showed that this wasn’t the case. Why wasn’t drive getting away from the gearbox? Again I applied capability to the motor and watched what actually transpired. The Things I found was even though cable might be heard rotating inside its sheath, that drive wasn’t progressing to the worm. Pulling the worm gear out and inspecting the square-section drive cable indicated that the final from the cable was actually a little worn plus it was slipping back from the drive hole from the worm. (The slippage was occurring within the area marked from the arrow.)
The fix was dead-easy – simply pull the drive cable from the sheath a little bit, crimp a spring steel washer into it (backed by way of a plain washer that here is out of sight – it’s fallen into the mouth of the sheath) then push the drive cable back down in their sleeve. Together with the crimped washer preventing the worn section of the cable from sliding back out of your square drive recess in the worm, drive was restored to the gearbox.
The mechanism could then be reassembled. New screws were utilized to change the Vicegripped ones, while the drilled-out rivets were also replaced with new screws and nuts (arrowed). The gearbox was re-greased before assembly and a smear of grease was put on the tracks that the nylon sleeves run using. During the seat, the mechanism dexqpky30 checked by making use of power – and worked fine.
So in this instance the fix cost nearly nothing, except a bit of time.
Since every one of the motors had now been turned out to be in working order, fixing the electric rearwards travel and front up/down motion could only be achieved together with the seat back in the car – it looked like it needed to be a wiring loom or switchgear problem. But whilst the seat was out, it made sense to wipe total the tracks and exposed cogs and re-grease them.
Fixing the remainder
Under the driver’s seat can be a control Power seat switch both relays and the seat memory facility. Close inspection of the plugs and sockets for both the unit and the associated loom revealed that some corrosion had occurred. (Perhaps at some stage a drink have been spilled onto it.) The corrosion showed itself like a green deposit in the pins plus some tedious but careful scraping having 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 off the deposit in the pins of the plug, that were otherwise impossible to gain access to to completely clean.
At commercial rates, fixing the seat would have cost several hundred dollars – both in labour time and in the complete replacement head restraint up/down mechanism. No-one could have bothered repairing the gearbox drive – they’d have just replaced the whole thing. The corroded pins? That could have been cheaper, but the total bill might have still been prohibitive.