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If you pick an older luxury car there are two things near certain: the initial one is that it may have Power seat motor, as well as the second is at least one of your seat functions won’t work! Now how hard is it to correct a defective leccy seat? Obviously this will depend a whole lot on which the actual dilemma is along with the car in question, but being a guide let’s look into fixing the seats in an E23 1985 BMW 735i. The seat architecture in other cars may vary, however if you don’t have idea where you’d even commence to fix such a problem, this story is certain to be of use for you.

The leading seats in the BMW are amongst the most complex that you’ll get in any older car. They 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 and so they don’t have airbags. (In case the seats that you will be taking care of have airbags, you must see the factory workshop manual to ascertain the safe procedure for concentrating on the seats.)

The seat functions are common controlled with this complex switchgear, that is duplicated in the passenger side in the car. As is seen here, the driver’s seat even offers three position memories. Incidentally, the back seat is also electric, with the individual reclining function for each side! Nevertheless in this car, the rear seat was working just fine.

The driver’s seat had three problems.

The button which moved the seat rearwards didn’t work. However, the seat could be moved backwards using one of the memory keys.

The front from the seat couldn’t be raised.

The top restraint wouldn’t move down or up, although in cases like this the motor could be heard whirring uselessly whenever the right buttons were pressed.

Having the Seat Out

The first task ended up being to take away the seat from the car to ensure that usage of each of the bits could be gained. The seat was electrically moved forward and then the two rear floor-mounting bolts undone.

But how was access will be gained for the front mounting bolts? Pressing the adjustment button didn’t increase the risk for seat to maneuver backwards, and also by this stage the memory button had stopped allowing that action as well! The best solution ended up being to manually apply capacity to the seat to activate the motor. All of the connecting plugs were undone and people plugs containing the heaviest cables inspected. (You will find wiring for seat position transducers and things such as that from the loom, but the motors will likely be powered by noticeably heavier cables.)

Employing a durable, over-current protected, 12V power source (this particular one was made very cheaply – see DIY Budget 12-volt Bench Supply), power was put on pairs of terminals connecting to the thick wires up until the right connections were found. The seat was then powered backwards till the front mounting bolts may be accessed. These were removed and then the Power seat switch moved forward until it sat in the midst of its tracks, making it easier to get free from the automobile.

Fixing your head Restraint

This is what the BMW seat appears to be underneath. Four electric motors can be viewed, plus there’s a fifth inside the backrest. Each motor unit connects into a sheathed, flexible drive cable that therefore connects to a reduction gearbox. Because I later discovered, inside each gearbox is actually a worm that drives a plastic gearwheel, which often drives a pinion operating on the rack. At this point, though, a simple test could be made from each motor by connecting ability to its wiring plug and ensuring the function worked since it should. Every function however the head restraint up/down worked, so the problems aside from the head restraint showed that they have to be in the switches, not the motors or associated drive systems. But exactly how to correct the top restraint up/down movement?

The back trim panel of the seat came off from the simple undoing of four screws. Much like other seat motors, the mechanism was made up of a brush-type DC motor driving a flexible cable that went along to the adjust mechanism. The motor worked fine with power connected, nevertheless the head restraint didn’t move. Feeling the beyond the drive cable sheath established that the drive cable inside was turning, therefore the problem must lie within the mechanism nearest to your head restraint itself.

The adjustment mechanism was held in place with one screw, which had been accessible together with the leather upholstery disengaged from small metal spikes that held it set up. The legs in the head restraint clipped into plastic cups about the mechanism (one is arrowed here) and they were able to be popped out with the careful use of a screwdriver.

The full upper part of the adjustment mechanism was then able to be lifted from the seat back and placed near the seat. Note that the electric motor stayed into position – it didn’t should be removed too.

To view that which was occurring inside the unit, it would have to be pulled apart. It absolutely was obviously never created to be repairable, and so the first disassembly step involved drilling out the rivets which held the plastic sliders in position on their own track. With one of these out, the action of the pinion (a compact gear) around the rack (a toothed metal strip) might be assessed. Neither looked particularly worn and applying ability to the motor demonstrated that actually the pinion wasn’t turning. To ensure meant the issue was inside the gearbox itself.

The gearbox was held as well as four screws, each with the oddly-shaped internal socket head that I don’t have got a tool. However, knowing that I really could always find replacement small bolts, I used some Vicegrips to undo them – which is, it didn’t matter if they got somewhat mutilated in the process of disassembly.

Inside the gearbox the worm drive along with its associated plastic gear could possibly be seen. Initially I assumed that this plastic cog must have stripped, but inspection demonstrated that this wasn’t the case. Why then wasn’t drive getting away from the gearbox? Again I applied ability to the motor and watched what happened. What 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 final in the cable was a little worn and it also 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 bit, crimp a spring steel washer into it (backed with a plain washer that here is out of sight – it’s fallen into the mouth in the sheath) and after that push the drive cable back in the sleeve. With the crimped washer preventing the worn section 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 utilized to replace the Vicegripped ones, even though the drilled-out rivets were also substituted with new screws and nuts (arrowed). The gearbox was re-greased before assembly and a smear of grease was put on the tracks how the nylon sleeves run on. During the seat, the mechanism dexqpky30 checked by using power – and worked fine.

So in this case the fix cost nearly nothing, except a little while.


Since every one of the motors had now been became in working order, fixing the electrical rearwards travel and front up/down motion could just be achieved with the seat back into the car – it looked like it must be a wiring loom or switchgear problem. But even though the seat was out, it made sense to wipe overall the tracks and exposed cogs and re-grease them.

Fixing the Rest

Underneath the driver’s seat is really a control Power seat switch both relays as well as the seat memory facility. Close inspection in the plugs and sockets on both the unit along with the associated loom revealed that some corrosion had occurred. (Perhaps at some stage a drink have been spilled on it.) The corrosion showed itself like a green deposit about the pins plus some tedious but careful scraping with 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 of the deposit within the pins from the plug, that had been otherwise impossible to gain access to to clean up.

At commercial rates, fixing the seat could have cost hundreds of dollars – in labour efforts and in the complete replacement head restraint up/down mechanism. No person might have bothered repairing the gearbox drive – they’d have just replaced everything. The corroded pins? That would have been cheaper, however the total bill might have still been prohibitive.