If you pick an older luxury car the two main things near certain: the first is it can have Power seat flexible shaft, along with the second is that a minimum of one from the seat functions won’t work! So, just how hard will it be to solve a defective leccy seat? Obviously this will depend a good deal on which the exact concern is and the car under consideration, but as a guide let’s take a look at fixing the seats inside an E23 1985 BMW 735i. The seat architecture in other cars can vary, however, if you don’t have any idea where you’d even start to fix this kind of problem, this story will definitely be of use to you.
The front seats in the BMW are one of the most complex that you’ll find in any older car. They have got electric adjustment for front/back travel, front of your 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. (In the event the seats that you will be working on have airbags, you need to read the factory workshop manual to find out the safe procedure for focusing on the seats.)
The seat functions are typical controlled with this complex switchgear, which happens to be duplicated about the passenger side from the car. As is seen here, the driver’s seat also offers three position memories. Incidentally, the back seat is additionally electric, with the individual reclining function for every single side! Nevertheless 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 might be moved backwards with one of the memory keys.
The top from the seat couldn’t be raised.
The top restraint wouldn’t move down or up, although in this case the motor could be heard whirring uselessly whenever the correct buttons were pressed.
Receiving the Seat Out
The first task would be to remove the seat from the car so that usage of each of the bits could possibly be gained. The seat was electrically moved forward and then the two rear floor-mounting bolts undone.
But exactly how was access will be gained towards the front mounting bolts? Pressing the adjustment button didn’t result in the seat to move backwards, and by this stage the memory button had stopped allowing that action at the same time! The best solution was 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 such things as that in the loom, however the motors will be powered by noticeably heavier cables.)
Employing a heavy-duty, over-current protected, 12V power supply (this was made very cheaply – see DIY Budget 12-volt Bench Supply), power was applied to pairs of terminals connecting to the thick wires until the right connections were found. The seat was then powered backwards up until the front mounting bolts could be accessed. They were removed and therefore the Power seat flexible shaft moved forward until it sat in the middle of its tracks, making it easier to get free from the auto.
Fixing the top Restraint
This is just what the BMW seat looks like underneath. Four electric motors is visible, plus there’s a fifth within the backrest. Each electric motor connects to your sheathed, flexible drive cable that in turn connects to some reduction gearbox. As I later discovered, inside each gearbox can be a worm that drives a plastic gearwheel, which in turn drives a pinion operating on the rack. At this time, though, an easy test could possibly be manufactured from each motor by connecting capacity to its wiring plug and ensuring that the function worked mainly because it should. Every function although the head restraint up/down worked, therefore the problems other than the top restraint showed that they have to be in the switches, not the motors or associated drive systems. But how to solve the head restraint up/down movement?
The rear trim panel of your 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 an adaptable cable that went to the adjust mechanism. The motor worked fine with power connected, although the head restraint didn’t move. Feeling the away from the drive cable sheath established that the drive cable inside was turning, so the problem must lie inside 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 set up. The legs of your head restraint clipped into plastic cups in the mechanism (the first is arrowed here) and they were able to be popped by helping cover their the careful use of a screwdriver.
The full upper section of the adjustment mechanism was then able to be lifted out from the seat back and placed next to the seat. Keep in mind that the electric motor stayed set up – it didn’t should be removed too.
To discover what was taking place inside of the unit, it would have to be pulled apart. It was obviously never designed to be repairable, and so the first disassembly step involved drilling out the rivets which held the plastic sliders set up on their own track. With these out, the act of the pinion (a compact gear) on the rack (a toothed metal strip) may be assessed. Neither looked particularly worn and applying capacity to the motor revealed that in reality the pinion wasn’t turning. To ensure that resulted in the issue was inside the gearbox itself.
The gearbox was held together with four screws, each with an oddly-shaped internal socket head in which I don’t have got a tool. However, realizing that I could possibly always find replacement small bolts, I used some Vicegrips to undo them – that is certainly, it didn’t matter once they got a bit mutilated in the process of disassembly.
Inside of the gearbox the worm drive and its particular associated plastic gear might be seen. Initially I thought the plastic cog should have stripped, but inspection indicated that this wasn’t the truth. So just why wasn’t drive getting away from the gearbox? Again I applied capacity to the motor and watched what went down. What I found was although the 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 demonstrated that the conclusion from the cable was actually a little worn and it also was slipping back from the drive hole of your 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 bit, crimp a spring steel washer onto it (backed from a plain washer that here is out of sight – it’s fallen into the mouth of your sheath) and then push the drive cable back within its sleeve. With all the crimped washer preventing the worn area of the cable from sliding back from the square drive recess in the worm, drive was restored on the gearbox.
The mechanism could then be reassembled. New screws were used to exchange the Vicegripped ones, whilst the drilled-out rivets were also replaced with new screws and nuts (arrowed). The gearbox was re-greased before assembly plus a smear of grease was added to the tracks that the nylon sleeves operate 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 proved to be in working order, fixing the electrical rearwards travel and front up/down motion could simply be achieved with the seat back into the car – it looked as if it would have to be a wiring loom or switchgear problem. But while the seat was out, it made sense to wipe total the tracks and exposed cogs and re-grease them.
Underneath the driver’s seat is really a control Power seat switch both relays and also the seat memory facility. Close inspection of your plugs and sockets on the unit and 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 around the pins and several 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 in the pins of the plug, that were otherwise impossible to gain access to to clean.
At commercial rates, fixing the seat might have cost large sums of money – within labour time as well as 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, however the total bill might have still been prohibitive.