If you opt for an older luxury car there are 2 things near certain: the initial one is which it will have Power seat motor, along with the second is the fact that a minumum of one of the seat functions won’t work! Now how hard would it be to correct a defective leccy seat? Obviously all depends a whole lot about what the actual issue is as well as the car in question, but like a guide let’s have a look at fixing the seats in an E23 1985 BMW 735i. The seat architecture in other cars varies, however if you don’t possess idea where you’d even start to fix this type of problem, this story is sure to be of use to you.
The front seats inside the BMW are one of the most complex that you’ll get in any older car. They may have 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 they also don’t have airbags. (If the seats you are concentrating on have airbags, you must look at the factory workshop manual to find out the safe procedure for taking care of the seats.)
The seat functions are typical controlled from this complex switchgear, which is duplicated on the passenger side in the car. As can be seen here, the driver’s seat also has three position memories. Incidentally, the back seat is likewise electric, with an individual reclining function for each and every side! But 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 could possibly be moved backwards with one of the memory keys.
The leading in the seat couldn’t be raised.
The head restraint wouldn’t move down or up, although in such a case the motor could possibly be heard whirring uselessly whenever the correct buttons were pressed.
Having the Seat Out
The first step was to take away the seat from the car to ensure entry to every one of the bits may be gained. The seat was electrically moved forward and so the two rear floor-mounting bolts undone.
But how was access gonna be gained to the front mounting bolts? Pressing the adjustment button didn’t cause the seat to advance backwards, and by this stage the memory button had stopped allowing that action as well! The best solution ended up being to manually apply capability to the seat to activate the motor. All the connecting plugs were undone and the ones plugs containing the heaviest cables inspected. (There will be wiring for seat position transducers and such things as that in the loom, nevertheless the motors will likely be powered by noticeably heavier cables.)
By using a durable, over-current protected, 12V power source (this was developed very cheaply – see DIY Budget 12-volt Bench Supply), power was put on pairs of terminals connecting on the thick wires till the right connections were found. The seat was then powered backwards till the front mounting bolts may 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 escape the automobile.
Fixing the top Restraint
And this is what the BMW seat seems like underneath. Four electric motors can be viewed, plus there’s a fifth inside of the backrest. Each electric motor connects to a sheathed, flexible drive cable that in turn connects to some reduction gearbox. When I later discovered, inside each gearbox is really a worm that drives a plastic gearwheel, which in turn drives a pinion operating on the rack. At this stage, though, a straightforward test might be manufactured from each motor by connecting capability to its wiring plug and ensuring the function worked as it should. Every function although the head restraint up/down worked, and so the problems besides the pinnacle restraint showed that they must maintain the switches, not the motors or associated drive systems. But how to fix the top restraint up/down movement?
The back trim panel of your seat came off with the simple undoing of four screws. Much like another seat motors, the mechanism was comprised of a brush-type DC motor driving a versatile cable that went along to the adjust mechanism. The motor worked fine with power connected, however the head restraint didn’t move. Feeling the outside of the drive cable sheath indicated that the drive cable inside was turning, and so the problem must lie within the mechanism closest to the head restraint itself.
The adjustment mechanism was located in place with one screw, which was accessible using the leather upholstery disengaged from small metal spikes that held it in place. The legs from the head restraint clipped into plastic cups around the mechanism (one is arrowed here) and these could be popped by helping cover their the careful consumption of a screwdriver.
The whole upper area of the adjustment mechanism was then able to be lifted out of the seat back and placed near the seat. Keep in mind that the electric motor stayed set up – it didn’t should be removed also.
To discover that which was going on inside the unit, it should be pulled apart. It had been obviously never built to be repairable, and so the first disassembly step involved drilling out your rivets which held the plastic sliders into position on the track. By using these out, the action of the pinion (a tiny gear) on the rack (a toothed metal strip) may be assessed. Neither looked particularly worn and applying ability to the motor demonstrated that actually the pinion wasn’t turning. To ensure meant that the issue was inside the gearbox itself.
The gearbox was held together with four screws, each with the oddly-shaped internal socket head where I don’t have a tool. However, with the knowledge that I really could always find replacement small bolts, I used a pair of Vicegrips to undo them – which is, it didn’t matter when they got somewhat mutilated along the way of disassembly.
Within the gearbox the worm drive and its associated plastic gear could possibly be seen. Initially I thought the plastic cog should have stripped, but inspection showed that this wasn’t the way it is. So 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 the cable may 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 final in the cable had been a little worn and yes it was slipping back out of the drive hole of the worm. (The slippage was occurring inside the area marked with the arrow.)
The fix was dead-easy – simply pull the drive cable out from the sheath a little, crimp a spring steel washer onto it (backed from a plain washer that here has run out of sight – it’s fallen into the mouth from the sheath) after which push the drive cable down again in the sleeve. Using 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 to the gearbox.
The mechanism could then be reassembled. New screws were utilised 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 plus a smear of grease was added to the tracks that this nylon sleeves run on. In the seat, the mechanism dexqpky30 checked by applying power – and worked fine.
So in cases like this the fix cost nearly nothing, except a bit of time.
Since all of the motors had now been became in working order, fixing the electrical rearwards travel and front up/down motion could just be achieved using the seat back into the car – it looked just as if it needed to 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.
Fixing the remainder
Beneath the driver’s seat can be a control Power seat switch both relays and the seat memory facility. Close inspection of your plugs and sockets on the system along with the associated loom revealed that some corrosion had occurred. (Perhaps at some stage a drink have been spilled onto it.) The corrosion showed itself as 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 in the pins of your plug, that have been otherwise impossible to access to clean up.
At commercial rates, fixing the seat will have cost large sums of money – within labour time and within a complete replacement head restraint up/down mechanism. Nobody could have bothered repairing the gearbox drive – they’d have just replaced the whole thing. The corroded pins? That might have been cheaper, but the total bill will have still been prohibitive.