If you buy an older luxury car there are two things near certain: the initial one is which it could have Power seat switch, as well as the second is one or more of your seat functions won’t work! So, just how hard will it be to solve a defective leccy seat? Obviously it depends a good deal on what the specific dilemma is along with the car in question, but as a guide let’s take a look at fixing the seats in a E23 1985 BMW 735i. The seat architecture in other cars may vary, but when you don’t have idea where you’d even learn to fix this kind of problem, this story will certainly be of use to you personally.
The front seats from 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 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 plus they don’t have airbags. (In case the seats that you are taking care of have airbags, you need to see the factory workshop manual to ascertain the safe procedure for working on the seats.)
The seat functions are all controlled with this complex switchgear, which is duplicated on the passenger side in the car. As can be seen here, the driver’s seat even offers three position memories. Incidentally, the rear seat is additionally electric, with an individual reclining function for each and every side! Nevertheless in this car, your back 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 might be moved backwards with one of the memory keys.
The front side of the seat couldn’t be raised.
The head restraint wouldn’t move up or down, although in such a case the motor could be heard whirring uselessly whenever the proper buttons were pressed.
Getting the Seat Out
The first step was to get rid of the seat through the car so that entry to every one of the bits could be gained. The seat was electrically moved forward and so the two rear floor-mounting bolts undone.
So how was access going to be gained on the front mounting bolts? Pressing the adjustment button didn’t cause the seat to go backwards, and also by this stage the memory button had stopped allowing that action at the same time! The best solution would be to manually apply capability to the seat to activate the motor. Each of the connecting plugs were undone and those plugs containing the heaviest cables inspected. (You will have wiring for seat position transducers and things like that within the loom, although the motors will be powered by noticeably heavier cables.)
Employing a durable, over-current protected, 12V power supply (this was created very cheaply – see DIY Budget 12-volt Bench Supply), power was placed on pairs of terminals connecting towards the thick wires till the right connections were found. The seat was then powered backwards before the front mounting bolts might be accessed. They were removed and therefore the Power seat motor moved forward until it sat in the midst of its tracks, making it simpler to escape the auto.
Fixing the pinnacle Restraint
And this is what the BMW seat appears like underneath. Four electric motors can be seen, plus there’s a fifth in the backrest. Each motor unit connects into a sheathed, flexible drive cable that therefore connects to a reduction gearbox. As I later discovered, inside each gearbox is really a worm that drives a plastic gearwheel, which drives a pinion operating on the rack. At this time, though, an easy test could possibly be created from each motor by connecting capacity to its wiring plug and ensuring that the function worked since it should. Every function although the head restraint up/down worked, hence the problems apart from your head restraint showed that they must stay in the switches, not the motors or associated drive systems. So how to fix the pinnacle restraint up/down movement?
The rear trim panel of your seat came off from the simple undoing of four screws. As with one other seat motors, the mechanism was comprised of a brush-type DC motor driving a versatile cable that went to the adjust mechanism. The motor worked fine with power connected, however the head restraint didn’t move. Feeling the away from the drive cable sheath revealed that the drive cable inside was turning, therefore the problem must lie in the mechanism nearest to the pinnacle restraint itself.
The adjustment mechanism was located 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 in the head restraint clipped into plastic cups on the mechanism (the initial one is arrowed here) which could be popped out with the careful usage 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. Be aware that the electric motor stayed into position – it didn’t should be removed as well.
To find out that which was going on in the unit, it must be pulled apart. It absolutely 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 his or her track. With these out, the action of the pinion (a small gear) in the rack (a toothed metal strip) might be assessed. Neither looked particularly worn and applying ability to the motor showed that actually the pinion wasn’t turning. So that meant the situation was inside the gearbox itself.
The gearbox was held combined with four screws, each with an oddly-shaped internal socket head that I don’t possess a tool. However, understanding that I was able to always find replacement small bolts, I used a pair of Vicegrips to undo them – that is certainly, it didn’t matter once they got a lttle bit mutilated during this process of disassembly.
In the gearbox the worm drive and its associated plastic gear could be seen. Initially I figured the plastic cog should have stripped, but inspection demonstrated that this wasn’t the case. So just why wasn’t drive getting away from the gearbox? Again I applied power to the motor and watched what happened. What I found was although the cable might be heard rotating inside its sheath, that drive wasn’t reaching the worm. Pulling the worm gear out and inspecting the square-section drive cable demonstrated that the final from the cable had been a little worn and it also was slipping back out from the drive hole of the worm. (The slippage was occurring inside of the area marked by the arrow.)
The fix was dead-easy – simply pull the drive cable out from the sheath a little, crimp a spring steel washer into it (backed by way of a plain washer that here has run out of sight – it’s fallen back into the mouth from the sheath) after which push the drive cable down again within its sleeve. With the crimped washer preventing the worn section of the cable from sliding back from the square drive recess within the worm, drive was restored towards the gearbox.
The mechanism could then be reassembled. New screws were used to switch the Vicegripped ones, whilst 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 the nylon sleeves run on. In the seat, the mechanism dexqpky30 checked by making use of power – and worked fine.
So in cases like this the fix cost nearly nothing, except some time.
Since every one of the motors had now been became in working order, fixing the electric rearwards travel and front up/down motion could basically be achieved with all the seat back in the car – it looked just as if it had to 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 remainder
Beneath the driver’s seat is really a control Power seat switch both relays as well as the seat memory facility. Close inspection of your plugs and sockets on both the machine as well as the associated loom revealed that some corrosion had occurred. (Perhaps at some stage a drink had been spilled on it.) The corrosion showed itself being a green deposit in the pins and several 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 inside of the pins of your plug, that have been otherwise impossible to access to completely clean.
At commercial rates, fixing the seat could have cost hundreds of dollars – within labour time and in a complete replacement head restraint up/down mechanism. Nobody might have bothered repairing the gearbox drive – they’d have just replaced everything. The corroded pins? That would have been cheaper, although the total bill could have still been prohibitive.