If you pick an older luxury car there are 2 things near certain: the very first is that it could have Power seat switch, along with the second is the fact one or more of your seat functions won’t work! Now how hard would it be to repair a defective leccy seat? Obviously all depends a great deal about what the exact dilemma is and the car under consideration, but being a guide let’s check out fixing the seats within an E23 1985 BMW 735i. The seat architecture in other cars varies, but when you don’t have idea where you’d even start to fix such a problem, this story is certain to be of use for you.
The front side seats within the BMW are amongst the most complex that you’ll get in any older car. They may have electric adjustment for front/back travel, front in the 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 don’t have airbags. (When the seats that you are currently taking care of have airbags, you must read the factory workshop manual to find out the safe procedure for focusing on the seats.)
The seat functions are common controlled from this complex switchgear, that is duplicated in the passenger side from the car. As is visible here, the driver’s seat also offers three position memories. Incidentally, the back seat is additionally electric, by having an individual reclining function for each side! Nevertheless in this car, your back seat was working just great.
The driver’s seat had three problems.
The button which moved the seat rearwards didn’t work. However, the seat could be moved backwards with one of the memory keys.
The front side from the seat couldn’t be raised.
The pinnacle restraint wouldn’t move up or down, although in such a case the motor could be heard whirring uselessly whenever the right buttons were pressed.
Receiving the Seat Out
The initial step would be to eliminate the seat through the car to ensure use of every one of the bits might 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 for the front mounting bolts? Pressing the adjustment button didn’t cause the seat to move backwards, and also by this stage the memory button had stopped allowing that action also! The answer ended up being to manually apply power to the seat to activate the motor. Every one of the connecting plugs were undone and people plugs containing the heaviest cables inspected. (You will see wiring for seat position transducers and things such as that from the loom, although the motors will probably be powered by noticeably heavier cables.)
Utilizing a durable, over-current protected, 12V power supply (this was created 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 until the front mounting bolts could possibly be accessed. They were removed and then the Power seat flexible shaft moved forward until it sat in the center of its tracks, making it simpler to get free from the car.
Fixing the top Restraint
This is exactly what the BMW seat seems like underneath. Four electric motors is seen, plus there’s a fifth inside the backrest. Each electric motor connects to some sheathed, flexible drive cable that consequently connects to some reduction gearbox. While I later discovered, inside each gearbox is actually a worm that drives a plastic gearwheel, which actually drives a pinion operating with a rack. At this point, though, a basic test could be made of each motor by connecting ability to its wiring plug and ensuring that the function worked mainly because it should. Every function however the head restraint up/down worked, therefore the problems other than the pinnacle restraint showed that they must stay in the switches, not the motors or associated drive systems. So how to correct the pinnacle restraint up/down movement?
The rear trim panel of your seat came off by the simple undoing of four screws. Similar to another seat motors, the mechanism contained a brush-type DC motor driving a versatile cable that traveled 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 indicated that the drive cable inside was turning, hence the problem must lie inside the mechanism closest to your head restraint itself.
The adjustment mechanism was held in place with one screw, that has been accessible together with 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 (one is arrowed here) and these had the ability to be popped out with the careful consumption of a screwdriver.
The whole upper part of the adjustment mechanism was then capable of being lifted out from the seat back and placed near the seat. Keep in mind that the electrical motor stayed into position – it didn’t must be removed as well.
To view what was occurring inside of the unit, it must be pulled apart. It was obviously never built 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 one of these out, the action of the pinion (a tiny gear) in the rack (a toothed metal strip) might be assessed. Neither looked particularly worn and applying ability to the motor indicated that in fact the pinion wasn’t turning. So that meant the problem was inside the gearbox itself.
The gearbox was held as well as four screws, each by having an oddly-shaped internal socket head where I don’t have got a tool. However, understanding that I was able to always find replacement small bolts, I used a set of Vicegrips to undo them – that is certainly, it didn’t matter when they got somewhat mutilated along the way of disassembly.
Inside the gearbox the worm drive and its associated plastic gear may be seen. Initially I assumed that the plastic cog will need to have stripped, but inspection demonstrated that this wasn’t the situation. 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 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 end of the cable had been a little worn and it was slipping back out of the drive hole from the worm. (The slippage was occurring inside of the area marked through the arrow.)
The fix was dead-easy – simply pull the drive cable out of your sheath a little, crimp a spring steel washer on it (backed by a plain washer that here has run out of sight – it’s fallen into the mouth of the sheath) after which push the drive cable back down within its sleeve. With the crimped washer preventing the worn section of the cable from sliding back from the square drive recess inside the worm, drive was restored towards the gearbox.
The mechanism could then be reassembled. New screws were utilised to exchange the Vicegripped ones, as the drilled-out rivets were also substituted for new screws and nuts (arrowed). The gearbox was re-greased before assembly and a smear of grease was placed on the tracks that the nylon sleeves operate on. During the seat, the mechanism dexqpky30 checked by applying power – and worked fine.
So in cases like this the fix cost nearly nothing, except a while.
Since all of the motors had now been became in working order, fixing the electric rearwards travel and front up/down motion could basically be achieved together with the seat in the car – it looked like it had 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 Rest
Underneath the driver’s seat is actually a control Power seat switch both relays and the seat memory facility. Close inspection in the plugs and sockets on both the system as well as the associated loom indicated that some corrosion had occurred. (Perhaps at some stage a drink have been spilled on it.) The corrosion showed itself as a green deposit around the pins and some tedious but careful scraping having a small flat-bladed screwdriver removed it. Once which was done, the associated plug was inserted and pulled out 20-30 times to scrape off of the deposit in the pins in the plug, which were otherwise impossible to access to completely clean.
At commercial rates, fixing the seat would have cost several hundred dollars – in labour efforts and in a complete replacement head restraint up/down mechanism. No person will have bothered repairing the gearbox drive – they’d have just replaced everything. The corroded pins? That would have been cheaper, but the total bill would have still been prohibitive.