If you buy an older luxury car there are 2 things near certain: the first is it can have Power seat motor, and also the second is that a minumum of one of your seat functions won’t work! Now how hard could it be to fix a defective leccy seat? Obviously this will depend a great deal on which the specific issue is and also the car in question, but like a guide let’s have a look at fixing the seats inside an E23 1985 BMW 735i. The seat architecture in other cars will be different, however, if you don’t have idea where you’d even commence to fix this sort of problem, this story is sure to be appropriate for your needs.
The top seats in the BMW are amongst the most complex that you’ll get 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 and they also don’t have airbags. (In the event the seats that you will be focusing on have airbags, you should look at the factory workshop manual to find out the safe procedure for working on the seats.)
The seat functions are typical controlled by this complex switchgear, which can be duplicated in the passenger side from the car. As is visible here, the driver’s seat even offers three position memories. Incidentally, the back seat is additionally electric, by having an individual reclining function for every side! But in this car, the rear 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 be moved backwards using one of the memory keys.
The front from the seat couldn’t be raised.
Your head restraint wouldn’t move up or down, although in such a case the motor could be heard whirring uselessly whenever the best buttons were pressed.
Obtaining the Seat Out
The first task would be to get rid of the seat through the car so that usage of every one of the bits could be gained. The seat was electrically moved forward and so the two rear floor-mounting bolts undone.
But exactly how was access gonna be gained on the front mounting bolts? Pressing the adjustment button didn’t increase the risk for seat to move backwards, and also this stage the memory button had stopped allowing that action also! The answer was to manually apply ability to the seat to activate the motor. Every one of the connecting plugs were undone and others plugs containing the heaviest cables inspected. (There will be wiring for seat position transducers and things such as that in the loom, however the motors is going to be powered by noticeably heavier cables.)
Using a heavy-duty, over-current protected, 12V power supply (that one was created very cheaply – see DIY Budget 12-volt Bench Supply), power was applied to 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. These were removed and so the Power seat switch moved forward until it sat in the midst of its tracks, making it simpler to get out of the car.
Fixing the pinnacle Restraint
This is what the BMW seat seems like underneath. Four electric motors is visible, plus there’s a fifth in the backrest. Each motor unit connects into a sheathed, flexible drive cable that subsequently connects to some reduction gearbox. While I later discovered, inside each gearbox is actually a worm that drives a plastic gearwheel, which often drives a pinion operating with a rack. At this stage, though, a straightforward test could possibly be made from each motor by connecting capability to its wiring plug and being sure that the function worked as it should. Every function nevertheless the head restraint up/down worked, hence the problems besides the top 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 back trim panel from the seat came off from the simple undoing of four screws. Much like one other seat motors, the mechanism consisted of a brush-type DC motor driving a flexible type of cable that visited the adjust mechanism. The motor worked fine with power connected, although the head restraint didn’t move. Feeling the outside of the drive cable sheath revealed that the drive cable inside was turning, and so the problem must lie from the mechanism closest to the pinnacle restraint itself.
The adjustment mechanism was held in place with one screw, which was accessible with all the leather upholstery disengaged from small metal spikes that held it set up. The legs from the head restraint clipped into plastic cups on the mechanism (the initial one is arrowed here) and they were able to be popped out with the careful use of a screwdriver.
The complete upper area of the adjustment mechanism was then able to be lifted out from the seat back and placed next to the seat. Note that the electrical motor stayed in position – it didn’t need to be removed also.
To view that which was occurring within the unit, it would have to be pulled apart. It had been obviously never designed to be repairable, so the first disassembly step involved drilling out your rivets which held the plastic sliders into position on his or her track. By using these out, the action of the pinion (a tiny gear) on the rack (a toothed metal strip) might be assessed. Neither looked particularly worn and applying capability to the motor revealed that in reality the pinion wasn’t turning. To ensure meant that the problem was inside the gearbox itself.
The gearbox was held along with four screws, each with the oddly-shaped internal socket head for which I don’t possess 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, it didn’t matter if they got a bit mutilated at the same time of disassembly.
In the gearbox the worm drive and its particular associated plastic gear might be seen. Initially I assumed that this plastic cog need to 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 power to the motor and watched what actually transpired. A Few Things I found was even though the cable may 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 showed that the final of the cable had been a little worn and it was slipping back out from the drive hole in the worm. (The slippage was occurring in the area marked by the arrow.)
The fix was dead-easy – simply pull the drive cable from the sheath a little, crimp a spring steel washer onto it (backed by way of a plain washer that here is out of sight – it’s fallen back into the mouth of the sheath) after which push the drive cable down again in its sleeve. With all the crimped washer preventing the worn portion of the cable from sliding back out of your square drive recess within the worm, drive was restored to the gearbox.
The mechanism could then be reassembled. New screws were utilised to switch the Vicegripped ones, even though the drilled-out rivets were also replaced with new screws and nuts (arrowed). The gearbox was re-greased before assembly and a smear of grease was positioned 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 bit of time.
Since every one of the motors had now been proved to be in working order, fixing the electric rearwards travel and front up/down motion could only be achieved with all the seat during the car – it looked as though it had to be a wiring loom or switchgear problem. But as the seat was out, it made sense to wipe total the tracks and exposed cogs and re-grease them.
Fixing the others
Underneath the driver’s seat is a control Power seat switch both relays as well as the seat memory facility. Close inspection of your plugs and sockets on the device as well as the associated loom revealed that some corrosion had occurred. (Perhaps at some stage a drink had been spilled upon it.) The corrosion showed itself like a green deposit around the pins and several 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 the deposit inside of the pins in the plug, that have been otherwise impossible to get into to wash.
At commercial rates, fixing the seat would have cost large sums of money – within labour efforts and in a complete replacement head restraint up/down mechanism. No one will have bothered repairing the gearbox drive – they’d have just replaced the whole thing. The corroded pins? That might have been cheaper, however the total bill could have still been prohibitive.