If you purchase an older luxury car there are 2 things near certain: the very first is it may have Power seat switch, along with the second is the fact at least one from the seat functions won’t work! So, just how hard could it be to repair a defective leccy seat? Obviously it depends a whole lot of what the exact dilemma is as well as the car in question, but as a guide let’s look into fixing the seats in a E23 1985 BMW 735i. The seat architecture in other cars will be different, however if you don’t possess any idea where you’d even begin to fix this type of problem, this story will certainly be appropriate to you.
The top seats in the BMW are one of 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 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. (If the seats that you are focusing on have airbags, you need to look at the factory workshop manual to find out the safe procedure for working on the seats.)
The seat functions are all controlled with this complex switchgear, which happens to be duplicated in the passenger side from the car. As can be seen here, the driver’s seat also offers three position memories. Incidentally, the rear seat can also be electric, having an individual reclining function for every side! Nevertheless in this car, the rear 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 might be moved backwards using one of the memory keys.
The front side in the seat couldn’t be raised.
The pinnacle restraint wouldn’t move up or down, although in this instance the motor may be heard whirring uselessly whenever the right buttons were pressed.
Obtaining the Seat Out
Step one was to get rid of the seat from the car in order that usage of all the bits could possibly be gained. The seat was electrically moved forward and therefore the two rear floor-mounting bolts undone.
But how was access likely to be gained towards the front mounting bolts? Pressing the adjustment button didn’t cause the seat to advance backwards, and through this stage the memory button had stopped allowing that action also! The solution was to manually apply capability to the seat to activate the motor. Every one of the connecting plugs were undone and others plugs containing the heaviest cables inspected. (You will have wiring for seat position transducers and such things as that within the loom, however the motors is going to be powered by noticeably heavier cables.)
Employing a durable, over-current protected, 12V power source (that one was made very cheaply – see DIY Budget 12-volt Bench Supply), power was put on pairs of terminals connecting on the thick wires before the right connections were found. The seat was then powered backwards till the front mounting bolts might be accessed. They were removed and therefore the Power seat motor moved forward until it sat in the middle of its tracks, making it easier to get rid of the automobile.
Fixing your head Restraint
This is what the BMW seat appears like underneath. Four electric motors can be viewed, plus there’s a fifth in the backrest. Each motor unit connects to your sheathed, flexible drive cable that therefore connects into a reduction gearbox. When 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 might be manufactured from each motor by connecting ability to its wiring plug and ensuring the function worked mainly because it should. Every function however the head restraint up/down worked, and so the problems aside from the head restraint showed that they must maintain the switches, not the motors or associated drive systems. So how to repair the pinnacle restraint up/down movement?
The back trim panel of your seat came off from the simple undoing of four screws. Much like one other seat motors, the mechanism contained a brush-type DC motor driving a flexible type of 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 the drive cable sheath revealed that the drive cable inside was turning, hence the problem must lie in the mechanism closest to the pinnacle restraint itself.
The adjustment mechanism was held in place with one screw, that has been accessible with the leather upholstery disengaged from small metal spikes that held it into position. The legs in the head restraint clipped into plastic cups about the mechanism (the first is arrowed here) and these had the ability to be popped out with the careful use of a screwdriver.
The complete upper portion of the adjustment mechanism was then capable of being lifted out of your seat back and placed next to the seat. Be aware that the electrical motor stayed into position – it didn’t must be removed also.
To view what was going on inside the unit, it should be pulled apart. It absolutely was 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 act of the pinion (a compact gear) on the rack (a toothed metal strip) could possibly be assessed. Neither looked particularly worn and applying capacity to the motor demonstrated that actually the pinion wasn’t turning. To ensure meant the problem was in the gearbox itself.
The gearbox was held along with four screws, each with an oddly-shaped internal socket head where I don’t have a tool. However, knowing that I could possibly always find replacement small bolts, I used a couple of Vicegrips to undo them – that is certainly, it didn’t matter when they got a lttle bit mutilated during this process of disassembly.
In the gearbox the worm drive along with its associated plastic gear might be seen. Initially I figured that the plastic cog need to have stripped, but inspection demonstrated that this wasn’t the case. Why wasn’t drive getting out of the gearbox? Again I applied power to the motor and watched what went down. What I found was even though cable could possibly be heard rotating inside its sheath, that drive wasn’t arriving at the worm. Pulling the worm gear out and inspecting the square-section drive cable demonstrated that the conclusion in the cable was a little worn and yes it was slipping back out from 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 of your sheath a little bit, crimp a spring steel washer onto it (backed with a plain washer that here has run out of sight – it’s fallen back into the mouth of your sheath) and then push the drive cable down again in their sleeve. With the crimped washer preventing the worn part of the cable from sliding back out of the square drive recess within the worm, drive was restored for the gearbox.
The mechanism could then be reassembled. New screws were utilized to change the Vicegripped ones, while 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 placed on the tracks how the nylon sleeves operate on. During 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 a while.
Since all 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 during the car – it looked as though it would have to be a wiring loom or switchgear problem. But even though the seat was out, it made sense to wipe over-all the tracks and exposed cogs and re-grease them.
Within the driver’s seat can be a control Power seat switch both relays and also the seat memory facility. Close inspection of the plugs and sockets on both the system and also 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 being a green deposit around the pins and several tedious but careful scraping using 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 inside the pins of your plug, which were otherwise impossible to get into to clean.
At commercial rates, fixing the seat will have cost hundreds of dollars – within labour some time and inside a complete replacement head restraint up/down mechanism. Nobody might 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 would have still been prohibitive.