If you buy an older luxury car the two main things near certain: the initial one is it can have Power seat flexible shaft, as well as the second is that one or more in the seat functions won’t work! Just how hard will it be to correct a defective leccy seat? Obviously it all depends a good deal on which the actual dilemma is as well as the car in question, but as a guide let’s check out fixing the seats inside 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 sort of problem, this story is sure to be of use to you personally.
The front side seats inside the BMW are amongst the most complex that you’ll find in any older car. They have electric adjustment for front/back travel, front of the seat up/down, rear in 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 will be working on have airbags, you need to read the factory workshop manual to find out the safe procedure for focusing on the seats.)
The seat functions are common controlled through this complex switchgear, which is duplicated on the passenger side of your car. As can be viewed here, the driver’s seat even offers three position memories. Incidentally, the rear seat is also electric, with the individual reclining function for each side! But in this car, the rear 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 could possibly be moved backwards with 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 cases like this the motor may be heard whirring uselessly whenever the right buttons were pressed.
Getting the Seat Out
Step one ended up being to remove the seat from the car in order that usage of all of the bits might be gained. The seat was electrically moved forward and so the two rear floor-mounting bolts undone.
But just how was access likely to be gained towards 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 as well! The perfect solution would be to manually apply power to the seat to activate the motor. All the connecting plugs were undone and others plugs containing the heaviest cables inspected. (There will be wiring for seat position transducers and things like that in the loom, nevertheless the motors will likely be powered by noticeably heavier cables.)
Employing a heavy duty, over-current protected, 12V power supply (this particular one was developed very cheaply – see DIY Budget 12-volt Bench Supply), power was applied to pairs of terminals connecting towards 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. These were removed and so the Power seat switch moved forward until it sat in the middle of its tracks, making it simpler to get out of the automobile.
Fixing the Head Restraint
This is what the BMW seat appears like underneath. Four electric motors is seen, plus there’s a fifth inside the backrest. Each electric motor connects to your sheathed, flexible drive cable that consequently connects to some reduction gearbox. Because I later discovered, inside each gearbox is really a worm that drives a plastic gearwheel, which often drives a pinion operating over a rack. During this period, though, an easy test might be made of each motor by connecting capacity to its wiring plug and making sure that the function worked since it should. Every function although the head restraint up/down worked, therefore the problems aside from the head restraint showed that they must be in the switches, not the motors or associated drive systems. But just how to repair your head restraint up/down movement?
The back trim panel of your seat came off with the simple undoing of four screws. Much like one other seat motors, the mechanism was made up of a brush-type DC motor driving a flexible 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 indicated that the drive cable inside was turning, hence the problem must lie from the mechanism nearest to the pinnacle restraint itself.
The adjustment mechanism was kept in place with one screw, that has been accessible together with the leather upholstery disengaged from small metal spikes that held it into position. The legs in the head restraint clipped into plastic cups on the mechanism (the first is arrowed here) which had the ability to be popped out with the careful utilization of a screwdriver.
The full upper portion of the adjustment mechanism was then able to be lifted from the seat back and placed near the seat. Keep in mind that the electric motor stayed in position – it didn’t should be removed at the same time.
To see that which was happening in the unit, it must be pulled apart. It had been obviously never made to be repairable, and so the first disassembly step involved drilling out the rivets which held the plastic sliders in place on their track. With one of these out, the act of the pinion (a small gear) in the rack (a toothed metal strip) could be assessed. Neither looked particularly worn and applying capacity to the motor revealed that in reality the pinion wasn’t turning. So that meant the situation was in the gearbox itself.
The gearbox was held combined with four screws, each by having an oddly-shaped internal socket head for which I don’t use a tool. However, knowing that I was able to always find replacement small bolts, I used a couple of Vicegrips to undo them – that may be, it didn’t matter once they got somewhat mutilated along the way of disassembly.
Within the gearbox the worm drive and its particular associated plastic gear could possibly be seen. Initially I assumed the plastic cog must have stripped, but inspection revealed that this wasn’t the situation. Why then wasn’t drive getting away from the gearbox? Again I applied capacity to the motor and watched what went down. Things I found was although the cable might 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 showed that the final of your cable was really a little worn and it also was slipping back out of your 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 bit, crimp a spring steel washer upon it (backed with a plain washer that here is out of sight – it’s fallen back into the mouth of your sheath) and after that push the drive cable down again in their sleeve. With all the crimped washer preventing the worn area of the cable from sliding back from the square drive recess in 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 replaced with new screws and nuts (arrowed). The gearbox was re-greased before assembly as well as a smear of grease was placed on the tracks the nylon sleeves are powered by. Back 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 a bit of time.
Since all the motors had now been turned out to be in working order, fixing the electrical rearwards travel and front up/down motion could only be achieved with the seat in the car – it looked as if it must be a wiring loom or switchgear problem. But while the seat was out, it made sense to wipe over-all the tracks and exposed cogs and re-grease them.
Fixing the remainder
Underneath 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 both the system along with the associated loom demonstrated that some corrosion had occurred. (Perhaps at some stage a drink ended up being spilled onto it.) The corrosion showed itself as a green deposit about 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 away from the deposit within the pins in the plug, that were otherwise impossible to access to completely clean.
At commercial rates, fixing the seat would have cost hundreds of dollars – within labour time and in the complete replacement head restraint up/down mechanism. No-one will have bothered repairing the gearbox drive – they’d have just replaced everything. The corroded pins? That could have been cheaper, however the total bill might have still been prohibitive.