If you buy an older luxury car there are 2 things near certain: the very first is which it can have Power seat motor, as well as the second is the fact a minumum of one in the seat functions won’t work! So, just how hard could it be to solve a defective leccy seat? Obviously it all depends a lot on what the specific concern is and also the car under consideration, but like a guide let’s take a look at fixing the seats in a E23 1985 BMW 735i. The seat architecture in other cars can vary, however if you don’t have any idea where you’d even commence to fix this type of problem, this story will certainly come in handy for you.
The leading 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 and they also don’t have airbags. (In the event the seats that you are working on have airbags, you should read the factory workshop manual to find out the safe procedure for taking care of the seats.)
The seat functions are controlled by this complex switchgear, which can be duplicated about the passenger side of the car. As is visible here, the driver’s seat also offers three position memories. Incidentally, the back seat is also electric, with an individual reclining function for every single side! But also in this car, the rear seat was working perfectly.
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 in 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.
Obtaining the Seat Out
Step one was to take away the seat through the car so that access to all of the bits may be gained. The seat was electrically moved forward and so 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 make the seat to advance backwards, and by this stage the memory button had stopped allowing that action also! The best solution was to manually apply capability to the seat to activate the motor. All of the connecting plugs were undone and the ones plugs containing the heaviest cables inspected. (You will have wiring for seat position transducers and things such as that inside the loom, however the motors is going to be powered by noticeably heavier cables.)
By using a heavy duty, over-current protected, 12V power source (this particular one was created very cheaply – see DIY Budget 12-volt Bench Supply), power was applied to pairs of terminals connecting on the thick wires until the right connections were found. The seat was then powered backwards till the front mounting bolts could be accessed. These were removed and then the Power seat motor moved forward until it sat in the midst of its tracks, making it simpler to get out of the car.
Fixing the Head Restraint
This is just what the BMW seat appears to be underneath. Four electric motors can be seen, plus there’s a fifth within the backrest. Each motor unit connects to some sheathed, flexible drive cable that therefore connects to a reduction gearbox. Because I later discovered, inside each gearbox is really a worm that drives a plastic gearwheel, which often drives a pinion operating on a rack. During this period, though, a straightforward test could be created from each motor by connecting capability to its wiring plug and ensuring the function worked since 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. But exactly how to correct the pinnacle restraint up/down movement?
The back trim panel of your seat came off through the simple undoing of four screws. Just like other 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 away from the drive cable sheath established that the drive cable inside was turning, and so the problem must lie in the mechanism nearest to your head restraint itself.
The adjustment mechanism was kept in place with one screw, which had been accessible together with the leather upholstery disengaged from small metal spikes that held it into position. The legs of the head restraint clipped into plastic cups about the mechanism (the first is arrowed here) and those had the ability to be popped out with the careful use of a screwdriver.
The complete upper section of the adjustment mechanism was then capable of being lifted from the seat back and placed near the seat. Note that the electric motor stayed in place – it didn’t must be removed as well.
To discover what was occurring inside of the unit, it would have to be pulled apart. It was actually obviously never created to be repairable, and so the first disassembly step involved drilling the rivets which held the plastic sliders in position on their track. With these out, the action of the pinion (a small gear) on the rack (a toothed metal strip) could be assessed. Neither looked particularly worn and applying capacity to the motor indicated that in reality the pinion wasn’t turning. In order that resulted in the issue was in the gearbox itself.
The gearbox was held along with four screws, each with the oddly-shaped internal socket head for which I don’t use a tool. However, with the knowledge that I could always find replacement small bolts, I used a pair of Vicegrips to undo them – that is, it didn’t matter if they got a little mutilated at the same time of disassembly.
Inside of the gearbox the worm drive along with its associated plastic gear could possibly be seen. Initially I figured that this plastic cog should have stripped, but inspection showed that this wasn’t the truth. Why wasn’t drive getting out of the gearbox? Again I applied capacity to the motor and watched what happened. The Things I found was although the cable could 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 revealed that the final in the cable had been a little worn and it was slipping back from the drive hole from the worm. (The slippage was occurring in the area marked by the arrow.)
The fix was dead-easy – simply pull the drive cable out from the sheath just 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 in the sheath) then push the drive cable back down in its sleeve. With the crimped washer preventing the worn area of the cable from sliding back out of the square drive recess inside the worm, drive was restored for the gearbox.
The mechanism could then be reassembled. New screws were utilized to change 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 as well as a smear of grease was added to the tracks the nylon sleeves operate on. Back into the seat, the mechanism dexqpky30 checked by applying power – and worked fine.
So in cases like this the fix cost nearly nothing, except a little while.
Since all of the motors had now been proved to be in working order, fixing the electrical rearwards travel and front up/down motion could simply be achieved together with the seat during the car – it looked like it must be a wiring loom or switchgear problem. But as the seat was out, it made sense to wipe over all the tracks and exposed cogs and re-grease them.
Fixing the Rest
Within 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 for both the device and also 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 a few tedious but careful scraping by using 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 away from the deposit in the pins of your plug, that had been otherwise impossible to gain access to to clean.
At commercial rates, fixing the seat will have cost hundreds of dollars – within labour time as well as inside a complete replacement head restraint up/down mechanism. No person would have bothered repairing the gearbox drive – they’d have just replaced everything. The corroded pins? That could have been cheaper, however the total bill could have still been prohibitive.