If you purchase an older luxury car there are two things near certain: first is which it could have Power seat switch, and the second is a minimum of one of your seat functions won’t work! So, just how hard will it be to solve a defective leccy seat? Obviously this will depend a good deal of what the particular problem is and the car under consideration, but as a guide let’s take a look at fixing the seats inside an E23 1985 BMW 735i. The seat architecture in other cars varies, however, if you don’t have idea where you’d even begin to fix this type of problem, this story will definitely be appropriate for you.
The leading seats within the BMW are one of the most complex that you’ll discover in any older car. They have electric adjustment for front/back travel, front from 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 so they don’t have airbags. (If the seats that you are currently working on have airbags, you have to look at the factory workshop manual to find out the safe procedure for concentrating on the seats.)
The seat functions are controlled by this complex switchgear, which happens to be duplicated around the passenger side of the car. As is seen here, the driver’s seat also provides three position memories. Incidentally, the back seat is likewise electric, with an individual reclining function for every side! But 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 could be moved backwards using one of the memory keys.
The leading in the seat couldn’t be raised.
The top restraint wouldn’t move up or down, although in cases like this the motor may be heard whirring uselessly whenever the best buttons were pressed.
Obtaining the Seat Out
The first task would be to eliminate the seat from your car to ensure that access to all the bits could possibly be gained. The seat was electrically moved forward and then the two rear floor-mounting bolts undone.
So how was access going to be gained for the front mounting bolts? Pressing the adjustment button didn’t make the seat to advance backwards, and also by this stage the memory button had stopped allowing that action too! The answer would be to manually apply capacity to the seat to activate the motor. Each of the connecting plugs were undone and people plugs containing the heaviest cables inspected. (You will find wiring for seat position transducers and things such as that inside the loom, however the motors will likely be powered by noticeably heavier cables.)
Using a high quality, over-current protected, 12V power supply (this was developed very cheaply – see DIY Budget 12-volt Bench Supply), power was applied to pairs of terminals connecting towards the thick wires before the right connections were found. The seat was then powered backwards till the front mounting bolts may be accessed. They were removed and therefore the Power seat flexible shaft moved forward until it sat in the center of its tracks, making it easier to escape the automobile.
Fixing your head Restraint
This is exactly what the BMW seat seems like underneath. Four electric motors can be seen, plus there’s a fifth inside of the backrest. Each motor unit connects into a sheathed, flexible drive cable that subsequently connects to a reduction gearbox. Because I later discovered, inside each gearbox is really a worm that drives a plastic gearwheel, which drives a pinion operating on a rack. At this point, though, a simple test could be manufactured from each motor by connecting capability to its wiring plug and ensuring that the function worked as it should. Every function however the head restraint up/down worked, and so the problems aside from the head restraint showed that they must stay in the switches, not the motors or associated drive systems. So how to solve the head restraint up/down movement?
The rear trim panel from the seat came off with the simple undoing of four screws. Similar to 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, but 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 within the mechanism nearest 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 into position. The legs from the head restraint clipped into plastic cups around the mechanism (the initial one is arrowed here) and they were able to be popped by helping cover their the careful consumption of a screwdriver.
The complete upper portion of the adjustment mechanism was then capable of being lifted from the seat back and placed near the seat. Note that the electrical motor stayed set up – it didn’t should be removed also.
To discover what was going on inside of the unit, it must be pulled apart. It absolutely was obviously never created to be repairable, so the first disassembly step involved drilling out your rivets which held the plastic sliders in position on their track. By using these out, the action of the pinion (a small gear) about the rack (a toothed metal strip) may be assessed. Neither looked particularly worn and applying ability to the motor revealed that the truth is the pinion wasn’t turning. In order that resulted in the issue was within 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, realizing that I could possibly always find replacement small bolts, I used a set of Vicegrips to undo them – that may be, it didn’t matter once they got somewhat mutilated in the process of disassembly.
In the gearbox the worm drive and its associated plastic gear may be seen. Initially I was thinking that the plastic cog should have stripped, but inspection revealed that this wasn’t the situation. Why then wasn’t drive getting out of the gearbox? Again I applied capability to the motor and watched what actually transpired. Things I found was although the cable could possibly be heard rotating inside its sheath, that drive wasn’t reaching the worm. Pulling the worm gear out and inspecting the square-section drive cable revealed that the conclusion of the cable was a little worn and yes it was slipping back out from the drive hole from the worm. (The slippage was occurring within the area marked by the arrow.)
The fix was dead-easy – simply pull the drive cable out of the sheath a little bit, crimp a spring steel washer on it (backed from 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 in its sleeve. Together with the crimped washer preventing the worn part of the cable from sliding back out of your square drive recess in the worm, drive was restored to the gearbox.
The mechanism could then be reassembled. New screws were used to change the Vicegripped ones, while 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 how the nylon sleeves operate on. During the seat, the mechanism dexqpky30 checked by utilizing power – and worked fine.
So in cases like this the fix cost nearly nothing, except a while.
Since each 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 with the seat during the car – it looked like it had to be a wiring loom or switchgear problem. But even though the seat was out, it made sense to wipe overall the tracks and exposed cogs and re-grease them.
Beneath the driver’s seat can be a control Power seat switch both relays and the seat memory facility. Close inspection in the plugs and sockets on both the unit and also the associated loom showed that some corrosion had occurred. (Perhaps at some stage a drink had been spilled on it.) The corrosion showed itself being a green deposit around the pins and a few tedious but careful scraping having a small flat-bladed screwdriver removed it. Once that was done, the associated plug was inserted and pulled out 20-30 times to scrape off the deposit in the pins of your plug, that have been otherwise impossible to access to wash.
At commercial rates, fixing the seat will have cost several hundred dollars – both in labour time and in a complete replacement head restraint up/down mechanism. No-one would have bothered repairing the gearbox drive – they’d have just replaced the whole thing. The corroded pins? That might have been cheaper, but the total bill will have still been prohibitive.