91 740 turbo starter or ring gear?

twlaub · Post by **twlaub** » 16 Dec 2009, 21:38

I've got a '91 740 turbo that will, with some regularity, make that horrible sound when the start gear does not completely engage the ring gear. My question is: Is it more likely to be a starter problem (not throwing gear out well enough or other) or a worn ring gear?

Post by **billofdurham** » 17 Dec 2009, 12:09

I would think it is more likely to be the starter. The mechanism picks up all sorts of grunge which will slow it down. Worn brushes or bad connections can also be detrimental. Unfortunately, there is really only one way to find out, remove the starter motor.

Bill.

twlaub · Post by **twlaub** » 17 Dec 2009, 17:53

Thanks for the reply. Now, do you think the starter motor and solenoid shaft/gear just need cleaning up or does the start need to be replaced.

I don't know how hard it is to replace a starter on the car. It is a five minute job on my suburban (of course I don't even have to jack it up). Is it hard to get to the starter?

Post by **billofdurham** » 18 Dec 2009, 15:58

I have had starters with so much rubbish on the shaft that the pinion couldn't move far enough to engage with the flywheel. A good clean was all that was needed. The only way to find out is to take the starter out and have a look.

Removing the starter motor is fairly easy.
Disconnect the battery negative lead, with radio code handy.
Remove the undertray.
Disconnect the wires from the starter motor solenoid, marking them if necessary.
Remove the two securing bolts. Sometimes a tail bracket is fitted and you need to remove that. I have never seen one!
Remove the starter motor.
Installing is, as they say, a reverse of the above.

If the shaft is dirty you will see it straight away.

Bill.

twlaub · Post by **twlaub** » 18 Dec 2009, 18:29

Thanks. I found the starter today. It is on the driver's side of the engine at the rear. Of course it is at the rear because it has to engage the ring gear, which is between the engine and the transmission. It looks to me like you get to it from the top and it is fairly unobstructed. I don't see any need to remove an undertray. Is an undertray what I might call a plastic shroud under the front part of the engine?

I will try to tackle this tomorrow if I don't get hijacked to some other project.

Post by **billofdurham** » 19 Dec 2009, 12:16

On some models it is possible to get at it from the top so you are lucky as you will only need to go under the car when you, inevitably, drop a bolt or washer.

The undertray is under the front of the engine.

Bill.

twlaub · Post by **twlaub** » 19 Dec 2009, 20:26

It turns out I had to work from underneath to get at the two bolts. One of those bolts gave me a devil of a time. It was very hard to break loose and the tight quarters made it even harder to get any leverage.

We ended up with a new starter because when I got it out I could see that the teeth on the starter gear were sheared off. Instead of being beveled at the end so they can slip into the ring gear easily they were worn straight.

The ring gear itself was fine.

Thanks for the help.

Post by **billofdurham** » 20 Dec 2009, 10:58

You are welcome. Thank you for the update.

Bill.