Strange starter problem
12-31-2009, 11:16 AM
#1
Intermediate
Thread Starter
Strange starter problem
Have a strange starter related problem with my 84 N/A 944. The car usually starts and runs fine, but every so often, maybe once every 30 or 40 starts, I'll turn the key and the engine won't crank. Just a loud thunk under the car. The battery, wiring and connections seemed to be fine, so I assumed it was the 25 year old starter motor brushes or the solenoid contacts plugged up with clutch dust. A couple of weeks ago I put in a rebuilt starter. All seemed fine until last night, when it wouldn't crank again.
The solenoid makes a healthy sounding clunk, but the starter motor doesn't turn over. With the headlights on, the lights do not dim at all, so the starter motor doesn't seem to be drawing any current. I rocked the car in gear and then it started right up. My assumption is that the bendix gear on the starter is hitting the flywheel instead of engaging the flywheel gear ring teeth.
Is that how these Bosch starters work? If the starter bendix gear is blocked from extending fully, will the solenoid contacts not be able to close and power the starter motor?
Can I inspect the flywheel for damaged teeth through the clutch inspection port, or do I need to take the starter back out? Or, do these starters ever require a shim to engage properly?
Couldn't find any postings on this so I assume it's not a common problem. thanks for your help. -Gary
The solenoid makes a healthy sounding clunk, but the starter motor doesn't turn over. With the headlights on, the lights do not dim at all, so the starter motor doesn't seem to be drawing any current. I rocked the car in gear and then it started right up. My assumption is that the bendix gear on the starter is hitting the flywheel instead of engaging the flywheel gear ring teeth.
Is that how these Bosch starters work? If the starter bendix gear is blocked from extending fully, will the solenoid contacts not be able to close and power the starter motor?
Can I inspect the flywheel for damaged teeth through the clutch inspection port, or do I need to take the starter back out? Or, do these starters ever require a shim to engage properly?
Couldn't find any postings on this so I assume it's not a common problem. thanks for your help. -Gary
12-31-2009, 12:20 PM
#2
Proprietoristicly Refined
Rennlist Member
Rennlist Member
Reviewing the basics...
Check the negative ground on the bell housing.
Put a piece of tape over the TDC hole to avoid dropping a bolt in the clutch.
The battery connections. Are they OEM or do you have a lot of corrosion and aftermarket battery cable ends?
Since you have tried another rebuilt and the symptoms returned, the problem should be in the wiring.
To inspect the ring gear, remove the starter and hand crank the engine. Taking the plugs out makes this easy.
The 2nd starter you put in, was it a new rebuilt or a used rebuilt? Some of the aftermarket rebuilts from AutoZone and others have 2 qualities. The inexpensive rebuild that cleans and paints or the Bosch "remanufactured" style that replaces normal wear parts instead of just inspecting.
Finally, on the selonoid, there are 2 solder points. Carefully resolder.
When you reinstall the starter, do you feel any sloppyness when you twist the starter on the mounting bolts when they are finger tight? No great movement should be felt when twisted. If you have movement, the starter may be binding on the ring gear.
Whew!
GL
John_AZ
Check the negative ground on the bell housing.
Put a piece of tape over the TDC hole to avoid dropping a bolt in the clutch.
The battery connections. Are they OEM or do you have a lot of corrosion and aftermarket battery cable ends?
Since you have tried another rebuilt and the symptoms returned, the problem should be in the wiring.
To inspect the ring gear, remove the starter and hand crank the engine. Taking the plugs out makes this easy.
The 2nd starter you put in, was it a new rebuilt or a used rebuilt? Some of the aftermarket rebuilts from AutoZone and others have 2 qualities. The inexpensive rebuild that cleans and paints or the Bosch "remanufactured" style that replaces normal wear parts instead of just inspecting.
Finally, on the selonoid, there are 2 solder points. Carefully resolder.
When you reinstall the starter, do you feel any sloppyness when you twist the starter on the mounting bolts when they are finger tight? No great movement should be felt when twisted. If you have movement, the starter may be binding on the ring gear.
Whew!
GL
John_AZ
12-31-2009, 01:23 PM
#3
Rennlist Member
Is your battery fully charged? Believe it or not, it matters. The solenoid won't throw hard enough if it's weak from an underperforming alternator and extended driving with lights/heater/etc on in the winter temps, which tend to be the last straw for batteries that are marginal.
12-31-2009, 11:50 PM
#4
Rennlist Member
This is a known problem that can happen when using a newer-style starter. I had the same problem. I was able to find a PCA service bulletin that described the issue, which is that the newer-style starter creates a stronger magnetic field that confuses the flywheel sensors. There's a special bracket for these sensors that the later model cars use that is supposed to shield them from this magnetic field. The problem was supposedly limited to early cars using the newer starter since early cars didn't have this shielding bracket. My car had the this bracket, but I still had starter thunk every now and then. I fixed it by installing a rebuilt older-style starter. That one grenaded a couple of months ago so I reinstalled the newer starter and I get a small thunk every now and then but at least I know what the problem is. If you do a search on "starter thunk" on this forum you'll get some more details, and as John_AZ said, tape over that TDC hole before changing that bracket.
01-02-2010, 01:57 PM
#5
Intermediate
Thread Starter
Thank you all for your comments and suggestions. I have another project car all apart in the garage right now so I have to work on the 944 in the driveway. With the snow we've been getting, I haven't been able to bring myself to jack up the car and crawl around in the slush yet.
John, it does seem that the problem should be the in the wiring, but, there's really not much to it. I had checked the wiring before I ordered the replacement starter. But, I will carefully recheck each of the connections again.
Covering the TDC hole is a very, very good idea!
I used the $99 Autozone starter. They told me it was a Chinese rebuild and for $140. I could get one rebuilt in US. When it came in, though, it was labeled rebuilt in TN. Didn't open it to check the brushes or solenoid but the bendix gear looked new. It's pretty unlikely that 2 starters would have the same intermittent problem. (unless it's were a well known problem)
Didn't notice any slop in the starter mounting, but I wasn't looking for it so I check when I pull it back out.
I'm still thinking that the most likely cause could be a damaged flywheel ring gear preventing the solenoid from extending fully. Checking that will be a 2 person job.
Ross, I have another battery in another car that is 13 months old. It has the same terminals and looks to be the same size. I'll see if it fits and swap the batteries. You have a lot of credibility with me after correctly diagnosing my intake restriction when I first bought the car in September!
JayVee, can't read the PCA service bulletin on the PCA site because I'm not a member, but from the description in this forum, it doesn't sound like the same problem. When I have the intermittent problem, my starter motor doesn't turn at all. It doesn't seem to be drawing any current either. The "thunk" I described is the starter solenoid. I will watch for that problem though. Thanks for pointing it out.
Thanks again for your help.
Gary
John, it does seem that the problem should be the in the wiring, but, there's really not much to it. I had checked the wiring before I ordered the replacement starter. But, I will carefully recheck each of the connections again.
Covering the TDC hole is a very, very good idea!
I used the $99 Autozone starter. They told me it was a Chinese rebuild and for $140. I could get one rebuilt in US. When it came in, though, it was labeled rebuilt in TN. Didn't open it to check the brushes or solenoid but the bendix gear looked new. It's pretty unlikely that 2 starters would have the same intermittent problem. (unless it's were a well known problem)
Didn't notice any slop in the starter mounting, but I wasn't looking for it so I check when I pull it back out.
I'm still thinking that the most likely cause could be a damaged flywheel ring gear preventing the solenoid from extending fully. Checking that will be a 2 person job.
Ross, I have another battery in another car that is 13 months old. It has the same terminals and looks to be the same size. I'll see if it fits and swap the batteries. You have a lot of credibility with me after correctly diagnosing my intake restriction when I first bought the car in September!
JayVee, can't read the PCA service bulletin on the PCA site because I'm not a member, but from the description in this forum, it doesn't sound like the same problem. When I have the intermittent problem, my starter motor doesn't turn at all. It doesn't seem to be drawing any current either. The "thunk" I described is the starter solenoid. I will watch for that problem though. Thanks for pointing it out.
Thanks again for your help.
Gary
