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Alas, sometimes just when you think you finally have a solution... here it comes again. Truck has two seperate problems: Failure of the starter to properly engage the flywheel to rotate the engine and intermittent stalling/dying followed by long periods of failure to start even when starter rotates the engine. I'll break this into two separate posts in case anyone wants to toss ideas at one problem and not the other. {Sorry for the length of this post, I wanted to get as much information down as possible.}

Starter/Flywheel engagement.

Vehicle is a 1995 C3500 with a 6.5 Diesel with 5 Speed transmission. VIN: 1GBKC34FXSJ109440. This truck has a long history of premature starter replacements and has been to several shops over the years without the problem being solved. (There is another post in the tips section of OnDemand5 under the vehicle listing (Electrical/Starter/Troubleshooting. I thought we had solved the problem but if anyone wants to look over those postings for clues it will be appreciated.)

Initial symptom is a nice solid "clunk" from time to time when the key is turned to START but no engine rotation. Sounded like the classic 'pitted' contact plate problem and since the customer also complained of the stalling/no start condition and is known to attempt starts repeatedly until the batteries run down. Watching the starter pinion we discovered the gear teeth would strike the flywheel teeth "dead on" with no rotation. This was the same thing we found recently. With a new starter the problem was the same which pretty much eliminated the idea of a pitted contact plate in the solenoid. The basics were checked, (shimming the starter mount bolts for proper clearance, wiring, voltage drop, amperage draw, etc.)

Comparing with other vehicles we found there was less initial clearance between the flywheel and the pinion gear when 'at rest' than other GM's we checked. After everything else we shimmed the flywheel .120 (between the crank & flywheel) and had over 100 consecutive starter engagements. Since past history never had more than 10 - 15 sucessful engagements it looked like all was well.

Customer took the truck and it worked good for a few days until it stalled and died. I tried to get him to bring it in so we could check the stalling problem but since it would finally start after an hour or so he kept at it for another two weeks until he finally couldn't stand it any longer. He finally got it started and drove it in and complained that it hwas 'clunking' again on occasion. While testing the vehicle we had a number of good engagements until finally it 'clunked'. I suspect he may have wore the starter pretty back since on the bench it will spin but draws over 600 amps. On the other hand I don't want to shove another starter in this truck until I find a cause.

Back to square one and we have teeth hitting face to face with no rotation. When the teeth mesh the starter turns. Has anyone else encountered something like this? It seems like we have to be overlooking somthing simple and obvious so any thoughts are welcome.

Thanks,

Max

Just a wild shot in the dark, but with it being a 5spd truck, could the ring gear be installed on the flywheel backwards? I am not sure on this truck but most flywheel gears have beveled teeth on one side that make it easier for the starter gear to engage. I remember some maximas from days gone by that I would bevel the end of the teeth on the starter gear to take care of a problem with the starter not engageing the flywheel at times, might be worth a try on this.

liljoe,

We checked the ring gear and it is beveled (and not installed backwards). I even heated the ring gear and drifted it to make sure it was properly seated.

It appears the pinion must start spinning just before the teeth engage. Initially the starter motor would not spin unless the teeth meshed. If they slammed face-to-face the motor would not spin. It wasn't until we measured the 'at rest' distance that I came up with shimming the flywheel to increase the distance and when we tested the theory on the bench (using some highly sophisticated techniques with open end wrenches of varying thickness) that we were able to simulate the failure. If travel was equal to the distance when installed the motor would not spin. If the distance was increased by just over .100" the motor would spin every time it was tested. Then we measured installed distance on other vehicles and found they all had between .100"-.120" greater gap while at rest.

After shimming I refused to let the truck leave the shop until we had over 100 consecutive engagements. (Wouldn't you think that was plenty? LOL.)

Thanks for the idea though and if you come up with anything else, even if it sounds obvious please let me know.

Thanks,

Max

hydrolock? this is within the "injector module" failure era. does the starter fail to crank cold or just after truck stalls? i've had issues with battery ground issues before as well. as you know the starters can't take long term cranking. the strain on them gets stronger and stronger as the batteries wear down and the starters will not take it well. the sealant surrounding the windings melt and allow corrosion. a failed injector module will not throw codes and if the resistor isn't balanced with the pcm it will cause intermittent no start or stalling issues. there are two tsb's that may help 0064G, and 87-63-04. i've had no start, stall issues with the injector pump that's caused the starters to burn up. check the ground points for the batteries, isolate and test batteries. these trucks were so prone to pump module failure from heat we would install the "cooling" kit. i'd buy it on e/bay. if the module has been replaced at another shop don't assume the resistor is correct or even present. i have seen issues that haven't thrown codes. it didn't break my heart when these faded away.

Steve,

I suspect the starter has been 'cooked' by long crank times and I'll end up replacing it under warranty. Like you said they don't take long start cranking well. I tried several times to explain to the customer and his drivers not to crank longer than 10 seconds and not to crank more than a total of 3 times without letting the starter cool down for at least 10 minutes before cranking again. Apparently folks think if they crank until the starter melts down or the batteries are dead that will increase their chances of driving the vehicle. Last time the truck was in we had to replace battery cables because the terminal ends were melted off. Duhhhh.

From the somewhat disjointed and differing stories I get from the owner, his wife, and two of his drivers, I "think" they began encountering the start problems about a week or so after the stalling issue began and it probably stems from long, long, long crank times. {Each story is somewhat different, apparently from the thought process that if they withhold facts or truth it will make the job go faster and cost less.}

I pulled and printed the TSB's you refer to and gave them to the tech to run through.

The truck does have a heat sink kit that was installed at another shop. We will go over that installation and look for problems while it is here.

One thing that has remained consistant seems to be that when the starter teeth mesh the starter will spin and rotate the engine. If the teeth hit face to face the starter will not spin. On the bench the starter is pulling over 600 AMPS with no load so I am pretty sure it has suffered much abuse.

I'll chase those things you mentioned and let you know the results.

Thanks,

Max

We replaced the starter after it was determined the customer had indeed 'fried' it. New starter is working fine and engaging properly. The stalling/no restart issue is directly relates since the customer apparently thinks that cranking the starter until it melts will solve his problems.

I had a ford 6.0 with high pressure oil regulator failure last week that the owner thought the same thing, the innards were melted out of the starter and laying on the frame.....