: engine braking a la overrun clutch



eldorado1
07-27-05, 07:38 PM
Semi-northstar related... Question is, when the shift arm is in overdrive, and the pcm wants 1st through 3rd gear, there's no engine braking.. It appears as though it's controlled through the over-run clutch? Is there any way to force engine braking under all circumstances? I do not mind drilling into the valve body. Just want to make sure that this is doable, and having the ORC on all the time won't be a problem...

danbuc
07-31-05, 08:55 PM
The over running clutch is what allows the starter to engage and disengage the pinion gear and flywheel so that it can mesh properly, and then be retracted once the engine takes over to prevent damage.

I'm not entirely sure what you mean by no engine braking when the PCM 'want 1st -3rd gear"? If you manually slect a gear and then run that gear out to it's maximum speed without redlining, as soon as you let off the gas (since are still in that gear) the engine will begin to brake the vehicle. In overdrive, you don't notice it, because the RPM's are so low, and on the highway the TCC is lock up too. For example, say your doing 75mph down a long hill, if you just suddenly pull your foot off of the gas, the engine will begin to brake the car, you just don't feel it as much because of the tall gears used in overdrive. Now if you had manually select 2nd gear for example and then ran the car up to 70mph, you would notice the engine braking much more, because the rev's are higher, and the gears are shorter as well. As far as purposely making the engine brake the car, all you have to doo is manually select a lower gear, as you let your foot off the gas.

eldorado1
07-31-05, 11:22 PM
The over running clutch is what allows the starter to engage and disengage the pinion gear and flywheel so that it can mesh properly, and then be retracted once the engine takes over to prevent damage.

I'm not entirely sure what you mean by no engine braking when the PCM 'want 1st -3rd gear"? If you manually slect a gear and then run that gear out to it's maximum speed without redlining, as soon as you let off the gas (since are still in that gear) the engine will begin to brake the vehicle. In overdrive, you don't notice it, because the RPM's are so low, and on the highway the TCC is lock up too. For example, say your doing 75mph down a long hill, if you just suddenly pull your foot off of the gas, the engine will begin to brake the car, you just don't feel it as much because of the tall gears used in overdrive. Now if you had manually select 2nd gear for example and then ran the car up to 70mph, you would notice the engine braking much more, because the rev's are higher, and the gears are shorter as well. As far as purposely making the engine brake the car, all you have to doo is manually select a lower gear, as you let your foot off the gas.

LOL! You're as confused as a baby in a topless bar! THe overrun clutch is what gives the car "engine braking". When you select manual second, and let off the gas...... the slowing down action you feel is because the overrun clutch is "on". BUT...... when you select overdrive, and say, the transmission loses power and defaults to second...... there will be NO engine braking. If you step on the gas, the rpms will jump from idle to whatever... say 4000rpms. let off the gas, and it'll jump down to idle.

The question is how to get engine braking when in O/D and the transmission loses power (or the PCM selects a gear other than 4th.)

danbuc
08-01-05, 11:26 AM
Nevermind, we're talking abotu two seperate things here. I thought you were referring to the cluth type assembly used on starter motors to prevent damage when the engine takes over. It is sometimes referred to as "and over-running clutch" to keep the motor from over-running when the engine takes over. As far as the tranny goes, I've got nothin' on that. Sorry for the confusion...hehe.