Reminder: Heavy braking can cause stall

[TurboMustang370]

I was lucky enough to have this happen and experience it without any issues.
A while back I recall reading a post one of the users here wrote about practicing heavy braking to see the effects of ABS and non-ABS trucks. So I did it on our farm on a dirt road and was not able to get the truck to stall.

Well, the other day I had the M932a2 out (removed 5th wheel and loading ramps, no rear weight) and some lady decided she was going to slam on her brakes in-front of me. It was in a 45mph zone and I was keeping a distance of about 6 car lengths but when I saw her rear tires lock up, I pushed a little too hard on the air brakes. Trans was in 3rd gear and even with the ABS the rears locked up for a second (I think because of no weight over the axles) and sure as ****, trans couldn't downshift and the motor stalled, steering went into manual mode.
Luckily I had a heads up from reading on this site and knew I needed to shift into Neutral and tap the starter. Started right up and all was well.

Sorry for the long BS story but I figured if it helps one person avoid a problem/issue like another user here helped me, its worth it.

 

[wheelspinner]

This is why the military uses "confidence courses" to teach driving skills in panic situations. Training is everything. ANyone who has a place to should practice emergency stop actions in their trucks and fully understand them before "some lady" or other ignoramous pulls out in front of you. Its not if but when it will happen, and it will happen. Thanks for sharing.

 

[NDT]

I thought shifting the Allison into neutral at high speed was a no-no.

 

[ichudov]

I was lucky enough to have this happen and experience it without any issues.
A while back I recall reading a post one of the users here wrote about practicing heavy braking to see the effects of ABS and non-ABS trucks. So I did it on our farm on a dirt road and was not able to get the truck to stall.

Well, the other day I had the M932a2 out (removed 5th wheel and loading ramps, no rear weight) and some lady decided she was going to slam on her brakes in-front of me. It was in a 45mph zone and I was keeping a distance of about 6 car lengths but when I saw her rear tires lock up, I pushed a little too hard on the air brakes. Trans was in 3rd gear and even with the ABS the rears locked up for a second (I think because of no weight over the axles) and sure as ****, trans couldn't downshift and the motor stalled, steering went into manual mode.
Luckily I had a heads up from reading on this site and knew I needed to shift into Neutral and tap the starter. Started right up and all was well.

Sorry for the long BS story but I figured if it helps one person avoid a problem/issue like another user here helped me, its worth it.

Thanks for sharing. So, after you re-started, did you come to a complete stop, or did you re-engage the transmission while the truck was still moving?

 

[Suprman]

I believe it is the torque converter not unlocking fast enough when rpms drop below the lock/unlock point which drags the drivetrain down with hard braking and stalls the engine

 

[jrobinson5093]

I have had this happen. IT was not in a MV but it was a F650 pickup. It had a cat c7 and a allision auto. I had to panic stop from some one pulling out in front of me and it stalled the engine. I dont know what it is about big trucks that make people want to get infront of it so bad, but I just know that one day I will end up running over some ones car. It actually seems like they do it on purpous sometimes.

 

[TurboMustang370]

I was on a perfectly straight road so I was able to allow the truck to coast for about 3-5 seconds before restarting the truck in neutral. I was only traveling about 25-35mph by the time the truck stalled and 20-25mph when I restarted the truck. When the truck started, the idle leveled out and I shifted back into 5th gear. I wouldn't do this on purpose but in this situation it worked for me. The road was a back road with no shoulder and drainage culverts on both sides, no place to take the truck out of travel.

 

[ichudov]

OK, thanks for the explanation. I think that I understand now. I have a habit of driving to try to brake as gently and as rarely as possible. Just a weird habit. Maybe it would also help. And I also hate those people who pull in front of heavy vehicles and slam the brakes.

 

[o1951]

. I have a habit of driving to try to brake as gently and as rarely as possible. Just a weird habit. .

That is a GOOD habit. I do that, and time lights too whenever driving heavy vehicles. If you can keep it rolling, fuel consumption improves a lot.

 

[ichudov]

That is a GOOD habit. I do that, and time lights too whenever driving heavy vehicles. If you can keep it rolling, fuel consumption improves a lot.

Also, it helps prevent people from rear ending YOU.And as you said, it helps with MPG.

 

[bsteinborn]

I'm glad to hear it worked out for you. My 5 ton doesn't have the ABS upgrade and I'm aware of the stall issue so I've actually practiced doing exactly what you did. Always worried I'll forget though if I ever need to do it. Again, glad to hear you had no issues.

 

[smoke]

I wonder if you change transmission fluid back to atf(dexon) from the motor oil that comes in it. It would help the torque convertor disengage faster during a panic stop. Remember that motor oil is use due to less friction modifers. So less slip when trans shifts w/ heavy load. Plus easy of one less fluid to carry. We normally drive unload so we don't need the hard shifts.We can get away w/ dexon fluid which will allow little more slip.Just my 2 cents

 

[TurboMustang370]

I wonder if you change transmission fluid back to atf(dexon) from the motor oil that comes in it. It would help the torque convertor disengage faster during a panic stop. Remember that motor oil is use due to less friction modifers. So less slip when trans shifts w/ heavy load. Plus easy of one less fluid to carry. We normally drive unload so we don't need the hard shifts.We can get away w/ dexon fluid which will allow little more slip.Just my 2 cents

That's a thought. I will be flushing my trans when I get around to doing a complete service.

 

[Suprman]

I swapped one of my trucks over to dextron. I used the stuff right from the allison dealer. It smoothed it out a little. There is an adjustment for transmission fluid pressure it comes off the throttle linkage assembly. You would think it was a kick-down cable if you played with muscle cars. It has a threaded rod end with a nut, screwing the cable in towards the front of the motor increases fluid pressure and makes for harder shifts and unscrewing it makes for less pressure and in theory softer shifts. The truck I switched to dex still shifts hard, actually harder than others I have that I did not switch. I have also seen when I want to drive slow I have to get the rpms up to get the trans into second gear and then I can let off a little and it will stay in second unless I really slow down.

 

[o1951]

There are a lot of different ATF's, with different characteristics. Perhaps one of these is better for Allison trans.
[h=2]Current fluids[/h]

• ATF+4 - Most Dodge, Jeep, and Chrysler [SUP][8][/SUP]
• Mercon V - Most Ford, Mercury, Lincoln
• Mercon LV - Some Ford(DuratecHE), MAZDA in Europe or Asia
• Dexron VI - Most GM and pre-2004 Toyota products, some Ford applications
• ATF DW-1 - All Honda and Acura (except CVT)
• SP-III - All Hyundai, Mitsubishi and Kia (except CVT and dual clutch)
• Matic S, Matic K, Matic D - Jatco transmissions, used in Nissan and Subaru vehicles
• Toyota ATF-WS - All 2004 and later Toyota including hybrids
• Honda DW ( ZF ) - All Honda Automatic (except CVT)

Synthetic ATF is available on aftermarket brands, offering better performance and service life for certain applications (such as frequent trailer towing).