M939/A1/A2 ABS vs. Non-ABS Trucks - Steel Soldiers::Military Vehicles Supersite

steelsoldiers · 01-06-2010, 09:22

I would like to address braking with a non-ABS truck. My 923A2 truck had the ABS MWO and would not lock up the brakes in a panic stop. I was driving my 925A2 on the farm road a few weeks ago and wanted to see what happens when you lock the brakes up on a non-ABS truck so I would be more prepared if it happened on the street. I tried this without the front clip, bed sides, or tailgate, so the truck was considerably lighter than it will be when I am done.

I got the truck up to around 35-40 mph and then jammed on the brakes to simulate a panic stop. It pulled the speed down very quickly, but it killed the engine. That is one of the safety concerns addressed by the ABS MWO because when the engine dies, so does the power steering and it makes it very hard to correct a skid situation. I freaked out a little when I lost steering even though I was on a farm road in a controlled situation. My first instinct was to flip the start switch to restart the engine, but the transmission has a neutral switch that requires you to be in neutral before you can start the truck. That caused me to panic a little more because I was rolling toward a soft field. Finally, I flipped the gear selector to N, restarted the truck, and steered away from the field.

All of this transpired in a matter of seconds. You can imagine the panic that would ensue if you were driving 50-60 down the highway, traffic stops, you slam on the brakes, the rear end skids out, the engine dies, you lose steering, and go careening toward the opposing lanes of traffic. Anyone that has driven a non-ABS truck with straight air brakes knows that you don't slam the brakes on when you are running empty, but all of that common sense will fly out the window if you are in a panic situation.

I plan on practicing some with mine to make sure I can maintain control during a panic stop. I am not recommending that any of the rest of you 939-series owners try this for obvious legal reasons, but please exercise caution if you own a non-ABS truck. Maintain the 40 mph speed limit suggested by the -10 especially if you are running NDT's. I am going to be keeping my eyes peeled for an ABS MWO kit to install on my truck as an added layer of safety.

Check out these videos from the ABS Mod website for an idea of what could happen:

halftrack · 01-06-2010, 09:30

AWESOME info Chris,

If there were any doubt about the "braking stall" problem with the trucks, you just cleared it up.

Now, just put a 18 yr PVT behind the wheel who doesn't have a care in the world and you just made the situation worst by 10 fold!

danomano · 01-06-2010, 12:33

Talk about the pucker affect..... the without is it!

Crash_AF · 01-06-2010, 13:11

In your search for ABS parts, I need a new ABS module for my 936 if you happen to come across one. The Army robbed the one off of mine before it was released.

Later,
Joe

rockman · 01-06-2010, 21:44

Wet pavement without ABS sure whipped that truck around..

NRG · 01-07-2010, 07:46

I'm not buying that wet pavement non-abs test. It looks pretty flawed. On the first wet pavement test the truck enters on the edge of the wet pavement and if you notice there is a strip of dry or considerately less wet pavement that he keeps the passenger front tire on, when he nails the brakes, of coarse its going to spin around, one side is almost or is dry and the other is soaked, they are setting it up to spin.

On the second test the truck enters on test in the middle of the wet pavement course and then hits the brakes. Both sides are in heavy water at that point and it does fine. In both tests the front tires locked up non-ABS and ABS. The only difference is they put one front tire on dry pavement on the non-ABS test to make it spin.

Also, a comment about the dry pavement tests, I have never seen a competent driver just leave the tires locked up and let it slide where ever it wants to. If it locks up then you let off and jab it again very quickly. You want to brake as hard as you can without locking the tires up. I think these guys tried make non-ABS tests look as dramatic and biased as possible. But thats just my opinion.

duncan · 01-07-2010, 08:03

Also, ofcourse the ABS is going to be better when you SLAM the brakes. It's a part.. wait, used to be a part, of good drivers training to stop a vehicle as fast as possible. Currently people are taught to slam the brakes and let ABS handle it. That's not how you brake though, you apply the brakes slowly and build them up untill they almost skid, then keep them there.

ABS fine in situations where:
- ABS works
- Your trailer has ABS as well
- The surface is solid

Ive seen people lose all braking because the ABS sensor failed, telling the computer the wheel was skidding, to which to computer tries to get it out of a skid by releasing the brakes.

Then the people slamming brakes "cause we have abs" with a trailer with regular brakes. Trailer locks up, jackknife.

On the surface... a proper braking move will outperform ABS on a lot of offroad surfaces like gravel and snow.

Sorry for the ABS offtopic rant Chris, quick, post some more excellent project progress photos!

Oldvw2 · 01-07-2010, 08:47

IMO, braking performance isn't near the problem that the engine stall that Chris mentions in his post is. With this series of trucks an engine stall can lead to loss of control real quick. This is the big advantage to the ABS MWO.
FWIW,
Chad

duncan · 01-07-2010, 09:26

I can see how stalling the engine is a problem, but I dont see how your engine stalls on an emergency stop? Dont you use the clutch? What am I missing here?

halftrack · 01-07-2010, 12:05

These trucks have automatic transmissions.