i have pulled many loads for the farm and try to keep them down below 6.5ton of weight. i feel the same about people pulling huge loads behind pickups if you are doing it all the time i would buy a over the road truck. i drove an old million mile daycab freightliner with a 350 cummins and thirteen speed for three years and had very little maintence on it. a/c was and issue and keeping the brakes adjusted up.

 

Everyone seems to have gone rather far a field. He stated the 'Allison had a provision to utilize the max HP rating of an engine'.

Some may be unaware but muffler or exhaust brakes are mediocre. The old rule of thumb was that exhaust brakes generated a maximum of 35% of an engines rating as BHP while a true Jake (Exhaust valve actuating) generated a maximum of 50% of an engines rating. The design of an engine is also a major factor. An I6 Cummins generated app. 315 BHP while V blocked Detroits could only generate 260 to 280 BHP (Large bore).

Hydraulic retarders are a completely different ball game. the CAT Brakesaver decades ago was capable of generating 100% of an engines rating. Very basically it worked by shooting a pressurized stream of fluid against veins in the opposite direction of driveline rotation. The unit could be installed on manual transmissions.

It is very effective and the fluid does get hot. But - It is quiet and smooth on engagement. The degree of retarding is selectable, by the driver, across a broad range, which is one reason these systems have been more popular on busses. Standard valve actuating Jakes can engage hard. Which could be too much for some passengers.

Remember he said "Provision for" which does not mean the item is currently installed on every Allison in service. If GM is about to offer a retarder it will very quickly put those weak little muffler brakes to shame. A properly installed hydraulic retarder can bring a vehicle to a near stop.

Hydraulic retarders are well proven. CAT's pit trucks use them when retarding is required. You cannot use Jakes on a 45 degree haul road that is probably wet. Retarders can be used safely in the rain while engine brakes especially Jakes (Valve actuating) should never be used in the rain.

Before someone corrects me I am indeed aware the Series 60 is capable of 450 BHP, the Signature 600 from Cummins was introduced with a 2nd cam specifically for operating the fully integrated engine brake. It generates 600 HP and 600 BHP. Mack/Volvo and CAT are also up but these are all due to new engine designs.

When one considers the loads guys on these forums claim to haul, their only choice should be either a hydraulic or electric (Driveline) retarder.

 

an allison transmission does automatically detect when you go down a hill, and it will downshift the transmission to allow better engine braking. It does it in tow haul mode, and normal shift mode. it is much more pronounced in tow/haul mode though. it does not stop the truck as fast as wheel brakes, but on a long hill it is very noticeable. I believe the permissives for grade braking are has to be on a downhill, you can't have touched the throttle for like 5 seconds, and as soon as it detects the brake pedal pressed for more than 3 or so seconds it will downshift the trans, and hold it in that gear until you are back on the throttle, or the engine goes above 4000 rpm. I do know the redline for a duramax is 3200 by the way, but it does hold it to 4000. Some hot shot haulers don't like that because it wears the engine faster, and there is no aftermarket products that tune grade braking.

 

upshift will happen at 4500rpm or so, maybe a little more.

As for the know-it-alls who think they know more than GM about the duramax and allison, they need to be quiet, put it in drive, tow/haul on, and let the engine/trans do its thing. The ECM and TCM will not let you hurt the engine or trans, no matter how much it "SEEMS" like you are going to hurt something at 4500rpm.

ben

 

I dont know all the technical specs exactly,, but I can tell you this,, I just happen to be a lucky guy and own both a dodge with a cr and a chevy with a duramax. Personally, the 48re that is in my dodge is wonderful for racing etc,,, not so good for towing. The allison, is phenominal for towing and not so good for racing,, . I tow a 13k 5er, and personally I would rather tow it with my chevy than the dodge. And trust me I am a big dodge fan, but I have to give credit where credit is due, the duramax/allison combo is very hard to beat,,,,,

Kevin

 

Our first duramax's brakes caught on fire coming down a mountain in CO while my uncle was driving it with god knows how much behind him. Im not sure how he slowed down, but he and the truck were unharmed.