Doesn't Ford put retards behind their diesels?

 

I rode in a big rig that had a retarder. It was a system that made the torque converter hold back. All of it's power, instead of being sent from engine to tranny, was sent from tranny to a fixed part somehow. It held back like an engine brake, all with hydraulics. Imagine a torque converter that is turned around backward. It's normal input shaft is now on the tranny and it's normal output shaft is now locked to the bell housing and cannot turn. As the vehicle moves and the tranny turns, all the force goes to a stopped shaft and adds a lot of resistance. The one I saw made a lot of heat and had to be watched on downgrades.

I don't know if it is the same thing in the motor homes, but it has been available in big rigs. A retarder. As far as stopping almost as fast as the brakes, hmmm...


John

 

Last I checked that was a fact!

My grandpas 05 Dmax will not come close to stopping a load trans only... Its downshift points even in tow haul are so low that it does very very little when trying to slow a load down... (keep in mind I'm used to my 6spd with an exhaust brake, 60psi of backpressure on wet roads will cause loss of traction! ).... The great Allison feels mostly like any other slushbox I've driven, inconsistent, mushy, and power robbing...

Grandpa's truck is pretty dang quick unloaded, but with any load over 10k it is an absolute dog...

Shifting into reverse going down the highway is pretty cool though!!

 

back in 1962 dad drove one of the first bucket trucks at the phone co. he was a lineman at it was a c65 chev with a allison and a retarter. it looked like a regular clutch pedal and it was 327 powered. this truck was still in use in 1982 and i wrenched on it while being a fleet mech there. the retarder would slow you down from hwy speeds but not much use under 30mph or so . been awhile and my memory isn't what it used to be. even the gasser new gms with the allison have the tow mode button. what ever happen to common sense towing.??????????

 

In my brother's case we are dealing with 18,000 lbs and it doesn't work. Physics applies to what's in the engine too, so please explain how a diesel engine which has no compression braking can magically find some by locking the TC. An exhaust brake is analogous to the throttle plate in a gas engine which provides the compression braking. My CTD will descend the longest grades with the heaviest loads at 60 MPH in OD, locked TC with the EB on, no service brakes. I can downshift to Drive and the truck will slow down because my TC remains locked. With EB off and TC locked it will pick up speed quickly, so that I must brake and downshift. Then I'm going down the hill a lot slower in a lower gear and I probably still need my service brakes, and the TC is locked. If I want to descend at 60 MPH the EB is required. This was exactly the situation with my brother's Dmax/Allison, no compression braking in tow/haul without the EB. Of course that statement is not strictly true because compression braking can be developed at high engine RPM but I consider that abuse, a result of poor system design.

Moving on to current CTD design, which has nothing to do with the argument above. I believe newer Dodges (mine is a '98) have tow/haul mode, I suppose to compete with the Allison in those years. Now the newest model has tow/haul with standard exhaust brake? A logical progression and exactly what my brother and I found necessary, full time lockup capability with EB.

 

the grade braking on the allison works sometimes and sometimes doesnt. It is not a passive "step on brake, downshift". The TCM looks at many different things before deciding whetehr to downshift aggressively, or just wait until the pre-programed closed throttle downshift points. I agree; sometimes it flat out sucks. Other times it downshifts right away and winds the engine out to 3500rpm helping to slow the truck right down. The higher the rpm the more aggressive it is. At 5000rpm it will upshift again, instead of holding the gear until the engine blows up. A result of poor design? How so? If GM didnt feel 5000rpm was not safe in grade braking, then they would ahve designed it not to alllow it. You do not need to second guess the transmission. The allison TCM is probably one of the most advanced trans computer out there; it will not let you hurt anything. WHen was the last time you heard of a dmax blowing up from overrevving...

WHat Ive found is the truck needs to be accellerating at "x" rate while at 0% throttle for "X" amount of seconds before aggressive downshifting will start. Otherwise its stupid and doesnt do anything. So a lot of the time I just put the shifter down in "3" and that works well for slowing loads down. Obviously not as well as an exhaust brake, but it works just as well as downshifting any manual trans.

downshifting is not the same on a dodge trans. They have sprags and overrunning clutches so there is ALWAYS some "free wheel" aspect. Correct me if Im wrong, but I beelive the dodge "tow/haul" mode was little more than an overdrive lockout.

the allison is not like any other slushbox out there...it shares no operating characteristics with any other auto. It was designed to move heavy loads and do it in the smoothest and most durable way possible. There is a reason allison owns the entire medium/heavy duty transmission market. All those fire trucks, city busses, dump trucks, medium duty GP trucks seem to run fine. I dont understand people who simply dismiss it because of assumptions, and/or they have some complex where "im not a real man if I have something do something for me, I know best how to do things and Im not gonna have some stupid computer try to be better than me". I kind of chuckle at these people because IMHO if you're not manually shifting 9, 11, 14, 18, whatever gears, double clutching, etc, you're not shifting diddly.

I ALWAYS give the cummins credit where credit is due and even tho I own a dmax, I still swallow my pride and regard it (the ctd) as the more durable and superior engine of the big three. So why does everyone refuse to give the allison any credit? If there was no need for a "real" automatic, we would still be seeing 727's and 2 speed powerglides in trucks.

just my oppinion

ben

 

5000 rpm would explain it. At that speed I suppose the turbo and exhaust system makes enough back pressure for compression braking. I could not abuse an engine like that, even though the maker OKs it. There are better ways to slow down. My brother is a retired firefighter, he drove the engine, the "engineer" on a three man truck. It had an Allison tranny, maybe with a hydraulic retarder, so he had high expectations with the Dmax. Finally had to get the exhaust brake.

"the grade braking on the allison works sometimes and sometimes doesnt" Pretty scary.

 

In your dreams maybe.

 

come on its got to be worth something... if you couldnt have an exhaust brake would you rather have an allison or a free-wheeling 47re?

It is not scary. The trans doesnt just suddenly let go and start coasting. It is always locked. WHat I mean by "it sometimes works and sometimes doesnt" is that sometimes the TCM does not command a downshift as soon as it should. So If the trans doesnt downshift when you hit the brakes, then take your right hand and shift it down manually yourself. It will slow down...Ill take a video of it this weekend because no one seems to beelive me.

 

Towed with my grandpa's today.. bout 10k... on the highway when going to slow down it did downshift, RPMs shoot up, heard the engine making more noise... Did it really slow me down any considerable amount? Not really, felt like an auto downshifting to me.. Nothing more nothing less...

Not saying the 47s or 48s are better than the almighty Allison, cause they are not, but it's not leaps and bounds above them either!

I like towing with a manual and an ebrake and nobody will change my mind of that... I've had too much bad luck with autos (for instance bout 2 months ago (In the dmax) towing a mini excavator and some accessories went to pull out onto the highway and the truck went into limp mode!! great oncoming traffic bout 15k behind me and I could get out and run faster than I'm moving!! Really ticked me off. Dealer couldn't pin point the problem and directed my grandpa to bring it back if it does it again, great) Now not to say that Dodges autos cant screw up, but the only way my truck goes into limp mode is if I start in 4th instead of 2nd on accident

 

I knew what you meant, I was just yankin' your chain.
I bought my truck used and not abused, about 35,000 miles on it. Within a year I had the ATS tranny, Commander, and PacBrake, even though the original was doing OK. This is the only way I would have it because it made a good truck into a great truck. I can adjust the lockup down to 8 MPH, where it will stall the engine when I stop, or I can turn the Commander off and it reverts to something like stock, only better. It stays locked during all upshifts and downshifts, absolutely no overrunning. I don't have to over-rev the engine to get compression braking, the EB is strong at 1700 to 2000 rpm. The EB is on when I say and off when I say, I select the gear. In the Rocky Mountains most vehicles are riding their brakes and I'm shifting from OD to Drive to 2nd before the hairpin turns and don't touch the brakes. It's not stock, but not one of a kind either, anyone can do this and have a great truck. On the other hand, my brother made his good Dmax into a great Dmax by adding the exhaust brake. We're both happy.

 

I do love the simplicity of the dodge tranny's tho.

The allison was designed to work reliably for a million miles (there is a 2001 dmax/allison 3500 silverado hot shot rig out there with 727,000 miles, original engine and original trans never been touched other than like 6 sets of injectors, if you can beleive that) towing heavy loads at slow speeds with stock power levels.

The TCM is absolutely critical to proper operation of the trans. One slip-up with the TCM and you have a grenaded trans. The TCM was not designed to deal with (and shift) 500+ rwhp. Lockup is at the mercy of the TCM (there is no way to lock the converter with a simple switch or something), shift timing is at the mercy of the TCM, everything is...

The dodge tranny's, because they are based on 30 year old simple technology, are wonderfully versitile. You can do anything you want with them as far as mods and stuff. The allison has a very specific way it is set up and MUST operate in a very small range of defined parameters or else it will not work at all....the downside of a clutch to clutch auto trans.

6.7 pickup truck guys...be happy you do not have the Aisin trans!! Aisin and Allison have a cooporation deal over in japan, so the Aisin trans used in the 6.7 C/C trucks is basically an allison 1000 clone. It will be unhappy at high hp levels just like the allison.

The allison is not a drag racing or high hp trans. The gear ratios are completely wrong for drag racing. 1st is way too low because it was designed to get heavy loads moving so you blow through it in about 1 second. In 4 low, 1st gear, you can only go about 7mph (yes, 7) with the engine maxed out at 3200rpm. The farthur we push the envelope with power, the harder and harder it will be to make the allison work properly. Its not that the hard parts cant take it (ie, its not a problem of simply developing hardend internals), its just that its methods of operation and nature of the trans do not support lightning fast shifts at huge hp.

ben

 

But did the truck take off? It may not slow you considerably, but if it maintains a safe speed, then you're in the clear. Note that I said MAINTAIN A SAFE SPEED. That's what it was designed.

Exhaust brakes are nice, but they don't compare to a big rig jake brake. When it comes to towing the tonnage that some people say they pull with their trucks, anything less than a medium duty trucks is stupid.

Even a jake brake won't stop a truck, unless you push the clutch in and coast to a stop. The motor is still idling in every case...........

 

no the truck has high rpms but still freewheels because there isn't any engine backpressure to counter the force...

I don't find 10k an unreasonable amount of weight by any means.... even 15k for that matter.. sure I've pulled more but only fairly short distances....

a jake would be better than an ebrake yes, but they are not made for the 5,9... ebrake works the best for our engine. mine works better than most, being its not a direct dodge aplication.. I use a 4" inline pacbrake that is set to 60psi for the most braking I can safely get out of the engine....

 

No, retards put the diesels in Fords.