| Author | Message | ||
| phil potter (216.234.125.32)
Rating: N/A |
Putting the above set up in my bus. I was reading topics on downhill and Jake brakes on this sight and found some that say they have transmissions that will automatically up shift while they are going downhill if the RPM's get to high. Does the HT748 do this? This past fall, we went down into S. Cal and came back out by way of Donner Pass. I liked putting my 4 speed manual into 2nd on the steep down grades, keeping it slow and using the brakes to keep me there. I don't like the sound of a transmission that chooses, on it's own to up shift. Help me out, what will this HT748 be like on the big downgrades? thanks, phil | ||
| Doug (68.83.22.144) Rating: N/A |
the 740 does it | ||
| Greg Roberts (Gregeagle20) (24.175.221.41)
Rating: N/A |
My 748 is push button controlled and can be put into whatever gear you wish. Beyond that the 748 also has a retarder built in that, by pressing the first 1/4" or so of brake, will activate braking from within the transmission. A large fluid cooler is also included to remove the extra heat generated from the braking action. I have this same set up in my Eagle 20 (which is not made of carbon steel) and it works extremely well and with out waking up the dead. | ||
| drivingmisslazy (66.168.164.139) Rating: N/A |
My 740 would not stay locked into first and would shift into second at about 15 mph. It would however stay locked into second or third, regardless of the speed or rpm. My belief is that maximum jake brake action occurs at the higher rpm, so I always tried to keep the engine in the 2000-2200 rpm range. Richard | ||
| James Maxwell (Jmaxwell) (66.81.60.1)
Rating: N/A |
Richard's comment seems to be about the norm with jakes. Install the 748 and forget the jakes--an ancient braking method that was only slightly advanced from thicker soles on your shoes. | ||
| Henry R. Bergman, Jr. (Henryofcj) (63.224.197.10)
Rating: N/A |
Have you heard the story about the fire engine which came South from the San Joaquin valley to the San Diego area to help out with the big fires, then... ...returned North after the fires were out and the firefighter got to drive as the Captain thought it was a good idea (at the time)... ...and he came down the Ridge Route on Eye 5 North bound with the retarder in the max position at 75 mph without touching the service brakes... ...because he had no experience driving fire apparatus and he though he could come down the hill at the same speed as a car and the trans... ...temp must have hit 400 degress and he melted a $15,000 Allision New World to the point that it almost caught fire and ruined the tranny totally. The fire engine was speced out for urban emergency responses of short duration and the transmission oil cooler was grossly... ...undersized for all the heat that was pushed through it. Moral of the story is that if the engine had had a Jake Brake, there would... ...have been no problem as about 70% of the heat generated by the Jake's operation is pumped thru the engine cooling water radiator which is... ...designed for such heat rejection. The other 30% goes out the exhaust pipe as hot air. The down side is that with the improper muffler... ...a Jake Brake can be quite noisy. However, since I am crazy by nature, the sound of a Jakes sounds sooosss COOL! Jakes Forever!!!  | ||
| phil potter (216.234.125.182)
Rating: N/A |
To answer my own question. The HT748 Allison does stay in the gear you put it in. | ||
| Johnny (4.174.103.101) Rating: N/A |
Uhh, I'd think a truck designed for city use would have a LARGER trans cooler than a highway truck. Of course, the obvious choice is simply to get a MANUAL transmission. | ||
| Buswarrior (Buswarrior) (64.229.212.164)
Rating: N/A |
Hello all. An Allison automatic will upshift, against the will of the driver and the tranny selector position, IF the driver allows the vehicle to reach an overspeed condition for the gear selected. Automatic transmission doesn't just mean it shifts gears for the driver, it will also protect the engine from an incompetent driver who allows the bus to run at an inappropriate speed for the gear selected. Usually this occurs while heading downhill, and is often induced under hard acceleration while trying to hold first gear. Poor bus drivers don't just burn clutches in a manual transmission, they also over rev the engine going down hills. Naturally, the usual disclaimer goes in here regarding the transmission's controls being properly adjusted, and the internals being in proper working order. If your manifold springs are aging/wrong ones installed or modulator adjustments are off, then all bets are off. happy coaching! buswarrior | ||
| Buswarrior (Buswarrior) (64.229.212.164)
Rating: N/A |
oh, and Phil, I applaud your downhill speed strategy. No need to roar down there. You are practicing the snub braking method? run up to governed speed and drag 5 mph off your speed and then let it coast back to governed speed and drag off 5 mph again. over and over to the bottom. Don't drag the brakes all the way down. Makes too much heat in the linings. happy coaching! buswarrior | ||
| phil potter (216.234.126.223)
Rating: N/A |
Yes I have always used the brakes as you just stated. I've seen some suggest to lighly hold brakes to maintain speed going downhill. Makes no sense to me. And I'm never in a hurry to go downhill, especially when driving in new areas. If I don't know what is ahead as I go downhill, I assume there is a steep decline just around the next bend. Keeping the rpm's in check is also great advice. I've had to do it by the sound of the engine and speed. If the bus goes 35 mph on flat roads in second, thats my top speed as I go down a hill in second. Is this good enough or would it be worth my while to put in a tach. for this pupose? On some downhills, I did like the comfort of putting my manual in 2nd gear going down unchartered steep hills and knowing if my brakes failed, I would stay under control, even if it damaging the trans. or engine. I Drive around with my wife and 13 kids. Choice between the bus damaged or my kids, easy choice. Perhaps I worry about downhills more that most, but I'm from MI and after hitting the big ones, I still like to come home safe. I was told that my new HT748 Allison will stay where I put it. I'm not sure that includes 1st gear. phil | ||
| Buswarrior (Buswarrior) (64.229.212.164)
Rating: N/A |
Hello Phil. Good job. You don't need a tach. Max speed on the flat is max speed for that gear. In this case, you would be going to the expence of installing another gauge to tell you the same info in different units. Speedo works just fine to tell you what's going on. If you continue what you are doing, the 748 will do what you ask it, since you aren't asking it to do something that its design won't allow. happy coaching! buswarrior | ||
| DrivingMissLazy (66.168.175.51) Rating: N/A |
Buswarrier, I have to respectfully disagree with you on the Allison automatic upshifting. At least on my 740 it would stay in the gear I selected to at least 2400+ rpm as measured by the tach, which was pretty accurate. And yes, I know you should not run the engine up at that range, at least not for very long, but I did it a few times and the tranny never upshifted from second to third or from third to fourth. I believe this is something that can be internally adjusted in the tranny, but what do I know? Richard |