Hello, I have been trying to find the driving differences of a B500 with a TC551 or a TC521 torque converter. The stall torque ratio is 1.79 for the TC551 and 2.42 for the TC521. I spent a couple of hours on Google and Youtube with minimal gain in knowledge. Both would be behind a Series 60.
Thanks, Bandsaw
The 521 will stall at 1500 ft lbs of torque @2100 rpm the 551 stalls at 1750 ft lbs at 1800 rpms you can find that information in the principles of operation manual,the 551 is used for the 12.7 and 14L series 60
Clifford beat me, but I wrote the thing so I posted it anyway... Brian
Just going from general auto transmission TC theory, the stall ratio is the amount of torque multiplication you get when the torque converter is stalled - getting power but not yet transmitting it. You also have a stall speed - the engine (or input) RPm that the TC stalls at. You get the impact of this when starting out from a dead stop. The engine goes to rise in RPM, the TC gets to it's stall speed, and multiplies the torque of the engine until the engine catches up to the transmission.
You could think of it like slipping a clutch on a manual transmission. Or like having an variable extra low gear for starting on a hill. In general, the higher torque multiplication will be less efficient, run hotter, be suited to a heavier load, have greater startability. The lower torque multiplication will be more efficient, run cooler, accelerate more smoothly with a well matched load, and be less jumpy when starting from a dead stop. When I bought a custom re-man transmission, we discussed the coach weight, the type of engine and rpm/power/torque characteristics, the shift rpm, and the technician consulted books (or just happened to know) and selected a torque converter and adjusted the lockup speeds and shift speeds to suit the engine. The B500 was, as I understand it, designed specifically to go behind engines like the S60 in highway coaches, so the best torque converter for your appliction is probably well known to the Allison shop.
The torque converters range from 521 to 561 for that transmission fwiw
Quote from: luvrbus on February 24, 2019, 06:52:31 AM
The 521 will stall at 1500 ft lbs of torque @2100 rpm the 551 stalls at 1750 ft lbs at 1800 rpms you can find that information in the principles of operation manual,the 551 is used for the 12.7 and 14L series 60
Cliff is the 551 also used behind the 11.1 S60?
Hello, have any of you driven a bus with the TC521 (2.42) in it? I have a very new transmission I am thinking of putting in the bus with the TC521. I understand the theoretical description. I would like to avoid tearing down the new transmission.
The transmission with the TC551 (1.79) is in the bus now, as shipped from Prevost. I have not towed with it yet. It has not shown any hesitation starting up a hill. It was rebuilt about 10,000 miles ago and it does a couple of things that make me nervous. The total miles is 670,000
Thanks, Bandsaw