Tranny diagnosis question
I'm wondering if I may need to replace my transmission, but I am not sure how to diagnose the situation -- or even if there's a problem. I have an '85 Thomas-built bus on an IH S-1800 chassis. The engine is a 9.0 liter V-8 that was rebuilt not long ago, and that has a dyno certification sticker on it for 180HP. The tranny is an AT-540 (according to the line ticket), but I'm not sure that is the original tranny, so it possibly could be an AT-545. It is a 4 speed tranny, for sure. The rear end is 6.50:1, so I know it it cannot possibly go above 50 MPH or so in that configuration, but speed is not the issue.
The bus won't maintain speed going uphill. I can get up to 45 or 50 going down a hill or on a stretch of straightaway, but when I get to a hill, it bogs down and bogs down and bogs down, and by the time I'm at the top, it has slowed to 20 or 25 MPH. I would think that with the 6.50:1 rear end, that it would be able to slog uphill without even noticing the grade. Eventually I would like to move to a 4.11 or 4.86 rear end, but I'm afraid to even consider that at this point: wouldn't a lower rear end ratio make the bus tend to lose speed even worse going uphill?
The hills I am talking about are moderate, maybe a hundred feet in elevation over a half a mile...4 or 5 percent grade, probably.
Does the tranny sound like it's going/gone, or am I expecting too much from 180 horses?
Oh, yeah, it appears that the tranny is leaking, as well, but I haven't determined the source yet.
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