My transmission scares me

[wal1809]

Fellas I noticed something today and it could be me or I might be headed for the tranny shop.  I noticed if I hit the pedal pretty good on take off the tranny is smooth as silk going into 2cnd gear.  If I barely hit the fuel and let it ease into 2cnd it hits pretty hard.  Enough to where my wife asked why it was doing it so we know it is a pretty good pop.  I did it several times back and forth and it definitely hits hard on a slow take off.  All other gears it doesn't matter how how hard or soft I am on the pedal it is like silk.  I checked the fluid and it was 2 quarts low.  I filled it up and it still does the same thing with no change.

Any transmission guroos on here?  Any and all opinions are appreciated.  I thank you in advance.

[John316]

What tranny do you have, pal? Ours downshifts rough into 4th, and shifts a little hard, when cold, into 2nd.

Does your do it all the time, or just when cold?

God bless,

John

[wal1809]

Allison 4 speed auto.  I guess I should have said that earlier.  It is funny what you forget when you don't do something for a long time.  I was a diesel mechanic when I was a kid.  Even went to school at TSTI for it.  I worked on street sweepers in Austin a long time ago.  I even took a transmission apart a few times and got it back together.  I for the life of could not tell which end of the transmission was up or down today.  I even forgot about some Detroits being 2 stroke.  When I saw a picture of the cylinder sleeve though it jogged me back to the days of old.

Anyhow does anyone have an idea if I am headed for a beating on this transmission maybe.

[TomC]

Sounds like your throttle position modulator is not working correctly.  That's why it is smooth on full throttle, but on partial throttle, since the throttle modulator is probably stuck at full throttle, the transmission shifts hard without the full throttle torque of the engine to smooth it out.  It is either a cable or air operated.  Also, if the modulator is operating properly, on partial or gentle accelerations, it should shift at a much lower rpm.  My HT740 will shift at 1500rpm, bringing the rpm down to 1000rpm on a very light shift.  Once again, if your transmission is only shifting at high rpm, your throttle position modulator is not working properly.  Good Luck, TomC

[wal1809]

Thank you TomC that is some good information right there.  I don't know if it is electric or manual.  I need to find a good mechanic in the out here somewhere that doesn't have a 90 day back up.  When I get home this evening I will get under there and see what I can find out.

[belfert]

My B500 slams into first gear when the tranny is cold.  Once it warms up it shifts just fine.  It seemed a little better when I first switched to Transynd but that only lasted a little while.  It may have just been my imagination that things got better.

[RickB]

Do you know if the transmission has transmission fluid or motor oil in it? Some bus lines only ran 10/40 rotella and that stuff really needs to be warm before you start driving you bus.

just a thought.

Rick

[Busted Knuckle]

wal1809,
You need to get to know Clifford aka "Luvrbus" he is a very well known & respected busnut & Eagle lover. He is sometimes in your area, and he knows many folks in the bus world and can lead to to who/where you need if you need.
Disclaimer; Clifford is not the only Eagle busnut, or maybe not the most knowledgeable busnut, but he is very knowledgeable and knows the rest of the folks you'll want to get to know!
Also Sonnie Gray & Paul, & Doyle come to mind when it comes to TX Eagle nuts!
 BK  

[wal1809]

This websight is the shizzle.  I tell you there is some good folks on here.  I did some reading on the TPS throttle possition sensor and it really sounds like what the problem is.  I have to get back home and get the number off of the tranny and then call for the part.  This might turn oout to be a very easy fix.

[RickB]

  This might turn oout to be a very easy fix.

Whoa nelly!! Careful.... the murphy's law bus dudes may be monitoring your emails!! lol.

Whenever any of us said "this might be an easy fix" the rest of us got very, very nervous for that person.

Just kidding,

RB

[johns4104s]

Wal1809

I have the same promlem. My MCI 9 has I think a 745 Allison  It shifts very hard from 1st to 2nd ans 2nd down to 1st. I am told it is because the 1st is very low, this transmission was built for garbage trucks, heavy duty. Several people have this transmission and have the same problem. I changed the oil to Hydro synthetic from Dallas Texas. It has made some difference.

John

[wal1809]

  This might turn oout to be a very easy fix.

Whoa nelly!! Careful.... the murphy's law bus dudes may be monitoring your emails!! lol.

Whenever any of us said "this might be an easy fix" the rest of us got very, very nervous for that person.

Just kidding,

RB

You know I read this and laughed out loud.  You are absolutely correct.  May the bus God's go easy on the rule violation of assumption.  I kind of got ahead of myself for being happy, thinking this could be a real easy fix.  I will correct the errors of my ways.

[bobofthenorth]

And I figured if it was shifting hard it must be working.  I never drove an Allison that DIDN'T shift hard.

[belfert]

It is actually better for an automatic to shift quickly and harshly.  Cars and pickups have nice smooth shifts because that is what customers expect and demand.  I had the automatic transmission in my Ford pickup upgraded to handle lots of power and towing.  It shifted pretty harshly after the upgrade and the shop said that is normal and better for the tranny.

If an Allison has been shifting nicely and the operation has changed I would start to worry a bit.

[Kirby-XL40-FL]

It's the modulator... been there, done that.  And, I'm fixin' to replace it again in the near future just to prevent a major failure as I had several years ago.