| Author |
Message |
John the newbie (199.232.240.124)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, April 28, 2004 - 9:59 pm: | |
I just had the opportunity to test drive an MCI 9 with a
6v92 coupled to a 4speed automatic. The automatic replaced
what was originally a 4sp standard. The engine was rebuilt
130k ago and needs a rear seal.
I drove charter bus many years ago, mostly Eagles, some fishbowls
and some MCIs. None were automatic transmission.
(well one fishbowl and a cpl early 50's transits)
This MCI I just test drove surprised me and I'm wondering if
it's just -me-, or there's something wrong with the way it
operates.
When I took my foot off the accelerator it did not slow
down with engine drag. It felt as if I was totally dependent
upon the brakes to do all the slowing. There was no noticeable
downshift as I slowed and it almost seemed to be free-wheeling.
Is this normal? Since this was a "converted" from standard into
an automatic, could there have been something left out?
I was informed that MCI and Allison does not recommend
manually downshifting their automatics to control speed,
that brake power alone should suffice.
The unit is clean. At under $9k I hate to be too picky, but
I'm uncomfortable with an automatic to begin with.
Input please? |
Buswarrior (Buswarrior) (64.229.212.58)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, April 28, 2004 - 10:15 pm: | |
Hello John the newbie.
Someone is feeding you a line of bull.
To get good drivability, smoother operation and some engine braking, the 4 speed allisons are shifted up and down manually. I'm addressing the HT 740 in this.
You start off with the slector in 2nd gear, the transmission does an adequate job of the 1-2 and 2-1 shifts. Beyond that, you shift just before the governor on the way up, and take note of the speeds, and shift down at the governor on the way down. Typically 2nd is good for below 35 mph, 3rd below 50 and 4th to 70.
These older automatics are prone to upshifting far too early under part throttle conditions, and then shift hard back down when you squeeze the throttle a bit more. Usually in city type driving.
These trannies also don't downshift for any braking effect on their own, so it feels like they are off sailing when trying to slow down, if you don't shift it yourself.
Pretty much think about how an older car 3 speed automatic used to work with small horsepower. Ran up to 3rd gear as soon as it could, and then downshifted again if you called for more acceleration.
Remembering that in the buses the alternative at the time was a stick shift, no one gave it a second thought that they had to select gears in the auto box. Everyone was just thrilled that the clutch pedal was gone!
As for a MC9 with the tranny swapped, go find one that is stock in the configuration you want. There's tons of them out there, auto and stick, don't mess with someone else's chop job.
happy coaching!
buswarrior |
Phil Dumpster (24.16.243.37)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 29, 2004 - 3:14 am: | |
Driven properly, you should not have to touch the shifter in an Allison equipped coach under normal driving conditions.
The key there is "driven properly."
Descending steep grades, manually downshifting the transmission is a normal and accepted practice. In normal service on the level and gentle grades the coach brakes and throttle are plenty adequate to control coach speed.
If you don't like automatic transmissions, then for God's sake buy a bus with a stick. There are plenty out there. |
John the newbie (199.232.240.24)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 29, 2004 - 8:28 am: | |
Well Phil ................
I'm trying to understand what you meant by "The key there
is "driven properly." With well over a million miles behind me
I suppose I could still learn, but my issue was with the complete
lack of deceleration --wait-- let me rephrase that:
with the - complete lack of deceleration - using the throttle alone.
I find that disturbing Phil. When one removes their foot from
the accelerator, they should expect the vehicle should slow,
not free-wheel. If this is typical of the MCI automatics, then
I suppose I'd have to give in to my old ways and demand a
standard. Either that, or drive it by manually downshifting
to provide better control (as "buswarrior" mentioned).
I'd be happy if you would provide some more input. I may
be a "newbie" to this forum and the much of the mechanical
aspects of buses in general, but I do have my share of safe
miles behind these things. Like most former bus drivers here,
I too carried the world's most precious commodity, not just
furniture and food. |
C Fred (67.72.98.56)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 29, 2004 - 6:00 pm: | |
Hi John you will get very little help from the motor. I drove a manual for years and both it and the auto acted the same when showing down. That is why most trucks use a jake brake. I have one on my coach, It really helps when going off the interstate.Autos are locked up solid when going at over 40 miles per hour. thus the same as manual. Try another auto to check it out. Fred North Florida Bus Conversion |
bob_damm (216.134.162.222)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 29, 2004 - 7:07 pm: | |
Hi John, I recently started driving an '81 MC9 with the 5 speed auto and 8v71. When I back off the throttle the bus starts to slow down, I can also feel it downshift. The Jake brake set on high will hold 50 mph down a 1/4+ mile long fairly steep (35 mph going up it)downgrade. |
Abajaba (12.217.192.62)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 29, 2004 - 8:26 pm: | |
I have driven a MCI 102 series with a Detroit 8V92
on an automatic and it had a Jake brake in it. If
the Jake was not turned on it felt like that old
girl would just keep on rollin' forever.
In our newer coaches with automatics they all have
a jake brake and it really helps. One can tell a
significant difference when it is turned on. Even
in the seven speeds with four stroke engines, the
coach wants to roll without the Jakes.
It just seems to be the nature of the beast that
they like to roll without an engine brake of some
type.
We don't have any coaches with retarders built
into the transmission so I don't know how those
work.
Take care and look at the possibility that you
might want to put a Jake brake on anything that
you purchase. |
TWO DOGS (63.185.81.193)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 29, 2004 - 9:13 pm: | |
NAAAAAAAA....stay with a standard !!!!!!!!!! |
John Rigby (24.174.238.253)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 29, 2004 - 9:14 pm: | |
I think I will stick with my 4 speed spicer.
John |
John the newbie (199.232.244.176)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 29, 2004 - 9:33 pm: | |
Thanks guys!
I'll have to look into the price of a jake brake and see if
it'd be worth the cost. I suppose I could just shift into a
lower gear when I need to and save a few bucks?
I remember many charters to ski slopes up north, where
the Eagle's air valve would freeze, leaving me without brakes.
I couldn't imagine driving it without brakes without the
benefit of that 4spd, an automatic would have been a disaster.
Here in Florida, I only have to worry about those gray
haired ladies and their stuck gas pedals.
I appreciate the input. Making a decision of what to buy
is more complicated than I first thought it would be. You
fellas' provide the thought process that makes it a bit easier.
Thanks again. |
Derek (24.85.245.203)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 29, 2004 - 9:42 pm: | |
The transmission retarders on the B500R Allison transmission works quite well... You can come to nearly a complete stop using it alone without your service brakes...
However you have to be careful. Using it is not like using a set of jake brakes... You can't just ride it down the hill. You have to keep an eye on your transmission temperature or you might be left without it. Repair is expensive. |
Johnny (4.174.112.8)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, April 30, 2004 - 10:52 pm: | |
"I find that disturbing Phil. When one removes their foot from the accelerator, they should expect the vehicle should slow, not free-wheel."
The TDH5300 (6V71/V730) at work does the same thing--it won't compression-brake unles manually dropped to second or low. |
John the newbie (199.232.240.182)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, May 01, 2004 - 10:10 am: | |
Thanks Johnny!
I don't have much experience with the automatics, so I
had been totally unaware of their lack of ability to do what
I had been expecting. I expected too much! What confused
me, was the owner/operator's claim that automatics should
not be manually down-shifted to slow the vehicle. He told
me so in err. He'd be correct if the downshift would
overrun the engine, but I wouldn't be attempting to shift into
3rd over 50mph. It's no different than a standard as
far as that goes: There's a gear to cover a speed range.
As someone mentioned on a much earlier thread, Greyhound
didn't use Jakes and did fine without them for years and
billions of miles. In my better years (driving charter), I would
never have used them. There's no quicker way of ruining
a trip for your passengers, than giving them a headache
from your driving habits.
I'll try this bus I've been looking at again this week and see
how it feels when I manually drop it into 3rd. In 50mph
traffic, leaving it in third might be a good option as well,
just as we always did with a standard.
I can live with an automatic, if I can have some control
over it. The guy selling it would have lost this sale due to
his comments, if it weren't for the input I received from this
forum. I do thank all for the comments. |
JImmci9 (209.240.205.68)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, May 01, 2004 - 11:03 am: | |
with properly adjusted linkage (not worn out or misadjusted) and a good operable transmission (not worn out or slipping, burned) the transmission will shift as the governor in the transmission allows it to.... the key here::: good transmission, properly adjusted..for instance::::if you are over the limit for 3rd.. and you manually shift down, A PROPERLY ADJUSTED TRANSMISSION IN GOOD OPERABLE SHAPE will not allow the shift...DISCLAIMER::::.if your transmission is having governor or shifting problems, there's no telling what it MIGHT do....as for feeling the braking, its really no different from your car, if you are cruising 70 and let up on the allelerator, it will start to slow down, but it will coast for a long time.. and you probably won't feel the transmission shift down in it either....but re-accelerate and the auto trans will choose the best gear for the engine/groundspeed....HINT::: jakes help the coach slow down, some are set "tighter' than others... just like a better tuned engine performs better than one that needs a tune-up....its up to you, the "operator" to maintain your coach, be educated about it... and then drive defensively and safely.... DISCLAMER:::: this is gonna catch some flack.... my .$0.02 worth..... jim |
Jimmci9 (209.240.205.68)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, May 01, 2004 - 11:25 am: | |
AND::::as food for thought, you can overspeed an engine with a standard tranny too.... if you acidentialy put it in 1st when you're trying to get it in 3rd....with worn/misadjusted mechanical linkage its possible....you got the clutch pushed it, it will go in gear!!!...with the engine in the rear, you probably won't hear the gears grinding away..... till you see the big cloud of smoke..... |
John the newbie (199.232.240.182)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, May 01, 2004 - 12:01 pm: | |
Haha. Good typing jimmci9!
Naw, I'm not insulted. I find the quick to dismiss comments
and "the other driver's always inexperienced" attitude among
numerous bus owners to be more humorous than anything else.
I guess I'll add this for the record: The (semi-retired) owner
of this bus once had 16 buses in his garage, all in use and at
work. I assumed he knew what he was talking about when
he told me that Allison does not recommend manually
downshifting their automatic; that it will do damage to it.
I found it to be very unnerving, to have only the brakes to
rely on to slow the vehicle. There are times when using a
lower gear (in traffic; a downgrade) would save much wear
and tear on the entire braking system. The owner was instead
suggesting that whatever gear the transmission selects, is the
only gear to use. And, he always used the 4th position on
this unit with the 4sp.
Of course, after reading all the comments (thanks buswarrior)
I see where I got some pretty impure info from the owner.
Aside from that? This is a great forum and I enjoy the
ability to learn from other's experiences. There's always room
to learn. In my case? More than enough room. |
Jim-Bob (205.188.116.135)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, May 02, 2004 - 9:10 am: | |
Sorry to disagree with JimmieMCI9 but you will NOT accidentally put a manual bus trans into first instead of 3rd! (assuming the bus is going more than 20mph) There's no way that non synchronized trans will go into a lower gear until the engine is at the high end of the RPM range for the lower gear.
But you can do a lot of grinding while attempting to. |
Johnny (4.174.103.64)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, May 02, 2004 - 1:02 pm: | |
I haven't even seen a SYNCHRONIZED tranny that will allow the driver to get third instead of first without ralizing it. |
Johnny (4.174.103.64)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, May 02, 2004 - 1:02 pm: | |
I haven't even seen a SYNCHRONIZED tranny that will allow the driver to get first instead of third without realizing it. |
Jimmci9 (209.240.205.68)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, May 02, 2004 - 3:39 pm: | |
you guys are missing the point.... i said in my posts "a properly adjusted transmission in good shape"... ive seen worn-out syncronized standard transmissions that you COULD get into the wrong gear....when the shift rails, forks and linkages are worn and sloppy, you can get a standard transmission into 2 gears at once...or hung into ONE....the key statement is "worn-out'..... like many of our busses are, when we first look at them, before any repairs are made.... with a new transmission, or 1 in great shape, i agree it might be next to impossible.... |
Tom Caffrey (Pvcces) (65.74.65.65)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, May 02, 2004 - 10:22 pm: | |
Jimmci9, I have to agree with Jim-Bob on this one, if you are moving at third gear speeds. Stopped or nearly stopped is another matter. You won't overspeed the motor because you can't get it into any gear such that the motor won't bring the gears up to speed.
I understand that a lot of different things can happen with worn gears, synchros and linkages, but the example that you used just isn't going to happen, as far as I know.
Even if you engage first instead of third at a low speed and then gain speed on a downgrade while holding in the clutch pedal, the whining of the gears will warn you that you're in the wrong gear.
For what it's worth.
Tom Caffrey PD-4106-2576
Suncatcher |