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Author Topic: MC-8 Manual Trans. Shifting  (Read 4214 times)
DavidInWilmNC
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« Reply #15 on: July 06, 2007, 07:38:18 PM »

But I'm working on it, and I believe I will get it right before I lose the tranny.  Grin

That's exactly what I'm hoping for.  That and hoping those riding with me don't lose confidence in me and the bus!  I'm curious if the other manual transmissions (5-speed MC-9's, etc) are all as difficult to shift smoothly.  The first time I drove it going to Timmonsville was a bit ... strange (for lack of a better word).  I tried to down-shift into 2nd, and I swear it felt like the transmission smacked my hand with the shifter as if to say "NO!"  It was scary.

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gus
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« Reply #16 on: July 06, 2007, 08:21:03 PM »

David,

You will find that shifting heavy truck trans w/out clutch is easier than a car or bike. So is the bus except that it is so hard to do smoothly, but no worse than with the clutch.

The only time I miss an AT is in close quarters, starting on a hill and in heavy traffic. I have two fire trucks with AT and they are easy to drive, especially when backing them into the close quarters of my buildings.

If anyone ever comments on my shifting in the bus I always offer them a try at it. So far there have been no takers and my wife and I cheer every time I have a good day of shifting. It is definitely a challenge and keeps you on your toes.

I'm convinced that the real problem is the long, flexible shifting rods and many rod/lever connections-there must be a dozen of them for each rod.

I completely overhauled my shift and clutch linkages-new rod ends and pins-much hard labor. It is a lot better, especially the clutch, but the shifting is still difficult. I just adjusted the 1-2 rod yesterday, they demand constant adjustment.
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« Reply #17 on: July 06, 2007, 08:23:46 PM »

Quote from: DavidInWilmNC
I'm curious if the other manual transmissions (5-speed MC-9's, etc) are all as difficult to shift smoothly. 

YES!

Quote from: DavidInWilmNC
The first time I drove it going to Timmonsville was a bit ... strange (for lack of a better word).  I tried to down-shift into 2nd, and I swear it felt like the transmission smacked my hand with the shifter as if to say "NO!"  It was scary.

Better for it to smack your hand than to "go off on you!" Ya know like KABOOOM!!!
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Don4107
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« Reply #18 on: July 06, 2007, 10:18:35 PM »

<I tried to down-shift into 2nd, and I swear it felt like the transmission smacked my hand with the shifter as if to say "NO!">

That was because you only had it part of the way into gear. When torque was applied it popped out of gear.  Or there was quite a bit of difference in gear speeds and it 'bounced' backed when it caught the edges.  Not a good thing to do to much.  You will learn to 'feel' the gear sliders just bumping each other with practice just before they match speeds.

Try to keep pressure on the shifter until you are sure its in all the way.  That is, keep pressure on until full torque either speeding up or holding back is applied.  Try to get in the habit of reapplying throttle or, letting off if down shifting, slowly.  There is an instant when there is no torgue as you reapply throttle or let off if down shifting which will let it go all the way into gear if it was only partially in.   Also a quick blip of throttle with pressure on the shift lever will make sure it is in all the way.  Works up shifting or down shifting. 

Clear as mud? 

My old bus has one gear that it does not like to stay in when going down hill.  Never comes out unless holding back against the engine.  I just have to remember to blip the throttle and pull it back in once in a while on long down hills.  More that likely a result of popping out when only partially engaged too many times. 

Remember, it it feels like it did not go into gear just right, blip the throttle slowly with pressure on the shifter.  You will feel if it goes the rest of the way into gear.

As they used to say, grind a pound for me.  Smiley
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Dallas
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« Reply #19 on: July 07, 2007, 03:16:20 AM »

Don't worry David,

Next year they are coming out with an upgrade to the spicer 4 speed transmission.

I hear the gears are made out of water so all you have to do is pour them in!   Roll Eyes Roll Eyes Roll Eyes Roll Eyes

I still think I like the Road ranger gear upgrade better... they are made from rubber so you can erase your mistakes!  Grin Grin

Sorry, I tried to resist, I really did!

Dallas
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DrivingMissLazy
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« Reply #20 on: July 07, 2007, 05:58:23 AM »

I hope you do not have an air throttle. I tried driving one one time with an air throttle and absolutely could not get a good shift when going down in gears. Also, a tach would be a great investment.
Richard
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« Reply #21 on: July 09, 2007, 02:44:53 AM »

"One is that it seems to shift better (less grinding) soon after starting it as opposed to shifting it after running for a few hours."

Possibly indicates a need to slow down the timing once the oil has warmed up and the gears spin more freely and take longer to slow down.
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Jeremy
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« Reply #22 on: July 09, 2007, 04:09:44 AM »


 I'm curious if the other manual transmissions (5-speed MC-9's, etc) are all as difficult to shift smoothly. 


I've been reading your posts with interest because I also have worries about the manual gearchange on my bus. I think the type of transmission must make a difference because I have never 'ground' the gears in mine (it is a syncromesh 'box), but I sometimes struggle to get it into gear; 95% of the problem I have is when changing into 2nd, and I'm not sure if it is an 'engine speed' thing, or whether I cannot physically find the gate. I suspect the latter, as the change from 1st-to-2nd happens at a very low road speed, and I think my problems stem from the fact that I always try to rush the change in an effort to maintain momentum. I imagine a non-syncro 'box that requires a double-declutch on the 1st-to-2nd change must be a nightmare, especially when pulling away from a standstill on a hill.

Downchanges from 3rd-to-2nd always worry me a bit as well, although at least you have a bit more time to make the change then. Changes from 2nd-to-1st I usually avoid altogther by braking to a stop, then selecting first when stationary.

I would like to understand more about how to judge the engine speed correctly when shifting gears - maybe I could benefit from fitting a tach to help me learn this, as the idea of running the engine up against the governer each time seems completely wrong to me - Screaming an engine in any vehicle goes entirely against my instincts, and I'm sure I've never had my bus engine against it's governer in the whole time I've had it - but then I've never been trained to drive big diesels, and it may well be that that is how they're designed to be used.

Jeremy
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DavidInWilmNC
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« Reply #23 on: July 09, 2007, 05:20:24 AM »

Jeremy,

If you have a 'synchromesh' transmission, I'd think that you'd have a much easier time changing gears.  From my understanding, worn synchronizers can make gears grind, too.  It's not too much of a nightmare, except when I've gotten it in neutral and can't get it into any gear!  Pulling away from a stop on a hill with a car close behind me is a bit unsetteling, but not to bad.  Since I do the DTS as described in the 'how to shift' post on the 'other' forum, I just keep my foot on the brake 'til I feel the engine pulling a bit, let up off the brake, and step on the throttle.  If nobody is behind me, I'll just start as normal.  One thing about these buses, they will roll at the slightest incline.  Perhaps your linkage needs some adjustment.

David
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Dallas
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« Reply #24 on: July 09, 2007, 05:37:49 AM »

Jeremy,
2 things come to mind with your setup.

The first is, since it's a syncro transmission, and the 1-2 gear ratio is extremely close, I would believe it's possible 1st gear is a deep reduction gear and as such should only be used when starting on a hill or pulling a heavy load. This means you should be able to start out in 2nd gear without doing damage to the clutch.

Most Heavy trucks in North and South America are set up this way, as well as Volvo, Bedford and Scania trucks around the world. I can't say for sure about other makes.

Try starting out in 2nd and see if you can do it without slipping the clutch or using the accelerator. If so, you should be safe doing it all the time. Check the operators manual for that transmission, whoever the maker is.

The next thing is, I believe your engine is a 4 stroke/cycle engine and it reaches it's maximum torque at a much lower RPM than our 2 stroke/cycle Detroit Dinosaurs which don't hit the peak torque until around 1900 rpm.
You won't need to run it against the governor since it's possible that your engine, like our Caterpillar, Cummins and Detroit 4 Stroke/cycle engines reach maximum torque as low as 1100 rpm and level off at around 1500 rpm, (IIRC).

By the way, as an aside, does Bedford still build engines in the UK? and if so, do they still make the Detroit based 2 stroke/cycle that was popular in the 50's, 60's and 70's?

Dallas
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DavidInWilmNC
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« Reply #25 on: July 09, 2007, 05:42:34 AM »

"One is that it seems to shift better (less grinding) soon after starting it as opposed to shifting it after running for a few hours."

Possibly indicates a need to slow down the timing once the oil has warmed up and the gears spin more freely and take longer to slow down.

Thanks for pointing out what I'm sure is a big part of the problem. it's so obvious that I must often overlook that aspect of shiftting and will make a more conscious effort to give the gears some time to slow down.  I wonder if a heavier weight oil in the transmission would help slow those pesky gears down?  Wink I'll change the fluid in the near future and see if any chunks of gears fall out from all the grinding. My dip stick is missing, so now would be a good time to take care of that.

David
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Jeremy
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« Reply #26 on: July 09, 2007, 06:56:27 AM »

Hi Dallas

Thanks for your post - you've put my mind at rest about a couple of things there. Firstly, 1st gear on mine is extremely low - as soon as the bus starts to roll you need to change up. In fact, when I first took posession of the bus the guy was delivered it to my house took me for a quick drive and demonstrated, amongst other things, shifting each gear from first up to fourth. "Hang On" I said, "it's supposed to have five gears". "Oh" he says, and has a fiddle with the gear lever and finds 1st for the first time.

But then, when I took the bus to a local HGV mechanic to have it inspected / tested, he said to use 1st every time, no matter how low it was, because he said that in something as heavy as a bus it is much easier to burn a clutch out than in a car - so that's what I've been doing, but I've always felt that it would be perfectly happy setting off in 2nd when on flat ground.

So, I'll switch to starting in 2nd in normal circumstances, which will also have the happy side-effect of avoiding the 1st-2nd change, which is the only one I tend to have any problems with.

Your point about 4-strokes not needing to be reved makes sense as well, so I'm glad my 'softly softly' approach on the accelerator pedal is ok (as an aside, I've always much prefered big cars with big torquey V8s or diesel engines, rather than small ones with revvy 4-cylinders'. Whether it's the sound or what I don't know, but for some reason I have always hated having to make engines spin quickly).

Lastly, to answer your question, Bedford sadly no longer makes any heavy commercial vehicles - in fact my bus was apparently one the last batch of seven coach chassis they made. The factory still builds vans, but GM badge them as Vauxhalls now (Vauxhall being GM's main car brand in the UK, similar to Chevy).

Jeremy
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« Reply #27 on: July 09, 2007, 07:09:14 AM »

Many years ago when I was involved in driving large vehicles, many, if not most, had what we called a granny low. It was especially useful here in the hills of West (by god) Virginia as there is typically only one way of starting, and that is uphill. LOL Normally not used except when heavily loaded or starting uphill.
Richard
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« Reply #28 on: July 09, 2007, 07:27:40 AM »

Jeremy -

A tachometer might be a worthwhile investment for you.  With a tach, you'd be able to determine the rpm splits between each gear, which can be very helpful.

What engine does your Plaxton have?

Running a diesel up to the governor won't hurt them - it's only (usually) 2100 rpm - about what your auto runs on the M1 at 70 mph.

FWIW & HTH. . .

 Wink
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« Reply #29 on: July 09, 2007, 07:58:14 AM »

Jeremy -

A tachometer might be a worthwhile investment for you.  With a tach, you'd be able to determine the rpm splits between each gear, which can be very helpful.

What engine does your Plaxton have?

Running a diesel up to the governor won't hurt them - it's only (usually) 2100 rpm - about what your auto runs on the M1 at 70 mph.

FWIW & HTH. . .

 Wink

Actually, I realised after leaving my earlier post that my bus does of course have a tach (Doh!), because I look at it all the time to make sure I keep the engine in the green zone on the tach dial (it's has green, yellow and red, green being 'economy mode'). It's just that I've never looked at the tach when changing gear, and don't know what RPMs I'm 'supposed' to be changing at anyway; do manufacturers actually publish recommended gear change points for each a particular engine/gearbox combination, or is it just personal experience?

My bus has a Bedford 500 Turbo engine; the 500 is 500 cubic inches. I've no idea what the power output is supposed to be, but you are about right on the gearing - the top of the 'green zone' is 2000rpm, which equates to just over 60mph, and is where the speed limiter (not governer) kicks in. Although as a private owner I am now legally entitled to remove the speed limter I haven't decided if I will of not - if I do I will inevitably use the extra speed and drink more fuel, but then overtaking would be an awful lot easier as 95% of trucks in the UK drive everywhere on their limiters at exactly 60mph.

Jeremy
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