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Author Topic: startability - 8V71 and Spicer...  (Read 3318 times)
bevans6
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« on: July 02, 2010, 12:03:43 PM »

I have questions about startability.  TomC posted some stuff on this a while ago, but it's impossible to find.  My situation is MC-5C, roughly 26,000 lbs, add in 3,000 lbs of toad and call it 30K.  Spicer with 3.73 differential ratio, 12R-22.5 tires.  I find that it's sometimes hard to start the bus on grades, particularly at those stop lights where you have to sit on the uphill grade, then try to smoothly get rolling.  Dead throttle start is remarkably hard to achieve in those situations.   My approach is to engage the clutch to the point where it is getting the bus moving then apply throttle smoothly to full throttle, and get the clutch out fast so there is minimal slipping.  Is this the "approved"  method?

Now, I have recently got into spots where rolling at 5 mph (basically just rolling along on idle), I did not have power to get up an incline.  Full throttle, bus was slowing down.  I was in a position where I could simply roll backwards and go a different route, but it makes me ask, what do you do when you can't get going without slipping the clutch a tad?  Or a lot?  Do you get say 1200 rpm, and slip the clutch, minimizing that to your best effort?  what happens if you are on a 6% grade and traffic comes to a stop?

Thanks for any and all thoughts.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
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Ed Hackenbruch
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« Reply #1 on: July 02, 2010, 12:18:20 PM »

What happens when you are on a 6% grade and traffic stops?  You start thinking that you should have bought one with an automatic in it.  Grin   Sorry, i know that doesn't help you any. I thought of that before i bought my bus and am so glad that it has an Allison in it. Wink
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1968 MCI 5A with 8V71 and Allison MT644 transmission.  Western USA
Bill B /bus
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« Reply #2 on: July 02, 2010, 12:38:38 PM »

I have been on a 6% and stopped for a traffic signal. 4 pm and in a line of traffic. Sweat! And more sweat. Used heel and toe for brake and throttle. And yes, I smelled burned clutch for a awhile. 1970 PD4108.
Now we have the automatic and you all know why.

Bill
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Bill & Lynn
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« Reply #3 on: July 02, 2010, 12:42:47 PM »

"I did not have power to get up an incline.  Full throttle, bus was slowing down."

Sounds to me like the clutch is slipping. Might be time for a clutch adjustment.


jeff
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bevans6
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« Reply #4 on: July 02, 2010, 12:47:41 PM »

Clutch is fine, just did not have power.  Engine was not revving up at all so the clutch was and is fine.  I am indeed considering a change to automatic at some point, but really  looking for more than "don't drive a bus with a 4 speed on a hill" here and now...    Wink

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Vintage race cars -
1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
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« Reply #5 on: July 02, 2010, 12:51:22 PM »

Back in the '70s when I drove for a living, all we had was 4 speeds with clutches. We did what we had to do, and clutches got replaced as needed. Some drivers were more abusive than others, as you can imagine. Starting on a grade, I would let the clutch out while my right foot is still on the brake. As soon as the clutch starts to engage, and holds the bus still, I would give it some fuel and get going. Yes it wears the clutch, but that's the only way. Sometimes if it was very steep, we would put our 4 way flashers on, and back down to a flat spot, traffic or not. Just make them get around you.

First gear on the 7 speed Eaton-Fuller of the D3 of the hockey team's is really low, so you can do a dead throttle start going up a wall. That is nice. The 5 speed on the Courier 96 is about the same with 1st really low.

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
Dreamscape
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« Reply #6 on: July 02, 2010, 02:13:29 PM »

On our Eagle I just set the park brake, let up on the clutch some then release the park brake. It's worked for us on slight inclines, haven't had the nerve to try it on a 6% one. Yes, we still have our spicer! Cry That will change someday! Cool

Of course if you have DD-3's, that won't work.
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Lin
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« Reply #7 on: July 02, 2010, 03:00:24 PM »

We once were unable to make a hill with our Spicer even in 1st.  I had the back down several times taking longer and longer running starts to make it.  That got me very concerned about the setup.  When the clutch went, we thought to replace it at first, but realized that it was just a waste to end up with the same inadequate combination.  Since the engine had to come out anyway, we looked into different transmissions like a Roadrunner, etc., but finally took the leap to an Allison.  I have not been in a comparable situation yet, but I believe that the automatic, and the bigger injectors will make the difference.

I do not think that there is a magic bullet technique that will solve the problem.  You do the best you can and will eventually need a new clutch.  I would say that at that time, count the money not spent on a new clutch as a credit toward your automatic.  You might even start gathering the parts you need so you will be able to get them at reasonable prices.  I know that there are some that say the Spicer was good enough for Greyhound, so it must have been good.  I don't believe it.  It was a poor choice for Greyhound and it is a poor choice for us.  They must have gotten them cheap and made a penny wise/dollar foolish decision.
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Barn Owl
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« Reply #8 on: July 02, 2010, 03:37:28 PM »

The beauty of an automatic is the torque multiplying you get that is especially handy starting on a steep grade. I have a hill in front of my house that is steep enough to have stalled my auto. I would have had a much different trip up into the Rockies if I had a manual tranny. 8 to 10% grades at over 10k ft is hell on anything. There is no good solution here for your problem. You get to smell burning clutch and save for the auto.
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RJ
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« Reply #9 on: July 02, 2010, 05:49:21 PM »

Brian -

To elaborate a little more on what JC was saying, you can get rolling with minimal clutch slipping, as long as you're not trying to get started on a hill that would be difficult for ANY vehicle (common sense, eh?).

One trick that worked well for me was to hold the coach stopped for any length of time with the parking brake.  Watching the cross-traffic light for the change to yellow, then cover the service brake while releasing the parking brake.  Let the clutch out until it just starts to take up, apply a FULL service brake, release and quickly stand on the throttle while releasing the clutch the rest of the way.  A little jerky, but with practice you can smooth it out.

This trick works because the service brakes take a second or two to actually release after you let off the pedal.

Of course, a challenge you have is the lower torque of the 6V71 vs the 8Vs in the majority of buses most commonly found converted.  As you're discovering, you have to learn to acclimate yourself to the situation and, again as JC said "do what you have to do."  Even if it means taking a different route. . .


Lin -

The four-speeds worked for Greyhound (and others) because 99% of the time they never got into situations where a lower first gear was needed - just like the "why" of the tall reverse for backing out of flat terminal stalls.  Their switch to automatics was based on a number of factors - the cost of clutch replacements over the life of the vehicle (more labor-intensive on the MCIs vs the GMs, for example), the improved dependability and fuel economy of the Allisons (especially the virtually bullet-proof HT-740), and, interestingly, the cost of training a labor force where more and more individuals do not know how to drive manual transmissions.




It's always amusing to me, as an industry veteran, how non-vets can get their coaches into situations they were never designed for in the first place, then grumble because the coach didn't do what they were expecting it to do.  Often brings a chuckle, sometimes an eye roll, sometimes a shake of the head ("what were they thinking?), but always entertaining!

FWIW & HTH. . .

 Wink

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RJ Long
PD4106-2784 No More
Fresno CA
Lin
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« Reply #10 on: July 02, 2010, 07:52:31 PM »

RJ,

I appreciate your experience and knowledge on this subject, and realize that Greyhound managed with the 4-speed for a long time, but I still do not think it was a good choice.  A 5-speed with a good low gear probably would have turned out to be more economical for them considering maintenance.   There is no travel in California without hills.  Many are challenging even with the Interstates.  My bus was on the road long before the Interstates, so I would guess that traveling over the pre-Interstate Grapevine would have involved lots of stopping and starting.  If you told me that the drivers picked the 4-speed, I would have to re-think my notions, but I doubt it was done that way. 

The complaints we make about that transmission are coming from not only the drivers, but the ones that pay for the repairs.  I really do not do much with this bus that Greyhound did not have to do also.  As with Greyhound, maybe the 4-speed is okay for us 99% of the time too.  That 1% though can be rather significant.  That would be one hour of clutch abuse for every 100 hours of driving.  How many hours of abuse do you get between changes.
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Fred Mc
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« Reply #11 on: July 02, 2010, 09:11:40 PM »

Actually, I don't have any problem at all with my spicer and standing starts on hills. For me the trick is to get the clutch fully engaged as quick as possible. I hold the brake, then rev the engine quite a bit, release the brake  and start to engage the clutch. As the clutch starts to engage and the bus starts to roll I ease up on the throttle and fully engage the clutch.

Fred Mc  GM PD4106/
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LarryN 4106
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« Reply #12 on: July 03, 2010, 05:28:32 AM »

Clutch is fine, just did not have power.  Engine was not revving up at all so the clutch was and is fine.  I am indeed considering a change to automatic at some point, but really  looking for more than "don't drive a bus with a 4 speed on a hill" here and now...    Wink

Brian

This is a timely subject. Just one week ago today, we were heading to Mountain View, AR. For you folks who think steep grades only exist in some select mountainous states, think again. We got off US 65 at Leslie, AR, then proceeded west on AR 66 to Mountain View. WE were immediately slammed with a grade that had me sweating bullets. I eventually had to shift into 1st gear and hoping that was enough gear to get me to the top. A dead throttle start on this hill would have been futile. I was in my 4106 with spicer and towing a Wrangler. I had never had to downshift into 1st for anything in Colorado, or NM.

Folks, when we came back that same route on Thursday, I had unhooked the Wrangler and told my wife she was going to drive it as far as Harrison, AR when I would hook it up again. What a difference that made. I also discovered that the grade outside of Leslie, AR was 11%. My bus has a relatively fresh Diesel Exchange engine (24,000 miles on it) and the clutch was replaced at that time. Last summer, I had vowed to "not tow" during the trips thru the steep grades but this grade surprised me. When we return to Mtn View (which we will because we loved camping on Sylamore Creek), the Jeep is going the last 70 miles on it's own power.

I think we ask a lot of these old girls, weight wise. Coming back, I never got below 3rd gear.
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bevans6
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« Reply #13 on: July 03, 2010, 05:38:28 AM »

Larry, are you saying the Wrangler made the difference between first gear and third gear on similar grades?  How interesting!  My towed car is roughly 2700 lbs on it's dolly.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Vintage race cars -
1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
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« Reply #14 on: July 03, 2010, 07:43:10 AM »

Brian,

In the incident I mention above, I was towing a car on a dolly.  Getting the car off the dolly wasn't to bad, but getting the dolly down the hill so I could back the bus down was the real adventure.  The road was one lane wide with no shoulder.  I may forget everything else about that trip, but I will remember why I stopped using a dolly.
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