A 4106 pushed by an 8V-71 on a 5% grade...

bwze · March 02, 2011, 07:49:20 AM

Well now that I've got my old girl ('64 4106 w/8V-71) up and running, and have finally figured out how to downshift "most of the time", I've really noticed the lack of power on the hills. I've got three 5% grades that are just over a 1/2 mile long within a few miles of my house. On my test drives, I approach these hills at around 55 mph.....after downshifting through third and into second, I seem to only be able to take 'em at around 30 to 35 mph. I'm not sure of the weight of my coach, but I was told by the PO that it was around 20k give or take.....(again, I'm taking his word on this). I had a buddy take a look at my throttle take up in the rear with me pressing fully on the accelerator pedal (until it hit the bolt stop under the pedal) and he said I still had some more to go for full throttle. I removed the bolt thinking that this would give me full throttle, but after trying one of those hills again, I still couldn't take it any faster. What do you other 4106 owners tend to see as far as speed in similar conditions?

Fred Mc · March 02, 2011, 07:51:51 AM

That is what I would get on my 4106. Basically wide open in second gear.

Barn Owl · March 02, 2011, 07:55:20 AM

Without a 6v92ta, what you have seems about right. I have a v730, so not a direct comparison.

Len Silva · March 02, 2011, 08:30:06 AM

That sounds about normal, though you do want to be sure you are getting full throttle.

I had a similar problem in my 4104. It seems that the cable may stretch after fifty years or so and may take a bit of modification to get it right.

bwze · March 02, 2011, 04:37:33 PM

Thanks all....sort of what I figured.

Len, I'll check out that throttle adjustment just to be sure....

Don Fairchild · March 02, 2011, 04:41:43 PM

As suggested make sure you are getting full throttle. If it were mine I would save my money and rebuild and turbo the 8V71 and forget about the 6V92 they don't have any low end to them. The 8V71 turbo built correctly will run away from a 6V92 any day of the week and get better fuel mileage doing it.

Don

luvrbus · March 02, 2011, 04:52:39 PM

I love the 8v92 but the 6v92 is not my cup of tea they are pretty much gutless on the low end think big block Chev not much difference, plus they sound like they are missing all the time the V6 thing

good luck

RoyJ · March 02, 2011, 05:22:09 PM

Quote from: bwze on March 02, 2011, 07:49:20 AM
Well now that I've got my old girl ('64 4106 w/8V-71) up and running, and have finally figured out how to downshift "most of the time", I've really noticed the lack of power on the hills. I've got three 5% grades that are just over a 1/2 mile long within a few miles of my house. On my test drives, I approach these hills at around 55 mph.....after downshifting through third and into second, I seem to only be able to take 'em at around 30 to 35 mph. I'm not sure of the weight of my coach, but I was told by the PO that it was around 20k give or take.....(again, I'm taking his word on this). I had a buddy take a look at my throttle take up in the rear with me pressing fully on the accelerator pedal (until it hit the bolt stop under the pedal) and he said I still had some more to go for full throttle. I removed the bolt thinking that this would give me full throttle, but after trying one of those hills again, I still couldn't take it any faster. What do you other 4106 owners tend to see as far as speed in similar conditions?

Billy, are you out of revs at 35 mph, or foot to the floor and can't pull to 2100?

My bus scales 26,000 fully loaded, has a 6v71 (4V, N70, 2500rpm), so probably similar power to stock 8v71 on N55/60 injectors at 2100rpm.

On a 6% grade, I'm tached out in 3rd, at 30mph and 2500 rpm. But I can just as easily pull a 10% grade at the same speed. For fuel economy, I typically pull grades at 25 mph and 2100 rpm.

bwze · March 02, 2011, 05:52:14 PM

Roy, I'm at the governor if I'm in second. Not sure of the engine speed since I don't have a tach. If I stay in 3rd, I can sense the engine speed, and road speed, is dying.....hence when I get to about 30 mph or so, I shift down to second.

rv_safetyman · March 02, 2011, 06:10:58 PM

bwze, a part of the puzzle is missing - altitude. I see that you are from SC, so maybe that is not an issue, but you loose a big percentage of power as you go up in altitude.

I have a good friend with an Eagle that had an 8V71 at the time and he was down to less than 10 MPH on a pretty steep climb out of Denver.

Jim

Chopper Scott · March 02, 2011, 06:31:18 PM

You should be able to feel the governor in second gear easily on a 5% grade unless you are at 10000 foot elevation. I figure what is the big hurry. If I want to go fast I'll get to once I get over the top!!!!

Barn Owl · March 02, 2011, 08:15:02 PM

QuoteIf it were mine I would save my money and rebuild and turbo the 8V71 and forget about the 6V92 they don't have any low end to them. The 8V71 turbo built correctly will run away from a 6V92 any day of the week and get better fuel mileage doing it.

I would agree. The reason I am such a big 6v92 fan is because it appears that they are plentiful and inexpensive. If I had the money I would love a 8v71 turbo but I am not seeing to many of those for sale. Another thing, is low end that big of an issue when you are running it into an automatic? I truly don't know. I do know that given the choice between a 8v71na and a 6v92ta I would go with the six every time. I have never driven a 4106 with the 8v71 turbo so I would have to rely on others to comment on it. Also, according to Allison you don't want to overdo the HP feed into the v730, but I don't remember the recommended number. I know there are others here that do and they can post them.

RJ · March 02, 2011, 08:49:31 PM

Billy -

Sounds perfectly normal for just about ANY coach with a stock 4-spd in front of an 8V71N.

One of Don's turbo engine's in your coach would pull that same grade about 10 - 15 mph faster, give or take a little, albeit with a close eye on the temp gauge.

Don't take the PO's word for the coach's weight, take it in "travel ready trim" (loaded for a trip) to a set of certified truck scales and get it weighed. Front axle alone, entire coach, rear axle alone. Now you've got good info to work with - including setting the air pressure in your tires correctly for the load they're carrying. Anything else is pure speculation.

Weight, speed and the driver's right foot are the three biggest enemies of fuel mileage.

Reinstall the bolt under the throttle pedal, it's there for a reason. Then adjust the throttle linkage per DA BOOK. Good excuse to lubricate the cable while you're at it - the old grease gets pretty gunked up over time. Heck, might as well service the entire pedal assembly (throttle and brake) while you're working on it - they're much nicer to operate when lubed properly. If you don't have DA BOOK, let us know, we can help.

Re-read this article about downshifting when pulling a grade - you may be downshifting too late:

http://www.busnut.com/bbs/messages/12262/16204.html?1167073154

Is the speed limit such that you could approach these hills at 65? If so, as short as they are, you might be able to pull them in 3rd by approaching 10 mph faster to start with. Just sayin'. . .

In the meantime, think about Aesop's Fable: The Tortoise and the Hare.

Enjoy the ride!

FWIW & HTH. . .

Fred Mc · March 02, 2011, 09:06:36 PM

My very first experience in driving a bus was with a friend who had an MC 5. We were cruising down the freeway at 65 mph and he said(as he got up off the drivers seat) take over as I have to go to the bathroom. O-K-A-Y, I said as I slid into place.
He was a low bed operator and was used to hauling heavy equipment so had the same problems we have in some older busses-not as much power as we would like to climb the hills. We live in mountainous country and he told me that he always drove looking ahead to the next hill as he would start to speed up as he approached the hill. Sometimes it would save him a gear on some shorter hills. I try and drive the same way.

pvcces · March 02, 2011, 10:35:09 PM

bwze, I'm sure that we have climbed 5% in third in our 4106 with the stock setup; our coach runs right at 27,500 pounds when on the road. We have experienced what you described, but when we installed our cruise control, we cleaned up and adjusted the throttle cable and got a big surprise. We found that even though the throttle cable was only stopping short a small amount, fixing it made a big difference in hill climbing.

We have went over Snoqualmie Pass from the west, and broke over the summit at 32 mph in third. That's 3,000 feet of elevation and a pretty good grade. I figure that you're way heavier than you think, you're losing power from lack of air and you're not anticipating hills by picking up speed, as much as you can, before you hit the grade.

Of course, it only takes a very slight loss of compression to cause enough loss of power in these two strokes to take you out of third gear on these grades. I would run down your facts until you are sure of what's happening with your rig. If you are running a continuous fan or have any cooling problems, that can take you out of third gear, as well.

Good luck on getting a handle on your rig.

Tom Caffrey