Eagles International Forum

Hi everyone, I'm very new to this site and I just bought my first Silver Eagle. I love the way it rides and handles. I am interested in possibly looking at other power plant options and moving to an automatic transmission. I'm sure someone has already done what i'm thinking about, so give me your thoughts on this topic. I'm a musician and this is a working tour bus. I'd like to add a trailer hitch but i'm not sure about the current gearing and whether or not it would have trouble pulling a 24ft enclosed trailer. I'm all ears

Hi

You didn't give any details about your particular bus for us to work with.

First, what year is it?

What engine and transmission does it have? It may have already been repowered.

The standard axle ratio is 3.70 and you likely have it if you already have the factory powertrain.

The standard powertrain up to early 1980 is a 285 HP Detroit Diesel 8V-71 with a Spicer four speed manual transmission. When the Model 10 was introduced later in 1980 this changed into a Detroit Diesel 6V-92 and an Allison four speed automatic. Some 1980 and later Model 10 Eagles still had the older 8V-71 and the four speed but a five speed manual was a factory option. The 8V-71 and the 6V-92 made about the same power but the later 92 engine had more torque because it was turbocharged.

Something to consider is how much total weight will come with the trailer. That includes the empty weight of the trailer, the hitch and electrics. Now think about how much weight will go inside the trailer and add the two together. Now add this to the fully loaded weight of your coach, including the passengers, full fuel and any onboard equipment to get total vehicle and trailer weights. Now divide this total weight by your horsepower to get the power to weight ratio. You have to do this division twice. Once with just the loaded weight of the bus and once with the loaded weights of both the bus and trailer.

With the power to weight calculation, a lower number of pounds per horsepower is better. Let's say the bus itself has a power to weight ratio of 50 pounds per horsepower. Adding the weight of the loaded trailer makes this (for example), 68 pounds per horsepower. The idea is to keep the power to weight ratio the same to get the same performance for acceleration and climbing. To bring the number back down to +/- 50 again, you need to add power until you get the ratio down to about 50. For better performance, bring it down to let's say 45. Of course more power means more fuel so there's a tradeoff to be made.

Another thing to consider is that repowering to most four cycle engines means a loss of up to about 300 engine RPM and will lower your road speed enough to notice. The cure for that is a different drive axle ratio to a lower number such as 3.30 or even 3.0. This causes yet another tradeoff. The higher (numerically) the ratio is, the better your acceleration and pulling power for hills will be but you get a lower top speed. And you'll use more fuel. On the other hand, a low ratio gives you better fuel economy and more speed but worse acceleration and pulling power. Of course the cure for this to to add more power but that comes with more of the disadvantages just mentioned.

A lot of folks on here have added trailer hitches and made various conversions. I'm sure most of them will be happy to share their knowledge with you in the future.

Hi Mike. Welcome to our forum

You are really asking two questions in your post. Let me address the engine/transmission first. First, I suspect you have read my series of articles (originally published in Bus Conversions Magazine) on the subject - in this category on the main website:

http://eaglesinternational.net/category/articles

You will see that there is a lot to consider when you consider an engine conversion. The typical conversions are an 8V92 (can be an issue with cooling), a Cummins M11/ISM which is very popular and does not require raising the bed, and a Detroit Series 60 (and series 50). With the four strokes, they like to run lower RPM and that suggests a gear ratio or transmission change (for overdrive).

I have done quite a bit of documentation on my Series 60 conversion in my project pages (see signature (below).

An engine conversion is not for the faint of heart (both in effort and cost). That said, I have never heard an owner say that they regretted an engine conversion.

Jim

The second part of your question involves towing a fairly large trailer. The two issues here are having enough power (you are addressing that in this thread). The second is a possible structural issue. We have had at least one person who experienced a frame failure as the result of towing a large trailer, while others have had no problem.

The big issue is the condition of the engine cradle structure. Part of the issue is address here:

http://eagles-international.net/forums/ ... ?f=5&t=350

I was very careful to "double tube" and reinforce all of the structure in the engine compartment. You can see the details in my project pages.

The tongue weight is the main issue. There are options that can minimize the issue. One excellent option is:

http://www.trailertoad.com/

Jim

Mike,

If you are already thinking about an automatic and more power, my guess would be that you have 4 speed Spicer manual, and a naturally aspirated 8V71 engine. You can upgrade to several engines and transmissions, but they all come at a cost. If you have the 4 speed manual, the frame will have to be modified to put in even a five speed, or a ten speed Roadranger, or an Allison automatic. The space that is available around the existing transmission is not wide enough to allow room for something bigger. If you are handy with metal fabrication and welding, it can be done at not too great a cost, but if you have to pay someone, the costs will skyrocket. If you plan to tow a good sized trailer, and not just on flat land, you may need a stronger frame and more power and more gear choices. It might be cheaper to trade up to an Eagle that is already equipped for what you want to do than to try to modify what you have.

In my own case, I bought a 10 speed Roadranger transmission to put in my 1975 Model 05 Eagle because I was going out west into mountainous areas, but between the frame modifications and fabricating shifting linkage, I gave up on that idea and bought a Model 10 with an Allison automatic. Another advantage is that the Model 10 has power steering instead of the air-assisted manual steering. Even with a Model 10, you would have to consider strengthening the rear frame area to make a suitable hitch arrangement. When you do the hitch you also have to allow for disconnection of it should the engine need to be removed. Its a can of worms, but many people have done it before you. There is plenty of knowledge on this board and others, so check the archives. Details about your Eagle, and pictures, would help us help you.

Thanks a ton for the advice. I will spend some time reading the already documented stories on here and i'm sure it will guide me in the right direction. Thanks again!

After you have digested the recommended reading and put your brain back together again (after it explodes ), get back with us with more questions.

Jim

I absolutely will do..you guys are a wealth of knowledge and much appreciated.

Hi guys, I do have another transmission related question.  So, somewhere along the way, my bell housing on my tranny has a huge crack and needs replaced.  Can anyone recommend where to get a replacement?  I have the 8v71 mated to the 4 speed manual.  I'm working on getting the serial number that should be stamped on the engine block but that is what I'm dealing with at the moment.