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CAT 3208 swap Phil 12-5-03  
I have a early 80's Ford school bus with a great running 370 gas motor and an Allison 4spd. But I want more power and mph! I have found a good CAT 3208 in a tank truck but it has a manual trans. I'm wondering if it will bolt to my Allison. I am not familiar with Allison transmissions but from what I've read I think it is a 545. Is the bellhousing bolt pattern the same? Will I need a different torque converter? Or, If the 3208 will not fit, is there a better or easier diesel to transplant??I understand that 3208's were in some Ford school busses in the mid 80's. I've got to do some measuring to see if the 3208 will physically fit in my bus and if it will I can make the swap but need some info about the trans since I have no idea. I appreciate any help.
Re: CAT 3208 swap Phil 12-7-03  
Just to show you how confused I really am. I've had several people tell me in the past few days that I would be crazy to go from gas to diesel. They tell me the Ford 370 is an excellent motor with plenty of power to pull my trailer (about 9,000 lbs.) at highway speeds. My only concern is that if I put enough gear (numerically lower) in the rear to run 60 or 65 at a decent rpm that I won't have enough gear to get the thing moving. I've already put a 2 speed rear in the bus that I was told was a great highway gear but it turned out to be the same gear I had in the bus to begin with. At the time I didn't know where to look to get the gear ratio of the 2 spd so I just took the mans word for it. I've since been told that it is stamped on the end of the pinion behind the u-joint. The only saving grace is that the 2 spd rear was given to me so I was only out some time, no cash. Another concern with the gas engine is mpg, or the lack of. A diesel should be much better, I would think. Someone please make up my mind for me, I'm going nuts here. Thanks
Re: CAT 3208 swap wrench 12-7-03  
I got a bluebird with a ford 391CID (about same engine that a 370 CID) and when it got 10 K behind you feel it. It's ok for a haul once in a while(not fast), but if you going to haul on a regular base you will need something else. A 3208 is not much stronger that a 370 CID. What ever the gearing you put in, is not going to give you more power, there is a ratio to respect with power/weight/speed, and there is no way you can change that with swaping gears.
EX: put your foot on a bicycle, higher the ratio, harder it is to push on the pedal & you have to have the capacity(be strong enough)but it goes faster & take longer to get at speed. But if you're lack of power you use lower ratio, but it's slower on top end but quicker to take off. Those are the law of physic & can not be change.
Hoping it help a bit.
Re: CAT 3208 swap Phil 12-7-03  
Thanks John, In searching for info on this swap, I have read that 3208's were put in Ford school busses in the mid 80's. I would assume that at least some or most of these had Allison's behind them. So is finding one of these bellhousings going to be that difficult or is that wishful thinking? And is a bellhousing and flywheel going to cost me an arm and a leg? I also found bellhousing SAE charts with their dimensions but could not find which bellhousing size the 3208 or the allison was. I could put the manual trans in my bus but really wanted to keep the auto for convenience and ease of driving but I am not anti-manual trans. Another good point with the u-joints. Hadn't thought of that one either. But I wouldn't think that would be a big issue in everyday, normal driving conditions. May find out I was wrong the hard way (on the side of the road, 300 miles from home!) Thanks
Re: CAT 3208 swap John the busboy 12-7-03  
The AT-545 has an SAE-#3 clutch wants to see a #3 flywheel housing. I believe the flywheel housing on the 3208 is a #2. I have seen picutes of an adapter that will adapt a #2 flywheel housing to the Allison 545 #3 clutch housing. I hope this makes sense.

Could be that Cat made a flywheel housing that is #2 on the engine side and #3 on the transmission side. Detroit Diesel did for the 8.2.

Why not put the standard transmission in when you put the engine in? Are your ujoints going to be strong enough to handle the extra torque?

Think it through.

John the busboy
Re: CAT 3208 swap Randy Markey 12-6-03  
Your 3208 will bolt up to the Allison transmission. You are correct on the torque convertor, you will need one for a diesel. But you will possibly need to respring the valve body, because the shift points will be too high and the bus will never make a shift. You will need to get the part number off of the right rear side of the transmission and the engine top end engine RPM. If you have any questions, feel free to call me at 715-273-0411.
Re: CAT 3208 swap Mark O. 12-8-03  
Swapping out a Ford 370 to a Cat 3208 is a doable project.

Swapping an Allison that is mated to a Ford 370 to a Cat 3208 is probably not worth the effort.

I am assuming the Allison behind the Ford is most likely the AT540 series transmission. If that is so, it won't last long if you put it behind a 3208. The Cat has too much torque for the AT540. Also, most of the gas engine AT540's had vacuum moderlators to make the shifts. With a diesel engine, you would have to add a vacuum pump to make the transmission shift. This is all in addition to having different bellhousings.

I would agree with the comments about the HP of the two engine being similar. I am thinking the Cat would pull a hill longer in a higher gear than the Ford would.

Another problem that has yet to be addressed is your cooling capacity. Switching to a larger engine with an automatic transmission is going to require a lot more cooling capacity than what you currently have. Particularly if you want to go faster.

I am thinking the best thing for you to do is poke along in the slow lane with your 370 until you can afford to upgrade to something with some real serious HP. Even if you get the Cat engine and transmission free you are going to be spending a lot of $$$ and a lot of time swapping everything around. I am thinking you can poke along in the slow lane a lot of miles before you would ever realize a saving in time and money.

Good luck and happy trails.

Mark O.
Re: CAT 3208 swap Phil 12-7-03  
Thanks Randy, You say it will bolt up to my Allison, but do I need a different adapter between the engine and trans? I had figured I would need a different converter but hadn't thought about the shift points. Good point though, and it makes sense since the two engines make power at very different rpm's. Is that something I could do myself (with some instruction), or is that better left to someone with more Allison knowledge? I am very mechanically inclined, just not familiar with Allisons. I am familiar with automobile automatics, though.
Re: CAT 3208 swap Randy Markey 12-11-03  
You should be able to respring the valve body yourself. As far as the u-joints, they should hold up alright. The vacuum modulator can be replaced with a cable modulator. If money is your concern, I have just priced out a regear for a 79' chevy C70 and parts (including cooler, adapter flange, modulator, flex plate, etc.) was around $1000.00.
Re: CAT 3208 swap scott 12-25-03  
Yes it would workford's are verey easey to work with. but i would gest stay with the 370 thay are verey easey on gasgood luck with the ford
Re: CAT 3208 swap David King 7-23-05  
I have 1990 Kodiak with an Eaton RT6610
transmission 1 to 1 Ratio. At 2200 rpm on 22.5 rubber I am going 55 mph, at 2400 rpm 60 mph. At 2600 rpm wide open 65mph. I can't find the rear end ratio anywhere on the differential (eaton). I have been told I have a 4.11 ratio. I would like to increase my mph while towing an 18,000 lb. trailer. I have considered changeing the transmisson to an overdrive or the rearend ratio. I need to have an idea of the difficulty of changing either one out and an idea of cost. Please advise.
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Re: CAT 3208 swap John the Busboy 12-16-03  
Reading your comments about your brakes....

If you shop around in old book stores and on the web you should be able to find a Ford Medium Duty Truck manual for whatever year of bus you have. It will save you tons of money and trouble in the long run.

Another thing worth doing is checking out the heavy truck salvage yards in your area. The one I deal with has given me quite a bit of help in the parts department. They seem to find my bus project interesting for some reason.

John the busboy
Re: CAT 3208 swap Phil 12-14-03  
Thanks wrench,
You are absolutely right. You cannot make up for a weak dog of a motor by simply changing the rear gear. But I do believe my bus is not at it's optimum setup. Afterall, it was not intended to run 60 mph. If I do decide to leave the 370 in the bus I think I can find a more "happy medium". I can't get what I am after, but I can get it closer than it is now.
Re: CAT 3208 swap John the busboy 12-14-03  
Didn't you say the 3208 is in a truck youown?

If so, why not swap out the running gear including the rear end?

Your 3208 will have enough torque to get you up to speed with a tall rear end. To calculate the engine speed at a given road speed you need to know how revolutions per mile your tires are turning and the drive axle ratio. Since 1 mile per minute equals 60 miles per hour all you have to do is multiple the revolutions per mile by the drive axle ratio to get the number of revolutions per mile the engine will turn......and this will be in revolutions per minute since it takes 1 minute to go 1 mile. The automatic will have some slippage in the torque converter so add about 10% to the engine speed number and you will be in the ball park somewhere near home plate.

For us, with an 8.2DD, 2200 equals actual 60 mph. Using the above method without the fudge factor at the end we get 2070 theoretical rpm. The torque converter slippage is about 130 rpm. Our tires are rated at 504 revs per mile and teh drive axle ratio is 4.11.

Hope this helps.

john the busboy
Re: CAT 3208 swap Phil 12-14-03  
Thanks John,
I agree, although I'm not that familiar with commercial diesel engines, I do think the diesel's torque should be adequate to accelerate and maintain a speed better than the old 370. Your rpm calculation is correct but that is assuming the high gear in the transmission is 1:1. If high gear is an overdrive, it would be something like.87:1. Which would drop the rpm's even more. I am not sure of my transmissions high gear although I would assume it is not an overdrive. As far as converter slippage, I know some Allisons have a lock-up converter which should mean NO slippage. Again I don't know what converter is in my Allison, but I would assume it is not a lock-up. I am going to measure the rollout of my tires, convert that to revs per mile, and use your calculation to determine a rpm. As you say, it will get me in the ballpark. To answer your first question, yes I think I can use the rearend. I did some quick measuring and I think they are about the same overall width and width at the spring perches. I could even use the manual tranny, just hang a clutch pedal in my bus, but I would rather stay with an automatic if it will work. Someone had mentioned an issue with vaccuum for the modulator valve on the tranny but the 3208 already has a vaccuum pump on it. My latest discovery is the brake system. My school bus has hydrostatic brakes which uses power steering fluid instead of a booster. No such provision for this on the diesel's power steering pump. The diesel truck has conventional vaccuum booster power brakes (ala the vaccuum pump on the 3208) which I may be able to fit to my bus. My bus is an '82 600 series while the diesel truck is an '84 700 series. I'll have to do some checking and measuring to see if I can swap the brake system. Anyone familiar with that?
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