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Old 09-28-2018, 07:32 PM   #1
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New to the 6.6 and 545 Allison

Hi all, I just purchased an f350 that the previous owner installed a 6.6 Brazillian and an Allison 545 out of a school bus into. Anyway, he tried to use a 4 speed manual behind the Allison as a divorced overdrive and the drive train has a bad vibration at anything over about 50. I am thinking that the vibration is coming from the divorced "overdrive" transmission and I am probably going to remove it. The truck has 4.10 rear end gears and stock sized tires. I am wondering if anyone could tell me 1) Will I be able to run 60-70, and 2) How will it do pulling a 7000 lb fifth wheel. I have been looking for information all over the net, and it seems as if everyone here may have the answers I am looking for. Thanks, William. Here are some pics of the Green Gobblin.
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Old 09-29-2018, 09:41 AM   #2
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I saw that truck for sale on a different site. I thought it was a neat swap. Anyways, your vibration is likely something else then the 4 speed auxiliary transmission. Check out your u joints and the angles their operating at. After you've done that, have the driveline balanced if it still shakes. Heck, make sure the tires are in decent shape.

It should be able to do 70 without a trailer behind it. It won't be a sports car by any means, but it will get you there. Not sure how it will do pulling a fifth wheel. Biggest issue you'll have is the at545 having a non-lockup torque converter. They don't do well at low rpms which is what that 6.6 is.
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Old 09-29-2018, 11:08 PM   #3
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Thanks Booyah. I got to looking at the driveline, and I think it is the angles on the final driveshaft, it has short and at quite an angle. i haven't checked the exact angle yet, but its pretty steep. Does anyone know what the optimal angle for a driveshaft is. Thanks again
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Old 09-30-2018, 08:21 AM   #4
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With custom driveline work having been done I would also check the driveline U-joint phasing. You'd expect someone who is taking on such a swap would be aware of phasing, but it's possible they didn't do it right.
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Old 09-30-2018, 09:16 PM   #5
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that is very true. I am going to check angle and phasing hopefully tomorrow when I get home from work. I'm thinking it may be more driveline angle than phasing, but could be a combination of both. I'll let everyone know as soon as I get some more info on it, and I will post some pictures as well. Thanks everyone
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Old 10-01-2018, 12:06 PM   #6
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For long life, the angle of the joint should be more then 0, but less then 3 degrees. But angles larger then 3 shouldn't cause a vibration. Vibrations usually occur because the U-joint is wore out, or the joint angles on the shaft don't cancel each other out, or the phase of the joints are out. The last one isn't common on one piece shafts because it's a welded assembly, however on shafts with slip joints it's easy to install the slip yoke a tooth off.

Here is a video on driveshaft angles and phasing.
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Old 10-01-2018, 08:31 PM   #7
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Thanks everyone for the info. I haven't had a chance to work on her yet. I am hoping to get a chance tomorrow. One other question for everyone. What would be a good pusher fan for the ol girl? There isn't enough room between the radiator and the water pump pulley to install a regular fan. Any ideas? Thanks, William
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Old 10-01-2018, 08:51 PM   #8
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Great info. Thanks for sharing. And yes...setting up a driveline "out of phase" is a very common problem. I've seen "pros" who had no idea it was even an issue.
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Old 10-01-2018, 11:24 PM   #9
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considering it has a slip joint on each shaft, if I remember right, it is quite possible thats what the issue is, as well as the angle of the rear shaft. It seamed really steep when I looked at it the other day
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Old 10-02-2018, 10:11 AM   #10
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Quote:
Originally Posted by thumper_65590 View Post
Thanks everyone for the info. I haven't had a chance to work on her yet. I am hoping to get a chance tomorrow. One other question for everyone. What would be a good pusher fan for the ol girl? There isn't enough room between the radiator and the water pump pulley to install a regular fan. Any ideas? Thanks, William
I'd try really hard to get a mechanical fan in there somehow. Yes, electric fans consume more hp then electric but the cfm difference is also pretty large in favor of a mechanical. That is why most of your heavy duty stuff still runs a mechanical fan(with an electric on/off clutch).

If you must use an electric fan, puller types are something like 20% more efficient then pusher types.
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Old 10-09-2018, 10:36 PM   #11
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I didn't have room to get a mechanical in there, just not enough room. I was able to get a puller fan in. Still working on getting the exhaust figured out, but did drive it a little today. She tops out at about 65, but will do it all day long, lol. She runs out good, and I can;t wait to see how she does pulling the trailer this weekend. One other thing, what would everyone suggest for a better transmission? I have been thinking of finding a road ranger 7 spd with a double overdrive. final drive is like .68. I was also thinking about changing the rear end gearing to 3.83 or 3.55 instead of the 4.11 that is in there now, but I don't want to sacrifice my pulling power. Ideas?
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Old 10-10-2018, 10:43 AM   #12
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As far as double OD manuals are concerned, I don't know of any that are less then 13 speeds.

Not really sure why you'd want a double OD manual anyways. You can get 7 speeds with a single od of .75:1, and they even have .65:1 options. Granted the spacing between the gears is pretty wide so make sure the engine powerband will work with it.

Pulling an at545 though, maybe a new double od allison will be a better option for you. Look up posts by cadillackid, He swapped iirc an at545 for an allison 1000 in his bus and did a write up on it.

My idea? Find an online gearing calculator, get your current information, and play with the ratios to see what will work best for you.
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Old 10-10-2018, 10:51 AM   #13
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What he said...for sure!


Don't play "guess the gearing". You can spend a bundle and come up really unhappy unless you do your homework first. Run ALL the numbers on an online gearing/speed calculator. Not just top end...but every gear. Much cheaper than swapping out two or three gearsets or trannies.
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Old 10-14-2018, 09:11 PM   #14
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very true. I'll start running some numbers. Used her to pull the camper this weekend, and she'll run 60 all day long up hill and down, but she's running really close to the governor doing it. She has plenty of power to offer, and I even liked the way the 545 did pulling the camper, just need to get a little more speed out of her and drop the RPMs. i haven't had a chance to run gearing numbers yet, but hope to do that in the next day or so. I'll post up a driving video and a few more pics after my phone charges. Thanks again everyone.


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Old 10-14-2018, 09:27 PM   #15
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Don't forget to also play with tire diameters. Often you can pick up some top end/lower your RPM's with just a drive-wheel tire change.
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Old 10-15-2018, 09:59 PM   #16
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Tango makes a good point. Do your due diligence before putting your money down.

I have a truck that is "overgeared". It has a six speed transmission that rarely sees sixth gear and get it's best fuel economy in fifth.

I spent the day moving trailers around the lot and found that having tall gears makes backing trailers up a real pain.

Do it right the first time
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Old 10-21-2018, 10:38 AM   #17
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Quote:
Originally Posted by thumper_65590 View Post
Thanks Booyah. I got to looking at the driveline, and I think it is the angles on the final driveshaft, it has short and at quite an angle. i haven't checked the exact angle yet, but its pretty steep. Does anyone know what the optimal angle for a driveshaft is. Thanks again
THe number of U joints in shaft determine the proper angle (if any)






Lots of information on this page Tom Wood's Custom Drive Shafts - Driveline 101
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Old 01-25-2019, 04:54 PM   #18
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I've wanted to do a swap like that for a long time. Granted, it's only 170hp now, but if you crank up the power any, that combo of transmissions will grenade. I would highly suggest an RTO6610 if you like a bunch of gears(10 speed), or one of the FSO variants for manual trans choices. For auto, an Allison 1000 would be great, or for a less costly alternative, an MT653. As mentioned, gearing calculators will be key.
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Old 02-25-2019, 09:49 PM   #19
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Well, I had some issues with the driveline, actually I had a crossmember break on the spicer, and let me tell ya, when it hit the ground at 70, things got a little exciting. Anyway, I figured since I have to redue the driveline anyway, it is time to upgrade the transmission possibly. I found an Allison MT643. Would this be a better transmission that the 545? Let me know and thanks, William
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Old 02-26-2019, 02:49 PM   #20
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Yes, the 643 is better then the 545. It's also substantially larger as well, so make sure you'll have room to fit it in the truck frame rails, fire wall, and floor board.
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