6.9 in a bus needs radiator. Upgrades?

franklin2

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I'd run a full radiator, but I'd be scrounging for one from a junkyard and expect to pay $200-300.
Those AT545 is reliable and cheap, but it also might well be the very worst transmission you can own in terms of heat production and efficiency. A new rear-end will just make it slip more and make even more heat. My Allisons are all behind 6.6/7.3 I6 motors, but swapping to an MT-series auto (643) should be possible. If so it would reduce your heat load while increasing felt power and speed. I have two trucks that are very similar in size/weight and the main difference is AT vs. MT series transmission and the MT truck is quite a bit faster and gets much better mileage. Of course an MD transmission would give you O.D. as well, so that would save you the rearend swap.

I think this is with a DT motor, so your process will differ: https://tatumskoolie.wordpress.com/2016/05/05/swapping-allison-at545-to-allison-mt643/
I was wondering that in the previous posts. Heat being generated by the trans is energy that could be put into motion rather than lost as heat in the transmission.
 

teletech

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The AT545 is very reliable and very common, but it's also a great way to emasculate a motor.
Yes, you are just turning fuel into heat with these things and they cost you about 5% of your speed to slippage.
 

Luke_IDI

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After a few weeks out of town, I am getting back home and back to thinking about bus matters. Picked up the new radiator in North Carolina on the way home, a 4-row copper-brass Northern Radiator unit purchased through Holst Truck Parts in Idaho, who had by far the most reasonable price I found—$895. I was not able to find any yards in my area that had anything similar. I had gotten a quote from an old-school radiator shop months ago to rebuild the old one for $800, but at this point the bus just needs to be driving as it is hurricane season down here (Gulf Coast) and it came in very handy as an evacuation camper last year during Hurricane Ida.

Of course this bus is lacking in the drivetrain department, and I have already been dreaming of all manner of swaps, but we fell in love with the old relic and plan to enjoy it the way it is for now, until the budget increases or the AT545 quits. A manual swap with more gears would be great, but automatic would be more friendly to the other driver! MT643 plus a lower geared rear end would probably make the most sense for both my lady and me. The 6.9 would get some significant performance upgrades if we go this route. The guy who swapped the MT643 behind the DT466 seemed very pleased with the resulting power. IDIs have a pretty dismal reputation in the Skoolie community, but maybe that’s because they’re all NA and in front of AT545s. I’d like to see how a turbo’d IDI, maybe with a mildly built injection pump, would move a bus in front of a lockup trans. My research so far has turned up no suitable all-mechanical lockup automatic with an overdrive (have I missed one?).

Booyah, if you have a link to a good tutorial on how to adjust the AT545 modulator or care to post the steps here, that would be much appreciated. It will be getting new ATF and filter soon, plus a temp gauge, and I’ll check the adjustment at the same time.
 
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Booyah45828

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After a few weeks out of town, I am getting back home and back to thinking about bus matters. Picked up the new radiator in North Carolina on the way home, a 4-row copper-brass Northern Radiator unit purchased through Holst Truck Parts in Idaho, who had by far the most reasonable price I found—$895. I was not able to find any yards in my area that had anything similar. I had gotten a quote from an old-school radiator shop months ago to rebuild the old one for $800, but at this point the bus just needs to be driving as it is hurricane season down here (Gulf Coast) and it came in very handy as an evacuation camper last year during Hurricane Ida.

Of course this bus is lacking in the drivetrain department, and I have already been dreaming of all manner of swaps, but we fell in love with the old relic and plan to enjoy it the way it is for now, until the budget increases or the AT545 quits. A manual swap with more gears would be great, but automatic would be more friendly to the other driver! MT643 plus a lower geared rear end would probably make the most sense for both my lady and me. The 6.9 would get some significant performance upgrades if we go this route. The guy who swapped the MT643 behind the DT466 seemed very pleased with the resulting power. IDIs have a pretty dismal reputation in the Skoolie community, but maybe that’s because they’re all NA and in front of AT545s. I’d like to see how a turbo’d IDI, maybe with a mildly built injection pump, would move a bus in front of a lockup trans. My research so far has turned up no suitable all-mechanical lockup automatic with an overdrive (have I missed one?).

Booyah, if you have a link to a good tutorial on how to adjust the AT545 modulator or care to post the steps here, that would be much appreciated. It will be getting new ATF and filter soon, plus a temp gauge, and I’ll check the adjustment at the same time.
Good score on the radiator. I feel that's the best deal for you at this point. Check your fan clutch too. If it's not audibly on for 30 seconds to a minute at start up, it's likely no good.

I'd recommend you enjoy it like it is now. I love mine, but it's night and day different compared to something 20 years newer. I've got a mt643 sitting on the shop floor for mine "someday". I also have a spare commercial 7.3 too. Most guys are pleased with the 643 swaps because of the better stall speed and the lock up clutch in the torque converter. Allison put a loose converter in front of the at545 and the inline 6 diesel guys suffer because they don't turn enough rpm for the thing to ever stop slipping. Ours run another 1000+ rpm more then them, and the converter is better matched to us.

They make lower stall, 6 pad converters for the th400, which is a direct swap onto an at545 AFAIK. I wanted to buy one and try it in mine, but I decided to go with a used 643 instead. LKQ in marshfield MO had NOS reman mt643's for 5-600 bucks a few years ago, which is cheaper then a rebuild kit, but I never found the time to drive and get one. You'll have to make your own flywheel-flexplate adapter for the 643/idi combo, as I've never seen that marriage from the factory.

Allison did make a mechanical trans with lockup and od, before they came out with the AT/MT/HT series transmissions. I think it was called an HT70, It's regarded as obsolete junk though, and not much info is around about them.

I don't have a tutorial on that. If you really need one, I can look into making one. All I did was hold the pedal wide open, pulled the modulator cable tight, and then adjusted the nut on the modulator cable until there was no gap between it and the pedal. You can play with adjusting it looser if the shifts are too firm or delayed. Mine was obviously out of adjustment when I got the bus originally as the trans shifted into 4th quickly and was the definition of a slush box while doing it. With the cable adjusted tight, it operates how it should.
 

Luke_IDI

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That’s great info. A quick google search of “AT545 TH400 torque converter” shows products advertised for both applications. What stall speed were you thinking about when looking into the lower stall converter? Do you happen to know what stall speed the AT545s came with stock? I will check next time I fire the bus up. That mod sounds like a great way to reduce the slippage on the cheap. The way the bus is now, it feels like it could benefit from a lower stall speed, but at the moment it is empty inside, so no drivetrain mods will be decided on until after it’s near its ultimate weight. It shifts pretty smoothly when under load, but the less the load, the harder the shift, so downshifts coming to a stop are pretty hard. Does that sound consistent with normal AT545 operation? I should have a chance to check the modulator cable next weekend.

I also have a spare 7.3 sitting around that I bought for $500 because it had a complete ATS 088 turbo kit installed. It’s a pickup engine. I thought I would put this kit on the bus for an easy drop-in turbo solution, but I’m concerned about clearances with the piping provided in the kit. I’m actually thinking that the AT545 might be too big crossover pipe to allow the crossover pipe to pass under the engine. I will disconnect the stock exhaust and try to fit it one of these days. If it does not fit, something custom would have to be fabricated, which would be a good excuse to think about other turbo options and layouts, and I’m sure the ATS kit could find a nice home in a pickup.

The IDI sits pretty close to the firewall in the bus. How were you planning to route your turbo piping, if you ended up going that route? I had thought of flipping the manifolds and routing the up-pipes over the valve covers, given how much room there is above the engine. Where did you plan to mount your intercooler and second radiator? Also, what turbo did you end up acquiring for your IDI and how did you decide on it for this application? Generally just curious about what may have been envisioned/done to turbo an IDI on the bus platform.
 

Booyah45828

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Stall speed is based off of torque applied, torque ratio of the converter, and rpm. There is a way to figure it, and I went through a bunch of calculations and stuff at one time to do so, and I think I came up with a little over 2000 rpm for the at545/IDI combo and the stock "diesel" converter. I was looking to upgrade and use either this one at 1200 rpm here or this one at 1000 rpm here. The 1000 rpm one actually has a review from someone using it with a 6bt and at545.

Many moons ago, a sled puller I know used a 6bt/at545 combo in a dodge pickup, got a super tight converter for it, which was custom at the time, and ended up burning the internals through slippage. Granted, sled pulling is tough on equipment, but that experience is what drove me to deciding on the mt643.

I can't feel my trans downshift, until the very last minute of stopping, and it's only a slight bump if that. Big thing I noticed was my trans went from being 3 quick and soft shifts where I'd be in 4th at 20 mph. To what I would think was correct shifting, 3300 rpm or so wide open throttle, with much firmer, well spaced out, and obvious shifts. My cable was way out of adjustment, and it was one of the first quick/easy things to check before digging deeper into the trans looking for mechanical faults.
 

Booyah45828

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Turbo kits....

I thought about using a pickup kit like you have, but had the same reservations about piping and clearances that you did. The big thing with any kit is the piping, and if the piping doesn't work, what's the point of the kit? So IMO none of the used pickup kits are suitable as the piping won't line up with the commercial manifolds and won't clear the flywheel housing/frame/firewall. And I'm not sure justin's (R&D) turbo kit would clear the flywheel housing or frame either. So you're stuck with buying/finding used the hypermax s-series kit, or making your own.

I went with making my own.

Interestingly enough, one of the first turbo kits available for the pickups/engines mounted the turbo off a custom exhaust manifold on the driver's side. They were called rayjay or rotomaster kits, and they're not really all that common anymore. Now, a fun fact is that an IDI exhaust manifold ports are symmetrical, meaning you can mount the exhaust manifold to both the right or left head. So I found and bought a rayjay manifold off of facebook, and intended on mounting it on the passenger side head. The manifold uses a t4 flange, and I'm going to try and use a powerstroke tp38 turbo with it. The tp38 is reverse rotation compared to traditional turbo chargers, and that reverse rotation should position the turbine housing away from the valve cover and over the frame rail, which would work out really well. I'd then use the original driver's exhaust manifold, build a custom cross over pipe, and likely route the turbo outlet through a 90° bend, down and past the frame rail, and out under the passenger's step well, hugging then underneath the frame rail in a similar position that the exhaust currently travels.

That's all in a stand still until I figure out what I'm going to do with the bus. I'd like to keep it for nostalgia's sake, but what's the point if it's not getting used, bus values are at an all time high, and I could put the money elsewhere.
 

Booyah45828

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Intercooler kit was an option/phase 2. I would have used this guy here, mounted in the space between the turbo and stock intake, above the valve cover. I was going to use a stock 6.4 powerstroke air filter setup, as they're cheap, packaged like it would fit between the turbo and air inlet next to the radiator, and they filter/flow reasonably well. The heat exchanger for the intercooler was going to be one of the large atf coolers I've got laying around, mounted in front of the radiator in the little bit of space between it and the grill. I was planning on watching intake air temps, and cooler inlet temps, and if that atf cooler wasn't enough cooling, I was going to look into the thin heat exchanger from frozen boost, or a thin all aluminum radiator out of a compact car.
 

Luke_IDI

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Thanks for taking the time to educate me on this....That setup sounds like it would be amazing. If you were going to do the turbo off to one side, of course the passenger side would make sense, as that's where the room is (no coolant reservoir or air compressor/power steering interference, combined with the reverse turbo and routing the exhaust along the passenger side....just a really cool idea that solves all issues with firewall/flywheel housing clearance.

I find the bus market a little hard to read, especially as regards these older rigs. There was an S1700 listed for $1500 on Marketplace in my area (Gulf Coast) that sat around for months before finally selling. I'm seeing early-mid '90s DT466 buses in good condition for $4-5k around here, maybe a bit more for something a little newer. And there is definitely a demand in this area, as "party buses" are very popular business, especially in the New Orleans area. The IDI/AT545 combo has such a rotten reputation on the Skoolie forum that I wonder if prospective Skoolie buyers would be scared away. And someone who is truly interested in an older bus like ours would have to be interested in something unique. Maybe executing your definitely unique turbo build would pay off in terms of potential sale price! The next few months are going to be financially tight for me, but if you do end up deciding to move on from the project, I might be interested in buying some of your spare parts and continuing on where you left off. Keep me posted if you think of it. It sure would be cool to see the Silver Bullet with that rig on it, though!

Over the weekend I installed the new radiator. Looks like a good quality part. No leaks! Ahhh.... I didn't get the chance to take it for a drive, but it feels good to have the cooling system finally buttoned up and filled with Fleet Charge. The modulator cable appeared to be adjusted correctly per your description. As I recall (It's been a while since I drove the bus), the upshifts happen at normal RPM points. It's just those hard downshifts that seem abnormal. It's definitely a significant jolt. When I first felt it, I thought the rims were slipping on the Dayton hubs! The fluid is somewhat dark, though not burnt-smelling. New fluid is next on the list of things to do. Recommendations for an affordable fluid?

Hopefully the AT545 still has plenty of life left in it (57,000 miles on the bus), but it's good to know what to be looking out for if the right deal comes along, and I have been giving a bit more thought to transmission options. An MT643 would be nice, in keeping with the all-mechanical simplicity approach. Still, with the direct drive ratio, 5.57 rears, and 10r22.5 tires (40.4" tall), you'd still have to scream along at 3000 rpm to hit 65 mph. For kicks, I looked up the gear ratios on the Allison 1000, and the .61 second overdrive of the six-gear version would give 70 mph at 2000 rpm without changing the rear gear. Even the five-gear version's .71 would only require turning 2300 rpm to hit 70 mph. It sounds like the tallest rear gear available for the Spicer F170S / International RA39 axle I have is 4.33, which would require 2500 rpm to hit 70mph. Not bad, but it being able to accomplish the whole thing with just a transmission swap sounds attractive, even if it does mean adding a computer to the mix. I should move these thoughts over to the Skoolie forum I suppose, and anyways, I'm still just dreaming. Got to get some use out of the thing first!
 

Booyah45828

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Bus market is hard to read, especially since covid hit. Covid seemed to have brought out a lot of unknowledgeable buyers. It's why you see em priced so high and goofy right now. Pre-covid, your high sellers went to your exporters, which were the dt466's, 6bt/isb and isc. That left a lot of your buses, those powered by any v8 or your smaller hp I6 and your cat engines pretty cheap. As covid hit, prices rose, buses for sale became scarce, the top of the line buses sold for $10k+, leaving people buying the cheaper units at 2-3x what they were worth. Some flippers also caught wind of the hot market and a few of them dabbled in the business, and got burned in the process.

It will settle out. Covid is almost a thing of the past, and so are quarantines. The whole landry/petito thing gave a lot of people second thoughts about the van/bus life too. Living with someone is hard. Way harder if you're crammed into 40 total square feet 24/7 miles away from home. You better be pretty square with the person you're with.

The idi's in a bus have a bad rap for several reasons. For starters they were the entry model, low power, low optioned bus. Then throw in all the problems with the idi platform, like air intrusion, glow plug systems, etc. along with the at545 issues. Then combine that with how stupid and hands off society has become with vehicle operation and maintenance, and you can see why people are told to avoid them. Most can't figure out if they have dead batteries or a bad starter on a no-start. Throw a bunch of other **** at them and they'll quickly lose interest.

Your trans modulator might have broke and is stuck in full throttle position. It'd give you normal shifts accelerating, and hard shifts decelerating. It's not the end of the world, but it shouldn't downshift hard, at least mine doesn't. Any c4/dex merc fluid will work. You don't need something expensive, and I wouldn't use anything low viscosity like a tes295 fluid either.

Trans swaps, especially upgrading to an electronic one, are thousands. I was eyeing either a pumpkin or axle swap in the 4.5-4.8 range. Or going with a auxiliary trans with and overdrive. With an "underpowered" engine, I felt going with a faster rear would lose a bunch of acceleration, which is why I was looking for auxiliary transmissions or a 2 speed axle. I've got the same f170s/ra39, and your options are pretty limited. Ideal would have been for me to find a cutoff assembly with air ride, 2 speed axle, and 4.56 gearing. Even if it was a 30k lb axle, with the shop I could about make anything work. Probably have to ditch the dayton wheels, but I'm indifferent to that.
 

Luke_IDI

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Interesting thoughts on the skoolie boom cycle....

Your suggestion that the modulator is possibly broken and stuck in full throttle position recalls that it does have a bit of a high-feeling shift point into 4th. I have to rev it up a bit around say 35-40 mph to get it to upshift, just as if it "thinks" it's at full throttle and is waiting to attain the right speed. After it does upshift, I can let the RPMs down to a comfortable level without it downshifting again. Owning this bus has been my first experience driving anything bigger than a pickup, and the transmission feels so different from anything light-duty that it's hard to tell what's normal and what's not. Maybe that odd upshift behavior could be explained by the modulator as well. Next time I look at it I'll crawl under there and see what I can observe while someone pumps the throttle.

Trans swaps.... My impression is the basic parts of the process are: bellhousing/flexplate adaptation, mount fabrication, driveshaft shortening, and wiring/computer interfacing. With most of these electronic transmissions being able to run on just a TPS signal (so I've read--maybe the reality is more complex?), the computer/wiring aspect seems like it should be pretty simple, and I would imagine that similar mechanical/fabrication issues would be presented by installing a new rear axle or an auxiliary trans. Would you think there would be a significant cost savings to going the auxiliary trans/two speed rear route over the electronic transmission route?

I read somewhere that 2-speed rears were usually meant to give a lower range for offroad, and a quick search shows most of them have gears even lower than 5.57. Did you have any axle models in mind that came with taller rear ratios? Air ride in the back would be an excellent upgrade. Also, from a quick search it seems 2-speed rears described by one ratio number. Is there a standard relationship between the two speeds in the rear end?
 

franklin2

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Here is a aftermarket trans controller. https://www.usshift.com/harness.shtml

The old school non-computer type transmissions needed road speed (governor in the trans), engine speed (pressure from the trans pump) and engine demand (vacuum modulator) to determine what gear it should be in. I have never hooked one up, but would think the trans controller would need road speed (speed sensor), engine speed (tach signal) and engine demand (tps sensor) just like the old school transmissions did. I think they also use inputs from the ranger selector switch that comes with the trans to determine which gear is selected by the operator, which was all mechanical in the old school trans.
 

Booyah45828

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Here is IMO the most comprehensive guide to swapping a world allison behind a non-electronic engine.


I believe you'll need a pwm based tps sensor. And then you'll need the tcm with the correct software, harness, and built transmission. If you don't have donor to pull that stuff from, it gets expensive. I just replaced a tcm in a box truck the other day, and it alone was 1400 bucks. With an allison 2000 swap, I'd guess you'll have $5k or so into it at least.

2 speed rears. Yes most 2 speed rear axles in the 20k lb range have ratios that are unusable. It's because they predominantly came behind gas engines, which have higher power bands. You'll occasionally find one that came behind a diesel, but even then the ratio will likely match what you currently have. If you go with a heavier axle(think semi truck), you can find 2 speeds with better ratios. There's a truck parts/scrap auction nearby that I bought stuff from before. I figured I'd wait until I found one there, and the most I'd have in that is a grand or so in it, at the most 2. To get it installed I'd likely have to change one of the yokes so the u-joint will work. Then I'd have misc. hardware for the install. Might have to do some brake work on the axle too. That's all if I do my due diligence and get something that's usable in the first place.
 

Booyah45828

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Oh, and I think the ratio drop is like 33% or some such amount. The ratio is planetary derived, so it wouldn't be too difficult to calculate if one wanted.
 

Booyah45828

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Here is a aftermarket trans controller. https://www.usshift.com/harness.shtml

The old school non-computer type transmissions needed road speed (governor in the trans), engine speed (pressure from the trans pump) and engine demand (vacuum modulator) to determine what gear it should be in. I have never hooked one up, but would think the trans controller would need road speed (speed sensor), engine speed (tach signal) and engine demand (tps sensor) just like the old school transmissions did. I think they also use inputs from the ranger selector switch that comes with the trans to determine which gear is selected by the operator, which was all mechanical in the old school trans.
Those are for ford stuff. We're talking medium duty with an Allison at545. An at545 can use a vacuum modulator, but most diesels use a cable one, unless it's an electronic engine, then it will use an electronic solenoid. The electronic allisons are clutch to clutch which requires real specific and accurate timing, I'm not aware of a functional aftermarket shift controller for an allison. Most custom guys use allison controllers and programming, but modified to suit their needs.
 
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