1989 Tucker 1644c

Blackfoot Tucker

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Perhaps anyone here knows more than I'm finding out.

When running the engine on the dyno Frank mentions that a 2800 rpm stall speed torque converter is recommended for the cam that is in this engine, and almost certainly the factory standard would have been 1800 rpm. Of course I'm not building a drag car, so I go to checking. Tucker was unsure of stall speed, but their new Allisons do come with the torque converter, not sure about back in 1989. Weller, the Allison dealer, said the at545 would have come with a torque converter, and Allison doesn't designate by stall speed but rather by percentage of slip. There is/was no lock up torque converter for the at545. They said there are only two torque converters available at this point in time, one for a gas engine, the 275 with 1.96 percent slip ratio, and the 290 with 1.72 ratio for diesels. There have been a couple others over time, pre 1992 the 275 was the 270 as mine is, and a 230 for diesels that was a 2.90 ratio. Higher percentage slip of course would equate to higher stall speed (smoother shifts?). Also seems the the at545 doesn't build up the pressure needed to lock up the internal clutches below about 2200 rpm iirc, which can cause damage.

It seems there is only one choice for the gas engine and that's what I have. It's recommended to replace or rebuild the torque converter when replacing or rebuilding the transmission due to build up or damage caused by shavings ect in the torque converter. My trans pan was very clean and magnetic plug were very clean so we just serviced the trans and putting it back in. I'm thinking the same with the torque converter.

The whole concern with the cam and stall speed of course, is not wanting the engine to die when put into gear at idle rpm because of the overlap of the cam. Even though we didn't try to idle below 850 rpm on the dyno because we couldn't unload the engine while hooked to the dyno, it idled very smoothly at 850 rpm. Guessing because of the stroker build and the efi.

Thoughts, knowledge, anyone? My gut feeling is I'm ok reusing what came out, but I just don't want to have to take it apart twice.

1BG,

I know Tucker has worked with their local Allison dealer over the years to refine the transmission to Sno-Cat relationship. In a conversation with the Tucker factory, they suggested I call that dealer, Pacific Power Products, and more specifically speak to a fellow named John Edwards. I did call and found him to very knowledgeable, friendly and helpful.

When it comes to Tuckers and Allison transmissions, I think he's probably THE guy to speak with...
 

1boringguy

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Thanks BFT,

I did in the past at your suggestion and did again the other day, try to find John Edward's at Pacific Power Products. They have several divisions/locations but the gal in the main office has told me twice now that they have no John Edward's registered as a company employee. I did get to Brad Robertson, field rep, who was helpful. He looked up my trans by assembly number, and also did some hunting about Allison torque converters.

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Brad said my assembly number showed this trans left the factory with a 275 TC (would have been for a diesel). I thought maybe the trans was a rebuilt given how clean it was inside, which could account for a different serial number, but no, numbers match the Tucker door build sticker info. So have to guess Tucker changed the TC to match a gas engine at the original build time. I asked Brad what the actual differences were between the 270 and the 275, thinking the 275 was some sort of upgrade for the gas engine since these two are both 1.96 slip ratio. But again, no. He sent me this;

"Jack,

I had to go all the way back to 1985 to find a document that listed out the differences between the 270 & 275 torque converter.

  • The 270 torque converter was originally built for both gasoline & diesel applications but in March 1985 the 270TC was transitioned to gasoline applications only.
  • November 1984 the 275TC was introduced to replace the 270TC in all diesel applications.
  • The 275TC utilizes brazed pump blades, thicker turbine blades and improved thrust washer material.
  • An increased capacity thrust bearing assembly is utilized in both the 270TC & 275TC.


Other than the changes listed above the 270TC & 275TC are identical."

So, what I think I know here.

Allison rates the AT 545 at, max input 4400 rpm, min idle under load 500 rpm, max weight of vehicle 30,000 lbs, max hp 235, and max torque 445 ft/lbs.

I have the 270 TC which is the 1.96 slip ratio. The 275 was a 1.96 slip ratio but was made for a diesel. All other Allison ratio TC were made for diesels. The 275 might be built to better handle additional torque of a diesel, but perhaps not higher rpms, idk. The 1.96 ratio is my best option ratio wise. Weller truck shows availability of only the 290 (1.72 ratio) and the 270. And the 270 only as a rebuilt.

In checking with about half a dozen after market TC suppliers I haven't found any options offered by them, other than rebuilding the one I have.

My thoughts, again.

Weller, who serviced my trans, thinks I have little or nothing to be gained by using a rebuilt TC at this point. Ok. Brad pointed out that my hp is well over what the trans is rated at, and the torque is right at the top end. I'm going with it anyway for a couple reasons other than all the work it would take to accommodate a bigger trans. First, assuming a normal operating range of 2500 to 3500 rpm, the torque stays under the max and hp only slightly over at the upper side of those rpms. Secondly, under my snowcat operating conditions ranging from ice to powder, only a limited amount of torque can be created in the system before ground slippage occurs. Thirdly, I don't generally drive like I'm on a mission from God.

So after delaying putting the engine back in pending this education exercise, I think it's going back together with the 270TC that came out of it.
 

Blackfoot Tucker

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1BG,

I wonder what happened to Mr. Edwards?

Sometimes in my phone conversations I'll keep notes, and I have "Pacific Power Products (800) 882-3860 John Edwards - Medford". My recollection of the phone call with Tucker (and that likely was with Jeff Godard) was that they worked with Pacific Power Products (and specifically John Edwards) in refining the Allison transmission setup in Tuckers. I recall talking with Mr. Edwards and I sought his advice on what he suggested to use as a transmission modulator. I found him knowledgeable and helpful...why I suggested him as a resource.

Out of curiosity I Googled "John Edwards Medford, OR" and got a few hits. If it's the same man, he is now the Regional Operations Director at Freightliner Northwest. But I think it's a fairly common name, so...

We're using the AT545 in both Thundercat and Snowzilla. Thundercat has an 8.1 Vortec engine and Snowzilla has a GM L94 6.2L engine. I purchased the 8.1 via eBay and I recall it came from a Chevrolet pickup truck. I purchased the AT545 from a truck salvage company in Colorado and it was originally installed in a Schwann's Food Company truck...behind an 8.1 Vortec engine.

GM offered that combination from the factory, and the 8.1 exceeds both the rated horsepower and torque numbers from Allison. I find it reassuring that GM thought is was a sound power train combination, despite Allison's limitations. The L94 makes a bit less torque, but more horsepower. Unfortunately it is more of a higher RPM engine and it makes its peak torque and horsepower at somewhat higher RPM.

I also subscribe to the theory that just about anything is okay...in moderation. As long as we don't thrash the heck out of them, I think we'll be okay. And it's not like these machines get a whole lot of use, anyway....
 

1boringguy

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BFT,

Thanks for the input too. I didn't realize they had paired the AT 545 with the 8.1, that is interesting. Definitely a vote of confidence by GM I would think, since they were standing behind some kind of warranty there. Anyway I'm pretty sure my snowcat is going to have an easier life than a school bus, so I'm not worrying to much about using the 545 either.
 

Blackfoot Tucker

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BFT,

Thanks for the input too. I didn't realize they had paired the AT 545 with the 8.1, that is interesting. Definitely a vote of confidence by GM I would think, since they were standing behind some kind of warranty there. Anyway I'm pretty sure my snowcat is going to have an easier life than a school bus, so I'm not worrying to much about using the 545 either.
1BG,

To expound a little bit on transmissions, some people think about the engines that the manufacturer has paired them with. For example Chevrolet put the Turbo 400 behind big-block engines for decades, or Chrysler put the 727 behind Hemis... so either should be more than sufficient in a snowcat....

But the typical automotive duty cycle is completely different than that of a snowcat. In an automotive application, the transmission is used to multiply the engines torques as it accelerates and shifts through the gears. Once up to speed, it really isn't subjected to all that much torque unless one climbs a long hill, and does so with a heavy load. Even in the Hemi example, in a drag race the transmission will shift from first to second and second to third...and that's it. Sure, it will be subjected to some serious shock loads and a lot of torque... for about 13 seconds at a time. But how much heat will the transmission build in 13 seconds? Now think about a school bus or a garbage truck. It weighs almost ten times that Barracuda or Charger/Challenger, and it is making frequent stops with accelerations between each; day after day after day. Almost always working...it's the difference between a thoroughbred and a pack mule.

In a rubber belted Tucker, the engine and transmission work hard almost continuously. For me, I think a transmission designed for medium duty trucks is more closely aligned with our needs than one designed for a station wagon or a muscle car. Back in the 1980s when Diesel engines were first introduced in pickup trucks, auto manufacturers paired those engines with one of their currently produced transmissions. And the result was a bunch of transmission warranty claims. Over the ensuing years, the Diesels have gained more power and the transmissions have gone through several evolutionary cycles of upgrades so they will hold up the rigors they're subjected to.

A turbo 400 transmission weighs about 135 pounds and a Chrysler 727 weighs about 160. Put them together and your right at what an AT545 weighs; about 289 pounds. I'm sure the difference in weight is not just the case, but rather beefier internal parts and clutches, etc.

But all that said, I'm not an automotive engineer. The above are the ramblings of a snowcat enthusiast, and Grade A knucklehead...
 

1boringguy

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Lol, kind of reminds me of welders.

One can get an gas engine driven 250 amp welder for about $2500-3000 (old prices), that is light weight easy to throw in and out of a pick up and is great for little projects. It has about 20% duty cycle and needs replaced after about 2500 hours.

Or one can get a diesel engine driven welder with twice the weight and size, that has 80% duty cycle, electronically controlled weld characteristics, and lasts 10,000+ hours, for $10,000 (again very old price). A gotta have, for pipes that can take 6+ hours to make a weld.

As with anything, it's good to understand what the differences are and use case. And that there is rarely any free lunch.
 

Mill666er

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My 1981 542A HD with the 4-53T was originally equipped with the AT540 which I read wasn’t a very robust design. The transmission was rebuilt/swapped by Stewart & Stevenson to the AT545. The 4-53T is 175HP @2500 and 440 lb ft at 1800 which takes the AT545 to its limit. It seems to run best or most bearable around 1900rpm and don’t think I have really taken it over 2300. I don’t have any info on the torque converter and didn’t pull it off when I had it out. It is a very hard shifting and knocks you back in the seat if that is possible below 12mph.
 

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1boringguy

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Mill666er,

Would be interesting to know if it has a number on it, or if it's something other than from Allison. Surely made for the lower rpm diesel applications though.
 

olympicorange

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all very good info & history ,... and yes these 545's will snap your head when put in a snocat,... most likely due to the weight difference from a school bus , medium duty truck, etc. and not letting up with the right foot,... but who else makes a tranny that you can mate up to just about anything, and is nearly indestructible. the down side is reverse is slow . i was sold on these 30 years ago when i had a customer with one in a timberjack skidder. we repaired just about everything on it , except the 545 ,.... there's tons of them around & they're cheap to buy,.... my 4 BT's can't kill them. the most important factor is a proper cooling system for the trans. keeping the heat down is the key to longevity . ..........
 

Mill666er

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Not sure when it was remanufactured, it was sold to Aspen Ski In 1981 but then was bought by Snoqualmie Ski area before I got it.
 

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