The factory Tucker hydraulic system is a simple design comprised of off-the-shelf parts. In most cases the system works okay, but being inquisitive knuckleheads, snowcat buddy Scott and I wondered if we could improve on it.
The first time we tested Thundercat we thought the hydraulic steering system was disappointing. At slow engine RPM it required more effort than it should to turn the steering wheel, and therefore by extension, to turn the tracks. I reached out to Tucker to pick their brain a bit. They told me the setup they were currently using on the machine closest to Thundercat’s configuration of long tracks and a factory blade. That meant reconfiguring the pump to greater volumetric output, as well as higher pressure. It also required installing a dual cross-port relief valve between the orbitrol and the steering cylinder. We made the system modifications and the next time out the steering system worked beautifully. Problem solved…or was it? One issue was the hydraulic reservoir tank was hot. Not just warm, but hot, as-in burn your hand hot. That’s not good. Hydraulic fluid shouldn’t be that hot.
But hey, the steering worked great so we thought about ways to cool the fluid. I bought the biggest Derale remote fluid cooler they make. We already use two Derale Hyper-Cool remote coolers for transmission fluid and for engine oil. But the Hyper Cool Extreme is even more capable, and can remove up to 67,000 BTUs of heat per hour. Of course that required Scott and I to re-plumb some of the custom bent steel hydraulic lines we made, and we mounted the new cooler under the bed. We thought this would surely solve the problem….
We're both firm believers in testing our snowcat projects to verify operational performance prior to general usage. Before SV 2022 we had been working on Putri-Zilla, and then Scott said he wanted to take Thundercat to SV 2022. Huh? No way can we get that ready in time! But to reach that goal we worked long hours and seven days a week. There simply was no time to test Thundercat before SV 2022, and we were darn lucky to get it all assembled and loaded on the trailer in time to make the event. Hopefully, everything would work okay….
But the hydraulic fluid temperature problem… had not been licked after all. Hydraulic system heat can come from radiated heat; being close to hot objects, such as an engine or an exhaust system, and we certainly have those issues, but the system itself generates frictional heat with the fluid circulating through the various system components with their inherent restrictions. The greater the volume and/or pressure, the greater the heat produced.
We had accepted Tucker’s recommendations as gospel, but maybe our faith was misplaced? In our various Tucker projects we’ve seen first hand some truly lousy workmanship, so maybe the factory’s recommendations weren’t so optimal? Hmmm….
Scott had long wanted a completely different setup. One pump for the steering and a second pump for the blade system. He also wanted the blade system’s pump to have an electric clutch like on a car’s air conditioning compressor. If you aren’t using the blade, let the pump's pulley spin freely without turning the pump. If you need the blade? Great: flip the switch to activate the clutch and presto: hydraulic volume and pressure. That sounded like a great idea, but it also sounded like re-doing a bunch of stuff, and it sounded expensive. My thought was an ac compressor's shaft would be different than the threaded shaft with a Woodruff key on our hydraulic pump. Another idea was to use a pump powered by a PTO off the transmission. That too, sounded expensive, and it meant a lot of time hand bending new hydraulic lines….
Thundercat’s engine was bought used, and came with all the engine driven accessories, pulley’s, brackets and belts, which included a power steering pump and reservoir. We kept the pump and reservoir, and they're plumbed to the rear hydraulic winch. Scott wanted to use that pump for the steering system. But research showed automotive power steering pumps produce significantly less volume, and less pressure, than the Tucker setup. Aftermarket modified pumps are available with greater volume and pressure, but still fall short.
This dilemma continued to chip away at my pea-sized brain while we worked on other projects. Scott’s brain is considerably larger, but I suspect it bugged him, too. Sometimes after working on another project and just "chewing the fat" (a disgusting phrase), the topic would come up - and we’d toss around ideas, but nothing definitive was decided. In researching the damping/cushioning cylinder for TUG, we calculated the fluid capacity of a cylinder, and that got me wondering… How much volume is in the Tucker’s steering cylinder?
The cylinder is 2 1/2” in diameter and has an 11" stroke. How much fluid does that hold? Doing the math shows a volume of darn close to 54 cubic inches. Isn’t that about the displacement of a Snow Trac engine? (Okay, that was The Infamous WBJ1’s bad influence on me... doing some poking of the Snow Trac mafia.) Back on topic:
So 54 cubic inches means nothing to me in terms of liquid measurement, but there are 231 cubic inches in a gallon. So 54 cubic inches is a bit under a quart. Wait a minute… if the steering cylinder holds just under a quart of fluid, and the hydraulic pump puts out six gallons a minute, that means you could cycle the steering from side to side at least 24 times in a minute. That seems ridiculous. Why would you ever need to do that? In talking with Scott, he pointed out that normally the steering would be straight ahead, so turning the system all the way to one side would use 1/2 the volume. Why do we need six gallons a minute? Tossing around various numbers can be mind numbing after a short time, and they tend to blend together. Some visual representations may be helpful.
This is just over a pint; the amount of fluid required to move the Tucker steering cylinder from center to one side.
And a quart; the amount of fluid required to move the steering from one stop to the other.
Now, six gallons, the amount of hydraulic fluid going to the steering system every minute.
And a comparison of steering system quantities:
What I haven’t mentioned is that Vickers rates their pump output at 1,200 pump RPM. The pumps are a fixed displacement pump. That’s engineer talk. Knucklehead speak says that means for every revolution of the pump, it moves a specific volume of fluid. Double the RPM, and you double the volumetric output. Vickers recommends a maximum of roughly 2,500 RPMs on their pumps (it varies based on the specific GPM of the pump). But 2,500 RPM at a 13 GPM rating means the pump is producing just over 27 gallons a minute. That is a LOT of fluid! And, the pump has a priority valve cover. That means six GPM, and only six gallons per minute, goes to the steering system, the rest goes to the blade, or gets returned to the reservoir. At 1,200 pump RPM the six-way valve for the blade is getting seven gallons a minute. But at 2,500 pump RPM, 21 gallons a minute for the blade system? The term overkill came about during the cold war in relation to nuclear weapons capability, but it seems apropos here, too.
Another pic. This is 27 gallons, the amount of fluid pumped in one minute at 2,500 pump RPM.
And the whole enchilada.
Really? Why are we pumping that much hydraulic fluid?
Being a knucklehead means a lot of things, but have you ever counted how many seconds it takes to pump a gallon of gas or Diesel when filling up at a self-serve pump? At Costco, where I buy too much gasoline, it takes about six seconds to pump a gallon. So, that’s 10 gallons a minute. And at maximum recommended RPM, the Tucker pump configuration is almost three times that output? Whoa there, pardner…. As discussed above, hydraulic volume equals heat. What if we reduced the volume to a more reasonable number? We’d take heat out of the system, and that would be a good thing.
So... one night we’re kicking this back and forth again and Scott says “What about a power steering pump from a semi?” Interesting thought! And that got me Googling. Many different pump configurations of volume and pressure are available, and both volume and pressure are greater than their comparatively wimpy automotive counterparts. However, the pumps are usually driven not by a pulley, but are gear driven by the engine. But... maybe we're on the right track….
Thundercat was bought for access to a remote cabin location in Montana, and a six-way blade was a requirement. But that property has been sold and the must for a blade is now questionable. I don’t want to remove the capability for a blade, but if the blade isn’t going to be needed, why mount it to the snowcat, and if it’s not mounted, why drive the hydraulic pump? Our hydraulic pump setup uses a separate 6-groove serpentine belt with a belt tensioner. Yes, Scott’s electric clutch concept is very cool, but it’s expensive and it means cutting into the wiring harness to add a wire, and a new switch on the already finished instrument panel means yet another new panel. Removing or installing the belt is easy-peazy. Why not drive the steering (and the winch) with a new semi truck-type power steering pump (with a remote reservoir) and take the belt off the Vickers pump? And while were at it, since that Vickers pump will be doing single duty as the source of blade volume and pressure, why not reconfigure the pump with significantly reduced volume and pressure?
At this point more research is required to determine what we think the optimal pump configuration will be for both pumps. It’s virtually guaranteed some components, such as pump pulleys and mounting brackets, will have to be designed and machined or fabricated. We don’t have the capability to do all of the machining, and one of my very best friends helped us with the design of the pulleys for both Thundercat and Putri-Zilla. He has those designs on his computer, so it would be fairly easy to make some dimensional adjustments on his computer for new pulley designs. Scott is pretty crafty at coming up with very robust mounting brackets in terms of both design and fabrication, so all of this is doable.
But, actually doing this stuff takes time and CMM 2023 is a week out. We decided to test our theory by significantly downsizing the existing hydraulic pump’s volumetric output. Going from 13 gallons per minute to eight is almost a 40% reduction, and since we had all the parts on hand to make that modification, we’ve done so. One of our previous hydraulic heat strategies was replacing the mineral oil based hydraulic fluid with Amsoil synthetic fluid. Unfortunately, we needed more and no local Amsoil dealers stock it. I placed an order and it arrived in a few days. The reservoir has been topped off and we plan to take Thundercat out for testing this weekend, and while we’re at it we'd really like to take the 1544 out at the same time for some head-to-head comparison testing in identical conditions.
Another benefit to a smaller hydraulic pump with less volumetric output is that it will take less power to turn it. A knucklehead mantra is “One can ALWAYS use more power…."
The first time we tested Thundercat we thought the hydraulic steering system was disappointing. At slow engine RPM it required more effort than it should to turn the steering wheel, and therefore by extension, to turn the tracks. I reached out to Tucker to pick their brain a bit. They told me the setup they were currently using on the machine closest to Thundercat’s configuration of long tracks and a factory blade. That meant reconfiguring the pump to greater volumetric output, as well as higher pressure. It also required installing a dual cross-port relief valve between the orbitrol and the steering cylinder. We made the system modifications and the next time out the steering system worked beautifully. Problem solved…or was it? One issue was the hydraulic reservoir tank was hot. Not just warm, but hot, as-in burn your hand hot. That’s not good. Hydraulic fluid shouldn’t be that hot.
But hey, the steering worked great so we thought about ways to cool the fluid. I bought the biggest Derale remote fluid cooler they make. We already use two Derale Hyper-Cool remote coolers for transmission fluid and for engine oil. But the Hyper Cool Extreme is even more capable, and can remove up to 67,000 BTUs of heat per hour. Of course that required Scott and I to re-plumb some of the custom bent steel hydraulic lines we made, and we mounted the new cooler under the bed. We thought this would surely solve the problem….
We're both firm believers in testing our snowcat projects to verify operational performance prior to general usage. Before SV 2022 we had been working on Putri-Zilla, and then Scott said he wanted to take Thundercat to SV 2022. Huh? No way can we get that ready in time! But to reach that goal we worked long hours and seven days a week. There simply was no time to test Thundercat before SV 2022, and we were darn lucky to get it all assembled and loaded on the trailer in time to make the event. Hopefully, everything would work okay….
But the hydraulic fluid temperature problem… had not been licked after all. Hydraulic system heat can come from radiated heat; being close to hot objects, such as an engine or an exhaust system, and we certainly have those issues, but the system itself generates frictional heat with the fluid circulating through the various system components with their inherent restrictions. The greater the volume and/or pressure, the greater the heat produced.
We had accepted Tucker’s recommendations as gospel, but maybe our faith was misplaced? In our various Tucker projects we’ve seen first hand some truly lousy workmanship, so maybe the factory’s recommendations weren’t so optimal? Hmmm….
Scott had long wanted a completely different setup. One pump for the steering and a second pump for the blade system. He also wanted the blade system’s pump to have an electric clutch like on a car’s air conditioning compressor. If you aren’t using the blade, let the pump's pulley spin freely without turning the pump. If you need the blade? Great: flip the switch to activate the clutch and presto: hydraulic volume and pressure. That sounded like a great idea, but it also sounded like re-doing a bunch of stuff, and it sounded expensive. My thought was an ac compressor's shaft would be different than the threaded shaft with a Woodruff key on our hydraulic pump. Another idea was to use a pump powered by a PTO off the transmission. That too, sounded expensive, and it meant a lot of time hand bending new hydraulic lines….
Thundercat’s engine was bought used, and came with all the engine driven accessories, pulley’s, brackets and belts, which included a power steering pump and reservoir. We kept the pump and reservoir, and they're plumbed to the rear hydraulic winch. Scott wanted to use that pump for the steering system. But research showed automotive power steering pumps produce significantly less volume, and less pressure, than the Tucker setup. Aftermarket modified pumps are available with greater volume and pressure, but still fall short.
This dilemma continued to chip away at my pea-sized brain while we worked on other projects. Scott’s brain is considerably larger, but I suspect it bugged him, too. Sometimes after working on another project and just "chewing the fat" (a disgusting phrase), the topic would come up - and we’d toss around ideas, but nothing definitive was decided. In researching the damping/cushioning cylinder for TUG, we calculated the fluid capacity of a cylinder, and that got me wondering… How much volume is in the Tucker’s steering cylinder?
The cylinder is 2 1/2” in diameter and has an 11" stroke. How much fluid does that hold? Doing the math shows a volume of darn close to 54 cubic inches. Isn’t that about the displacement of a Snow Trac engine? (Okay, that was The Infamous WBJ1’s bad influence on me... doing some poking of the Snow Trac mafia.) Back on topic:
So 54 cubic inches means nothing to me in terms of liquid measurement, but there are 231 cubic inches in a gallon. So 54 cubic inches is a bit under a quart. Wait a minute… if the steering cylinder holds just under a quart of fluid, and the hydraulic pump puts out six gallons a minute, that means you could cycle the steering from side to side at least 24 times in a minute. That seems ridiculous. Why would you ever need to do that? In talking with Scott, he pointed out that normally the steering would be straight ahead, so turning the system all the way to one side would use 1/2 the volume. Why do we need six gallons a minute? Tossing around various numbers can be mind numbing after a short time, and they tend to blend together. Some visual representations may be helpful.
This is just over a pint; the amount of fluid required to move the Tucker steering cylinder from center to one side.
And a quart; the amount of fluid required to move the steering from one stop to the other.
Now, six gallons, the amount of hydraulic fluid going to the steering system every minute.
And a comparison of steering system quantities:
What I haven’t mentioned is that Vickers rates their pump output at 1,200 pump RPM. The pumps are a fixed displacement pump. That’s engineer talk. Knucklehead speak says that means for every revolution of the pump, it moves a specific volume of fluid. Double the RPM, and you double the volumetric output. Vickers recommends a maximum of roughly 2,500 RPMs on their pumps (it varies based on the specific GPM of the pump). But 2,500 RPM at a 13 GPM rating means the pump is producing just over 27 gallons a minute. That is a LOT of fluid! And, the pump has a priority valve cover. That means six GPM, and only six gallons per minute, goes to the steering system, the rest goes to the blade, or gets returned to the reservoir. At 1,200 pump RPM the six-way valve for the blade is getting seven gallons a minute. But at 2,500 pump RPM, 21 gallons a minute for the blade system? The term overkill came about during the cold war in relation to nuclear weapons capability, but it seems apropos here, too.
Another pic. This is 27 gallons, the amount of fluid pumped in one minute at 2,500 pump RPM.
And the whole enchilada.
Really? Why are we pumping that much hydraulic fluid?
Being a knucklehead means a lot of things, but have you ever counted how many seconds it takes to pump a gallon of gas or Diesel when filling up at a self-serve pump? At Costco, where I buy too much gasoline, it takes about six seconds to pump a gallon. So, that’s 10 gallons a minute. And at maximum recommended RPM, the Tucker pump configuration is almost three times that output? Whoa there, pardner…. As discussed above, hydraulic volume equals heat. What if we reduced the volume to a more reasonable number? We’d take heat out of the system, and that would be a good thing.
So... one night we’re kicking this back and forth again and Scott says “What about a power steering pump from a semi?” Interesting thought! And that got me Googling. Many different pump configurations of volume and pressure are available, and both volume and pressure are greater than their comparatively wimpy automotive counterparts. However, the pumps are usually driven not by a pulley, but are gear driven by the engine. But... maybe we're on the right track….
Thundercat was bought for access to a remote cabin location in Montana, and a six-way blade was a requirement. But that property has been sold and the must for a blade is now questionable. I don’t want to remove the capability for a blade, but if the blade isn’t going to be needed, why mount it to the snowcat, and if it’s not mounted, why drive the hydraulic pump? Our hydraulic pump setup uses a separate 6-groove serpentine belt with a belt tensioner. Yes, Scott’s electric clutch concept is very cool, but it’s expensive and it means cutting into the wiring harness to add a wire, and a new switch on the already finished instrument panel means yet another new panel. Removing or installing the belt is easy-peazy. Why not drive the steering (and the winch) with a new semi truck-type power steering pump (with a remote reservoir) and take the belt off the Vickers pump? And while were at it, since that Vickers pump will be doing single duty as the source of blade volume and pressure, why not reconfigure the pump with significantly reduced volume and pressure?
At this point more research is required to determine what we think the optimal pump configuration will be for both pumps. It’s virtually guaranteed some components, such as pump pulleys and mounting brackets, will have to be designed and machined or fabricated. We don’t have the capability to do all of the machining, and one of my very best friends helped us with the design of the pulleys for both Thundercat and Putri-Zilla. He has those designs on his computer, so it would be fairly easy to make some dimensional adjustments on his computer for new pulley designs. Scott is pretty crafty at coming up with very robust mounting brackets in terms of both design and fabrication, so all of this is doable.
But, actually doing this stuff takes time and CMM 2023 is a week out. We decided to test our theory by significantly downsizing the existing hydraulic pump’s volumetric output. Going from 13 gallons per minute to eight is almost a 40% reduction, and since we had all the parts on hand to make that modification, we’ve done so. One of our previous hydraulic heat strategies was replacing the mineral oil based hydraulic fluid with Amsoil synthetic fluid. Unfortunately, we needed more and no local Amsoil dealers stock it. I placed an order and it arrived in a few days. The reservoir has been topped off and we plan to take Thundercat out for testing this weekend, and while we’re at it we'd really like to take the 1544 out at the same time for some head-to-head comparison testing in identical conditions.
Another benefit to a smaller hydraulic pump with less volumetric output is that it will take less power to turn it. A knucklehead mantra is “One can ALWAYS use more power…."
