The Stovebolt Site Forums The Parking Lot Big Bolts To Brownie or not to Brownie

That is the question...

I'm hoping the smart people here can help shed some light on something I've been thinking about. My project is a 1953 GMC 2-Ton that has a 1350 2-Speed rear axle. The high speed ratio is 5.833, and the low speed is 8.11. This thing is really beefy, and I'm sure it's conservatively rated at a total weight over the rear axle of 13,000 lbs. Plus, the low speed is super handy to get going with a heavy load on a steep slope. I would love to keep the 2-Speed 1350 in this truck.

I also have a need to take this truck on some long trips. 2,500+ miles one-way kind of trips. I've already planned for more modern bigger disc brakes on all four corners, and a Hydro-boost for a comfortable pedal. I will also be running tubeless 9R22.5 balanced radials, and of course, a more powerful engine. I would really like it if I could cruise on the highway at a speed of at least 75 miles per hour.

So I thought to myself, "I'll just use an overdrive Brownie!" That should keep my engine RPM's down low enough to get better gas mileage on the open road. But then I realized something that might be a problem...

With a 5.833 high speed ratio in the 1350, and a 38" diameter tire, the pinion shaft on the 1350 would be spinning 3,866 RPM at 75 MPH! Something tells me this is not safe. At 65 miles per hour, the pinion would be spinning 3,352 RPM. Even this seems high to me for long stretches of driving. At 55 MPH, the pinion would be spinning at 2,837 RPM. This I'm guessing is much safer. I can imagine 55 MPH was probably the original safe top speed for this truck to begin with. Way too slow for our modern interstate highway system for sure.

With a pinion speed of 3,866 RPM, I imagine the gear oil would cavitate at that speed, and that would lead to lack of lubrication.

I understand the overdrive Brownie is used to help lower engine RPM on the highway at higher speeds. But at what cost to a rear axle with a high gear ratio?

I would appreciate any thoughts you guys and gals might have. Maybe my imagination is not correct, and these types of pinion speeds are normal? Maybe I need to be satisfied with a 65 MPH top speed?

Thanks in advance for your time on this.

David

I have a one 62 one ton which at one point had a 5.38 rear end and 30 in.tires . I installed a over drive with a .63 final ratio and traveled many highway miles at the 75 mph range without issue . I'm not a techie but I figure if a crankshaft can turn at 3000 rpm for long periods a pinion shaft should be able to as well.

John

David, nothing on these old girls was designed for todays highway speeds, handling would be my biggest fear. Even with new brakes, tires, engine, aux. trans I don't think you will be happy with the unit for 2500(5000) mile trips. I would look for a modern straight truck the same approximate dimensions and swap the '53 cab/front end over to it. My 57 with 7.2 rear axle tops out at 45 mph against the governor, Chevrolet says 4000 RPM was the intended speed.

You have neglected to give us one important detail- - - - -What engine are you running?????????? Stacking up tall tires on top of an OD gear of any kind is going to create a lugging situation on any gasoline engine. Also, overdrive, whether in a Brownie or integrated into the main transmission, is a power and torque hog. A F-350 wrecker owned by the towing company I used to manage had a 5 speed OD transmission and a 460 V8 engine. Running in OD with a vehicle on the hook almost doubled the fuel consumption over using 4th. gear (direct drive) for the same trip. If you're willing to install some sort of Diesel engine that grunts along at sub-2K RPM ranges, your idea might work, but trying to make even a GMC 302 pull that load at those speeds is a pipe dream. Just because it works on paper doesn't mean things are that simple out in the real world where the too-tall rubber meets the road. Once you get below the effective torque range of the engine you'll be rowing it with that Brownie lever, dropping out of overdrive to direct or underdrive every time somebody even whispers "hill".
Jerry

Thanks for the replies!

You know what I love the most about this community? It's the fact that you people care about each other and their safety. I completely agree these trucks were never made for the normal speeds on the highway we see today. But you need to know, I'm taking expensive and very time consuming steps to make this thing safer. And in the end, I may need to be happy with a slower top speed.

Someday I will create a build thread on this project and you will see what I'm trying to do. Though I admit to being a little reluctant. I don’t want to offend the purists. My plan is to have the outside of the truck, and inside of the cab look stock. Underneath and under the hood, it will not be even close to stock.

Luckily, I don't need to take many long trips. This truck will mostly be used for when I move my wife and I to our retirement forever home (which I will probably build myself). I also have a need for a long trip when I finally pick up the crankshaft grinder I'm after.

My modest, but very capable machine shop, welding and fab tools, forklift, cabinet shop, and electronics lab... you get the idea, will take quite a few trips to move. I ONLY want to be as safe as possible when I'm 26,000 lbs with truck and flatbed trailer rolling down the road.

OK, at the risk of getting off topic from my original question, I'll try and respond:

panel fan:

Thank you. It’s helpful what you say. At 65 MPH, the pinion in my truck would be spinning at 3,352 RPM. Maybe that's a safe pinion speed for the 1350 rear differential?

78buckshot:

I can't agree with you more. Safety is my main concern. Some of the things I'm pursuing suspension wise for my build is bigger brakes (like I mention before), but not the P30 conversion. I have no disrespect for those who pursue this path on their 1-1/2 Ton and 2 Ton trucks. I'm just not comfortable with de-rating my truck. So I'm pulling the entire braking system over from a 2000 C6500 Kodiak. And everyone please know, there is nothing remotely to being a "bolt on" experience for this brake conversion. Sad, I know. I will be adapting this system myself. I'm building front and rear sway bars. I'll also bring over the heavy duty shocks from the C6500 Kodiak.

I'm researching using longer leaf spring packs for both the front and rear axles. I'm shooting for at least a foot longer if possible on each corner. The Ford F550 leaf springs (I know, I just used the "F" word here) are something I have my eye on.

It's interesting you say the original in-line 6 can be run at 4,000 RPM. I know the engine I'm using would never be happy at those speeds for long stretches. Not for any real expected engine life anyway. I could see 3400 RPM working, but at a huge cost of fuel.

HotRod Lincoln:

Jerry, I always appreciate your responses on this forum. And don't worry, you can never offend me. I'm not a particularly formidable person, but my skin is thick. I also greatly respect those who have walked their talk.

The engine for my project is purpose built. It's a Gen IV big block Chevy that will be getting a 4.25” stroke forged steel crankshaft with longer forged steel rods. The pistons are forged aluminum with a bore of 0.030" over. The final displacement is 489 cubic inches. The heads, cam, exhaust, and EFI induction is all designed for the purpose of being a towing vehicle. The recipe I'm following for this engine is from people who are a LOT smarter than I am.

I would be open to the idea of using a diesel, but around these parts of the country, diesel engines are made from 24 carat solid gold. So I'm building a kind of "poor mans" diesel.

Well, I hope I covered everyones concerns. This place is a grate community to be a part of.

Thanks again.

David

David, just to clear up one point, my '57 has a 283 V8, that is the example I was using with the 4000 RPM governed speed. It sounds like you are doing lots of homework for your project, I like the idea of the Kodiak brake system, how about using the complete running gear and having an axle ratio closer to what you want.

78buckshot,

I would LOVE to place my cab on something like a 6500 Kodiak chassis. The problem is the track width of the front tires is a lot wider on the C6500. The tires would never fit inside the front fenders of my 53 GMC. Here is something I just found: the distance between the center of the two front tires on my 1953 GMC 2-Ton truck is only 58 7/8" wide (as per GM Heritage Documentation). The distance between the center of the two front tires on the C6500 is 86.5" (as per GM Upfitter Website for the 2008 model). The outside width of my fenders is 74 7/8". The outside width of the C6500 fenders is 96"... It would be impossible to fit my cab on a newer truck like that.

You just got me thinking about something... maybe that's why our older and narrower 2-Ton trucks are not as safe at higher speeds? Narrower footprint?

And for those who are already wondering about this, the rotors I'm using for my braking system I've chosen is commonly found on Chevy and GMC trucks that range from years 1980 to 2002. The sizes of trucks are from the C50, C60, C70, and C5500, C6500, C7500 Kodiak Chevys. Why the same part numbers for the rotors show up for that broad range of capacity, I have no idea.

Hope this helps!

David

David, I used longer, 2.5" wide, two leaf total front springs on my '37 GMC from a 'F' vehicle, moved the shackle to the rear for a smoother ride, has worked well, I believe I mentioned when you were here.

Ed

OK- - - -it looks like you've got the torque problem addressed, if not completely solved. Do you plan to do any dyno work before you assemble things? I'd be looking for a very flat torque curve, one that will avoid having to downshift frequently. With a Brownie and a 2-speed axle, you'll have a good variety of ratios to choose from, and probably even a few selections that won't be needed if you make good choices of camshaft and ignition timing.

Do you have a crankshaft grinder yet? I might be able to help out on that subject, but that conversation would be better by PM.
Jerry

Ed, you did mention that. That 37 GMC project is progressing beautifully. Your fab skills are amazing. Thanks so much again for allowing me to visit. I learned a LOT more about these old trucks.

David

This sounds like a really interesting project. I'd like to travel faster too in my 3800 with camper but I'm unwilling to pay the fuel bill. I run right around 60MPH at engine 2850RPM. The brownie has a 17% overdrive and 24% underdrive plus direct. Gas mileage before 10% alcohol was added was ~11.5 MPG. Now it's barely 10. As I travel east from Washington State gasoline prices go down and speed limits go up. When I hit Idaho it's 75. When I hit Utah for a while the sign said 85 but now it's 80. Montana now has a speed limit on interstates, 80MPH, at least on I15 north of Idaho. Last month when I drove to Salt Lake City air temperature was around 100. I was concerned about tire temperature and held speed below 60. I'm right at the limit of tire capacity at max inflation pressure. On interstate 84 there were many alligators (chunks of truck tire) to dodge in the slow lane particularly at the bottom of hills. Guys blow by me in the hammer lane like I'm standing still; then an hour later I pass them sitting by the side of the road with the triangles set up. It's a long way from Sublett, Idaho to the nearest tire repair shop. Super singles are not your friend out here.

So aside from oil starvation in the rear axle, there are other considerations to traveling at modern interstate speeds. I added oil temperature gauges to the engine, brownie and soon the rear axle. Big trucks (class 8) have such gauges and they are not to be ignored. Climbing mountain passes temperatures go up by 100 degrees or so over the flats, much more than that and you've got bearing beginning to fail. Mind you these are manual gearboxes. Automatics are a different story.

Jerry,

The only dyno I have close to me is a chassis dyno (It's actually just across the street from me). I would prefer an engine dyno, but anything would be helpful to know what's up. I'm told the engine will make more torque than horsepower. The cam choice will cause the engine to start to fall off at around 5,200 RPM, and the sweet spot for towing up a steep grade under heavy load to be somewhere around 3,600 to 3,800 RPM. Conservative estimates are 500 max HP at 5,100 ish RPM, and 550 foot pounds of torque at 3,800 ish RPM. I'm also told to expect at least 450 foot pounds of torque at about 2,000 RPM. We will see. The EFI will help me extract more power from this engine more safely. Being able to electronically detect detonation and control spark advance prevents damage under less than ideal conditions.

I will read your PM.

Thanks,

David

A trick we used on the dirt track cars was to use a small cooler for the rear axle lube- - - -made from the condenser coil for a mini refrigerator. The flare fitting for the flex tubing from the rear end to the cooler was drilled and tapped into the rear end housing where the spray from the ring gear gave enough pumping action to move the fluid, and the return line was plumbed into one of the axle tubes near the center section. It made a LOT of difference in the rear end temperature.

Too bad you're not closer to Tennessee- - - -I've got a water brake bellhousing dyno that has handled up to 700+ HP so far.
Jerry

1Ton_Tommy and Hotrod Lincoln,

Great ideas on managing rear axle gear oil temps. EdPrus also suggested running a synthetic gear oil. If a person where to run synthetic gear oil, monitor temps and actively cool the oil, it all sounds like a great way to make the rear diff last a lot longer to me!

So now I've got good news, and bad news...

Good News first!

I think my worry about the pinion speed being to high is not as bad as I thought. This is what I've learned:

I decided to compare the Eaton 1350 2-Speed in my 53 GMC to a more modern comparable rear axle (in ring and pinion size that is). The Dana S110 and S135 commonly found in the Chevy/GMC 4500, and 5500 trucks, and the Ford F450 and F550 trucks (both respectively class 4 and 5 vehicles) have a ring gear of 12.5" in diameter. My 1350 has a ring gear of approximately 12.25" in diameter (I know, the 1350 is ancient, so maybe a poor comparison).

So how fast does the S110/135 pinion spin at 75 miles per hour? For my example, I chose a 2002 F550 with the V10 gasoline engine. The factory rear gear ratio is 4.88 to 1, and the stock tire size is a 225/70R-19.5. This tire is 31.9 inches in diameter. The truck is built to cruise at 75 miles per hour all day long. With a 4.88 ratio S135 and a 31.9" diameter tire, traveling at 75 miles per hour, the pinion is spinning at 3,855 RPM. My Eaton 1350 with a 5.83 ratio and a 38" diameter tire, traveling at 75 MPH, spins the pinion at 3,866 RPM. Only 11 RPM difference. I consider that good news for sure.

And now the bad news!

I drained the gear oil out of my 1350 this afternoon and immediately suspected I had a problem. The first half gallon of liquid that came out was water! I then pulled the rear diff cover off, and after careful inspection, the ring gear is in really bad shape. Because the main ring gear in my truck is heavily worn, I predict the pinion will be in much worse condition. The pinion gets an additional amount of wear, multiplied by the ratio of the two gears. So in my case, my pinion will be 5.83 times more worn out then the ring gear!

Aren't these old trucks so much fun!!! And we roll with the punches... LOL!!!

But seriously, there are very few things in life more satisfying then solving problems.

Take care everyone!

David

David, the ring gear extends to the bottom of the case, however, the pinion only extends part way down, so, perhaps the pinion didn't get wet with water, however the bearings are a different situation.

Ed

I don’t know how your doing your calculations but I’ve found this site to be a great way to calculate rpm vs speed at various gear ratios:

www.4lo.com

I use the Wallace Racing Automotive Calculators site.

The cheapest and quickest thing to do is scout your favorite truck wrecking yard for a suitably heavy axle assembly. If you're lucky it'll have the same U-joint flange. Also it would be nice to not have to move the spring saddles. You may even have some choice of Gear ratios. Forty years ago I got one out of a GMC450 and put it in a 57 350 but I had to buy a 12V shift motor. The 450's was 6 volt and spun way too fast. Once the dust settled it ran until the owner died about 10 years ago. He called once to see what oil he should put in when he changed it. He hauled lumber for his construction business. He worked it all that time.

1Ton_tommy,

I love stories like that. EdPruss has turned me on to several yards near me that I'm planning to check out. It's funny, I've lived here in Fort Collins for 30 years, and until now, I've never had a need for a wrecking yard. I'm sure something will turn up.

This is awesome, I had the same idea with my '56, I had a spare 454 lying around so we built it to run like a diesel. Conservative compression, but a nice cam profile that dynos at 408hp but makes 525ft-lbs of torque at 2,700rpm. Great vacuum, nice idle, and pulls from 600RPM to 6,000RPM with a super flat torque curve.

I'm running 22.5 tires also, I really like them. Handles great on the highway.

PS be careful about building the 454 with high HP, I talked with some drag racers ( and my machinist that builds a lot of race engines) about my build and they talked me out of going much higher than 400hp in an application like ours. Reason being is those HP numbers usually require higher compression and a bigger cam, which takes away from its nice off-idle manners. i.e. it'll surge under load off idle, and it's harder to make good torque down low in the RPM range. So I went with their recommendations, kept mine at 8.5 to 1 compression and the cam they recommended, and they seem to be correct. This engine makes great vacuum, and is very strong off idle under heavy loads with no surging. It performs like a diesel, almost ~30% more torque than HP. I can get specs if you're interested.

I like your engine builder! Building for torque instead of HP has another advantage- - - - -you can burn regular-grade gas instead of midgrade or premium. With the amount of gas that rig is going to burn, a few dimes a gallon will add up in a hurry. With a smooth combustion chamber that's had all the rough spots polished away, compression ratios up to 9.5:1 are possible on regular gas. Longer connecting rods help, also. The closer you can get to rods twice as long as the stroke, the better- - - -that keeps the piston up near the top of the cylinder where the best power and torque is developed for a longer time as the crankshaft is rocking over center and starting down the power stroke. The only reason for having high compression is to bring the cylinder pressure with a radical cam back to where it used to be before nearly half the compression stroke is taken up before the intake valve closes and pressure begins to build in the combustion chamber.
Jerry

Gentlemen! I appreciate the replies on the engine ideas.

As much as I would love to talk engines here, it's making the original reason for this thread too far off topic. I take blame for being a part of it.

My original question of using a Brownie and the resulting high pinion rpm speeds has pretty much been answered from others sharing their experiences and more research I've done myself.

Lets move the engine stuff over to the "Engine Shop" or the "HiPo Shop" section of the forum (I'm still too new here to know for sure which sub-forum location would be best). I know such a thread would be super helpful to me, and I'm guessing it would be helpful to others as well. A thread like "A Poor Mans Diesel" for gasoline engines with a focus on low RPM and high torque building recipes. It doesn't mater if it's a inline 6 or V8. They all apply! I'm sure there are many here who already have something to contribute from earlier builds. As my project progresses, I'm happy to reveal the steps and parts I use in complete detail.

If a moderator could share which sub-forum would be best, I would be happy to start it!

I mean no disrespect, and I hope I haven't offended anyone with this post.

David

The simplest way to do that would be to start a thread in the engine forum and let this one die a natural death from neglect. You'll get all sorts of off the wall commentary from a few guys who think the only way to develop power is with multiple carburetors and astronomical RPM, but a few of us old geezers know better. Most of those guys have built a drag race engine or three over the past 30 years, and they think they're the Lord's gift to hotrodders! Have fun!
Jerry

Hello guys. Interesting listening to all the ideas. I will jump in with my project as I am doing a few things that may be of interest. I am starting with a 160 inch wheelbase 2 ton frame, 302 GMC, 205v Clark 5 spd main, 5831B spicer auxiliary, Dana 80 from a 98 GMC 3500 HD with 10 bolt wheels and rear suspension from a 2002 Ford with a GVW of 15000 Lbs. The rear suspension is rated at 11000 lbs. I picked this rear suspension because it fits so perfectly on the frame and Dana 80. My frame width is 36 inches and when all together the spring ubolts sit about 1/2 inch inside the rear calipers. My biggest concern is that of driveshaft RPM/ujoint angle. I will be ending up with about 11 degrees of ujoint angle between the A box and rear diff which is getting a bit excessive depending on the RPM that shaft will be turning. I hope to regear the rear diff to get the driveshaft RPM as low as possible and yet not put that 302 into a lugging situation. I will be running the 8R 19.5 rubber and am considering either 3.73 or 4.10 rear diff ratio. If someone has advice on optimum RPM to run a 302, I would like to hear what you have to say.
Front suspension is a 1990 Grumann straight axle with the 19.5 wheels/tires. I went with the grumman front springs so had to fabricate new spring hangers, placing the shackle at the rear. From how the suspension feels from bouncing it, it should have a much smoother ride than the original. Springs are about 16 inches longer than the originals. It has all gone together well so far but waiting to get the engine together before body goes on.
GasHog

GasHog, sorry for the delay. I sent you a PM.