The Stovebolt Site Forums The Parking Lot Big Bolts 51 Chevrolet 6500 questions.

Hi guys,

I posted some questions about this truck a while back and got some great responses and great information. So now that I think this project is going to happen I have more questions for you.

The truck I have is a 51 Chevrolet 6500 , as the title says, and the original engine and transmission are long gone but on the plus side it has a three speed brownie box and a single speed rear. The plan I have is to repower it with a Cummins 12 valve motor and five speed out of a dodge truck which should be more then enough for the type of driving and hauling that I plan to do with the truck. I have done many engine swaps and I am a fabricator by trade so this part of the project is no sweat.

The couple of questions I have. I have been asked by my pops to find out about power steering for it but I have also read on here that a well rebuilt front end steers just fine, what people's thoughts here? If I do want power steering is there something that can be adapted either a later steering box or a power assist ram like I have seen on some other (slightly later) medium duty trucks? The Cummins is heaver then the stock motor so power steering might just be welcomed.

Can someone tell me the easiest way to determine the gearing of the rear end (maybe a stamped number on the pumpkin)? I could just jack up a wheel and count the number of turns of the drive shaft but I'm lazy and would also like something slightly more accurate. This truck had (from the factory) a two speed rear (I think) but somewhere along the line a single speed pumpkin replaced it and I would imagine that the brownie box was added around the same time. All this is for is to determine if it is geared suitably for the diesel.

And on to brakes. I will rebuild or replace wheel cylinders, brake shoes and lines as needed but the master cylinder... I could rebuild the hydrovac and replace the pedal actuated master but I think that I would really rather just do away with all that and go to a more modern dual master and either vacuum booster or hydro-booster under the floor. What size bore will be needed with a modern master cylinder? As I understand it the original is 1 1/4" but is that the M/C at the pedal or the M/C that is run by the hydrovac unit? And with a dual M/C system would I need to go bigger/smaller bore or stay the same?

The link to pictures up top goes to my Flickr album for this truck and has pictures of it in it's original resting place and slightly newer pictures of it since I pulled it out and pressure washed it. Heres a link to another stovebolt I put back on the road too, 37 Chevy 1/2 ton Pickup

Thanx for any input that you can give me and I am sure I will have more questions in the future.

Thanx
Jaysin

Hy JaysinSpaceman, lots of questions, as to the rear axle ratio, there my be some numbers stamped into the front of the pinion, just wire brush the heck out of it when you get the driveshaft off, there will be a part number for the pinion and hopefully some other numbers which represent the ratio, something like 6 - 42. As to the power steering there may be something in Tech Tips, or go over to the Old GMC trucks site Grigg is doing a Detroit Diesel swap with power steering, that is also where you will find ideas for Hydro-boosted brakes, hope that helps.

I drove my old beast on paved & unpaved roads with the box loded up with 10K of dirt all day and the steering really didn't bother me at all. The ratio makes for a lot of turns lock to lock, but short of needing to be tightened up it was easy to drive. I haven't found that I need P/S unless dealing with really bad roads, and even then a simple bolt on dampner could fix that. Personal preference I suppose.

Even the single M/C with the hydrovac has worked fine for me, I replaced everything I could, rebuilt the rest, and installed all new lines. With the HydroVac pushing 7/8" slaves up front and dual 2" in back, even at max weight it stops quickly. Also between the HydroVac bypass and my rebuilt shaft brake, even if I lose vac pressure I can stop easily enough. A properly rebuilt and well maintained system works great, but the added safety of a dual circut system would be nice if you deal with a lot of hills (or idiot drivers with cranial-rectumitis).

Thanx for the Idea of where to find the rearend ratio, I'll try to get a few minutes to check it out today. I'll do some looking on the Old GMC website and see what I can find on the power steering but it isn't high on the list right now, brakes and figuring out if the gearing will work with the diesel is top of the list. Freq2002, I have read elsewhere that these old trucks steer pretty well without power steering, but I live in the California gold country and the ratio might be a bit slow for all the windy roads up here. It would probably be a great upper body work out, spinning that wheel back and forth. I've done several brake systems on cars that I have built and the ones with dual reservoir masters just inspire a bit more confidence in your safety. And with a diesel I will either need to run a vacuum pump for a vacuum booster or the PS pump for the hydroboost and if I do end up with power steering the hydroboost makes a bit more sense. I just need to get the bore ratios sorted out.

I'm sure I'll have more questions and I'll post my answers as I find them.

Thanx
Jaysin

OK, so I was looking around here the other night and I followed someone's link in their signature to this picture. Ram assist steering. Sorry, I can't remember who? This is the type of thing that I am thinking about. Where the stock steering box would remain, maybe, and the ram would be added with the extra linkage. Does anyone know if this was a factory item or something aftermarket? Any help or info would be appreciated here.

I haven't gotten around to checking the rear end ratio yet, but I am hoping to get a few minutes to do so today.

Thanx
Jaysin

The manual steering box is still used on that system, with a push-pull pilot valve incorporated into the boost cylinder to direct fluid to opposite ends of the cylinder ram as the Pitman arm moves. It was a stock setup on some trucks, but the parts are scarce and pricey now. The weak link is the hoses- - - -they flex constantly and spring leaks pretty often. If you can find a salvage yard truck with the P/S system intact, grab it all, and adapt it to your truck. Challenging, but doable for someone with fabrication skills. Just be sure and build the frame brackets twice as strong as you think they need to be. Heavy loads and pothles in the road combine to put some nasty stresses on steering linkage.
Jerry

I took a look at the end of the pinion shaft yesterday evening and the best I can tell it looked like it was stamped with a 6 in a little square and a 31 in a little square which would make it a 5.17:1 gear. Does that sound right? If it could be, then I would be happy as that is in the range of OK for the diesel conversion I would like to do.

And while the driveshaft was removed I checked the Brownie box that I have and it is indeed a three speed. It is also an under/1:1/overdrive. I still don't know what the ratios are but it's a start.

Jaysin

Even with an OD and 40" tires 5.17 sounds way to slow for a diesel conversion.

For example I've got a 0.80 OD, 38" tires, and 3.54 gears (may later want 3.73), for sure not 5.17.

But it all depends on the engine you choose and how fast you want to go (or can go) with how much of a load.
Try a gear calculator like this to plan what ratios and combinations may work well.
http://www.onlineconversion.com/bigger_tires.htm

Have any more details on what conversion you have planned?

Grigg

5.43 and 6.17 were the factory options I'd expect to find under that truck. 5.17 is much closer to what was put under 1-ton trucks, though that number was 5.14.

What are you planning to run for tires? Tire height can make a big difference. And as Grigg points out, Diesel motors don't turn real fast so deep gears can severely limit speed potential.

Of course with that Brownie box you have some options that might help. It would be interesting to know exactly what OD ratio it has.

I still need to verify that ratio as I am not real sure about the numbers stamped into the end of the pinion shaft, pretty poor stampings.

From my searching the brownie overdrive ratio could be .74-.86 and with a Cummins and 5 speed out of a dodge the over drive there in 5th is .73:1. Assuming that the brownie is an overdrive of .86 (worst case) and the rear end is a 6.17 single speed. I can have as tall a top gear as, .73 x .86 x 6.17 = 3.87:1 and I think this combined with 8.25-20 tires at nearly 36" diameter wouldn't be too bad for the diesel. I would be at 2000 rpm at 55 mph and 2350rpm at 65mph. And if the brownie is taller in OD then it just gets better from there.

I will do my best to figure out the brownie ratios here soon. The more I look into what I have to work with here the better off my odds seem to get to where I want to go with regards to the cummins diesel part.

Thanx
Jaysin

Grigg

The comment that the 5.17 gears would be OK with the diesel is based on the fact that I have the brownie box with the overdrive, either .86 or better yet .74. Even with a 6.17 it wouldn't be too bad, the gear calcs are in the above post.

As far as the rest of the conversion goes, I am looking at the Cummins 12 Valve with the NV4500 trans. The stock axles and brakes will most likely get rebuilt and stay in place. A question I had in my first post was about the possibility of some sort of powersteering conversion or add on ram assist, I'm still looking for any Ideas here.

The last thing I would like to do is build a rollback flat bed for it like modern tow trucks have. I really don't think that this would be too hard to do, either by buying a used one or even starting from scratch. I am leaning toward starting from scratch as I would really like the bed to look like something out of the proper era, ie. wood deck and a period looking headache rack. We will see.

Thanx for your input Grigg, you have been very helpful with your wealth of knowledge.

Jaysin

I'd count turns if the model number or other stamped plates don't make it clear. Same thing with the rear axle.

Which Cummins do you plan to run? Maybe you said but if so I've missed it.

OK then, double overdrive can make up for slow axle gears, although may not be the best solution to speed it up just to slow it down again and the friction losses that come with that.

What model auxiliary transmission? I may be able to tell you the ratios if you have the model number.

If a 6BT then I most often hear that 1,800 rpm or there abouts is a good highway cruising speed for fuel economy and engine life.

If a usable and fast work truck is your goal the original axles may not be the best idea.
Might not be a problem, but newer axles with better brakes, available gear ratios, and easy to find/cheap replacement parts may make more sense, they did/do to me.

Stop by www.4btswaps.com
If you haven't already.

Grigg

Old Sub and Grigg,

I would love to just have a number for the brownie, it would make life easier. But alas the plate on the side seems to be gone. I haven't completely degreased it, there is a nice layer of dirt and gear oil covering portions of the box, but I don't really think the tag is there anymore. From pictures I found on the web I would say that it is a 6xxx spicer, 3 speed under/direct/over.

The truck's use is probably going to be moving my tractor between my house and my father's house and moving old cars that I have a tendency to bring home, with the occasional use of my fab business to move steel stuff (gates, weldments, material, etc...). Mostly it will spend it's life on slow mountain roads. I wouldn't mind going to newer axles but seeing what you had to go through to get a front axle (narrowing and all) and the fact that I would need different wheels and a host of other things the expense starts to outweigh the somewhat better drive-ability. Not that I am closed to the Idea but it might take some talking to change my mind. I've read your write-ups on this topic and love your truck and what you've done but finding some of the parts you're using for a reasonable price is a bit difficult at best and the front axle narrowing is a difficult process as well. If there was a possibility of swapping the P-30 spindles on the stock front axle I think it would be a more appealing swap, is there any possibility of this or is it totally out of the question?

The 6BT/12 valve Cummins is the motor I am looking at. The completely mechanical nature of the motor and the large availability of it and parts makes it a natural choice to swap. I've done quite a bit of reading over at 4btswaps.com and it really seems like the best fit for the AD trucks, power and size.

So this is where I am thinking about going, please let me know what your thoughts are. I am always willing to listen and if the argument is good enough then I might just change direction slightly.

Oh, by the way Grigg, you're Detroit powered 10 speed is the cat's meow. There is an original Detroit powered GMC dump truck that runs around in my area that is the coolest thing to hear coming up the driveway to deliver gravel.

Thanx,
Jaysin

That picture is of Grant's Dump truck. His login is Heavyhauler.

I don't see this usage as real challenging for what you're working with though I may be picturing too small a tractor. Some of the key words though are mountain roads and you'll want to be sure your brakes are up to stopping the truck with your tractor or something else heavy loaded on back.

And brakes would be my biggest concern using the old axles. The '51 still uses Huck brakes which aren't quite as good as the slightly later Bendix brakes. Even a few years later front and rear suspension might make a dramatic improvement in stopping power. I assume a 6500 has a hydravac and you'll want to assure its in good shape.

You're doing two things that make the brakes critical. Hauling heavy loads (even a small tractor is heavy) and increasing the top speed. The braking power required to stop a vehicle does not increase on a linear scale as you go faster, it increases much faster than that. If you are going to haul that tractor at 60 to 70 even on flat ground between the hills I would encourage you to look hard at ways to improve the brakes.

You don't need to read a lot of threads here to see I'm not a Diesel guy. Don't like the noise or the smell. But I do respect the pulling power they make and I'm sure you'll find the 6BT will do what you need.

Be aware that the 6BT is long enough that most installs require cutting into the firewall to make enough room. This means moving that loud and hot motor into the passenger compartment. I've seen a number of people argue and then build using the 4BT instead because they felt the power would be adequate and the compromises to make the motor fit much less.

Personally I'd choose a big gas V-8 instead so my opinion may not matter!

So as I've reviewed what I've written I think I'll also offer an approach to the brake problem.

You're dealing with a large flatbed so the exact width of the rear axle is not critical. Probably the wider the better for stability, meaning the Dana 70 HD or even Dana 80 from a dually might be a good choice if you can find one. You should be able to find these with disk brakes, but even modern drums on a 10,000 pound rated axle could be adequate.

You may find yourself going to 8-lug wheels in this process. I would not have a problem with that though others might.

If you search for olblue here on Stovebolt you'll find a thread about converting a dually front axle to disk brakes. He is converting a Task Force 1-ton but the process is going to be very similar for an AD truck like yours. Problem is he is building a 1-ton and using the 1-ton axle and spindles.

If you look up the specs on your 6500 you'll find your front axle is rated higher than that of a 1-ton but that a 4400 is rated the same as a 1-ton and in fact shares most the part numbers. You can downsize your front axle to the 1- or 1-1/2 ton type and then follow John's disk swap pretty much exactly as he did it.

Again you're converting to 8-lug wheels in the process, but you may find it easier to get modern wheels and tires having done so. And you really do want modern wheels and tires if you're going to run this rig down the road loaded and at speed.

I'm rashly assuming your tractor isn't real big. I often haul a John Deere 770 which sits nicely on my trailer and doesn't seem to weigh enough to challenge my equipment. If you're hauling some 10 ton behemoth ignore my suggestions and buy a bigger truck.

Don't have a lot of time for a response, but here are my first thoughts.

You could use your original wheels with newer axles, the centers would need to be bored out to 5.25" about.
Yes there would still be a host of other stuff to deal with.

I looked into swapping just spindles and at the time decided it was not the best idea, it's been a while and I don;t recall the exact reasoning or problem with that idea. Please do investigate and if it looks like a good plan fill us in on the details.

Not sure where you decided that a 6BT in an AD truck is "the best fit for size"?? Power yes, but I've only seen one Ad truck with a nicely done 6BT, looked like lots and lots of work to do it well. I've seen plenty of ugly and crude 6BT AD conversions. Length is probably the major issue.
If narrowing a front axle is a stumbling point, then a clean install of a 6BT in an AD truck is probably as much or more of a job than axle narrowing. The axle can be done in a day or two, or a week if your first time, the engine will take weeks for sure, probably months.

Grigg

I was looking at the possibility of swapping spindles from a later truck (5/10 P-30) to the stock front end and it looks doable but I will need to see all the parts in hand. After I said something about the wheels not fitting I then saw the info about boring out the centers of the stock wheels, my bad. My "problem" with narrowing the axle is not the "doing of it" but the final product. I have my concerns about welding a large truck axle back together, not from the welding standpoint but the fact that the joint, no matter how well done and x-rayed and magnafluxed will never be as strong as the original forged axle was. Should it be a concern, I don't know, but it does bother me. If it was acceptable in industry then manufactures would narrow their own axles instead of spending millions on new tooling for each different width axle they make.

As far as fitting the 6BT in an AD truck engine compartment, the space is there for the most part. Plenty of height, slightly narrow (but with a little metal shaping to make clearance where needed in the inner fenders it shouldn't be a problem) and length, the "hard" one, the 6BT (from web resources) is only 6"+/- longer then the stovebolt it replaces, I can push the center of the fire wall back to give clearance at the rear of the head and maybe hump up the tunnel for a bit more clearance. I've swapped a 354 hemi into a 53 Studebaker Commander without cutting the hood, it doesn't get much tighter then that. And Grigg, you should know about tight engine compartments those Detroits are giant hunks of cast iron.

The dana 70s and 80s that come out of the P-30 trucks, how do they stack up to the stock rear for capacity? They seem to be somewhat lighter duty and the next step up in modern equipment seems to be 2 1/2 ton or bigger. There doesn't seem to be a real 2 ton style rear end out there anymore, it's either a big light truck rear or a heavy duty truck rear. This isn't a huge concern, just more wondering on my part.

Thanx for the input and questioning, it makes me do more research and that can only help the project to go smoother and the end result be better.

Jaysin

I presume you are thinking one of the straight axle trucks. I suspect Grigg has already researched this option some and may have some good reasons why it doesn't work. But please keep us posted on what you learn because it would be great to find a solution for these trucks.

While I can appreciate your concern and if I were the one doing the welding I'd be worried, I believe a good welder can make a joint that will be as strong or stronger than the surrounding material.

The choices manufacturers make are based on manufacturing scales that mean many of their decisions are backwards from the economies of making a single part.

I've studied a number of these swaps both online and in person. The 6BT is a long motor and does not really fit in the AD truck engine compartment without modification.

The best looking swap I've seen was done by a guy local to me. I have a bunch of pictures of the truck, though my focus was on the IFS conversion rather than the motor swap. I have long since rejected the 6BT as an option for my own project.

It will take some poking around to find it, but its the 1-ton GMC with the full body camper in these three sets of pictures.

The old guy standing next to it built it about ten years ago and says he has driven it tens of thousands of miles since. I believe him.

Aug 08

Feb 09

Aug 09

This swap looks good enough to have come out of a pro shop. None of the others I've seen are nearly that clean and well executed.

I believe you are correct. I'd suggest starting with a calculation of exactly how much capacity you need. You may find that these axles are not up to your task.

If we assume the 6500 weighs 6000 now its going to get heavier with the 6BT. Its rated for 16,000 now I believe. I don't know the ratings on the 70HD and 80 rears but suspect you're giving up some GVWR going with one of them. I can easily see building a truck to carry 10,000 or 12,000 using one of these rears, but keeping the 16,000 rating isn't likely.

I've not come up with my numbers just out of the air. My P30 motorhome has a GVWR of 12,600 pounds so I assume those drivetrain components are up to that much.


Jaysin I'm currently on temporary disability and those days I can get my head into the game I enjoy nothing more than trying to figure this kind of stuff out. I'm happy to be part of the dialog and really appreciate having something interesting to think about!
[/quote]

The P30's with 5/10 lugs are typically rated in the 14,000 lb range, in comparison to our stock 16,000 lb. Not sure what the 80 version is rated over the 70HD, but I figured I'd be just fine for my use of hauling and towing stuff with the newer axle combo.
I agree that the next larger newer axles available are a half a size to large.

Before completely dismissing the axle narrowing consider the size of the stock I-beam, and the size of the new P-30 axle beam. Wish I had a section of the stock axle to show beside the section of the new one, but it is about twice the size. I feel that with a good welding job and the added factor of safety from the larger physical size it's still an acceptable method.

Yes the 4-53T is large, but height is no problem, inner fenders may suffer some trimming, and I know I need to widen the depression in the fire wall, but pretty sure don't need to make it any deeper. It'll be some work I'm sure, and I'll just have to do it, never said or implied my swap/project was an easy one, but it is the one I want.

Grigg

I would check with your local truck inspection facility too make sure any of these mods would pass an inspection before I spent too much money.You wouldn't want your insurance to be void in an accident or the DOT to condemn your truck after all that work.

Grigg,

First, I want to say that I in no way think your swap is anything but the coolest, in fact after seeing yours I went on a search for a Detroit (but alas they are hard to find on this coast and terribly expensive). As I said before there is an original GMC running around up here with a Detroit and I drool every time I hear it.

Second, I did not know that the P-30 I-beam was that much bigger, that does make me feel a bit safer about the narrowing. I just know that when a forged part is welded back together it will never be as strong as the original forging as the grain structure is now interrupted instead of continuous. I do have a degree in Metals and Manufacturing with a bit of background in metallurgy so I at least have some Idea of what I'm talking about.

Anyway, this truck isn't going to be used for long haul type stuff and while I wouldn't mind a wee bit more speed on the highway so I'm not a rolling roadblock I by no means need it to be anything more then a slow lane machine. I would probably drop a small or big block in it but it would be near the same amount of work to make them fit (more in the case of the BBC) and I would be lucky to see 10 mpg, I would think. So as long as I am going to be doing some cutting and welding I figured I would squeeze in a diesel.

I think that I will find a way to do a disc brake swap to the front at least (P-30 narrowed or P-30 spindles adapted) but I am going to have to do more research where it comes to the rear end before I make any decisions. I may even try the swap with the stock rear as I can always go back and swap it latter.

One more question for you. on the 4btswap site you mention that you see the 5/10 P-30 chassis regularly. If worse comes to worse and I can't find a front axle out here would you have any interest in possibly supplying one, fully paid for of course?

Thanx again,
Jaysin

I'll keep my eyes open for axles and send you links when I find them. Please remind me if you don't hear anything from me in a few weeks. They seem to pop up and I bet I can point you to one, but don't want to be a middle man in the deal.

Detroit's are reasonably common everywhere, last several good deals on 4-53T's I've seen were in CA. And I'm in CA at the moment and was playing with a 4-53 earlier in the week.. Saw two Detroit conversions at a show today also in CA.
Just look around and most anything you want will show up given some time.

Not suggesting you need one, but decide what you do want and look for it, you'll find whatever it is soon enough.

Grigg

I find with patience I can always find what I want for free or nearly so too. Though sometimes its better to pay a little more.

Check out this thread over on the ATHS forum
http://forums.aths.org/Instantforum414/Topic88541.aspx?PageIndex=2
Close to the end a guy in Oregon offers a 4-53T and 5 speed for sale.

Grigg