C30 heavy duty rear axle top speed

[Jscompto]

Hey everybody!
I had a question for those of you who have some good knowledge of these trucks....
I inherited my uncle's 1969 C30. It's a dump truck and it has a 350, a 4 speed manual transmission (including Granny gear) and an 11,000 lb rear axle (I assume it was a cab and chassy from factory). It's in pretty great shape and it all works too.

My question is this...what is everyone's consensus on top speed for these trucks?

The truck will only go about 40mph tops...it seems like it needs a 2 speed rear end in it or something because it is super slow. It will haul and dump whatever you put in it but it is just a snail on the road. I would have thought it would at least go 55-60mph...but no. I attached a few pictures of it as well. Can anyone help me figure out why it's so slow? Obviously I'd love to change either the rear end gearing or the axle out completely but I also don't want to change a whole lot of stuff on the truck. Thanks in advance!

[burnin oil]

How many lugs are on the rear axle? If it's 10 you need to swap axles. The 8 lug Ho72 can be had with 4.10, 4.57, or 5.14 gears. Even 5.14s should go faster than 40mph. If you don't like those ratios you are looking at swapping in a later 14 bolt or Dana 70 axle.

Edit. I just saw the lug count in your signature. You are going to be swapping axles if you want more road speed. Also price your brakes and that should be enough to justify swapping.

[factorystock]

First of all, looks like a very clean and solid HD C 30, I see you already have the solid 19.5 rims, which is a good thing. The 5 lug 10 lug 11K rear axle ratio is 6.17, which is responsible for a lower top speed for sure. Lucky you inherited this truck, now you can spend some good money for upgrades. There are threads on this site where the NV 4500 5 speed overdrives were installed successfully in 1 tons. Another option is the gear vendors overdrive unit which bolts on the end of your trans. Do you have a parking brake drum on the back of your trans? That might be the biggest issue with an overdrive set up. A .73 overdrive with a 6.17 would bring you down to around 4.56, which is a strong ratio for hauling for a heavy truck and comfortable speeds up to 55 ish. Another route would be to find a same capacity rear axle out of a later model 90's-2000 Chevy HD 3500 with the 5 -10 lug system that came with higher ratios. Sorry don't have books on those years, but there is probably much more knowledge of these trucks in the newer truck forums. Similar to this type of truck. https://www.purplewave.com/auction/1..._or_Van-Kansas

[LockDoc]

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Have you performed an overall tuneup on the engine? It may need points, plugs, rotor, distributor cap and timing re-set.

You could also put an overdrive transmission in it like I did in my C-30...

http://67-72chevytrucks.com/vboard/s...d.php?t=673588

Mine will drive 70 mph on the interstate all day long.

LockDoc

[kwmech]

I used to have one of those in my 69. I replaced it with a D70hd and 4.10s

[burnin oil]

Nv4500 swap is a great idea and will do wonders but you may still feel a little slow. We have a jeep with 4.88s and a 5spd on 32s. It is a perfect runabout around town but the interstate is a little fast for it.

For an axle swap thats 10 bolt there is always the f450 (not the pickup bed model) or dodge 4500/5500. They are 10 lug but I believe metric. The dodge version has really nice disc brakes and came with 4.10, 4.44, and 4.88s. It is a Spicer S-110 axle. These trucks had the same lug patterns and 19.5 wheels.

[jocko]

I'd keep the rear and install an NV4500 or a GV o/u drive unit behind the trans. While the od feature of the GV unit is nice, the gear splitting feature of it is also very applicable in a heavy duty application like this.

[Jscompto]

The GV overdrive unit sounds like it would work well If it is able to get me up to 55 or 60 mph as a top speed. It sounds also like it would probably be the least amount of modification to the truck? Is that correct? Exactly how is this unit installed? Maybe I am misreading something, but from what I can understand from the posts above, it seems like this just bolts on to the truck behind the transmission? Thank you all for all of the responses so far!

[burnin oil]

Gv bolts on like a transfercase to the rear of the transmission. When you buy it new it basically a gear splitter and then the correct adapter to mate to the transmission. They are pretty slick units. The downside is cost. Look around but unless you find a screaming deal the NV4500 will be a cheaper way to go. The only catch here is the dump bed. I assume that its PTO drive off the transmission. You would need a new PTO for the NV4500. If you have the ebrake of the transmission yoke then you will have to deal with this either way. My parts 68 c30 has the pedal mount.

Seriously though look into the brake costs for your current axle. I saw some of them when I was looking for HO72 brake parts. Neither is cheap but that 11k axle is pricey!

Don't let me saying to swap axles full you. I like the old ones and going through a 5.14 HO72 rear for my 57 GMC dually currently. Depending on usage you could always go up to 22" tires from a semi. This would also help bring the gearing into reason. I have to run the 19.5 mud grips on my 5500 and burn through tires. I am halfway through set number 3 at 80k miles. I have tried both the BFs and Kuhmos. I do run heavy with a lot of torque which doesn't help. Next set is semi tires since ride doesn't matter.

[Jscompto]

Originally Posted by burnin oil

Gv bolts on like a transfercase to the rear of the transmission. When you buy it new it basically a gear splitter and then the correct adapter to mate to the transmission. They are pretty slick units. The downside is cost. Look around but unless you find a screaming deal the NV4500 will be a cheaper way to go. The only catch here is the dump bed. I assume that its PTO drive off the transmission. You would need a new PTO for the NV4500. If you have the ebrake of the transmission yoke then you will have to deal with this either way. My parts 68 c30 has the pedal mount.

Seriously though look into the brake costs for your current axle. I saw some of them when I was looking for HO72 brake parts. Neither is cheap but that 11k axle is pricey!

Don't let me saying to swap axles full you. I like the old ones and going through a 5.14 HO72 rear for my 57 GMC dually currently. Depending on usage you could always go up to 22" tires from a semi. This would also help bring the gearing into reason. I have to run the 19.5 mud grips on my 5500 and burn through tires. I am halfway through set number 3 at 80k miles. I have tried both the BFs and Kuhmos. I do run heavy with a lot of torque which doesn't help. Next set is semi tires since ride doesn't matter.

Yes, the dump is ran off a PTO from the transmission. There's no e-brake on the transmission yoke though. Just has a split drive shaft with a carrier bearing. I'd consider either option (NV4500 or GV o/d). No clue which would be better though.
We basically won't be using the truck too much...It sits a lot of the time and when we do use it, it's just to move something somewhat short distances. I just had about 8 loads of dirt to move to a house yesterday and today about 15 miles away and it was taking forever to make a round trip going 35 mph. Now, I did get the truck up to 55 mph, but that was empty on the way back on one of the trips and it sounded like I was about to explode the engine. I'd like to have the ability to go about 55-60 mph at a comfortable cruising RPM...unlike it is now.
How hard is doing each of these options? I'm not totally against switching axles either but I'd like to keep the tires and wheels I have no matter what option I go with.

[jocko]

A GV o/u drive attaches to your trans in place of the tailshaft housing in most cases. Your 6.17 would become a 4.81. If you tell us your rear tire diameter, can give you an idea what rpm you'd be doing at different speeds. 4.81 still sounds like a very deep gear, however, your larger tire diameter offsets that, so am curious what the outside diameter is.

[Jscompto]

The tires are 225/70R19.5......online it says the diameter is 31.9 inches.

[jocko]

with a GV od and 31.9" tire:
55 mph = 2788 rpm
65 mph = 3295 rpm

Your current rpm, for comparison:
55 mph = 3574 rpm
65 mph = 4224 rpm

[Richard2112]

My C30 was similar when I first acquired it. 40 mph was a lot of rpm. Now with a 14 bolt rear w 3:73 and an nv4500, I can easily cruise 70 all day long. More if I wanted. I feel your pain. Or did.

[burnin oil]

Jocko. The CH465 doesn't have a tailshaft. It has a really large plate on the rear which acts as a bearing retainer and seal holder for the yoke. Remove the yoke and bolt if off. The GV would then bolt up like a transfer case.

In honesty the GV would be the easiest install but like I said they are pricey, around 3 grand. You wouldn't have to pull the trans to install but the driveshaft will need to be cut down.

If you have a pull a part near by you should be able to pull a NV4500 pretty reasonably and be all in with a new clutch for under a grand but then would need a pto. Swapping rears is just the cheapest and easiest way to get there. Unfortunately you will be going 8 lug. I bet that the front dually adapters could be swapped for the 8 lug setup. Now the issue is you want to keep your rims and tires.

Best bet for you is an auxiliary transmission. I think I paid 200 bucks for mine years ago. Check them out on YouTube. A 3spd aux would give you 12 forward gears and approximately a .75 od. If you don't want to shift them you don't have to. Stick it in Od and drive like normal. Some old timers called these brownie boxs. This option would bolt up just like a divorced transfer case so you would need to cut the rear shaft and get a jack shaft to go between the aux and 4spd transmission.

[projectking]

I have an HO72 rear end in 60462 if you need it.

[projectking]

Originally Posted by projectking

I have an HO72 rear end in 60462 if you need it.

I actually have the front spindles/drums and a set of wheels too

[Jscompto]

I love the discussion this has brought up as well as all of the options available. It's definitely not something I am going to do right at this moment but probably in the future at some point. I'll keep my options open and look to see what exactly is like to do. Would a 2 speed rear end from say a c70 or something work as well? What would need to happen for that application to work?

[burnin oil]

A 2 speed won't work since the gearing will be just as bad. Usually the high side is geared about where you are now. 2spd rears came in medium duty sized trucks that had semi tires. Low profiles are 36" and full size are around 42". Then the fun part is that alot of them are air brakes instead of hydraulic.

I think your 2 best options would be take advantage of the axle offer above or look at the auxiliary transmission. Option one gives you easier to find parts and a better gear. Option 2 gives you more pulling gears and OD. These are the most cost effective routes.

[jocko]

Originally Posted by burnin oil

Jocko. The CH465 doesn't have a tailshaft. It has a really large plate on the rear which acts as a bearing retainer and seal holder for the yoke. Remove the yoke and bolt if off. The GV would then bolt up like a transfer case.

In honesty the GV would be the easiest install but like I said they are pricey, around 3 grand. You wouldn't have to pull the trans to install but the driveshaft will need to be cut down.

If you have a pull a part near by you should be able to pull a NV4500 pretty reasonably and be all in with a new clutch for under a grand but then would need a pto. Swapping rears is just the cheapest and easiest way to get there. Unfortunately you will be going 8 lug. I bet that the front dually adapters could be swapped for the 8 lug setup. Now the issue is you want to keep your rims and tires.

Best bet for you is an auxiliary transmission. I think I paid 200 bucks for mine years ago. Check them out on YouTube. A 3spd aux would give you 12 forward gears and approximately a .75 od. If you don't want to shift them you don't have to. Stick it in Od and drive like normal. Some old timers called these brownie boxs. This option would bolt up just like a divorced transfer case so you would need to cut the rear shaft and get a jack shaft to go between the aux and 4spd transmission.

Thanks burnin oil, I wasn’t sure so just said in most cases. Clearly this rig isn’t the everyday case though 😀 Appreciate the clarification - this is great info!!

[factorystock]

Like all upgrades, it usually boils down to cost, the reason most of these older trucks don't have these upgrades already. The gear vendors in an excellent unit, but it will cost around 3K+ new. Don't know the price on a good used GV for a 465 Chevy trans. A used NV 4500 is around 1.5K, don't know the price for a new NV 4500. As I mentioned earlier, your lucky to get this truck free to offset the cost of an expensive upgrade. I would seriously look at Lockdoc thread on his NV 4500 conversion, it probably the most cost effective conversion. Jocko pointed out something interesting, the GV overdrive is .78 and the NV overdrive is .73. The NV will get your rpms down a little lower.

[jocko]

If you have more money than you know what to do with, you can link GV units in tandem... Your top speed would probably be limited by wind resistance at that point , but you'd have the coolest dump truck on the planet.

[burnin oil]

Even more fun. Gear vendors under drive hooked to an overdrive. This would give you enough gearing for a small cam and still yank a load.

NV4500 prices are similar here but you can find people selling a conversion for that price also. Pick and pull doesn't care what the trans is so thats the place to score one. I got my neighbor a nv3500 with tcase, computer, clutch and all that to do a conversion for $400. Since they don't care a 4500 would have been the same price. I wish I knew then what I know now. 10 years ago I could grab nv4500 Chevy for $75-150 every week on Craigslist.

FYI there is an adapter to put a dodge NV4500 behind a factory Chevy bellhousing from advance adapters. It uses a Ford throw out bearing or you can have the front bearing retainer machined to accept the standard chevy bearing. I did this in my 72 K20 since I had one out of a diesel laying around.

[gvw5400]

Since we are all dreaming up solutions, (and spending your money) he he he.
you might look a an Advance Adapters Ranger II overdrive.
It mounts between the bellhousing and 465 trans. and is around 7-8" long.
still expensive, but it allows you to split gears giving 8 forward and 2 reverse ratios.
You keep the pto., BUT need to shorten driveshafts and fiqure out shifter locations.
Have a blast working with that sweet dumper.
All the Best
Dirk

[Aruba1]

This is Mexico, lol. https://www.youtube.com/watch?v=hxXJ5wyZ4gY