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Heavy Truck Transmission and PTO Questions


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  #21  
Old 10-10-2017, 10:49:16 PM
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Default Re: Heavy Truck Transmission and PTO Questions

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Originally Posted by Heins View Post
The two speed rears don't have two ring and pinion sets, they have one.
This is true. They use a sliding gear which does the actual secondary reduction to the final drive. The shift motor is connected to a fork which engages the sliding gear and this fork is spring loaded to default to the high or low range without actuator power applied. Electric or air both work well and both are trouble free if not abused and maintained.
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  #22  
Old 10-10-2017, 10:51:07 PM
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Default Re: Heavy Truck Transmission and PTO Questions

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Originally Posted by Vanman View Post
Ooh, the 6610, that's the smallest one, isn't it? If I found one of those I'd want to bolt it up to a turbo 453 and stuff it in my Dodge van.
Yup. Lightest (ha!) of the dual countershaft units. They actually shift quite well and fast depending on how much flywheel is on the engine. Might be a bit slower to shift in a bus with the 14 miles of linkage to get the monkey motion up front.

*And if I had the cash to piss away I'd build up a 4-53T/RTO6610 and swedge it in a bagged rat rod pickup. Then drive it around all day going deaf.
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  #23  
Old 10-10-2017, 11:04:31 PM
Vanman Vanman is offline
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Default Re: Heavy Truck Transmission and PTO Questions

Somehow I'm not surprised at the error about there being two ring and pinions. Almost every thread I read descended into at least some degree of indecency. Makes me appreciate all the folks here even more!

So, would you consider a two speed rear end to be a reasonable option for my application?

I really want the solution that most economically delivers:
More speeds, and
Taller overall ratio in high gear.

I could not determine the ratio of the two speed unit itself. I assume one of them is direct. And would guess that the other is some degree of reduction. Ahead of whatever ratio the ring and pinion is, of course.

But, if I really can make the RT-910 I already have into an overdrive unit, and swap it over from my Detroit (patiently awaiting an overhaul) to the Cummins, that really sounds like a lot of bang for the buck. I could leave my rear end well alone.
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Old 10-10-2017, 11:24:50 PM
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Default Re: Heavy Truck Transmission and PTO Questions

I can't say from experience that the RT-910 can be made into an overdriven transmission but I know of two others which were converted and they did not hold up long. The stresses during use are shifted internally on the countershafts and the design doesn't take this into account translatng into accelerated wear.

A two speed rear axle uses much wider spacing in the transmission gearset than a transmission designed for use with a single speed rear axle. What you will find is the engine never where you want it to be during a pull. Not saying you cannot operate it as such but you will be much happier with a driveline that is "balanced".

I assume you are running either 10.00X20, or the modern equivalent 11RX22.5 tires so this needs taken into account also. The first step is to discern what ratio and axle is installed so you can build from that or know where to go for final installments. If I had an NH-220 Cummins engine I'd be looking for a 590 series turbocharger to boost the power rather than the donor engine's if installed to clear up the smoking at low engine speed under power. That helped the power regardless but a 590 and a higher flow manifold will give you significant upgrades in both power and torque.
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Old 10-11-2017, 10:41:41 AM
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Default Re: Heavy Truck Transmission and PTO Questions

A 2 speed rear with the existing 5 speed trans is a good idea, but you might want to sit down and calculate all the transmission/rear end gear ratio combinations ahead of time. The link below is to a catalog that lists Eaton/Dana two speed rear end ratios. If the
2 speed rear isn't matched to the transmission, you can wind up with some goofy ratios.

If you have the room, and everything bolts up, the Roadranger might be the way to go. Then you could just change the ring/pinion to give you the "overdrive" final ratio you want, and downshift when necessary.

http://www.wellertruck.com/lit/Welle...talog_2011.pdf
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Old 10-11-2017, 01:11:34 PM
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Default Re: Heavy Truck Transmission and PTO Questions

Thank you for the link. Assuming that the units listed there are largely representative of what might be found in a bone yard, it looks like I won't find a two speed axle to do what I want.

The step between low and high is about equal to the step between the gears in my existing trans. And the tallest ratio I could find was 3.55, which would get to about 75 mph, at maximum engine speed. So I could split the low to second shift, but none of the others, and have an extra top gear compared to what I have now. It would be a seven speed with fairly broad steps.

From 75, I'd have to bog all the way down to 55 before I could downshift lol. Things keep pointing back to that 10 speed I already have. If converting it to overdrive is going to damage it, I won't. That might not even get as much as I'd like anyway as my current axle ratio seems to be somewhere in the ~mid 4's. SLOW.

The original tires would have been 11.00-20 it now has the modern equivalent of those, 12R22.5.

For the turbo, if I'm wasting my time with the one I have I won't bother. I'll leave it as is for now, and consider the options in the future. It does look rather small. The nice thing about it is that it bolts up to the existing exhaust manifold. There is a special manifold for the horizontal turbo engines that may be difficult to come by.

I wouldn't want to get too carried away with more fuel / boost anyway as I believe that the NA engines are higher compression. And, although she runs great, she's old. A little bit more power, and a little less smoke would be welcome.
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Old 10-11-2017, 02:35:39 PM
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Default Re: Heavy Truck Transmission and PTO Questions

I get that this is a budget project.
Regarding the generator step-up drive...........
I don't know any reason why a small automotive manual transmission couldn't be run "backwards" off of whatever PTO is available with the Roadranger. First gear in these little guys is right around the 2.75/1 that you're looking for.
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Old 10-11-2017, 05:47:54 PM
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Default Re: Heavy Truck Transmission and PTO Questions

Well that certainly sounds like a clever idea!

I could remove the unused gears to reduce parasitic drag. And, if it has synchromesh, I could rig it up with a small air cylinder to shift in and out of gear, if or when that may be desired. I will definitely file that idea away for future reference.
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Old 10-11-2017, 06:25:32 PM
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Default Re: Heavy Truck Transmission and PTO Questions

You could remove the main and countershaft gears from a trans and build spacers to keep the kept gears from moving in the case. No need for clutching this in and out as your pto could be connected rigid to the input shaft, (normal output shaft) and the pto shifting in and out would be your clutching apparatus. Seen this done on a lot of conversion of old machine tools from line shaft drive to engine, or electric motor drive. I would use an aluminum cased manual transmission to keep the weight down. An old A833 New Process, (Chrysler) from the 70's into the early 80's works well in the application.
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  #30  
Old 10-11-2017, 10:51:43 PM
Gary Barber
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Default Re: Heavy Truck Transmission and PTO Questions

You must have an attachment to these Crowns There are much better choices for a bus conversion if that is all you want to do beware of starting with the wrong base I like the looks of the old crown but not enough to have one for an rv conversion TO EACH THEIR OWN and if that is your choice then that's good because not everyone is the same Being the owner of 2 bus conversions (a 1953 gmc 4104 with a 6V71 and manual 4 speed and a 1978 MCI5C with an 8V71 and again a manual 4 speed) Probably the only bit of useful advise you might consider from me is do some research and look into an oil cooled belt driven (I know you don't want belts but check into it u just might like the concept) Delco 50DN alternator they are capable of about a 300 amp continuous output they are brushless and just about bulletproof 300 amps will feed a 3,000 watt inverter all day long if the inverter is properly cooled (just how much power do you need while you are moving?????) After being around a lot of bus conversions and working on several if I was to start on 1 now I would find a 3 axle MCI with 6V92t power and Allison automatic and a diesel genset (probably 1 of Dick Wright's units from Eugene Or) Hopefully I haven't raised your blood pressure but thought I might have a little info to offer Thanks for your time Gary
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