Dodge Cummins Diesel Forum banner

361 - 371 of 371 Posts

·
Registered
Joined
·
240 Posts
All of the info that I've researched says no, have to buy new gears.
 

·
Registered
Joined
·
20 Posts
I broke tranny #7 (I think lost count by now) twisted the plate right of the gear about 2800 miles, 4-5% grade, 22k gross about 50ish lbs boost @ 78 mph. Second or third time this has happened. Running for now without OD.

I sat down with the engineer last week. To see where things were at. The plate is a weak link he calculated at best may hold 1100-1500 Ftlbs torque with a marginal safety factor (hardly any). By splining the plate on it would drastically increase strength. So hopefully he’s not too far off from getting it engineered. I guess that why the factory design was for 400ftlbs of input torque on this gear. (550x.73= 401.5).
Other things that must be considered by making this gear stronger

1 will the pocket bearing be able to handle the increased radial load from the shafts trying to push apart?
2. Is the end of the main shaft (where the pocket bearing goes) going to hold up to the increased power?
3. If the answer is no on either of these the inside pocket on the main shaft must be made larger. To do this requires a larger input gear and smaller countershaft drive gear. This would make every gear a higher drive ratio (except 5th that’s direct).
4. Do I want to spend 3-4K just for two gears (6th mainshaft and 6th countershaft) when I am not sure the rest of the components will hold up? Not really

5 Why does a 48 overdrive seem to hold up? It is a 6 pinion planetary. The helix angle is 15 degrees, just guessing that’s about 1.5 tooth contact per pinion times 6 pinions makes 9 teeth in constant mesh. The ring gear contains everything so it is all balanced and not side loading any shafts. The nv5600 helix angle is much steeper and is 1.8 teeth in constant mesh. Also the reason the heavy truck transmissions have 2 countershafts. The the main shaft is in a neutral plane not forced to either side.

With that said I will be making a decision on what I am going to do depending on cost of high quality gearing.
 

·
Registered
Joined
·
240 Posts
Do you or the engineer your working with think just a plane billet gear would hold up better than stock? The reason I'm asking because I've heard it wouldn't.
Can you explain this spiral gear a little more your talking about?
 

·
Registered
Joined
·
20 Posts
Yes a high quality material would last longer. However given the way the gear is shaped it couldn’t be billet. It would have to be two pieces. There just isn’t room to cut the teeth and have the plate part of the gear through the machining process. As to a spiral gear I don’t know what your talking about.
 

·
Registered
Joined
·
240 Posts
My plan (at least in my head) was to reverse engineer and have a cad file using faro technologies.
Wouldn't a multi axis cnc machine be able to make that happen?
 

·
Registered
Joined
·
20 Posts
My plan (at least in my head) was to reverse engineer and have a cad file using faro technologies.
Wouldn't a multi axis cnc machine be able to make that happen?
Reverse engineering is easy (to make a matched set). Most information is published if you look hard enough. The problem is making sure everything will work together. The bearings for example. Changing the helix angle of any gear will change the thrust load on the bearings. The input thrust load is forward into the case the output shaft thrusts backwards and the counter shaft essential floats. The pocket bearing takes radial load from the gears trying to push apart. As the counter shaft has small bearings but all torque goes through it in all gears except direct. If one optimizes any gear for strength and makes a change to the helix angle and exceeds load rating on the counter shaft bearings now there’s a new problem. I don’t want to end up spending 20-30k getting my 5600 all built building multiple sets of gears and upgrading to bigger bearings, output shaft, input and everything else in between by the time it’s all said and done. I want to make sure it will all work together. As for the part about one piece with a multi axis cnc. Yes you could probably mill it out with the plate on but it won’t be of good finish quality. Most gears are cut, carburized (depending on material) or heat treated then finish ground to exact size and surface finish. This is where you get the problem of being able to get the grinder head accords the surface of the tooth and the cutter for that matter, the end mill would stick out so far it would probably chatter horribly. High hp towing is the hardest on the tranny for long life with high torque at low RPM for extended periods of time it stresses the small components beyond what they can handle. Remember a inline 6 produces an explosion hammering force every 120 degrees of rotation and the slower it is turning the harsher it is on everything that’s hooked to it. The heavier clutches don’t help either as they amplify this force. The higher the rpm the engine is ran the easier it is on the tranny it can take more power higher up because the torque drops off. Obviously you can get to a point where nothing was rated for the rpm and then there’s another set of problems but most cummins can’t turn that fast.
 

·
Registered
Joined
·
20 Posts
Well I am finally going to abandon building high quality gearing. Talking with the engineer again about my plan it has a few flaws. The gear design itself is ok at best for a low torque application. Making the OD gear out of high quality material helps but not enough. He went through some calculations with me this morning on tooth strength and there isn’t a material that exists that would be strong enough to handle 1000+ lbft of torque for any period of time deemed ok. On a side note he compared the Eaton FSO-8406a to the NV5600 OD gear only. And the Eaton appears to be over 8 times stronger. This is due to the gear just being much larger. As small as the nv5600 gear is slight increases in size drastically increase strength.

Next one might ask why not make the nv gears bigger. Well this would be very costly due to the center distances of the shafts in relation to each other these would have to change which requires case changes and all other gears to change. Can it be done yes, but not with my pocket book.

So to steelhead he was right in it being in adequately designed especially for a diesel. Guess that’s why Chrysler abandoned it. I clearly had to high expectations for what a high quality material would do. It would help but not enough.
 

·
3 footin' through life
Joined
·
12,340 Posts
Discussion Starter #368
Bingo. That was pretty much the exact verbatim summary of last time we tried to go through that process. I appreciate your effort on the topic though. :)
 

·
Registered
Joined
·
240 Posts
Ordered 5th and 6th cs gears from Blumenthal's, specifically asked for the best gears they use and they showed up today AT stamped on them made in Taiwan. I could not find any info where to buy the best for sure. The guy from Blumenthal's said these are the gears they use. Is AT the best out there? Nobody seems to want to give any info who makes the best. I'm a little disappointed.
 

·
Mountain Man Customs
Joined
·
2,504 Posts
There is nothing good available.

AT is junk Taiwan parts.

"Circle K" is less junk Korean parts.

Those are the options. Anyone "building" these transmissions is using one or the other supplier. They are both sub-par quality compared to OEM.
 
361 - 371 of 371 Posts
Top