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Thread: M135 M211 2 speed transfer case mod

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    So again, if we're talking 50's deuces, what's the weak link in their driveline? If we've got 80 years of "learnin' ", well, we have still got to understand how they did things then in order to properly repair/modify them. I'm no metallurgist or engineer, but I do work on modern cars/trucks. In my experience, the old stuff was built big to get strength where new stuff is designed with lighter components. I kinda like big and heavy for durability.

    If they are loaded so that the tires won't spin, what breaks first (or most likely breaks first)? My truck needs this low gear transfer case mod because the truck is powered by a small block chevy w/4 speed manual trans. It's weak link taking off from a stop when loaded....is definitely the clutch at this point. I'd question the driveshaft (joints) between trans and transfer case, until a low geared transfer case mod which would put more torque to the shafts after the transfer case.

    Duuane, what do you think would break first in your truck? Would you want a weak key to fail if it could do so without major shaft/gear damage?

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    Well..if all goes as planned my rig will have an allison..so the 1st to 2nd full throttle shift will most likely be the short side axle shaft killer.
    From what i can tell there is no mechanical coupling between the gear cluster and the shaft save for the key..so the power is being sent through the gear cluster and the shaft is only supporting the cluster. I think the key serves only to prevent relative movement between the cluster and shaft during shifts and float/coast conditions to prevent wear to the shaft and gear bores.
    So if you beat the transmission hard with shifts on the governor or 1st rev 1st rev trying to get out of a jam likely the key would take a beating due to absorbing the inertia of the related parts..
    If it cut the key and spit it out..and the shrapnel didnt end up between two gears and explode the case..the magnetic drain plug might save you and you would probably never know till you did the fluid change at PM. In that scenario a $0.43 key and some swearing to replace it isnt such a bad deal.
    A hard as diamond key and a chunk blown out of a hard to come by shaft from the distant past..i dunno. I would say better key than mild steel but softer than the shaft and an intelligent operator.
    I have a 13" clutch setup for chev that will allow you to bolt up a spicer 3053a or a clark 280v close ratio direct in 5th 5 spd..i can send you pics and part numbers if you like..that way you get a lower 1st gear..might be an option for you if youve already installed a pedal and clutch linkage.

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    Quote Originally Posted by DUUANE View Post
    Well..if all goes as planned my rig will have an allison..so the 1st to 2nd full throttle shift will most likely be the short side axle shaft killer.
    From what i can tell there is no mechanical coupling between the gear cluster and the shaft save for the key..so the power is being sent through the gear cluster and the shaft is only supporting the cluster. I think the key serves only to prevent relative movement between the cluster and shaft during shifts and float/coast conditions to prevent wear to the shaft and gear bores.
    So if you beat the transmission hard with shifts on the governor or 1st rev 1st rev trying to get out of a jam likely the key would take a beating due to absorbing the inertia of the related parts..
    If it cut the key and spit it out..and the shrapnel didnt end up between two gears and explode the case..the magnetic drain plug might save you and you would probably never know till you did the fluid change at PM. In that scenario a $0.43 key and some swearing to replace it isnt such a bad deal.
    A hard as diamond key and a chunk blown out of a hard to come by shaft from the distant past..i dunno. I would say better key than mild steel but softer than the shaft and an intelligent operator.
    I have a 13" clutch setup for chev that will allow you to bolt up a spicer 3053a or a clark 280v close ratio direct in 5th 5 spd..i can send you pics and part numbers if you like..that way you get a lower 1st gear..might be an option for you if youve already installed a pedal and clutch linkage.
    If that key is only "supporting" that gear then remove it and put shims in it's place. The fact is that key is there to make a mechanical connection to that shaft. That is the only reason woodruff keys are used. To make a mechanical connection.
    As far as your suggestions "Ashley P" about the "good old days" let me tell you they built that way because the metal quality was not near what it is today. I know as I worked on them. Your a mechanic so you know what size the gears are today. Well I also was a mechanic for 45 years (retired) and as a gear specialist for most of that time I can honestly say the reason those gears where "big" is due to the lack of strength of materials then. They didn't use "4140" or "Marange steel" or any of the new metal we have now. It didn't exist. It was very common for ring gears to develop wear "spots" on the gears due to moisture in the differentials. The small "explosions" of super heated steam would literally tear out small pieces of the gear. That was normal so you would set-up your gear and lash like normal and call it a day. In todays differentials I have never seen that happen to the gears. They are too hard of material. Also no one ever heard of "sintered" steel back then, it didn't exist. We now can compress steel powder into extremely hard and difficult to make shapes that can handle extreme pressures.
    I don't know how old you are "Ashley P" so I don't know if you have any experience working on a daily basis on this old equipment like I do. So I would suggest you look up some references comparing old gears to new modern gears.
    It will answer all your questions.
    Now before anyone says I'm being "condescending" here, I'm not. I'm trying to help. So keep it to yourself or shove it where the sun don't shine as I don't need to hear it.

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    No doubt..metalurgy has come a long way since these trucks rolled off the line..and that was what i was getting at..using a nasa grade key in a soft shaft might not be the best. The key doesnt support the gear. It prevents the gear cluster from rotating on the shaft. The shaft is supported by bearings at both ends and it is the gears that are driven not the shaft so i dont think much if any torque is transmitted through the key.

    Talking about 40's and 50's metal..one of the things we've found in messing with M37's is that there was quite a variaton in dimensions over the years. Axle ahaft lengths and side gear spline locations. So much so that if you do a field mix and match with good used parts and dont blueprint everything, use sealant instead of gasket material, you can end up with interferance and failures.
    Also canadian M37's seem to have different axle material than us trucks and civvy power wagons..even with 40" gama goat tires and 3/8" plate adapters i was never able to break them..and especially the fronts..they would come out looking like chro-mo all super shiny. Even from the ones we dug out of the bush.
    Ive beat the **** out of a small mountain of eaton ho72's..had them run dry..had the ring gears worn so badly that they were so loud on the highway that after a 20 minute run your ears would ring..and they never broke..never lost an axle shaft.. maybe ive been lucky but i think those kind of faliures can be linked to other damage or fitment/assembly issues. Or a really...really poor operator.
    Last edited by DUUANE; 12-10-2018 at 02:51.

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    [QUOTE=DUUANE;2179914]No doubt..metalurgy has come a long way since these trucks rolled off the line..and that was what i was getting at..using a nasa grade key in a soft shaft might not be the best. The key doesnt support the gear. It prevents the gear cluster from rotating on the shaft. The shaft is supported by bearings at both ends and it is the gears that are driven not the shaft so i dont think much if any torque is transmitted through the key.

    OK, we need to address an issue here before we can go on. I believe your operating under a false assumption of the power flow in this transfer-case. Those keyed gears are transmitting power through the gear to the shaft and then on to other gears.

    Scan0158.pdf When I was talking about just leaving out the key I was being "ironic" . As you can see from the TM 9-1819AC page 86 , it clearly shows the power being transmitted through the gears then into the shaft (via the KEY) then on to other gears again through a "key" to another shaft. I cannot see what your saying that the key holds no other function except to hold the gear in place. Like I said earlier, "ALL" keys transmit torque through them. They hold no other purpose in a transmission or transfer-case. Maybe I'm totally missing what your doing here and somehow you have eliminated the need for the keys which I cannot see. If so can you draw up a diagram so I can follow it.
    Thanks.

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    There is only one gear keyed to the shaft and its on the output end. The gears are dogged together and the dogs do the job of transmitting the torque. The shaft merely keeps things aligned. The gears on the shaft relative to each other, and the assembly relative to the other gears/shafts in the case.
    That is my assertion. There is just no way that a .002" clearance fit gear and shaft is going to transmit power and surely a 1/4"x3/4"mild key on the output side would never do that job in this gvw range.
    The 3 gears on that shaft cannot rotate relative to each other, effectvely acting as a hollow shaft to transmit the torque. The inner shaft merely supports and aligns them. The key prevents relative motion between the gear cluster and the inner shaft only.

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    Quote Originally Posted by DUUANE View Post
    There is only one gear keyed to the shaft and its on the output end. The gears are dogged together and the dogs do the job of transmitting the torque. The shaft merely keeps things aligned. The gears on the shaft relative to each other, and the assembly relative to the other gears/shafts in the case.
    That is my assertion. There is just no way that a .002" clearance fit gear and shaft is going to transmit power and surely a 1/4"x3/4"mild key on the output side would never do that job in this gvw range.
    The 3 gears on that shaft cannot rotate relative to each other, effectvely acting as a hollow shaft to transmit the torque. The inner shaft merely supports and aligns them. The key prevents relative motion between the gear cluster and the inner shaft only.
    Exactly. That key holds that gear to the shaft. I know the gears are spinning freely on the shaft in general and when the shifter moves it "dogs" them into each other. I still think we are looking at this from different angles.
    OK, try and imagine that gear on the output end without the "key" . What would it do ? It would just spin on the shaft without transmitting any torque. That key is "vital" to the function of that gear. Is what I'm saying making any sense to you ? It is so hard trying to get an idea across just using words.
    I've just been trying to show you that it makes sense to use "alloy" keys instead of cheap soft keys. You know, at the end of the day it really doesn't matter what kind of woodruff key you use. Just enjoy this hobby !
    Take care "C" .
    Rustystud.

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    I understand what youre saying..but in this instance the power transmission is all through the gears on this one shaft in particular. Input shafts and output shafts yes, splines on the shaft get the job done. I appreciate your input G.

    I'm always having fun

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