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gears again

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gears again Empty gears again

Post  jjtjr on Tue 17 Nov 2020, 11:30 pm

I installed the new gears as per the assy instructions. Yesterday I moved the car about 20 feet and it stopped and would not move. I pushed it into the shop and dropped the diff. To my suprise the pinion gears teeth were broken off on all pinions again. The axle gears were ok. I'm at a loss as to why this is happening. What I need if any one knows the pressure angle of the gears is it 14.5 or 20 degs.
Dean do you have any thoughts on this problem.
jjtjr
jjtjr

Number of posts : 190
Age : 72
Location : New Jersey,usa
Registration date : 2009-07-28

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Post  Grier on Wed 18 Nov 2020, 12:15 am

When you tighten the wheel castle nut were you able to bind the bearings up a bit where the wheel was stiff to turn? Once that occurs you need to back off just enough to where the wheel spins freely. This would mean that the two taper bearings are set with minimal to no freedom to allow the axle to move. Also I would suggest that the pinion gear teeth can be faced off even more further away from the axle gear. There is plenty of gear face to drive everything and a little less won’t matter in the grand scheme of things.
I’m so sorry to hear this has happened again. But something is allowing the movement of the axle for this to have happened again.

Grier

Number of posts : 51
Location : Topsail Beach, NC
Registration date : 2015-05-15

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Post  jjtjr on Sat 21 Nov 2020, 9:51 pm

opened the diff and this is what I found on both halves. Could not find any problems with the assy. There was plenty of clearance. I have a bucket of broken teeth. The car was moved 20 feet and this happened.  Could it be the cast gears that are the problem?
gears again 20201111
jjtjr
jjtjr

Number of posts : 190
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Post  Grier on Sun 22 Nov 2020, 2:24 am

So as I understand this differential, the outer case is driven by the chain and sprocket from the engine and the torque of that is transferred to the axle gear by way of the smaller pinions in the differential. The pinions are actually stationary if you are driving a straight line and only rotate when taking a turn etc. so all of the power goes through these pinions to the wheel axle gears. The failure I see is that the pinion gears failed in transferring that torque to the wheel axles while turning or cornering. The pinions were stripped in the inner portion where this torque or power from the chain and sprocket is transmitted. You stated the larger wheel axle gears were okay and looking at your photo that is also showing by way of the outboard sections of the pinion gears being relatively still intact.
So this is a different failure from your first failure I believe. The pinion gears failed possibly because your surrey is heavier? That’s possible, or there is something else binding in the axle torque tubes? Out of curiosity did you try spinning the axles? Did it feel normal? Another possibility is that one side or wheel was dragging putting pressure on the inner pinion gear portion and the teeth snapped.
Finally if it were me I would make the pinion gears out of 1040 cold rolled steel. Previously you asked about pressure angle and the most typical nowadays is 20 degrees. 14.5 was an older standard that is still in use but not as frequent now.

Grier

Number of posts : 51
Location : Topsail Beach, NC
Registration date : 2015-05-15

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Post  jjtjr on Sun 22 Nov 2020, 1:10 pm

Grier, Since I have the diff. out of the car I will jack up both wheels and spin the axles and check to see if there is any binding.  Before I make any gears I am checking with STW, I don't want to assume the pressure angle is 20 degs. The plan would to make the pinion gears from 4140 steel which can be case hardened,  I  already purchased the bar stock, and cut  them and  have the gear case hardened,  somewhere around .010" to .020" deep, its best not to hardened the whole gear only the teeth because it will become to brittle. Dean and I have a phone call set up on monday to discuss the problem. Its interesting how the original gears lasted around 10 years and now the new gears worked for 20 feet. Once I confirm the pressure angle is 20 degs  I will order the cutters and try to make them this Dec. since I will be flying back to New Jersey for the holidays and be there for about 4 weeks.
After degreasing the diff. I placed half of it on the axles  and looked to see if the axle gears was trying to strike  the other pinion gear, from what I was able to see there was clearance  so that wasn't the problem that caused them to break. This would mean if my thinking is correct  the cast gears can't handle the torque. I'm wondering  why the gears were cast in the first place, I would thing any gear that transmits torque would be heat treated. When I did an HRC test on the pinion gears I think it was below 40. I was using the HRC file kit which includes 5 test files  from 65 HRC to 40 HRC. When testing it was below 40. All the specs. that I read on pinion gears the HRC number should be  between 50 to 60. If there is no binding this could be the problem and making the new gears would fix the problem. In the meantime Dean is sending me another set of pinions gears. The car is with me here in florida since I go to quite a few car shows in the area. I would like to get it fixed asap its still early in the season.
jjtjr
jjtjr

Number of posts : 190
Age : 72
Location : New Jersey,usa
Registration date : 2009-07-28

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Post  jjtjr on Sun 22 Nov 2020, 1:22 pm

When the car was first built as a two seater its weight about 900 pounds dry, when it got extended it now weighs 1500 pounds dry. Could this contributing  to the problem ?
jjtjr
jjtjr

Number of posts : 190
Age : 72
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Registration date : 2009-07-28

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Post  Grier on Sun 22 Nov 2020, 2:19 pm

4140 is a good choice. I have used this steel also for spur gears. Also thinking some more on the failure, going only 20 feet really points to something binding up quickly. I know on my differential I had to enlarge the holes a bit on my pinion bolts to make sure that my gears did not bind up. Meaning I had to move the pinion gears apart some to get some backlash - not much, but enough so that the gears were able to rotate fairly freely and not bind.

Grier

Number of posts : 51
Location : Topsail Beach, NC
Registration date : 2015-05-15

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Post  jjtjr on Mon 23 Nov 2020, 2:07 am

That's a good point, when I get the new gears I will make sure that they turn freely.  Since I will be flying back to NJ did you want me to assy a control board for you? If so let me know. You will have to fabricate a  box for it to fit into. I could take some photos with measurements, Its easy to bend one up using brass sheet. A brake works best you get nice bends.
jjtjr
jjtjr

Number of posts : 190
Age : 72
Location : New Jersey,usa
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Post  jjtjr on Wed 25 Nov 2020, 12:18 pm

Here is the latest on the gears, Ian from STW called me on my cell phone USA from England, The call was very productive there plan is to make new pinion gears from steel not cast iron and mail them to me, I then can if I desire to have them case hardened. I asked if they could be made from 4140 steel or there equivalent, he said that was  possible. The lead time was about 2 weeks. STW  is doing a great job with this problem. Thanks again to the team at STW.  My next trip to England after the virus is over I will visiting the team at STW.

Jim Trotta
jjtjr
jjtjr

Number of posts : 190
Age : 72
Location : New Jersey,usa
Registration date : 2009-07-28

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