1956 D7 17a gearbox problem

I have owned this since 2000, it has been a wonderful machine with a hydraulic dozer blade and Hyster D7 winch. I am a farmer and use it a lot on the chalk roads for levelling and in the woods for log hauling and stump removal. Last year I was pushing up a big heap of brash when there was a loudish bang as I reversed out of the heap and thereafter a nasty noise in first and second gears but less in third and fourth and very little in fifth. I sent it away to be repaired and they took out the gearbox to find that the bearing at the engine end of the main shaft had collapsed. Driving it gently back to the yard, half a mile there were no really bad noises like a broken tooth and when the gearbox was dismantled the teeth looked fine. However it had slightly bent a couple of selectors. The main shaft was replaced expensively ($2500)with a new one from the USA and the shafts laid out and checked for straightness and all seemed fine. However when the box was put back together and tested although first and second gears seemed fine, there was a horrendous grinding in both third and fourth gears. Not a broken tooth sound just a sound like something just touching. The gears worked all right but I did not dare try under load. Before the rebuild third and fourth gears were not nearly as noisy, although not right they were relatively quiet. The men doing the rebuild have a good reputation and much experience and cannot figure it out. I must add that when the initial bearing went the rollers went down through the box and were found at the bottom of the box. I would have expected a broken tooth or two had the roller meshed through the gear but this was not the case. However it did bend a couple of selectors slightly and they were replaced

Any thoughts anyone before we take the whole thing out again?

My thought is to assess whether the shafts are true. Is the grinding noise rhythmic? If so, that could indicate a bent layshaft despite them being checked for straightness. Also, we shouldn't assume the new mainshaft is true - both should be checked in a lathe between centers for runout. The other item to look at is inspecting the bearing housings in the transmission case. If something (e.g. a bearing roller) went between the teeth, it could have caused damage to the housings as well as the shaft. One question - is the bearing that collapsed the main bearing on the input shaft, or the bearing between the input shaft and the mainshaft? If the transmission is designed that way, then the "other" shaft (the one not replaced) should also be inspected. Which gear is direct out 3rd, 4th, 5th? Which ever one it is I would think would be the the quietest - probably fifth. In your serviceman's reference, there may be a flowchart of the gears involved in each speed (1st through 5th). If 3rd/4th are the noisiest, inspect them for changed tooth wear pattern. Although it would be unlikely, also check if they're bottoming out between teeth. A small change in wear pattern can account for a significant change in gear noise. Are the gears meshing correctly with the new selector forks fitted? You can select each gear, then lift the cover off to confirm that the gears are in correct mesh. Its possible the new selectors might not be quite setting the engagement correctly.

Good thought there Neil, thank you. Yes I was wondering about the casing or the bearing housing. Also I think you are right that we should do a more accurate assessment of the shafts rather than just rolling them on a flat surface. The noise is very loud and constant making me think that it is not a bent shaft but perhaps incorrect shims somewhere if shims are fitted As I said before initially the noise was quite bad in first but less in second even less in third and fourth. Now the noise in third and fourth is louder than the original noise in first. This makes me think that something has not be put back properly. Are there shims involved?

The other clue is that when in the Initial problem there was a noise in first, when I put it in reverse there was no noise in either first or second reverse. I can visualise the shaft being forced down when going forwards and forced up in reverse thus creating no noise

However the new noise in third and fourth is the same forwards or backwards again making me think something has been assembled with the wrong clearance. Since I was not involved with the rebuild my imagination is running wild!

Did you check your oil level in transmission and I was all time use 80\90 gear oil in and the noise could be wrong clearance on bevel gear.

If it was on the bevel gear surely the noise would be there in first and second which are very quiet. I am now wondering if a gear was put back the wrong way round on the third fourth shaft ,so for seventy years it had bedded into its opposite number and now was meshing the other way making the noise??? Of course since I have never seen the insides of the gearbox I finding it difficult to imagine

I go down next Friday to talk it through with the mechanics so I will report back any findings

Went down and tried it. First and second gear seemed fine in both forwards and reverse, but move the gear lever over to third and fourth and it sounds like the noise that you get when trying to force a change on a non synchro crash box in both gears forward and reverse. No noise in neutral . Same in fifth. The clutch lever does not seem to be as easy as before and the clutch brake does not seem to work very well although he claims to have put a new lining on it.

So it has had new main shaft, new bearings other shafts checked for straightness on a level surface. I think if they were bent the grinding noise would not be constant. New selector forks.

Do you think that a gear has not disengaged fully on the first second shaft, but I cannot see how this can be. it seems a though the whole unit needs to come out again to be assessed

Who is the main man Expert on a 56 D7 in the USA, may have to fly him over for a holiday!

Billhook, does the machine move in third and fourth gear? I am wondering if a selector fork could be in opposite way around or that it maybe bent?(had bent brand new oem parts before) I would imagine either of these would reduce travel and increase travel on gear selection, also possible selector fork could be in wrong position if they are similar. Some selector forks run a pad/block fitted in the end of fork to push against in the rear of the gear (slot), some have this pad/block part of fork casting that could reduce travel to release a gear movement to neutral if it is missing,

I would ask if anything was done in the clutch housing apart from the clutch brake. dry pivot possibly or any other new parts installed.

If it is possible to remove the Trans plate/lid with selector forks to see what you can this may show fresh marks on teeth if you can see them to help indicate the particular area to look closer to find the cause of the issue, If it is grinding I would think not selecting properly if you have no travel movement, if you have grinding and movement it suggest another gear is still in partly selected to drive and not neutral

I hope this helps some how

Those are very helpful comments Busso. The Cat still moves in third and fourth but with the gnashing sound as above so bad that I would not operate it for more than a few seconds . Selector forks is a good call. He replaced one that had been bent by the roller passing by it in the initial bearing failure, but he may have overlooked another or as you say put one back the wrong way round (unlikely) or perhaps they need shims that are critical. I think it may be possible to take the transplate lid off to have a look without removing the whole gearbox but the machine is elsewhere at the moment so I must wait till it returns. There is also the gearshift interlock mechanism to consider, but again I do not think that is the culprit. Perhaps we also need to consider the gearshift interlock mechanism.

But here is the Gate lock Quoting from the service manual. " A swinging gate lock(3) which follows the lateral movement of the speed selector lever, prevents any but the desired fork from shifting when the gears are shifted rapidly

The spring loaded plunger assembly (5) is a stop which contacts the gate lock when the operator shifts from first or second into third or fourth. To shift into fifth requires additional lateral effort on the lever. This aids the operator in selecting different speeds."

When I went to test it the engineer told me that although third and fourth were noisy, fifth was ok. But it was not and to make things worse the lever would not come out of gear. He could not pull it so I managed to pull it out, and I am fairly strong but it took all my strength. So that could be the clutch not disengaging properly which I would have thought is a different issue to the noisy gears

I am not a happy Chappy at the moment!

You need to look closer into the gear selection mechanism. Look for worn plunger detent notches, worn or damaged plungers and shafts, damaged or worn springs, etc. Also properly adjust the interlock mechanism. Damage or excessive wear to these components affect gear position selection. Also make sure the selector yokes a firmly clamped to the shift rails.