10 replies to this topic

[Rick Anderson]

I am just finishing up a rod change gearbox rebuild due to a cracked casing and everything was going fine until I torqued the 1st and 3rd motion shaft nuts. As per instructions, I temporarily disconnected the gear selector shaft and interlock spool from the bell crank levers in order to lock reverse and third gears. I torqued both nuts to 150 ft/lb then re-connected the spool and gear selector shaft. Everything appeared to be fine until I tried to insert the detent sleeve into the side of the case and found that the groove in the interlock spool does not align with the hole in the casing so the detent sleeve cannot push in fully. You can see from the arrow in the photograph that the interlock spool is slightly bias to the right so a few mm of it prevents the sleeve from pushing in and engaging. If you look closely there is a small "B" stamped in it which you can see in the photo of it with it disengaged and pulled slightly out of the case. My initial "fix" was to file a small groove on the end of the detent sleeve so that I could fit it in order to check operation. Everything appears operate well but I can't figure this out. Any help would be greatly appreciated. 

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[Spider]

Most likely you can just lever the Interlock Spool in to position. If you feel some definite resistance, then you've likely assembled one or both of the Syncho Hubs with the inner back to front.

 

By the way, how did you end up with this job ?

https://www.theminif...spension/page-3

 

 

[Rick Anderson]

Most likely you can just lever the Interlock Spool in to position. If you feel some definite resistance, then you've likely assembled one or both of the Syncho Hubs with the inner back to front.

 

By the way, how did you end up with this job ?

https://www.theminif...spension/page-3

 

 

 

Thanks Spider. There is definitely something misaligned so I suppose I need to tear it down again to see what is going on.   I replaced all the syncro hub detent balls and springs as well as all the bearings and sycros so maybe I goofed something up. It is so frustrating to get this far then have to tear it apart again, especially since the locktabls are so difficult to come by here. 

 

The radius arms turned out nice. 

[Spider]

Thanks Spider. There is definitely something misaligned so I suppose I need to tear it down again to see what is going on.   I replaced all the syncro hub detent balls and springs as well as all the bearings and sycros so maybe I goofed something up. It is so frustrating to get this far then have to tear it apart again, especially since the locktabls are so difficult to come by here. 

 

The radius arms turned out nice.

 

It's somewhat easy to muddle up the Hubs. I'd done 100's of gearboxes over the years, having done one early on with one hub back to front, I've looked in the book every time ever since.

 

Unless they are genuine BMC locktabs, I'd actually suggest not fitting any. I've found that they 'ooze' out over time with the high pressures on them. I just clean the threads and use 243 loctite, been doing them that way a very long time now.

 

Glad the arms came out OK.
 

[Rick Anderson]

It looks like a dodgy double roller bearing which has a lot of side-to-side movement. I took everything apart to inspect and the moment I loosened the bearing retainer the interlock spool aligned. Unfortunately I can't post a video here because I'd like your opinion. 

 

 

 

 

Thanks Spider. There is definitely something misaligned so I suppose I need to tear it down again to see what is going on.   I replaced all the syncro hub detent balls and springs as well as all the bearings and sycros so maybe I goofed something up. It is so frustrating to get this far then have to tear it apart again, especially since the locktabls are so difficult to come by here. 

 

The radius arms turned out nice.

 

It's somewhat easy to muddle up the Hubs. I'd done 100's of gearboxes over the years, having done one early on with one hub back to front, I've looked in the book every time ever since.

 

Unless they are genuine BMC locktabs, I'd actually suggest not fitting any. I've found that they 'ooze' out over time with the high pressures on them. I just clean the threads and use 243 loctite, been doing them that way a very long time now.

 

Glad the arms came out OK.
 

 

[Spider]

Just to check with you here, the Mainshaft (Double Row) Bearing has been fitted with it's shoulder clip ? It's just a thin C that's fitted to the groove in the outer ring of the bearing.

 

Also, the Mainshaft Bearing inner races are 2 separate parts, held together with a clip. Without something clamping the inner races hard together, they will have some play in them.

Check the Hubs are assembled the right way around of course.

On the Diff Cap, there's a date code - what date is yours ?

[Rick Anderson]

Spider, I believe I solved the issue. Upon further investigation I realized that the main shaft bearing was not pushed fully home with the c-clip against the casing as it should be so when I torqued the nut it pulled the mainshaft a few mm toward the bearing which caused the selector hubs to be slightly to the left which, in turn, caused the levers to be slightly more inward which then caused the spool to be slightly too far in the case for the sleeve to push home into the spool groove. The geometry is such that a tiny bit out multiplies to a huge problem, I am going to reassemble it next week but I'm fairly confident that it will be OK now. I know you said you don't use locktabs but does that include the main shaft nuts that are torqued to 150 or just the bearing retainer? 

 

 

Just to check with you here, the Mainshaft (Double Row) Bearing has been fitted with it's shoulder clip ? It's just a thin C that's fitted to the groove in the outer ring of the bearing.

 

Also, the Mainshaft Bearing inner races are 2 separate parts, held together with a clip. Without something clamping the inner races hard together, they will have some play in them.

Check the Hubs are assembled the right way around of course.

On the Diff Cap, there's a date code - what date is yours ?

[Spider]

 

Spider, I believe I solved the issue. Upon further investigation I realized that the main shaft bearing was not pushed fully home with the c-clip against the casing as it should be so when I torqued the nut it pulled the mainshaft a few mm toward the bearing which caused the selector hubs to be slightly to the left which, in turn, caused the levers to be slightly more inward which then caused the spool to be slightly too far in the case for the sleeve to push home into the spool groove. The geometry is such that a tiny bit out multiplies to a huge problem, I am going to reassemble it next week but I'm fairly confident that it will be OK now. I know you said you don't use locktabs but does that include the main shaft nuts that are torqued to 150 or just the bearing retainer? 

 

All locktabs.

There is an issue I have found with the later gearbox cases, on the shoulder that the Mainshaft C Clip seats on. In all the late cases I've found, that shoulder was around 0.018 to 0.027" deeper than it should be. This will have a result of moving the whole mainshaft forward in the case and give you the issue you have with the selector forks. It also results in 3rd gear (or sometimes top) baulk ring burning out. The factory (rudely !) compensated by machining these baulk rings thinner. I correct them by adding a shim to the Mainshaft Bearing tunnel, that relocates the shaft back to where it should be.
 

[Rick Anderson]

 

 

Spider, I believe I solved the issue. Upon further investigation I realized that the main shaft bearing was not pushed fully home with the c-clip against the casing as it should be so when I torqued the nut it pulled the mainshaft a few mm toward the bearing which caused the selector hubs to be slightly to the left which, in turn, caused the levers to be slightly more inward which then caused the spool to be slightly too far in the case for the sleeve to push home into the spool groove. The geometry is such that a tiny bit out multiplies to a huge problem, I am going to reassemble it next week but I'm fairly confident that it will be OK now. I know you said you don't use locktabs but does that include the main shaft nuts that are torqued to 150 or just the bearing retainer? 

 

All locktabs.

There is an issue I have found with the later gearbox cases, on the shoulder that the Mainshaft C Clip seats on. In all the late cases I've found, that shoulder was around 0.018 to 0.027" deeper than it should be. This will have a result of moving the whole mainshaft forward in the case and give you the issue you have with the selector forks. It also results in 3rd gear (or sometimes top) baulk ring burning out. The factory (rudely !) compensated by machining these baulk rings thinner. I correct them by adding a shim to the Mainshaft Bearing tunnel, that relocates the shaft back to where it should be.
 

 

 

That is interesting. Is the shim something you can sell me if I have one of these cases? And how do I tell if I have that case? The reason I am going through all this is the prior owner used large head ARP bolts on the mains without machining a relief in the gearbox case so when they bolted the gearbox on it cracked in a few places near the moon seal. So I found a DAM5626 replacement case and now I'm trying to get it together. 

[Spider]

I can sort you with a shim if you need one.

 

 And how do I tell if I have that case?

 

On the Diff Cap, there's a date code - what date is yours ?

 

 

Or if you have a set of 12" verniers, you can measure your case;-

 

 

 

[Rick Anderson]

Are the cases and caps matched sets? I was intending to use the cap off my other gearbox since it seems to be in better condition and I am not sure if the cap that came with the replacement case is original anyway. 

 

 

 

I can sort you with a shim if you need one.

 

 And how do I tell if I have that case?

 

On the Diff Cap, there's a date code - what date is yours ?

 

 

Or if you have a set of 12" verniers, you can measure your case;-

 

 

Edited by Rick Anderson, 08 December 2024 - 06:12 PM.