48 replies to this topic

[76lxhatch]

If that's the pressure plate side of the clutch in your photo, it looks like there may be witness marks on end of the centre spline from over-travel. Are there marks on the inside centre of the diaphragm fingers too?

[Bigfella237]

And you just reminded me of another possible cause...

 

If the clutch plate can't slide freely in the splines of the input shaft, such as it being rusty like that, it can also make the clutch drag.

[lemonaro]

If that's the pressure plate side of the clutch in your photo, it looks like there may be witness marks on end of the centre spline from over-travel. Are there marks on the inside centre of the diaphragm fingers too?

No marks on the other side of the diaphragm fingers

[lemonaro]

And you just reminded me of another possible cause...

 

If the clutch plate can't slide freely in the splines of the input shaft, such as it being rusty like that, it can also make the clutch drag.

Clutch plate slides freely on the splines, when you look at it in the flesh its probably more grease than rust, i was wondering if too much grease?

[yel327]

Thanks for the advice about pulling it apart but I'm struggling for room, Most of the work im doing is on the ground, I have stuff all room to work in and my work bench isn't much of a bench. The wife won't let me bring the gearbox into the dinning room!

Im still thinking the problem is from the input shaft/clutch plate dragging so see how I go with that. If I notice anything with the side cover off then I'll reassess my  approach with the gearbox.

I agree with you that the clutch or clutch area are most likely your problem. However, my suggestion about the internals is based upon experience, and you now have the box out. I have pulled apart dozens of these over the years from all sorts of sources, either out of wrecks or $50 boxes from swap meets or even out of driving cars. I have never pulled one apart since the late 80's that has not had one of the three main wear problems at least developing. As I said those being:

 

Case hardening on the inside of the counter/cluster gear on the 1st/reverse end.

Case hardening inside the clutch gear (input shaft) where the bearing runs for the main shaft nose.

Circlip holding 1st gear onto the main shaft.

 

Virtually every box I've tried to rebuild as opposed to just pulling apart (eg smashed to bits inside) has needed apart from the small parts kit at least 1st gear and a Cluster gear. And these are boxes pulled out of running, driving cars like yours. They work but eventually they will fail and break a lot more inside. Years ago, we used to put bronze bushes up the guts of the cluster gears but nowadays it is cheaper to buy aftermarket ones. If the input shaft and cluster both have worn case hardening you could even buy yourself a pair of XU1 input and cluster and turn it into an XU1 (close ratio) M20 rather than a standard M20 - all of the rest is the same assuming the box you have is original to the Commodore - I think all of the remade XU1 input shafts are replicas of the VB Rally car input shaft with the neoprene front seal, not the old scroll/slinger type seal like most XU1 had. But the same problem would exist anyway with any aftermarket normal M20 input, you'd have to confirm your box isn't an older one out of a HQ with the early seal.

 

They aren't that hard to pull apart, inspect and replace bits. The most fiddly thing is the needle rollers, but a piece of wooden dowel the same size as the layshaft and some grease or Vaseline and it is easy. You can do it on a 300mm wide plank across two stools.

[lemonaro]

I agree with you that the clutch or clutch area are most likely your problem. However, my suggestion about the internals is based upon experience, and you now have the box out. I have pulled apart dozens of these over the years from all sorts of sources, either out of wrecks or $50 boxes from swap meets or even out of driving cars. I have never pulled one apart since the late 80's that has not had one of the three main wear problems at least developing. As I said those being:

Case hardening on the inside of the counter/cluster gear on the 1st/reverse end.
Case hardening inside the clutch gear (input shaft) where the bearing runs for the main shaft nose.
Circlip holding 1st gear onto the main shaft.

Virtually every box I've tried to rebuild as opposed to just pulling apart (eg smashed to bits inside) has needed apart from the small parts kit at least 1st gear and a Cluster gear. And these are boxes pulled out of running, driving cars like yours. They work but eventually they will fail and break a lot more inside. Years ago, we used to put bronze bushes up the guts of the cluster gears but nowadays it is cheaper to buy aftermarket ones. If the input shaft and cluster both have worn case hardening you could even buy yourself a pair of XU1 input and cluster and turn it into an XU1 (close ratio) M20 rather than a standard M20 - all of the rest is the same assuming the box you have is original to the Commodore - I think all of the remade XU1 input shafts are replicas of the VB Rally car input shaft with the neoprene front seal, not the old scroll/slinger type seal like most XU1 had. But the same problem would exist anyway with any aftermarket normal M20 input, you'd have to confirm your box isn't an older one out of a HQ with the early seal.

They aren't that hard to pull apart, inspect and replace bits. The most fiddly thing is the needle rollers, but a piece of wooden dowel the same size as the layshaft and some grease or Vaseline and it is easy. You can do it on a 300mm wide plank across two stools.

Much appreciate the reply, I'll seriously consider your point of view and I now what you are saying makes sense. I've got a while before I get to play with it again so gives me time to consider my options. I'll have to see if I can find a manual on the Aussie 4 speed box to see whats involved and how to rebuild.

Edited by lemonaro, 08 February 2023 - 09:08 PM.

[RallyRed]

Theres a couple of these by old mate...
https://youtu.be/UGgWGSnqzmE

[claysummers]

I rebuilt one of the similar 3 speed all synchro recently and just used the Gregory's manual as a reference. I have the VH Gregory's manual and can scan the relevant pages if you get stuck. No doubt someone on here will have the factory version though.

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[Bigfella237]

Was there ever such a thing as an M15 three-speed VH Commodore??

[yel327]

No. After HZ the 3spd only remained in WB and from memory only in 6cyl applications.

Edited by yel327, 09 February 2023 - 05:16 AM.

[claysummers]

No. I used the HKTG Gregory's for the three speed. It has the 4sp as well but I also have VH manual which is more current for your box I think. By no means compressive though.

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Sorry, OPs box.

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[yel327]

HK-HG won’t have Aussie 4spd in it. You want the HQ Maintenance Manual, volume 3. To rebuild a HQ Aussie 4spd is identical to a WB or VK apart from the input shaft seal and the reverse idler construction (it was two piece early on as a 3spd case was used, after a certain time the Aussie 4spd got a unique case so a single piece reverse idler could be used). They are not rocket science, the easy bit is pulling apart and putting back together. The harder bit is knowing what needs replacing by look/touch/feel.
Note also most kits don’t come with one of the circlips, either the one on the input shaft of the one on first gear. Can’t recall which.

[Bigfella237]

Am I right in thinking that the V8 M15 was only ever optioned behind the 4.2L? Was there ever a 5.0L three-speed manual?

[claysummers]

Ok Byron there were two or three 4 speeds in there. Possibly Saginaw, Muncie and opel.

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[yel327]

Andrew,

Not quite. M15 was only ever optional in HK behind 6cyl. From HT to WB it was standard unless another box over-rode it. For example M20 Phillipines 4spd was standard in HK-HG GTS, or HJ Premier was standard with M40. Or if you optioned L31 from HT to HZ an M21 4spd was standard unless auto was already standard.

I think GMH intended to put the M15 3spd as standard on all V8 HT other than V8 GTS, GTS350 and Brougham, as the HT V8 M15 is a higher power/torque box than all the others. It is to a normal M15 as an M21 Aussie box is to an M20 Aussie. It is closer ratio. Basically it appears the intent was if you optioned L31 on most V8 HT you would have kept the standard V8 M15. But that changed and like HQ-HZ if you optioned L31 you also got M21 standard. Those V8 M15 boxes from HT were always sought out by Speedway racers as they were pretty tough boxes.

Clay, HK-HG only have three different 4spd boxes:

6cyl were M20 Phillipines 4spd Opel design (like LC) and M22 (Saginaw with 2.85:1 1st) mostly on HK-HT commercials. M21 was optional on a few 6cyl but not many.

V8 were M21 (Saginaw with 2.54:1 1st).

Both of the above box designs are of little use to help with an Aussie 4spd.

Edited by yel327, 09 February 2023 - 09:52 AM.

[claysummers]

Yes, that's why I offered the VH manual for the 4spd. I used the ktg manual for the 3spd. It's an early one. Smooth case with oil slinger and no front seal.

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[lemonaro]

Theres a couple of these by old mate...
https://youtu.be/UGgWGSnqzmE

Perfect, just watched his videos. Love his work space!

[RallyRed]

Yeah, a tidy shop indeed. Old School.

[lemonaro]

I rebuilt one of the similar 3 speed all synchro recently and just used the Gregory's manual as a reference. I have the VH Gregory's manual and can scan the relevant pages if you get stuck. No doubt someone on here will have the factory version though.

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I also rebuilt a 3 speed box at trade school about 35 years ago. Thanks for the offer of scanning the manual but I do have a VB Gregory's manual and a factory manual also at home which I will look at in a couple of weeks.

[claysummers]

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[lemonaro]

[attachment=103707:gearbox parts.jpg

Just a quick update.

Finally got to pull gearbox apart and found 1 broken circlip and some wear on the layshaft. No wear inside the cluster gear, synchro's all good, all looks pretty good and can tell the gear box has been rebuilt before with signs of silastic here and there, don't know when. 

Did notice that prior to pulling the box apart, if I turned the input shaft clockwise whilst in neutral the output shaft would also turn clockwise as if there was a small amount of drag on the shaft, wondering if this is normal? or should the output shaft not turn at all. I could turn the input shaft and hold the output shaft still no worries. 

Have a rebuild kit ready to go but obviously the large circlip is not included in the kit. Hopefully will put this back together on the weekend or it might be another month or two.

Attached Files

•  gearbox parts.jpg   184.35K   3 downloads

[yel327]

You have found two of the most common issues on these boxes, they are why I recommended you pull it apart! Although I don't think that is a 1st gear circlip. might be one of the others.

 

It looks like that circlip remained basically in its slot, they start to disintegrate. If its a 1st gear one bits go under 1st gear into the slots on the main shaft that the gear runs on. Also damages the nose of 1st gear. So check that part of the main shaft that 1st gear runs on and the nose of 1st gear. Also check the synchro teeth on 1st gear - compare them to 3rd gear. 1st gear teeth always wear out faster.

 

Also check the case hardening on the front of the main shaft and the inside of 4th gear (clutch gear) - it often goes like that layshaft but looks more like pitting as the case hardening is better. That layshaft looks like an aftermarket one, the case hardening wears out really quick on those. We always used to use genuine layshafts but I doubt you'll find any today. I actually bushed a few clusters years ago rather than run needle rolllers on non-genuine layshafts. I'd talk to the guys that build these boxes for decent hp and find out where they get their layshafts from.

 

As for the output shaft turning, it really shouldn't. In neutral the clutch gear just turns the layshaft and 1-3 gears should spin freely on the main shaft - they all spin the main shaft at different speeds when engaged. My guess is 1st gear is dragging on the main shaft where some of the circlip has gone under 1st gear and damaged the shaft. In the picture below, the splines on the right are for reverse and the output drive, the rear bearing is on the next flat surface but the splined bit after that is what 1st gear runs on. Check for damage on this area, make sure 1st gear spins freely when it has a little oil on it.

 

 main shaft.jpg   9.16K   4 downloads

[lemonaro]

Thanx Yel327 for the above advice.

The circlip is the big one that retains the bearing into the adapter/housing located to the right in the pic above. You were right, the majority of the circlip remained basically in the slot, only the 2 ends (one end is not in the pic but is basically the same size as the other broken end) were located in the bottom of the box as I pulled it apart. 

I've had a look at the above mentioned parts and all looks pretty good.

Hopefully with a good clean and a new kit through it, I have a win and have years of trouble free gearbox issues 

[yel327]

Just watch the quality of the layshaft in the kit. And try spinning each of 1st-3rd on the main shaft and see which one is sticking. My money would be on 1st.