23 replies to this topic

[RallyRed]

Hi,

 

Wondering if anyone has had this particular issue - 

 

Aussie 4 speed, rebuild 12m ago. Was running perfectly.

Rebuilt by a guy who 100% knows what he is doing, did 2 boxes for us. The other one is perfect.

New bearings and gears as required etc, new synchros. New oil.

Was all good for around 10 months. Car has only done about 200 road km and about the same on circuits.

The crunchy-new started as minor, and could be covered up if you heel and toed it. Now it just crunches, regardless.

Pulled the box out and drained the oil...99% brand new.

Selectors all good, shifter good.

If I select 1st, 2nd, 3rd, 4th  up and down with my fingers inside the actual box, it all happens smoothly and gracefully.

No evidence internally of any metal to metal type activity. Gears & Synchros look brand new.

 

Before removing the gearbox , jacked up arse end of car with it in gear, and got a mate to try and rotate the rear wheels, and yell out when they moved, ( as I pressed the clutch in.) = about 1/2 way between foot off the pedal  - and pedal on floor. Assume this is good.  No drag once disengaged.

 

Have not removed bellhousing and clutch to inspect, as don't see a need to?

 

Only thing I have found even slightly iffy is the main input bearing seems sloppy...strange, as it is clearly new.

Could that slop transfer down the shaft and cause enough misalignment to cause the crunch as gears slide into the required selection?

TIA

[claysummers]

As long as the snout is a snug fit in the spigot bush a bit of lateral play in the end of the shaft is normal.

How about trying some fresh oil with Morey’s additive, shift improver etc?


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[LCK186]

Hi it sounds like a syncro mesh may have split 

[RallyRed]

Ta Clay....this box has the fully shot peened, isotropic treatment etc and they normally shift as smooth as a baby's bum.

This box shifted perfectly and has just degraded regarding the crunch, fairly quickly with low kms.

 

We have 2 boxes the same, done up roughly the same time, using the same processes. The other one has done more, harder work and is perfect. Both boxes run the same oil. Penrite Transgear 75w - 90 Semi syn. 

 

Thanks for the idea re the smooth shift additive, have used that previously and believe it works. Just can't get my head around why this box is doing it and the other one isn't. An internal inspection has them looking identical inside.

 

The gearbox guy is away ATM, and I don't know enough to start stripping it, well I do.........but putting it back together correctly is a different issue altogether.

 

Current plan is to swap the other/good box into this car and see if the problem is still evident..i.e. clutch issue? or if it's definitely the crunchy box.

Col

[RallyRed]

Hi it sounds like a syncro mesh may have split 

Ta mate...is this evident to the naked eye, without stripping it?

p.s. excuse my total ignorance....but is the 3rd to 2nd synchro a different part to the 2nd to 3rd one? i.e. the 1 and 2 gears are at the output end of the box, and the 3 and 4 gears at the front? 

Sorry if that's dumb.

[S pack]

Ta mate...is this evident to the naked eye, without stripping it?

p.s. excuse my total ignorance....but is the 3rd to 2nd synchro a different part to the 2nd to 3rd one? i.e. the 1 and 2 gears are at the output end of the box, and the 3 and 4 gears at the front? 

Sorry if that's dumb.

Hi Col.

You would have two cracked syncro rings for it to be crunching when selecting either 2nd or 3rd gear, one for each gear.

I doubt it is syncro rings as 2nd gear is on the same syncronizer hub as 1st gear and 3rd is on the other syncronizer hub with 4th gear.

I think best to get the box back to the guy who reco'd it and get him to check it over.

My first thought would be clutch not disengaging fully but it seems that it is disengaging ok albeit a bit further off the floor than it should.
 

[RallyRed]

Thanks Dave....reckon thats what I'll do.

[axistr]

Col check the end float in the syncro hub assembly. If a circlip has moved the end float can cause the issue your experiencing.  

[tuxedoss]

Who did the rebuild ? I’m looking to get one rebuilt by someone who does good work . Preferably in NSW

[RallyRed]

Col check the end float in the syncro hub assembly. If a circlip has moved the end float can cause the issue your experiencing.  

Ta mate....

[RallyRed]

Who did the rebuild ? I’m looking to get one rebuilt by someone who does good work . Preferably in NSW

Sorry, no good on that one mate, he is retired, and is now retiring altogether.
No longer doing them.
Just finishing the last of his existing jobs, supposed to be fiinished by end Sept.

[tsn007]

Andrew Grima from Lithgow just did mine

 

[RallyRed]

Nice work Tony...good to have a second ( new) source.  Thanks.

[rodomo]

Col check the end float in the syncro hub assembly. If a circlip has moved the end float can cause the issue your experiencing.  

Sounds like the hub or mainshaft has popped a circlip.

[RallyRed]

OK, I just need to be clear on this Hub thingo.

Can that be checked in situ or does it need to be dissasembled? Can you circle it in a pic? Ta

Thanks

 

Also wondered about the clutch, but cant see anything wrong there, and it seems to disengage ok at garage speed.

The pics show funny marks on the plates, but I think these are just left over from painful maneuvering the car in the garage/off the trailer etc?

 

Also, I tried to find data on the P/P and plate, but PBR seems hard to find?

Closest replacement in Exceedy would be the GMK 6074 HDTOY or HDBTOY?

 

Thanks

 

 

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[S pack]

Col, the syncronizer sleeves slide on the syncronizer hubs to select 1st and 2nd gear on one hub and 3rd & 4th on the other hub.

If a circlip had broken allowing a hub to move on the mainshaft I would expect you would have difficulty selecting one gear only eg: 2nd gear but not 1st, and 3rd & 4th would not be affected as they are on the other hub. In your circumstance you would need to have two broken or dislodged circlips, one for each syncronizer hub.

A broken mainshaft circlip retaining the 1st & 2nd gear syncronizer hub was a fairly common problem with these boxes but most repairers machined the groove in the mainshaft to accept a sturdier circlip.

I believe GMH eventually adopted this modification into production.

 M20 parts.jpg   321.56K   9 downloads

Edited by S pack, 02 October 2022 - 04:21 PM.

[rexy]

Sounds like clutch to me.

[RallyRed]

Ta Dave, and thanks to everyone who suggested the syncro hubs ( cant see anything wrong there, have eyeballed and poked around to compare this box against a perfect one ).

I am liking the clutch idea, not sure how it manifests itself, but assume there is not full release, even though it seems good in the shed).

Plan is  -

1. take the pressure plate and clutch to a clutch place on Tues and get advice.

Will then either get a new Exceedy, or declare clutch ok, and get back onto the gearbox guy for advice.

Will also consider throwing the original clutch & perfect box into this car and see if problem still there...i.e. must be the clutch.

Thanks again.

.......buy a Torana....get a hobby.

[Ice]

Surely you must have a river close by 

[RallyRed]

...don't want to pollute a river with this stuff

[axistr]

If the clutch pressure plate was giving problems and not disengaging properly you would have problems shifting into reverse and difficult getting any forward gears. If the clutch plate centre or spigot bearing was faulty than 4th gear shifting would be an issue. The circlips retaining the mainshaft rear case bearing and gear hub did have issues on these boxes.

 

Because the problem is isolated to 2nd gear, check for a cracked 2nd gear syncro ring and clearance between the gear and syncro ring when pushed up to the gear. Check any 2nd gear or 2nd gear hub assembly for end float by using a screw driver and leaver them in both directions, and finally you will have to strip the box but have a look at the 1st / 2nd gear hub energizer springs and locking pals. Ensure the pals are correctly aligned and spring not broken, moved or popped off the three pals.  The problem will most likely lye in one the areas listed above.        

[RallyRed]

Thanks mate, good info.  

To be honest the car has sat for a while, so I only recall the 2nd and 3rd issue. Maybe the other gears were sketchy too.

Will drop the clutch into a shop tomorrow to have it assesed, then will scope out the gearbox.

[Pallbag]

Andrew Grima from Lithgow just did mine

 

How much was the rebuild and how much involved .. the entire box?

[RallyRed]

Just a little follow up one this one.

 

For good measure we did replace the clutch plate, pressure plate and a new thrust bearing. Checked the shift fork etc.

Re installed box, adjusted to factory spec ....still the same. Crunchy in 2nd only, when going from 3rd..

 

Can get rid of it by doing a double clutch, which to me is just a human synchro i.e. covers up the fact that the synchro is not working properly.

Yesterday arvo, did a quick box swap to the other recently rebuilt box.  

Perfect. No crunch.

Thus...as suggested, the original box must have a 2nd gear synchro issue.

Probably obvious really, but I just didn't this a new box would suffer it. 

 

For those asking who does them in NSW, I have found a place called ATC in Wagga, seems to have a pretty good rep. with race boxes etc, They have a full suite of mods for track work etc.