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Issues with Borg Warner M76 5 speed

Started by _mick74lh_ , Jul 05 2015 08:47 PM

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#1 _mick74lh_

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Posted 05 July 2015 - 08:47 PM

G'day guys,

The M76 5-speed gearbox that I'm running in my 6-cylinder VK daily has started making horrible grinding noises whenever I start the car up from cold in neutral - sort of sounds like a synchro trying to mesh. So I flick the car off again for a couple of seconds and start it again, and it runs okay - except while I'm driving there is a subtle sound like something loose or lightly trying to mesh when it shouldn't while driving.

I've done about 90,000kms now since putting this gearbox in and really flogged it the whole time, so truthfully it has been great, but I can't really afford to go spending for something better at the moment.

I'm thinking of pulling it out to rebuild it.

If anyone has had experience with these gearboxes, can they please suggest firstly what might be the cause of the issues described? Obviously I will only find out what is truly wrong by pulling it apart and inspecting but if anyone could even provide pointers as far as disassembly, bits which should be looked at, and reassembly go that would be great.

Yes, it does have plenty of oil in it. A few pointers would be really appreciated before I pull it out and dismantle it.

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#2 rodomo

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Posted 05 July 2015 - 09:02 PM

You #@$^%& it.

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#3 _mick74lh_

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Posted 05 July 2015 - 09:29 PM

You #@$^%& it.

Haha thanks Rob! Its still going, just not sure how much longer it will go for now its doing this.

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#4 rodomo

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Posted 05 July 2015 - 09:34 PM

I have 2 of them and a manual to fix em.

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#5 UCSLE

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Posted 05 July 2015 - 10:06 PM

are you sure its the gearbox and not something like a clutch bearing or the starter motor not disengaging properly ?

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#6 hawk

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Posted 05 July 2015 - 10:14 PM

Is it the thrust bearing? Had a guy at work with a similar problem in his commodore and thats what it was

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#7 _mick74lh_

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Posted 06 July 2015 - 08:15 AM

It'd be great if that's all it was. My first thought was starter not disengaging properly. So will have to check that first. The thing's about due for a new clutch so I guess it's possible there could be something broken. Thanks Troy and Steve for the suggestions. I guess the only way to find out is to pull it out and look.

I have 2 of them and a manual to fix em.

If I'm stuck is there any chance I could borrow the manual?

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#8 _reefhog_

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Posted 09 July 2015 - 07:04 PM

Those boxes are very weak, which is why they didn't use them behind the EFI 3.3. They came with the trimatic only. The cheapest thing would be to find a second hand box that is still in good nick. Might be hard to find though. I wouldn't spend money fixing one,.

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#9 EunUCh

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Posted 09 July 2015 - 07:50 PM

the 0507 xxxx (m76) were also behind 3.3/4.1 XE/ZK falcon/fairlane.

You won't get a rear extension housing bush anywhere, (get one made or make one out of bronze bushing material) , the tapered roller bearings that hold the shafts in place are nothing special , the end float (sort of critical) on both shafts is set by shims from the bellhousing end and they are NLA, (make them as well,much fun) , the bolt that holds the overdrive gear in place is a left hand thread job, (TO REMOVE IT,TURN THE SPANNER IN A DIRECTION AS IF TO TIGHTEN a right hand thread(normal) bolt/nut ), not much too them...literally...they don't look very strong when you see the size of the gears compared to an m20/21...but if it has copped a caning so so far...?

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#10 rodomo

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Posted 09 July 2015 - 09:42 PM

, the tapered roller bearings that hold the shafts in place are nothing special , the end float (sort of critical) on both shafts is set by shims from the bellhousing end and they are NLA,

I've been told that this pre-load IS critical and should be set above factory specs given that preload will reduce virtually instantly as load comes on the bearings and as soon as it starts "working".

You're welcome to the manual Mick................................If I can find it?

Having said that, I haven't pulled either of mine apart to look at the gears?

Is your noise foot on? or off? the clutch in neutral?

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#11 _mick74lh_

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Posted 10 July 2015 - 10:42 AM

Thanks for the advice fellas. I haven't had time yet to pull it out. Hopefully it'll keep going until I get the chance. The initial grinding noise was in neutral, clutch out, and the other subtle rattling is clutch out, both idling in neutral and in gear while driving.

I'm hoping to pull it apart late next week. Are there any critically important diagrams or specs in the manual Rob?

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#12 rodomo

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Posted 10 July 2015 - 11:35 AM

Dunno? I haven't looked that hard at it.

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#13 Steve TPF

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Posted 10 July 2015 - 06:28 PM

I've got a copy of the manual. 35 pages. Can get housemate to scan if you want.

Seeing as you can't buy them new any more I don't think there's any harm in sharing.

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#14 Steve TPF

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Posted 10 July 2015 - 06:34 PM

From the manual:

"Noisy in intermittent gears and in neutral:

1: Incorrect axial end float of the mainshaft or counter gear

2: Gear tooth shape variations or damaged gears

3: Damaged bearing"

Any of those will require a teardown to fix. You can still get the overhaul kits but its probably cheaper to get a rebuilt M20. Of course that means sacrificing 5th and you'll need a longer tailshaft.

I'll see if I can get the manual scanned but it won't help you unless you are willing to spend the time/cash to fix it.

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#15 _mick74lh_

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Posted 11 July 2015 - 02:28 PM

Hey Steve thanks very much for that. If you are able to get it scanned that'd be awesome.

I really prefer to keep the 5 speed as I'm running 3.45 diff gears from a VL now and it'd scream on the highway if it didn't have overdrive. So prefer to rebuild this one. Hopefully its salvageable. If not could I buy one of yours off you Rob?

Been driving it today and touch wood it's still going - just need it to go a little longer before pulling it apart.

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#16 Steve TPF

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Posted 11 July 2015 - 05:04 PM

Housemate says he'll scan it tonight when he's not busy.

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#17 rodomo

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Posted 11 July 2015 - 06:30 PM

Sorry Mick, mine aren't for sale....................maybe in the distant future?

Both are unknowns anyway.

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#18 Steve TPF

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Posted 11 July 2015 - 08:01 PM

Manual is scanned, but photobucket won't accept PDF files. Give me your email address and I can send it to you. Might take a few emails but at least you'll have it.

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#19 Steve TPF

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Posted 12 July 2015 - 10:33 AM

Page 1

Attached Files

CCF.pdf 678.3K 34 downloads

Edited by Steve TPF, 12 July 2015 - 10:33 AM.

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#20 _mick74lh_

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Posted 19 July 2015 - 07:50 PM

Thankyou very much Steve. Sorry I haven't been on the forum for a few days.

My email is [email protected]

I'll be getting Rob's hard copy manual also, so that could be adequate information if you're unable to upload/send the whole thing. Apologies for not keeping track of this thread.

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#21 Steve TPF

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Posted 19 July 2015 - 08:48 PM

No probs. I tried to post it here but all posts after the first got added to the one above and replaced the pic WTF?

Anyway, will send to you via email so you have it.

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#22 Steve TPF

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Posted 19 July 2015 - 09:02 PM

Sent, let me know if it worked.

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#23 _mick74lh_

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Posted 20 July 2015 - 09:11 AM

Sent, let me know if it worked.

Yep, that's awesome. Thankyou very much.

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#24 StutUCTorana

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Posted 28 March 2021 - 01:24 PM

Hi.

Is there any chance someone could email this manual to myself.

I have an M76 semi disassembled and would like to tray and reassemble it correctly

[email protected]

Thanks in advance!