Tecno drive tmc40 problem

[chrisroberts37]

I have the above gearbox fitted to my Lamborghini engine. The gearbox has a single nut holding the coupling on the drive shaft which when coupled to the the prop shaft is inside the two couplings. Problem is the nut keeps undoing itself and the drive shaft parts when I put in reverse leaving mm email with no drive at all forward or backwards. I have to take it apart every home it happens , tighten the nut, put lcktite on a bed burr the ends but to no avail. After a while it comes apart again as the nut had loosened and fell off. What can I do to stop this happening?

 

[Tony Brooks]

How are you locking the gearbox output shaft so you can tighten the nut? I am sure the TMC 40 is a hydraulic box so putting it in gear will not work. There are special tools that have pegs that fit into two of the bolt holes or perhaps use a very large set of stilsons on the coupling but the tool would be more positive.

 

Those nuts are usually very tight. maybe someone here has the torque setting required.

 

If you are already locking the coupling then I fear the splines or key/key way on the output shaft and in the coupling may have worn so allow movement between shaft and coupling. If so Loktite make a product that may work. Possibly Stud & Bearing Lock.

 

 

[Grebe]

Other points for further into any investigation.

 

Is it the correct nut?

Is the nut thread in good condition?

Is the shaft thread in good condition?

 

If the thread contact areas are worn you may get the threads to tighten up with your spanner/locking system, but the load through the shaft will cause the 'grip' to fail.  Look up 'Effective thread diameter'

[Boat&Bikes]

Is there room for another nut  so you can lock them together? 

[dor]

3 hours ago, Tony Brooks said:

How are you locking the gearbox output shaft so you can tighten the nut? I am sure the TMC 40 is a hydraulic box so putting it in gear will not work. There are special tools that have pegs that fit into two of the bolt holes or perhaps use a very large set of stilsons on the coupling but the tool would be more positive.

 

I'm pretty sure that the TMC40, like the diabolical TMC60, is a mechanical box with mechanically operated cone clutches.

 

To the OP: A photo of the coupling would be a great help in arriving at a solution.

[Tony Brooks]

8 hours ago, dor said:

I'm pretty sure that the TMC40, like the diabolical TMC60, is a mechanical box with mechanically operated cone clutches.

 

To the OP: A photo of the coupling would be a great help in arriving at a solution.

Cheers for that.

 

Even so simply relying upon the engine's compression to stop the shaft turning I doubt would get the nut tight enough. I would lock the engine by  a mechanical means. Probably by removing the starter and putting a large screwdriver/lever bar into the flywheel teeth.

[Alan de Enfield]

Would the simple remedy of drilling thru' the nut and shaft (or replacing nut with a castellated one) then slipping a split pin in do the job ?

[Tony Brooks]

58 minutes ago, Alan de Enfield said:

Would the simple remedy of drilling thru' the nut and shaft (or replacing nut with a castellated one) then slipping a split pin in do the job ?

That depends upon the design of the coupling. There is a good chance the nut will be recessed into the coupling. Even so if there is wear in the splines/key drilling and pinning may only be a temporary solution. It might eventually sheer the pin.

 

Those nuts are usually self locking nuts nowadays so is  the OP replacing it with anew one or reusing the old one (bad practice)?

 

Until the OP gives us more info we are just guessing what may be wrong.

[chrisroberts37]

I've attached a few pics of the whole thing together and apart.

[dor]

There doesn't seem to be any way of locking the nut.  Should it have a locking tab or lock washer underneath it?  The spline socket looks quite worn which probably doesn't help keep the nut tight if the shaft can rattle in the socket.

If you want to get it really tight, you could use a cold chisel and hammer on the edge of one of the corners, but t helps to have some experience of this or you can make a mess of the nut.  Or use a centre punch on the top of the nut to lock it to the thread.

[bizzard]

It should be a self locking nut. The nut is rather a thin affair, not terribly strong I would have thought as far as its holding power is concered. That big flexible coupling lolloping about can't be helping, especially if the engines a bit out of alignment with the shaft. Those little boxes usually use the cheaper, small, simple, light weight R&D plastic flexible couplings, but I doubt if your shaft would be long enough to fit one of those.

Edited May 21, 2018 by bizzard

[Tony Brooks]

Just from the photos:

 

The dish in the coupling seems not to allow the nut to sit on a flat face, is there a special washer missing?

 

Should there be a washer of any type under the nut?

 

The self locking collar part of the nut looks rather chewed up to me.

 

Too much blue stuff around the nut in the phoot but does the shaft have a slot in the thread that would allow you to stake the collar into the slot (Stake = punch).

 

 

[Boater Sam]

If there is a groove, nick, cut in the end of the shaft, then the nut collar should be staked into it after it is torqued up.

That nut looks knackered to me, get a new one. There should be a cone washer under the nut.

It needs to be tight, I would suggest in excess of 55 ft/lbs, you will have to lock up the flange with a pin wrench or stilsons.

Bearing fit Loctite on the spline will take out any slop but you will have a devil of a job getting it off again after if you ever have to.

[Tony Brooks]

Thanks Sam, my thoughts exactly except I have never worked on one so could not be sure.

 

When I had slop on my Aquadrive splines the distributor said use Loctite so I queried the getting apart bit. He told me getting the part nice and hot with a blow-lamp usually  freed it enough- not tried that bit yet.

My gut feeling is that 55 ft/lbs is a bit on the low side so the OP needs to get the exact figure. I bet 55 Ft/lbs is far tighter than he has got it so far.

[Iain_S]

It does look like a very well used staked nut. On the third picture it looks like there is a semi circular recess on the shaft for staking purposes. These nuts are really single use, as when they are re-assembled the previously staked bit ends up in the same place. 

[Flyboy]

2 hours ago, Tony Brooks said:

Thanks Sam, my thoughts exactly except I have never worked on one so could not be sure.

 

When I had slop on my Aquadrive splines the distributor said use Loctite so I queried the getting apart bit. He told me getting the part nice and hot with a blow-lamp usually  freed it enough- not tried that bit yet.

My gut feeling is that 55 ft/lbs is a bit on the low side so the OP needs to get the exact figure. I bet 55 Ft/lbs is far tighter than he has got it so far.

The manual says to torque the nut to 125nm.  which is 92 ft lbs. There is no mention of any locking so I assume it's a self locking nut.

 https://allpa.nl/media/manuals/Technodrive/TM/Workshop Manual/Workshop manual TMC 40P.pdf

[Tony Brooks]

2 hours ago, Flyboy said:

The manual says to torque the nut to 125nm.  which is 92 ft lbs. There is no mention of any locking so I assume it's a self locking nut.

 https://allpa.nl/media/manuals/Technodrive/TM/Workshop Manual/Workshop manual TMC 40P.pdf

I don't think it is, it looks very like a nut to be locked by staking and Sam seems to have confirmed it. I suspect Technodrive assume that anyone dealing with the gearbox knows about and recognises the need to stake the nut flange.

 

I would have guessed around 100 ft lbs so that confirms the torque figure you give.

Edited May 21, 2018 by Tony Brooks

[bizzard]

Just googled a photo of the back of that box, defineatly a stake nut. Photo won't upload.

[Flyboy]

1 hour ago, Tony Brooks said:

I don't think it is, it looks very like a nut to be locked by staking and Sam seems to have confirmed it. I suspect Technodrive assume that anyone dealing with the gearbox knows about and recognises the need to stake the nut flange.

 

I would have guessed around 100 ft lbs so that confirms the torque figure you give.

Looking at the state of the nut, a new one is definitely required.

[WotEver]

1 hour ago, bizzard said:

Just googled a photo of the back of that box, defineatly a stake nut. Photo won't upload.

Shows clearly here...

[Iain_S]

10 hours ago, Tony Brooks said:

Just from the photos:

 

The dish in the coupling seems not to allow the nut to sit on a flat face, is there a special washer missing?

 

Should there be a washer of any type under the nut?

 

(snip)

 

Just had another look at the photos, and it looks as if the corners of the nut have been catching the sides of the recess. Also, comparing the picture of the assembled nut with the picture of the gearbox posted by Wotever, your nut is going a couple of threads further up the shaft than it should. Therefore, as Tony suggested, there is a special washer missing. Without it, the torque figure on the nut is meaningless, as it will unscrew a lot easier than it will screw, while cutting its way into the recess. 

 

So, new nut and washer, Loctite on the splines (or new flange) if its a wobble fit rather than a sliding one, correct torque to 92 ftlb, punch the nut collar into the shaft recess, and it'll never come apart again ... (unless you want it to)

[Flyboy]

10 hours ago, Iain_S said:

Just had another look at the photos, and it looks as if the corners of the nut have been catching the sides of the recess. Also, comparing the picture of the assembled nut with the picture of the gearbox posted by Wotever, your nut is going a couple of threads further up the shaft than it should. Therefore, as Tony suggested, there is a special washer missing. Without it, the torque figure on the nut is meaningless, as it will unscrew a lot easier than it will screw, while cutting its way into the recess. 

 

So, new nut and washer, Loctite on the splines (or new flange) if its a wobble fit rather than a sliding one, correct torque to 92 ftlb, punch the nut collar into the shaft recess, and it'll never come apart again ... (unless you want it to)

There is no washer shown on the assembly diagram in the manual. The nut appears to have a step machined on the face to enable the hex. on the nut to clear the flange. Adding a washer may stop the nut getting a full thread on the shaft. 

[bizzard]

Washers are very often not used under nuts and bolts anymore. With just two perfectly machined surfaces,'' the nut-bolt and whatever they're holding gives better grip with only one surface to slip and let go instead of two. Car manufacturers have used this policy for most main mechanical things for a long time now.

[Tony Brooks]

As I don't know the box I can only go by the photos. Whilst I agree with Biz about precision face to face fitting there appears to be slight difference between the photo posted by Tony and the photos from the OP.

In Tony’s photo you can clearly see what looks like a flat face and clearance around the nut.

 

Although the OP does not show a photo of the coupling nutted onto the box it looks to me and presumably to Ian as if the corners of the nut will foul the dish/taper in the coupling. However Flyboy says there is no washer shown in the manual and I tend to go by manuals rather than individual opinion so I wonder if there has been a modification and the manual is for a later edition of the box.

 

I think at the least the OP needs a new nut from Technodrive so they are as sure as they can be that it is correct. Whilst ordering it they can confirm exactly what is fitted to his box so he may need a gearbox number. Then hopefully he will come back and tell us.

[bizzard]

6 minutes ago, Tony Brooks said:

As I don't know the box I can only go by the photos. Whilst I agree with Biz about precision face to face fitting there appears to be slight difference between the photo posted by Tony and the photos from the OP.

In Tony’s photo you can clearly see what looks like a flat face and clearance around the nut.

 

Although the OP does not show a photo of the coupling nutted onto the box it looks to me and presumably to Ian as if the corners of the nut will foul the dish/taper in the coupling. However Flyboy says there is no washer shown in the manual and I tend to go by manuals rather than individual opinion so I wonder if there has been a modification and the manual is for a later edition of the box.

 

I think at the least the OP needs a new nut from Technodrive so they are as sure as they can be that it is correct. Whilst ordering it they can confirm exactly what is fitted to his box so he may need a gearbox number. Then hopefully he will come back and tell us.

Although washers are still generally used on things that have highly differing temperature ranges,'' movement'', like cylinder head bolts. Washers are often not used on things like, drive lines, bell housing bolts, certain suspension items and other temperate things.