NVH - placement of gearbox in transmission tunnel

[ScottR400D]

55 minutes ago, AlastairA said:

I was thinking of ChrisC's comments here:

 

 

As Chris implies, alignment wasn’t the issue. His prop was failing. 
If you research the alignment issue you’ll see it needs to be far more out of line than  a 7 would ever be. 

[AlastairA]

Apologies for my lack of clarity - it was the following that I was referring to and I was just suggesting to the OP that it might be worth checking it is fitted:

 

• ChrisC
• Member
• • 2.3k

 

Posted November 30, 2021

I have it in writing from CC, it was added for clearance between the chassis and the gearbox.  If you think that statement through, that means clearance is marginal without it, something that's been known for some time.  Given the price and how easy it is to fit, for me it's a no brainier, on any pre 2021 5 speed Mazda boxed car, especially if your working on the car in that area.

That said, the reason it dramatically reduced my cars noise wasn't because of clearance, it was because it altered the prop working angle slightly, which combined with a faulty front UJ meant a reduction in noise and vibration.  Ultimately my car was only fixed of vibration and unexplainable noises with a prop replacement.  
 

As Chris implies above - clearance between the chassis and gearbox is marginal without the spacer.

Edited April 30 by AlastairA

[ScottR400D]

25 minutes ago, AlastairA said:

Apologies for my lack of clarity - it was the following that I was referring to and I was just suggesting to the OP that it might be worth checking it is fitted:

 

• ChrisC
• Member
• • 2.3k

 

Posted November 30, 2021

I have it in writing from CC, it was added for clearance between the chassis and the gearbox.  If you think that statement through, that means clearance is marginal without it, something that's been known for some time.  Given the price and how easy it is to fit, for me it's a no brainier, on any pre 2021 5 speed Mazda boxed car, especially if your working on the car in that area.

That said, the reason it dramatically reduced my cars noise wasn't because of clearance, it was because it altered the prop working angle slightly, which combined with a faulty front UJ meant a reduction in noise and vibration.  Ultimately my car was only fixed of vibration and unexplainable noises with a prop replacement.  
 

As Chris implies above - clearance between the chassis and gearbox is marginal without the spacer.

And as he says the clearance or lack of wasn’t the issue. 

[ScottR400D]

Still waiting for HWMs words of wisdom. 
 

 

[Peter_V]

On my 2024 build the gearbox is tight everywhere but without the spacer it would be resting on the lower chassis rail on the LHS. So not an alignment concern but worth having for clearance if you have issues at that same point. Picture of gap to chassis.

[ScottR400D]

So no enlightenment from HWM? 

[JAL73]

They are currently working on the car. I popped in to see them yest pm, the technician had just left for the day but the service advisor seemed to be of the opinion that the gearbox can be realigned to NOT touch the tunnel. There is clearly some space for the gearbox to move into on one side, whether its enough space to fully clear all points of contact on the other side where its touching remains to be seen.

They also showed me my gearbox mount which had the small spacer already sitting in it, it looks like its only a few mm thick. Also my gearbox mount was slightly bent in places where it attaches to the chassis so thats being replaced, im also going for new engine mounts as they are not expensive. 

Hopefully I'll have the car back on Friday so will have a definitive answer then.   

Still not had an anwer as to whether the circled appendage (see bottom pic below) is required for Caterham or is a redundant item from fitting to a Mazda MX5 or similar. If that can be removed and blanked off it would certinaly help. Anyone on here know if its a critical part for Caterham fitment?

Edited May 1 by JAL73

[ScottR400D]

Fair enough. I hope this is warranty stuff? 

[Jonathan Kay]

2 hours ago, JAL73 said:

Still not had an anwer as to whether the circled appendage (see bottom pic below) is required for Caterham or is a redundant item from fitting to a Mazda MX5 or similar. If that can be removed and blanked off it would certinaly help. Anyone on here know if its a critical part for Caterham fitment?

Please can someone remind us how Mazda describe this gearbox.

Thanks

Jonathan

[SteWi]

From a French 275S manual it is referred to as an M15M-D

[Peter_V]

2024 build 420R 5-speed the mazda box said M53F-03-000

[aerobod - near CYYC]

M15M-D is the Mazda transmission type, M53F-03-000 is the Mazda part number for that transmission. Here is a link to a manual for it: https://www.mellens.net/mazda/Mazda-Miata-2005/manual_transmission_5spd.pdf

[AlastairA]

5 hours ago, aerobod - near CYYC said:

M15M-D is the Mazda transmission type, M53F-03-000 is the Mazda part number for that transmission. Here is a link to a manual for it: https://www.mellens.net/mazda/Mazda-Miata-2005/manual_transmission_5spd.pdf

This is really helpful - thanks!

The manual refers to adding sealant when replacing plugs - would Loctite 243 be suitable (concerned about being able to remove for alter services of course)?

[Jonathan Kay]

Thanks for the part number ID and the manual.

I can't be sure from the pictures... is it a blanked off speedometer port?

Jonathan

[Ainsley]

So you were not missing the spacer then, but the gearbox mount was bent ?

I'm not sure how you can move the gearbox, its not like the holes in the chassis, mount or gearbox are slotted.

 

[ScottR400D]

1 hour ago, Ainsley said:

So you were not missing the spacer then, but the gearbox mount was bent ?

I'm not sure how you can move the gearbox, its not like the holes in the chassis, mount or gearbox are slotted.

 

I think you can occasionally lever it against the mounts and tighten up and hope it stays. As you imply though, something will be stressed. 
 

I’m still far from convinced it’s relevant. 

[JAL73]

So I got the car back and I’m very disappointed.
 

ScottR400D and Ainsley seem to be correct. 

Garage told me they had moved the gearbox clear of the tunnel walls, but it’s still in EXACTLY the same place. Engine mounts and gearbox mounts were replaced and it’s made no difference to NVH. The old mount had the spacer in it, as does the new mount.

As Ainsley pointed out the gearbox mounts are not slotted for side to side adjustment, only fore/aft. The gearbox mount itself is asymmetric with the mounting channel offset to the passenger side so it seems Caterham has deliberately chosen to have it skewed to the passenger side tunnel wall for some reason?!?
If the mount was symmetrical or offset the other way I guess the gearbox would be set more centrally in the tunnel.

 

Why Caterham has designed the mount asymmetrically I’m not sure, maybe to keep the gearbox output flange parallel to the diff input flange? 

The only way to get everything sitting perfectly in the middle of the tunnel would be have asymmetric engine mount arms and/or a symmetrically scalloped gearbox mount. This would keep the gearbox and diff flanges parallel I think and prevent touching. 

Anyway, this issue seems to be common to all Duratec/Mazda gearbox cars. See the video below from 5:25 which perfectly illustrates this. Interesting to note Caterham inserted a recessed cutout panel in the passenger footwell to try to accommodate this but mine is carpeted so I was unaware of it until seeing it at the end of the video below. 

Finally, I had a look at an S3 chassis car from  below whilst at the garage and the gearbox seemed to touch on BOTH sides, I guess because the tunnel is even narrower than on my SV chassis. I’ve never heard of S3 chassis cars having more NVH than SV chassis cars, so as ScottR400D suggested maybe the gearbox touching the tunnel wall is a red herring in terms of NVH because it’s just touching the heatproof padding and not really applying any pressure to the metal tunnel wall behind it thanks to the recessed cut out panel, though the jury is still out on that one for me…

Edited May 7 by JAL73

[ScottR400D]

As long as you have a Titan LSD in there, which being a 420R I assume you have (you’ve avoided confirming every time I’ve asked) you’re never going to get even reasonable ‘NVH’. 
The thing is the diff is bolted pretty solidly to the chassis. From it emanates all sorts of grunting, harshness and vibration. The engine and box are pretty closely coupled too so there’s little chance of refinement of any level. 
The angular alignment is a complete red herring flashed about to distract from the real issues. 
I've driven and experienced several 7s with the Titan diff and of course the Tracsport which was my final resolution. I never found one that was acceptable in terms of noise and harshness until the Tracsport was fitted. 
 

[Ainsley]

[JAL73]

Yes mine is the sintered plate titan. 
my understanding is that the titan LSD really only makes a noise when cornering and the clutch plates are engaged, my noise happens in a straight line and i though it was more likely crownwheel and pinion noise rather than the Titan going straight. 
 

I’ve been in a car with a tracsport diff that was even noisier than mine and other cars with Titans that were much quieter than mine, so I’m not sure in my particular case the Titan is the culprit 

[Ainsley]

Try new / different oil in the diff.

[ScottR400D]

CWP noise is down to the CWP nothing to do with the LSD, it’s just set wrong. 
Yes theoretically the LSD shouldn’t make a noise in a straight line but the slightest cornering will have it protesting. Mine certainly made all sorts of noises going ostensibly straight. But then in hindsight I think mine was basically FUBAR at just 4/5k miles. 
In contrast I can’t detect any LSD noise from the Tracsport. I get the CWP overrun chatter which most of us do but no CWP whine or any other noise from the diff. 


. 

[SM25T]

2 hours ago, Ainsley said:

It's not just noise .... the whole car is buzzing !!

[Ainsley]

You sure you have some rubber engine mounts then ?

[JAL73]

yes, new engine mounts and gearbox mounts, and new Redline diff oil as recommended by Road&RaceTransmissions. 

Was out in a friends roadsport which has a 2L duratec with 420 cams but not lightened flywheel. It has a ford 5 speed box (doesnt touch tunnel walls) and open BMW diff. That car had almost no NVH, no chattering on over run, silky smooth and very fast.