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my new gearbox? (Mazda MX-5 to TR)


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Ups, the adaptors are already delivered, I'm really surprised about the laser cut surface! Tomorrow will be first fit, please keep fingers crossed for me.  

Thanks Russell and Andi, thank you very much, all worked well, fit was 100% on first attempt, the 8 mm drills are exaxtly to the point they have to be for the 5/16" bolts! Btw, the bar is on

Talking of gearbox changes, back in the 8o`s when I was involved with Jaguar racing we converted a V12 XJS from a GM 400 auto box to a Cosworth T6 manual 5 speed by a cut and shut of the two bell hous

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15 hours ago, Z320 said:

hope this is not an endless and boring story to you, if it is, please be gentle with me.

You must be joking Marco! I am certain that I am not the only one fascinated by your skills and vision to be able to attempt this project. Each posting is like an advent calendar awaiting the next day to see what chocolate you have.:D keep it coming.

Paul

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24 minutes ago, Harbottle said:

You must be joking Marco! I am certain that I am not the only one fascinated by your skills and vision to be able to attempt this project. Each posting is like an advent calendar awaiting the next day to see what chocolate you have.:D keep it coming.

Paul

I can;t wait till the 25th to see the baby Jesus turn the Ignition key and select 1st gear  :)

 

Roger

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Ok,

so you can open another door on your advent calendar today,

but I'm not shure about baby Jesus or me turning the ingnition key already on Dez 25th....

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Currently I'm not pleased about my pipe routing design (to direct, not enough length to have +/- 1 cm)

and I'm not shure about the best position for the bleeding nipple and the connector.

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Perhaps I have a look on the car from below from the pit.

Ciao, Marco

 

Edited by Z320
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Hi Marco

What about using some long braided pipes and clips fastened to the two bolts in the picture to allow for vibration between the box and car body before going with hard lines.

Andy

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Just one other thing to consider Marco from experience is the 10 or 11 grade 8 "green" long cross case bolts which thread into the bell housing. These have a tendency to shear as they meet the bell housing. I used to swap them out for 12.9 grade cap bolts as the case flexes even in standard power form, any increase in torque sees them fail in a domino succession, some you can get out without dropping the box out (in a MX5) but those that are captive its a box out job.

2 hours ago, Z320 said:

best to get the gearbox in the car is end with two connectors screwed in the gearbox housing....

Makes sense but would mean four joints rather than two. 

Andy

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Hi Andy,

I don't know the original Madza bolts, but they must be indeed 10 or 11 of M10 or M12 and at least 2 dowels.

If you tell me they shear of - they do, but I can't expain myself why. By accident my bolts are indeed 12.9 grade.

The connections are no problems,

they will be less than you maybe expect and the pressure in the clutch system is only max 16 bar (my own calculation).

So it will not be a problem to get them sealed, if this is your worry?

Ciao, Marco

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Correct just thought that having two less joints to leak would be better as you can almost guarantee if you have a leak it will be the one that's the most difficult to get to!

The bolts shear as the case flexes due to the helical gears forcing the case apart even in normal use the bolts will occasionally fail. Once you put more torque through them more so. I don't know how much torque a 2.5 Engine produces but if its more than the Mazda engine it will eventually be a problem.

I was pushing about 320ft/lbs through these boxes in the end by changing the bolts the case stayed together but then the 4th gear would then be the weakest link.  

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Hi Andy,

thank you to expain again, now I understand what you mean:

I have the 2 connections in the gb bell on the hydraulic unit which I cannot avoid and which could leak,

and two more on my connections in the gearbox housing which I chould avoid by using hoses or pipes through the housing, as I did on my TR gb hydraulic units.....

Shure It would be better to go this way, thank you,

but to keep attention on the hoses / pipes going through the gb while getting it in the car is annoying,

and I never and any leak hydraulik connection, so I further will go this way.

But for others this may be an idea to do it different.

Today I ordered the rear flexible TR gb mounting at Rimmer and hope I get it before Christmas.

I waited too long to order because I also see other options, while to modify the original mounting could be the best way.

Ciao, Marco

 

 

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Good morning Andy,

after sleeping a night over your suggestion and 3 mugs of coffee I decided to go your way,

I will guide the pipes directly through the gearbox housing, the connectors and bleeding nipple will be outside.

Thank you very much for your advice, Marco

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Your welcome Marco I and many others have taken a lot more from your posts and look forward to reading your progress reports.

Andy

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40 minutes ago, PodOne said:

Your welcome Marco I and many others have taken a lot more from your posts and look forward to reading your progress reports.

Andy

++1

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On 12/15/2020 at 7:34 AM, Z320 said:

but they must be indeed 10 or 11 of M10 or M12 and at least 2 dowels

I think he means the long bolts that hold the 4 sections of the gearbox casing together.  These are M8 x 160 (either 8 or 10 of them, I forget) plus two dowels.  Coincidently I bought some today, but that was because I need two slightly longer as I'm using the top two to hold my new selector mechanism on.

Having a bit of a nightmare arranging the rear mount - very limited space on the GT6!

Ordered an Omega slave cylinder this week.....  I think the Saab one could also work.

Nick

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Hi Nick,

I don't know much about the Saab hydraulic unit,

but by the photos at eBay it seams like there is only ONE pipe connection,

so bleeding is special but I have an idea how it could work with a special "beeding unit" outside the gearbox.

The piston (ring) of the Opel Omega (Sachs) unit is d = 35 x 46.7 mm, some suppliers tell the Saab one with 34 x ??.?? mm,

Means: you have to cut one millimeter more off from the Mazda guiding cylinder and I expect it will not fit at all the TR gearbox shaft.

The Opel Omega (Sachs) unit is a good choice.

Ciao, Marco

 

 

Edited by Z320
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I had a Saab one in my hands last week.  This is the earlier one that fits 99, 900 etc.  For the most recent Saabs seems to be the same unit as Corsa C, Astra and others.  Maybe they even interchange (some listings seem to imply this) but not identical.

They have two connections, side by side, both 10mm.  In the 99 and 900 applications there is a bleed nipple fitted directly into one of them as the unusual layout of the Saab means that it is exposed and accessible but no problem to extend.

Overall dimensions are quite similar to the Omega one.  Centre bore is a bit smaller so the Mazda guide tube would have to be cut off.  It has no loading spring - or maybe this is just because the one I saw did not have the external gaiter fitted (which seems to include the spring on the Omega one).  Also seems to cost more in general, even though it is supplied without the release bearing.

Will be experimenting with this as soon as I complete my rear mount - after consulting your previous write up very carefully!

Nick

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Hi Nick,

to take the unit in pieces you best move off the gaiter (this only hides the spring, it is not inside the gaiter),

than take a sharp knife and make one cut throught the plastic ring to take it off, than bolt out the screws.

When you see it you will understand.

I'm ready today with my multible threaded connectors (stainless steel), the upper ine is to bleed the system, the lower is to bolt the clutch hose on.

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Next I make the (stainless) steel plate to bolt on the gearbox,

have to look for the sketch from my hydraulic release bearing project from last year, hopefully I filed it....

 

 

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21 hours ago, Nick Jones said:

I think he means the long bolts that hold the 4 sections of the gearbox casing together.  These are M8 x 160 (either 8 or 10 of them, I forget) plus two dowels.  Coincidently I bought some today, but that was because I need two slightly longer as I'm using the top two to hold my new selector mechanism on.

 

Correct those are the culprits.

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Hi Andy and Nick,

here you see the 4 sections of the gearbox, one dowel and 4 bolts M8 on the left side, the same on the right side.

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Which one of them brake, please?

And in combination with which engine?

Ciao. Marco

Edited by Z320
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Hi Marco

One of the two bolts on the top of the box go first then the others follow in a circular pattern.

My engine was 1.6 115bhp with no mods had one fail as soon I went to 250bhp it was a fairly regular occurrence so swapped them out for 12.7 cap bolts which solved the issue even at 350bhp and 319ft/lb of torque. They are generally very strong little boxes. Mazda's original design for the MX5 was to team it up with a V6. Wish they had!  

Andy

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I found my sketch,

this it is from the front

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Rear

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With the adapter plate on the MX-5 gearbox

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The pipe routing

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It needs some modification of the design.

Ciao, Marco

 

Edited by Z320
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hydraulic pipes are ready

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as Andy recommended I have now only 2 connections in the gearbox bell

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I want to have TÜV in May 2021 with the TR gearbox in the car - and then swap over to the MX-5 gearbox because of my historic registration.

So I guess I should slow down the project or soon have nothing to do for the next months ..... :lol:

Ciao, Marco

 

 

Edited by Z320
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