Mazda gearboxes....... (some b'stard told me it was impossible so I had to do it!)

[Fuelish]

Nick, nowhere near what you achieved to maintain the original position.

This is what I managed today after picking up a Mk1 box and following Manana's example. Need to shorten the tube and selector shaft but, this slides freely. Need to make a rear support bracket but have shortened it 148mm (could make it 6" easily enough) which I think will be fine for me and it also means no major surgery to the handbrake position.

Also ground away the side were the PFF mounts, think I will also mount it the using original holes again, as Manana. So much easier when you follow some one else's hard work - thanks both!

 

[Nick Jones]

Quick work!  I think it is the smart way to go. Modifying the tunnel is much easier than re-inventing the shift mech!

[manana]

Nice work there Fuelish.  When we did mine we left the shifter rod in there and slid the Change Control Case forward until it hit the case, then it was really easy to see what needed to be trimmed to get a snug fit against the casing.  Of course the biggest thing to look for is free movement of the rod.

Nick, I know that you are past the notion of relocating the Hand Brake, but in case you're interested in the details of how I did it, I've added that section to my site.

https://stevew10.wixsite.com/spit16/copy-of-fuel

Looking forward to seeing yours in action.

 

 

[Fuelish]

I did follow your example and could have ground the top of the casing a little more and cut 2mm more off the front of the 'shifter' housing but for me a relatively disproportionate amount of work to gain 1/4". One thing I have been fortunate with is the seal on the rod tube; I managed to ease this off gently one end without damage. Now the tube is cut down to bridge the gap I can reuse the sleeve seal with some blue Hylomar or vulcanising glue. 

Have read you blog on moving the handbrake with interest. I have something planned here as trying to go for rear discs but want proof of concept before opening my mouth 

[Fuelish]

Brief update with all bits ready for final assembly, shortened selector moves freely and shaft tube seal is glued back on with rubber solution. Not gone overboard with a super strong rear support but it is rigid, using one bolt hole and an original centre dowel to locate. Bracket needs a tidy and like to use Zinga to protect.

Look forward to NJ's solution for an 'as original' position.

[manana]

Nice, you're actually further forward than me.  Shaving down the case got you a bit more. TU.

Nick, I'm wondering if you are going to put a dog-leg in your shifter like the Spit has?  It may be very close to the panel, no?

[Nick Jones]

Nice, quick work Fuelish. Looks good.

3 minutes ago, manana said:

Nick, I'm wondering if you are going to put a dog-leg in your shifter like the Spit has?  It may be very close to the panel, no?

Yep. Lever needs a kink in it or you punch the dash.

Prototype. Both sides of the kink have been shortened since this pic was taken. It’s actually very similar to the stock GT6 one.

[Nick Jones]

I wrestled the box back out and did some clutch related measurements in the bell housing. The flywheel and backplate went onto the spare engine and got measured too, as did the chosen slave assembly which is from a Vauxhall Omega as recommended by Marco on the TRR forum.

He’s done a lot of work on concentric slave cylinders for TRs and more recently his own MX5 gearbox conversion. Detailed thread on it here with lots of useful info 

https://www.tr-register.co.uk/forums/index.php?/topic/68790-hydraulic-clutch-release-bearing-for-tr4a-tr6/&tab=comments#comment-616926

This showed that things were tight and would only be possible if the clutch set height (rest position of the diaphragm fingers relative to the flywheel face) was in a fairly narrow band. I bought a new 215mm Mazda clutch plate (8.4mm thick uncompressed)and measured the finger position compared again. I also measured with no friction plate at all and with the most worn one I could find (7.6 mm thick uncompressed) all of which gave me some understanding of how it works.

The other question was how much stroke is needed to fully release. Having failed to find anything published, I plonked a flywheel/clutch assembly on the mill table and used that to compress it until I could easily move the friction plate.

6mm.

With those numbers I could draw myself a picture to see if it could work.

Yep. Still tight, but possible. Time to bother some metal.

[Nick Jones]

The object is to build something that accepts a bog-standard slave assembly as a direct bolt-on.

It needs to be accurately concentric with the gearbox shaft.

As space was extremely tight, the gearbox bearing cover/guide tube needed shortening - quite a lot. In fact to the extent where I did wonder about making a new one from scratch before deciding that it was too fiddly and the scope for cock-up on the concentricity front too great.

Matters were complicated by the thing being too big to swing on my rather small lathe. So out with the mill turntable again. That meant making a little spigot to centralise the casting on it, which was easy enough and worked very well.

Then I had to make an adapter plate. This couldn’t be more than 5mm thick overall and needed a 1.3mm tall spigot in the centre to locate the slave, so I used steel.  A piece of 100mm wide x 5mm flat(ish) strip.

First step was to drill and bore the central hole on the mill and then make it roughly round with the grinder before popping it one the lathe. Was a bit fiddly and time consuming but came out ok.

It’s centralised by being a snug fit on the slightly slimmed-down and shortened stump of the guide tube. It sits on the remnants of various casting features and will be further supported by 4 spacers picking up on mounting bolts as I’m not certain how able the now fairly thin casting is to take the clutch thrust load. Probably overkill, but easy enough to do now.

[Escadrille Ecosse]

All looking rather smart Nick

[Nick Jones]

Thanks. I’m quite pleased with it so far. Pity it will be well hidden.

So long as it works and keeps working, I’ll be happy.

My main worry is that because the CSC has a fairly strong spring in it to keep the bearing in constant contact with the clutch fingers, even a small amount of runout will quickly cause problems (destruction of the CSC most likely).  I think this last lot of work is pretty much bob-on, but the same need also applies to the bell housing adapter etc and I’m less confident about that.

Possibly the spring in the CSC could be removed but not quite sure how that would go....

The other question that arises is how well the fairly flat faced release bearing (designed for use with curved spring clutches) will play with a flat spring clutch.......

Might have done better with the Saab CSC but the decent ones are fearsome expensive..... and they have a much shorter working range without their basic length being any less.
 

 

[Fuelish]

Impressive job! People don't always appreciate all the hidden work underneath, just shinny paint! 

[Nick Jones]

Sunday was cold. Garage temperature 2C, but at least it was out of the wind.

I did venture out long enough to make the 4 spacers from a length of aluminium bar stock.

They sit like so

I made them very slightly long so the plate sits about 5 thou above the centre pad. This to ensure load is taken by the spacers first. Seemed like a good idea at the time.

I milled the bolt pads on the original casting first so they are all identical thickness and spent some time making sure all the spacers are the same length. I’m serious about getting everything concentric and perpendicular.

Of course this means four of the OE bolts are now too short. Some rummaging among bolt stocks found three that are absolutely perfect in every way .... I need four though..... There were four, I remember where they came from, what I can’t remember is whether I used the other already of if it’s “at large”. There is a lot of “stuff” in my garage......

[Nick Jones]

I’ve been adding pipes

The selector thingy got heat-treated (maybe), cross-drilled/tapped and the neutral switch hole plugged with a chopped down M14 bolt.

Have done a test re-assembly to check I’d got the cross-drilling (yep, thankfully, the age of miracles is not quite past) it all came apart again so I could give the rear case a final swill out before fitting the selector shaft oil seal. It’s a strange size hole @20.5mm,  so a 20mm seal falls in (and out) but 21mm is flipping tight. Got it eventually after making a tool.

Mostly assembled. Made some covers. Not intended to be oil tight but should keep the wort of the grime out.

Even got a little plug for the end. It’s got a 1.5mm hole at the top to allow it to breathe as the shaft moves.

Getting quite close now.

[Nick Jones]

I’ve been adding pipes

The selector thingy got heat-treated (maybe), cross-drilled/tapped and the neutral switch hole plugged with a chopped down M14 bolt.

Have done a test re-assembly to check I’d got the cross-drilling (yep, thankfully, the age of miracles is not quite past) it all came apart again so I could give the rear case a final swill out before fitting the selector shaft oil seal. It’s a strange size hole @20.5mm,  so a 20mm seal falls in (and out) but 21mm is flipping tight. Got it eventually after making a tool.

Mostly assembled. Made some covers. Not intended to be oil tight but should keep the wort of the grime out.

Even got a little plug for the end. It’s got a 1.5mm hole at the top to allow it to breathe as the shaft moves.

Getting quite close now.

[Nick Jones]

Time to try the 'box on an engine with all the clutch parts in place.

Didn't have a centering tool to suit the Mazda sizes so I made one

Who needs splines......

Performing its duty

Apparently it worked.

Then poke the phone inside to see how things were sitting. 

The bearing is definitely in contact (which it should be), but can't see how compressed it is.  The engine still turned over fine - no funny noises from the bell.

Will do some more measuring tomorrow to double check.

[Nick Jones]

Run out of excuses to put it in properly.....

quick photo line-up first though

Our victim is the one in the middle....

It then got wrestled into place (I'm getting better at it, and I had help) without incident.  I didn't take another at home pic, but it looks like it did before.

The I remembered that I had to finish to angle drive as the back of 'box needs to be lifted quite high to fit it in.

Seems to work well....... hope it really does as it was fairly fiddly to do and getting at it will be a big job.....

Once that was in I could drop it down on the mounts and fit the prop. (it's the middle one again)

Then the interesting part.  Connect up and bleed the clutch.  Access is a bit of a sod, and that's my own doing, though the options weren't that great.  Seemed to bleed ok but the clutch pedal is ridiculously light.... and it doesn't actually release...... Bled it some more and got a little air out, but not really any different.  I did stick my hand inside the bell (carefully!) and have an assistant work the pedal.  It was stroking.  Because the action is so light throughout the stroke it's not completely clear when it actually starts to take up, so it's not impossible there is still a little air in it.  If I put a big screwdriver in the UJ yoke  I find can turn the engine with it with the clutch up, but the clutch just barely slips first with the pedal mashed to the carpet.....  Need more stroke....

.......But the calcs say I should have enough and some to spare....   My tests on the exact same clutch parts bolted to the same flywheel showed that 6mm was enough for complete release and the current hydraulics  (5/8" M/C) should give just over 8mm.  I've been discussing this with Marco over on the TRR who has been using the same slave cylinder for TR conversions with great success, even with the 5/8" M/C and he seems convinced there must be a some air still in there.  So, I will try a couple of different bleeding tricks and if that doesn't work, I'll try a 0.7" M/C.  The bigger M/C might also produce something that my left foot actually recognises as a clutch because at this point it's the lightest pedal action I've ever encountered.

 

[manana]

Nice,

I was astounded at how light the Miata clutch was when I did my swap (all Mazda parts).  I had forgotten which parts you were specifically using for that, but it seems that from your post on the 6th of Nov it's the Miata stuff.

I guess the good thing is if you find that you need more binding force and go with an aftermarket clutch, a stiffer clutch pedal won't be much of an issue.

[Nick Jones]

Hi Steve,

It’s actually a standard 215mm Borg & Beck Vitesse/GT6 cover with a 215mm Miata friction plate to give the correct spline. Same cover as was fitted before. Wasn’t heavy then, but very much lighter now. 1 finger. Literally.

[Gt64fun]

54 minutes ago, Nick Jones said:

1 finger. Literally.

That is going to require a novel driving technique!

[Nick Jones]

Looks like I need a 0.7” cylinder which will up the weight a little....... but yep, will take some getting used to. Especially in contrast to the Vitesse which is fairly weighty.

[Nick Jones]

Bloody exhaust doesn’t fit anymore. Box is lower and now occupies some of the space the exhaust wants. Not much, but enough to be a nuisance. Tried a spacer (6.5 mm with gaskets) between manifold and down pipe. Better but not enough.... I knew it was going to be close, but was hoping not so close. Bah!

 

 

[Gt64fun]

Nick

I had a mandrel bent stainless front section of my exhaust made by Torque Technique in Wilton ((Mick Poulton), to replace a truly awful crush bent mild steel one. Could be made to ease your clearance issue. www.torquetechnique.co.uk 01722 744747

Ian

[Nick Jones]

Thanks. He’s handily close to one of my customers as it turns out.

Did he keep the strange wiggle of go more direct? Presumably the strange wiggle is to provide drain plug access, but the plug is 8” further back on the Mazda box.

May have a slightly ghetto solution, but would be nice to do something nicer in the longer term once the swap is proven. The whole system is the standard steel one as came with the car so is on the “for development” list anyway.

[Gt64fun]

Hi Nick

Pretty much the standard shape, but tweaked slightly to get the back of the pipe on the actual centreline of the car. Really nice bends, but the flange was a bit disappointing and needed some fettling. I thick premade flanges may be readily available.

Ian