Mx5, Chapter 2

[The American]

Doh! Where I've written "RE03S" in the two posts above, read "RE11S"...

[smy0003]

Ahhh okay was searching around for more I do in the re03s. From memory the re11s is advertised as a track only tyre whilst the a050 is legal in the road (as ridiculous as that would be)?
Interesting discussion about tyre hardness (or softness), seems a bit silly to measure a tyres compound at 25deg when I'm practice they will be operating much hotter than that. Seems to be what you found, good work on branching out and sharing the info!
28psi hot seems a bit low to my uneducated mind, what was the reasoning for that?

Sent from my LG-H815

[rascal]

28psi hot seems a bit low to my uneducated mind, what was the reasoning for that?

I'm running A050 mediums now and Traction Tyres in rowville said for my mx5 running sprints that 28 hot and no more was the sweet spot from their feedback.

I used to run 30-31 on the Nittos and found A050s worked better at 28 than 30. I'll have to drag out the pyrometer for next meet as I reckon I might even go lower based on seat of the pants feel at Winton

[The American]

28psi was recommended to me based on the mx5 being a relatively light car. Doing short sprints, I find this works out to be 26psi cold. So long as I've got 26 or more before I leave for an event, I can adjust to 28hot after the first run. I've got a tyre probe for temps, but I haven't used it yet. Can't have it in the car, don't have pit crew, and often have to idle back to dirt pit bays that have been wet down for dust - by then I think the readings would be junk.

[The American]

Well, I had planned to head to Magpie's place for the Dodgy Day on Sunday, but I got carried away in the garage on Saturday afternoon.
I ended up in the shed attempting to swap in the Super Miata engine mounts. By 9pm, I had the two old engine mounts out of the car and the new driver’s side mount in place. There was no way the passenger side mount was going to come out without removing the turbo downpipe or dropping the sub-frame – I spent rather a long time and plenty of knuckle skin coming to that conclusion. The DP on my set up was fouling the firewall when jacked and preventing the engine from being jacked high enough to create room to remove the mount or to turn it over to disassemble it. Unbolting and dropping the passenger side of the front sub-frame and coil-over ended up being the solution and gave just enough room to get the mount turned around so I could put a socket on it to separate it into two parts, which could then be slid out between the underside of the rail and the sub-frame through the wheel arch. On the driver’s side, I had also removed the intake manifold brace to give more room to manoeuvre the stock mount.

I called it a day at that point and went to bed.

Early Sunday morning, I discovered that the new mount for the passenger side would not fit out-of-the-box. After much wrestling, I gave in and ground about 2mm of material off the upper trailing edge of the mount so that it could sit tight against the block without causing a misalignment of the rear-most engine block mounting bolt hole.

By the time I had both mounts installed, and all the bolts and torqued, and sub-frame re-attached, the morning was gone and I gave up hope of heading out to the Dodgy Day :sad face:.

My tips for the engine mount replacement:

1. Use some mechanics gloves. My 'office hands' look like someone left them in a bucket of angry sand crabs for a few hours.
2. 18" worth of socket extensions and a universal joint will make your life easier.
3. Have a selecting of pry bars/levers handy, and experiment with the jack when trying to align the bolt holes on the block.
4. If I had to do this again, I'd make sure I had enough jacks and stands to support the body and engine and would lower the front subframe from the start. Or I'd just take it to Automotive Plus.

Given that I was already in the garage, the car was already on stands and my hands had already been eaten by angry crabs, I decided to swap in the spare 3.63 T2 and the Energy Suspension Diff bushes while I was at it.
Thanks to the configuration of the axles, the NB is a little more involved than the NA I had done previously. The NA process is simpler because you can unbolt the two-piece axles and remove the diff with the stubs in place. The NB requires you to completely withdraw the axles from the diff while it's in the car. I removed the brake callipers and unbolted the upper A arms to allow the hubs to be pulled out and down, bringing the axle with it on each side. The reverse of the process involved pushing the upper A arm up and out of the way, and then guiding the axle into the diff, ensuring that the splines engaged, and then pushing (firm shove) on the hub to slide the axles and circlips into place.

My tips for the diff removal:

1. At the gearbox end of the PPF, leave the forward most PPF bolt in place (loosened), but remove its rearward twin and bolt that goes into the bracket that attaches to the PPF to the tail of the gearbox. Once you've detached the PPF from the diff, you can then pull the PPF and driveshaft to the side and out of the way. I used a length of rope to tie them to the driver side LCA.
2. The little collar in the diff housing that must slide down to disengage from the top of the PPF at the diff end, may appear stuck. It moves more easily if you lift or jiggle the nose of the diff up and down.
3. Drain the oil from the old diff before you attempt removal (not necessary if it's an NA with stubs that unbolt and stay with the diff during removal)
4. Use a wide based trolley jack to raise and lower the diff and carrier.

Long story. Short version, the new diff and poly engine mounts and poly diff bushes were all on the car by late afternoon Sunday.
Given that I had gone for the stiff poly option at both ends, I was expecting my car to have transformed into an intolerable Rattle Monster. It actually was not too different to the feel of my two diesel-engined cars, one of which is my daily. Lots of internet babble and the vendors themselves caution against putting the solid urethane mounts into a daily car. If you’re goal was to maintain factory NVH, then you would not do it. However I would not say it is intolerable – we will see if anything falls off.

Back to the diff…

Before the last event, I drained the oil from my old Torsen and refilled it with lightweight shockproof. The oil that came out had a lot of golden sparkles (brass I assume) and there were a few chips attached to the magnet on the drain plug. When I drained the oil again for the removal, there were again chips on the plug but the oil looked ok.
I turned the new and old differentials over by hand on the bench and they were quite different in feel. The old one feels quite coarse and you can hear a bearing that is not rolling smoothly when just turning it by hand. By contrast, the new one is absolutely silent and smooth. I will pull the old one out of the housing in the next few days to see if I can see what ails it. If the ring and pinion are ok, it will become the base diff for a future clutch-pack LSD.

[ManiacLachy]

I'm so glad I got Dann to do my engine mounts!

The diff bushes are on my list for one day (you just beat me to Minx's) Are you running poly control arm bushings too?

[The American]

I'm sure a real mechanic would laugh at my description and get the job done in a 1/4 the time it took me.

All my suspension bushes are stock at the moment. It is not something I have explored as yet because the existing bushes have not seemed to be a problem.

Apparently a full kit of polysuspension bushes can cause binding. If I get back to exploring that in the future I will re-read Madjak's thread.

[Magpie]

So glad you opted to do the engine mounts and diff at home and not on the dodgy day

[pepejesus]

All my suspension bushes are stock at the moment. It is not something I have explored as yet because the existing bushes have not seemed to be a problem.

Apparently a full kit of polysuspension bushes can cause binding. If I get back to exploring that in the future I will re-read Madjak's thread.

I know I link to a lot of miataturbo.net stuff, but why re-invent the wheel when someone has done all the hard work for you (if I can mangle a metaphor): http://www.miataturbo.net/suspension-brakes-drivetrain-49/miata-bushing-megathread-heirarchy-diy-delrin-dimensions-info-discussion-87573/

[The American]

I know I link to a lot of miataturbo.net stuff, but....

That thread is a good read!

[pepejesus]

Go spherical or go home!

...says the guy with stock rubber bushings.

[The American]

I popped the diff out this evening expecting to see at T2, and there was this instead:



This looks like an OBX brand torque sensing differential to me. The internet has plenty of commentary about the belleville washers dying, so much so that some replace them when new. Apparently what happened to mine is standard failure mode for these.

There's even a bloke in the US who's made a business out of selling rebuilt kits http://rbryant.freeshell.org/obx_washers.htm for $40US posted.

With this diff as it is now, the innards of the LSD can be moved in and out quite a lot, which is what I was observing with the axles. The rest of the diff appears to be in good shape.

[Okibi]

Great website and write up, ordered a kit?

[The American]

Go spherical or go home!

...says the guy with stock rubber bushings.

I'm sure I will find my way to some upgraded bushings at some point, particularly given the stickier tyres!

[The American]

Great website and write up, ordered a kit?

Not yet, but I will get on to it. One of the things the internet mentions is that the gears can be dropped in, reversed which is the alignment required for FWD, which if used in RWD, leads to accelerated wear of the washers that sit in the middle. Given that mine went from fine to fail relatively quickly, I am curious...