Gabriel

Hi everyone, I can't find any info on this, it seems like no one has had this issue...

I called Martin to ask him how hard it was to use the 8.8s with his kit, and he told me, the only difference is i have to weld the front plate instead of bolting on... otherwise it should be no issue.

so, I bought the 8.8, now received my first box from Martin, and the diff mount is definitely not going to work.... (pics posted below)

I tried to call Martin this morning, but understandably it is Saturday and I'm unable to reach him. Was he supposed to send me a different mount? did I just end up with an odd differential?





Either way I'm a bit bummed out as i'm now assuming I either bought the 8.8 for nothing, OR have to fabricate my own mount even though I paid for the kit so that i wouldn't have to... any info would be appreciated.
Thanks.
Gabe.

cvx_20

A quick look at Rockauto shows the differential cover gasket, which corresponds to the cover where Martins bracket bolts on, is indeed different from 7.5 to 8.8. Check 92 Tbird.

I can't imagine it would work, I would think the bracket would have to be different. I've never actually seen a 7.5 in person, but the pics I've seen show it to be different than the 8.8.

HTH, Mike

Gabriel

Ya I'm realizing this...

I called Martin twice before buying to make absolute sure it would work... so this is a bit annoying.. I'm wondering if Martin has 2 different hangers depending on the diff and he accidentally sent me the wrong one... I'll find out when i get a hold of him hopefully monday..

tbone heller

He sent the wrong one.

Gabriel

Thanks tbone! I figured it must have been that...

annoyingly enough it cost me a ton in brokerage fees to get the kit across the border!! now to send it back... uurrhh...

charchri4

Yep that is a 7.5 mount. the 8.8 looks like this..
Jim and Jenna build diary, Miata LS1 Conversion: The other half of the back half

For what it's worth if I was to do it again I would not have used either of these mounts though. I would have built one that is easier to adjust and sits on poly bushings rather than the Tbird caged mount. But that's just me, Martins set up is a good mount.

Gabriel

charchri4! thanks for that link - great write up!

when I spoke to Martin about the 8.8 a few weeks back I misunderstood that the kit was the same, but required welding for the 8.8, and since these diffs were interchangeable in the t-birds, and since I had no idea how his hanger was made, it made sense that it would be the same hanger for both diffs... otherwise i would have made certain to remind him just before he sent me the first box! as i can tell he's a very busy man and probably forgot about our convo about the 8.8 i was buying.

so maybe something to note for future newbies that may read this thread, if going with 8.8, and Martin's kit, make sure to let Martin know and remind him that you're using the 8.8 before he ships you the first box of the kit as the hangers ARE different.

Gabriel

Update on the situation - got a hold of Martin this morning and he is shipping me an 8.8 hagner, suggested I hold on to the 7.5 for now he may or may not get me to ship it back.

so all is well! MY 8.8 will live to see the sun rise as it looks from under the backend of a 1990 miata!

Thanks everyone for the input.

MRM331

The mm mount does work with poly bushings. Mine's installed with two upper Miata bushings and two front Ford ones.

-Jason

cvx_20

But that's a 7.5 mount that uses the Miata biscuits and bolts solidly to the rear end housing, right? The pics Jim put up show a very different rear mount setup that uses the stock Tbird funky looking rubber mount and a welded on bracket.

I personally don't like the Tbird rubber mount, which led me to this:

MiataV8 Conversion: Rear subframe

Mike

charchri4

Jason I think this is the first time I have ever thought you were, eh, well not completely 100% right about something...

Yes the 7.5 is a great design and poly bushings are readily available for the front and back of it. However MMs 8.8 design is completely different and built around the factory tbird rear mount. Technically you can get a poly version of the rear tbird cage mount but it's like 350 bucks. I just ran a couple of bolts through mine to stiffen it up and called it good.

I am as big of fan as anyone of Martins work but I would never advise anyone to use his 8.8 mount. This is the way it should be made IMO MiataV8 Conversion: Rear subframe Easy, clean and very adjustable.

charchri4

Yep


^ Not mine web photo but looks about the same as this.

The rest is my Monster supplied stuff.

Gabriel

cvx_20, awsome write up on your build, looks great.

I'm curious, why is it that no one seems to like Martin's 8.8 mount using the stock Tbird rubber? is it too wobbly? not stiff enough?

MRM331

So the above pictures are of Martin's 8.8 rear or your design? I'm sort of confused.

-Jason

charchri4

Jason I added the center gusset on the rear mount and the 2 gussets on the front mounts other than that it's all Monster 8.8 stuff.
Just to be clear I also added the front to back connectors at the lower control arms too but they have nothing to do with the diff mount.

IMO the front mount is OK (with the added gussets) but the back mount makes no sense. It’s huge and a whole lot of horsing around to use the stock Tbird rubber and the only possible advantage I can see is it might be a little eaiser to open up the diff with it still in the car.

Gabriel yes the stock Tbird rubber cage is soft and my mount came out of a 95 supercoupe so between the age and hitting it with twice the torque IMO it is not the best choice for a mount.

I was very dissipointed when I opened up the box from Monster and saw this. Besides it being $1100 in a tiny box I never expected to see this mount. No matter how you slice it the 7.5 mount is a much better design.

MRM331

Sorry about that Jim. I worked on a 8.8 equipped monster Miata conversion a few years ago and the mount was essentially the same as the 7.5 mount in form, it just held the diff a little lower. He must have changed it to gain more ground or exhaust clearance. That's a shame as I felt the beauty of Martin's original design was that it takes the Ford differential housing and basically modifies it to work with Mazda's superior mounting system. I don't like that mount at all but maybe there is something going on structurally I'm not aware of.

Martin, if you are out there could you comment?

-Jason

charchri4

Looking at Gabriels mount in post one I think you may be on to something Jason. With the cross bar above it like that I bet that would hang down much farther than my set up. Martin may have changed the mount along the way to gain clearence and perhaps he figured guys would have the stock rear mount anyway so he may as well put it to use. I can see how this could come to be.

It will be interesting to see what shows up in the mail for Gabriel.

cvx_20

It seems to me that the placement of the original Miata mounts [in this adaptation] puts the mount way too close to the center of rotation of the axles, reducing the ability of the mount to resist the torque forces trying to twist the rear end. The incorporation of the Tbird mount may be an attempt to gain back some of that leverage, and in that event, the Tbird mount is probably superior. It's just ugly and way too floppy.

Mazda's superior mounting system included the PPF and the front mounts as well. Eliminate them and the system is somewhat less superior.

Mike

Gabriel

I will certainly update everyone with a few pictures of the new mount when i receive it, however since i'm leaving on vacation in a couple weeks, I had Martin hold the 2nd box for now so that it doesn't show up when i'm gone... as it can take over 2 weeks to get here accross the border.. so we'll have to wait until then to see what it looks like

charchri4

Mike you have a really good point I that had not thought about. The newer mount puts the load on the rear of the frame rather than the center of it on the original Mazda mount. Being 6 inches farther back than the center mount has got to give it a much better leverage point against the axle torque.

Another thought I had about changing it is he is using the same axle shafts from both the 8.8 and 7.5 so maybe using the overhead mount put the 8.8 too low for the length of the axle shafts. Perhaps guys with really lowered cars had problems with the shafts being too long and moving the diff higher corrected that.

Also a good point Mike on the PPF and something I thought about when I did all that bracing back there. That PPF makes a huge lever against the torque for sure and it bothered me it was not there. But I did waffle on it because the Tbird managed without one and surely put more torque on the diff than the Miata ever did. Still a couple of hunks of tube from the rear frame to the chassis makes an easy fix so the madman with the welder strikes again!

Yeah I know it's a bit harder to drop the rear frame now...

So if the goal was to move the mount from the center to the rear frame and move the whole thing higher, I still see no reason to use the big Tbird rear mount. To me it would have been easier for Martin to just do the same thing on the back as he did on the front with the flat plate adapter. It may need to be a tad shorter but it would work and easy to use the same poly front bushings back there. He would just need make a bracket to hold the bushing and attach to the 2 large holes in the rear of the diff.

We should send a link to this thread to Martin so he can give us the scoop...

Gabriel

Next time i talk to Martin, i'll see if i can get some info on this and post it, I'll also mention the thread to him if he wants to come chime in

MRM331

I had to think about this for a while because I always thought the larger left-right placement of the Mazda mounting points would give the mount more leverage. I didn't realize that you were refering to the torquing of the axles, not the drive line. From that point of view this does make more sence and I suppose may actually help eleviate wheel hop.

Anyone with more than my armchair level of engineering knowledge wish to comment. I'd really like to find out more about this.

-Jason

Gabriel

Hi Everyone!!

So i got a chance to chit chat with Martin about this tonight. and hopefully i can remember enough of this conversation to shed some light here. He informed me that his 8.8 hanger is the product of much trial and error, as is the 7.5 hanger. First of all, the style of the 7.5 would not work on the 8.8 due to the size 8.8, the 2 inch bar in the mount that goes above the diff, would lower the 8.8 where it would no longer be in optimum alignment with the transmission.

He also noted that one reason he originally designed the 7.5 hanger to not utilize the stock T bird mount, is primarily because he didn't like the idea of having novice DIYers that were purchasing his easy-to-put-together kit, have to perform a critical weld of such an important part. --I suppose the front torque plate is easier? not sure-- Also, he liked the idea of keeping the diff fully visible, for aesthetics, instead of hiding it behind the hanger, as the 8.8 hanger kind of does.

THAT being said - since that style of hanger could not be used on the 8.8, he proceeded to design the hanger to work as it did on the T-bird.

And last important point - the reason he did not use the 2 small pieces welded directly on the stock rear frame with round poly bushings - doing away with the tbird bracket - as shown in the link that Jim posted, is because in his opinion, that stock frame is not strong enough, he said previous similar mounting methods caused several of his customer's cracked stock miata rear frame mount... so his mount as you can see is welded along that frame, ------ing the load out along it... as opposed to smaller pieces that would start ripping off (the way I understood it), and would end up causing a fair amount of damage before someone would notice it

He is supposed to send me a picture he took back in the day of a customer's rear frame that was severely damaged from nothing but the torque imposed through the differential, if he does get around to sending me this, i will post it.

well, there was much more detail coming from him, but this is about all i can remember!! lol

tbone heller

That makes sense to me.

charchri4

No question he has a proven track record and a good R&D process but in this case I think he missed the mark. His mount puts the entire load beyond the rear edge of the frame and even with the center gusset I added the legs are only welded to 3 areas of sheet metal.

IMO it doesn’t take more than a handful of common sense to see which mount centers the load and supports the frame better.