PPF bolt "sleeves"??

revhead · Postby **revhead** » Tue Jun 03, 2014 7:41 pm

I have purchased a torsen diff to replace my open diff in the na8 so I have started researching install methods and reading over the workshop manual I have.

One thing confusing me is the mention/image of threaded sleeves around the PPF bolts on the diff side? What are they, how do I remove these bolts, how do I reinstall these bolts without damaging anything?

Surely replacing the diff is something I can tackle myself with a socket set, breaker bar, torque wrench and a support jack?

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manga_blue · Postby **manga_blue** » Tue Jun 03, 2014 8:00 pm

If you're working under car stands it can be a pig of a job because of the weight and the cramped space. The only extra things I'd get are a really good set of stands and a mate who does bench presses. For safety I'd also stack 2 pairs of wheels under the chassis.

revhead · Postby **revhead** » Tue Jun 03, 2014 8:04 pm

I have 4 jack stands, two jacks, and spare wheels. Plan was to have car on stands, one jack to support gear box, and one to support diff?

Going to be difficult for me as this is the biggest mechanical job I have attempted myself aside form standard servicing procedures.

Seems pretty straight forward, i have the manual for torque specs amd guidance. Just iffy with this whole ppf frame thing

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zossy1 · Postby **zossy1** » Tue Jun 03, 2014 8:30 pm

PITA. Mazda really messed up that design.

There are many pics out there if you search. It is difficult to explain until you have done it, but i'll try.

There are two PPF bolts going through the diff. The front one (the one closest to the gearbox) is thicker for half its length, and the rear one is the same thickness throughout. Remove both bolts.

Then... the front bolt hole, on the bottom of the PPF, has a removable sleeve. It is identifiable as it has a slot on both sides of its base that allows you to put a screwdriver (or other similar lever) under it and lever it out. So... get two flat blade screwdrivers, and work both sides out at the same time.

Then... it depends on your PPF but I think the NB PPFs have at least one removable threaded sleeve on the top of the PPF too. This is not the case for NA8s, at least early Torsen 1 cars I think - as I just pulled one out last week and it did not have one. Anyways, if yours has one, the way to get it out is to take your long bolt, thread it a couple of turns in, and then bash the bolt from the underside to punch the sleeve(s) out.

Then... and this is the tricky bit, the thing still won't come off as there is a sleeve going through the front hole *in the diff housing*. This sleeve needs to be pulled down 3-4mm through the housing in order to release the top of the PPF. It is not easy. I have used a few methods to move it in the past but big pliers are one option. If you cant get it to shift, take a flat blade screwdriver and pound it as a wedge into the gap between the PPF mount and the diff, next to the front hole at the top of the mount. Once it is clear of the sleeve (which stands around 3mm proud), the PPF will slide off.

Another way on earlier diffs is to remove the lower PPF mounting on the diff housing itself... but this is also held in place by a proud sleeve through the front hole (one that can't be moved! It is cast and machined into the housing) and still requires a wedge to slide the PPF off.

Either way, it is a $hit of a job. I have done it on jack stands in my garage and it can be done but it ain't pleasant. Give yourself a lot of time to do it, especially if you have not done something like this before. It will take you ages.

manga_blue · Postby **manga_blue** » Tue Jun 03, 2014 8:38 pm

I've had the PPF off my NA8 half a dozen times. I simply have never been able to work out what all the instructions and warnings about the spacers in the PPF are all about. All I've ever done is loosen and withdraw the two long bolts and swing the frame off the diff.

Another word of advice. Mazda added some instructions in the NB8A manual about aligning the gearbox and PPF frame. They apply to NAs as well. Read that section on Page 5-11-6 in the NB8A manual here and have a check of how your gearbox is positioned before you disconnect the PPF at the gearbox end.

revhead · Postby **revhead** » Tue Jun 03, 2014 8:39 pm

Ahhh that doesn't sound fun at all

the car is my daily so the last thing I need is to run into an issue that prevents me from using the car for a couple of days. I may have to hold off until I can get someone to help me, or even someone that has access to a work shop with a lift. Stupid open diff!

Thanks for the detailed info. I will use it while I raid the Internet for all the info and pics I can find.

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manga_blue · Postby **manga_blue** » Tue Jun 03, 2014 9:07 pm

It's only a few hours work. You can do it alone but TBH it's much easier to have someone there with you just when you lower the diff and raise it into place. That means there's someone to pass you levers or tools while you're stuck holding something in one hand or to help hold or position things.

revhead · Postby **revhead** » Tue Jun 03, 2014 9:09 pm

Yeah very true. I might try and tackle it this or next Saturday morning so I have 2 days to try and sort it out

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zossy1 · Postby **zossy1** » Tue Jun 03, 2014 9:51 pm

Phil, check your diff - the sleeves are *supposed* to wedge into the PPF in order to hold it in place and align it properly. The sleeves can be removed with the diff out and they may have been with your diff which is why you don't have this problem.

However, having said that, I have seen at least two different designs for this mounting... there may be another I haven't seen!

zossy1 · Postby **zossy1** » Tue Jun 03, 2014 10:00 pm

manga_blue wrote:It's only a few hours work. You can do it alone but TBH it's much easier to have someone there with you just when you lower the diff and raise it into place. That means there's someone to pass you levers or tools while you're stuck holding something in one hand or to help hold or position things.

If the car is on stands, and the exhaust is out, and the bracing, etc is off, then you can put the diff assembly on a jack, roll it under the car, and jack it up into place. One person job.

revhead · Postby **revhead** » Tue Jun 03, 2014 10:03 pm

That's the plan. Remove everything out of the way, car on stands, place diff below its two mounting points and lift it up to mate it to the chassis and the annoying/confusing ppf.

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manga_blue · Postby **manga_blue** » Tue Jun 03, 2014 11:12 pm

zossy1 wrote:Phil, check your diff - the sleeves are *supposed* to wedge into the PPF in order to hold it in place and align it properly. The sleeves can be removed with the diff out and they may have been with your diff which is why you don't have this problem.

However, having said that, I have seen at least two different designs for this mounting... there may be another I haven't seen!

Now you've got me thinking, Chris. I've got everything that's in the parts catalogue in there, basically 721, 722, 723, 724 and the floating spacer thingy at the top at the back.

Then again there's been this mystery knock in the back for the last 9 years... If I find it and fix it how much improvement will I get in lap times?

I think I need another 2 secs to help me look like I can drive. :roll:

greenMachine · Postby **greenMachine** » Tue Jun 03, 2014 11:27 pm

Dynabolt is your friend.

Seriously.

When we put the new diff in the racecar, and in the GM a few years ago, we rattle gunned the two diff/PPF bolts out, slipped the dynabolt up the hole and tightened it so it gripped the inside of the sleeve, then gently tapped down on the big washer we had put on the dynabolt and ... easy-peasy... well no, it needs a good dose of penetrating oil left soaking for an hour or two to come out easily.

Don't want to put you off, but if your diff has never been out, or the PPF never come off, it may be pretty well stuck. They can be buggers. So I would give it the treatment the weekend before, take that bolt out, squirt the penetrating oil up there, and around the top, bolt it back up and let the oil do its job for a week. On the other hand, if it does slip out easily, you are laughing.

Oh, don't ask me what size dynabolt you need ... :oops:

aka_juffa · Postby **aka_juffa** » Wed Jun 04, 2014 12:03 am

If I may add one comment.....don't drop the diff on your finger.

http://forum.miata.net/vb/showpost.php? ... stcount=39

At least the blood provided some lubrication.

J

Trackphotos · Postby **Trackphotos** » Wed Jun 04, 2014 12:36 am

I did a full diff swap myself a couple of weeks ago in my NB8A. Wasn't too hard, like people have said you just need a few axle stands, flat blade screwdrivers or prybars, a big mallet, and the usual sockets, spanners etc. A jack to lower the old diff and raise the new one removes the need for a second person, although I suppose it would be easier with more hands keeping everything in place. My two suggestions are 1) don't undertighten the diff mount bolts, the clunking sound it causes is kinda scary

and 2) DON'T overtighten the manual adjustment screw when you refit the brake calipers. I wasn't thinking, tightened one up way too far and just about caught that brake pad on fire during the 800m test drive afterward.