I have one in my hillclimber that seems a bit tired. I'm having trouble finding a guide to rebuilding the thing though.
I know we had a member rebuild one recently but I can't find the thread nor whether they posted up steps of how they did it.
Reveal yourself, and help me make the most of my 10" slicks!
86-88 (clutch) or 89-91 (viscous)
both manuals available here: http://foxed.ca/index.php?page=rx7manual#secondgen
here is right from mazda's contingency site under tech info. And it looks like they spelled hypoid wrong.
Differential See General Information - Setting Up the Ring and Pinion - Installation Tips General Information
As a rule, differential temperatures should stay below 200° Fahrenheit range. Consistent temperatures above this level can reduce the service life of the limited slip and differential significantly.
A new differential and limited-slip unit should be broken in over a period of approximately 200-300 miles. Operating temperatures that slightly exceed 200° F during this period are normal. A 9OW hyoid gear oil should be used for the break-in period. Thereafter, we recommend switching to a synthetic gear lube that is compatible with limited-slip differentials. Torsen-Gleason differentials do not require limited-slip gear oil. Setting Up the Ring and Pinion
Use the stock factory specifications in your shop manual for adjusting the ring & pinion. Attaining the proper tooth contact pattern is essential to obtaining the optimum service life from the ring & pinion. For racing purposes, a tooth pattern that contacts at the edge or "toe" side of the teeth is preferred. This type of contact pattern will make more noise than a "centered" contact pattern; however, it will reduce the chance of tooth breakage. Gear marking compound will provide the most accurate display of the ring-to-pinion gear tooth pattern.
After obtaining the desired tooth pattern, follow the recommended preload specifications in your factory service manual. We recommend use of a new crush collar each time you rebuild the differential. Replacing the pinion bearings is also recommended. See the Mazda Special Tool section in Appendix A of this website for a listing of differential tools available (to be added at a future date). Installation Tips
When installing a limited-slip unit, new side bearings should be purchased, as old bearings are normally damaged when removed.
If you are installing the competition limited-slip unit in a 1980 or earlier model, the axle shafts must be modified. Remove 1/8" from the inner end of each axle.
Also, I know that you can run a tighter lock up in the S4 gen by adding an extra clutch pack, there is also mazdaspeed components that make each disc .1mm thicker and more robust springs/bearings etc.
edit: now I finished reading the title, S4 clutch type. dur
Somewhere I have a '88 RX7 FSM with the specs and stuff. I'll see if I am smart enough to email you the relevant pages.
Section 9 page 30 (9-30) is the section on LSDs in the FSM you can read on the Foxed page Fidelity linked to. Mazdatrix has the stock clutch plates as well as upgraded stock plates if you're looking for stronger lock-up. Of course, if you're a Mazdaspeed Motorsports member, you can get the plates for much cheaper (provided Mazda still sells them).
http://www.mazdatrix.com/g8lsd.htm
Cheap rebuild:
Disassemble, scuff all of the plates, make sure they are installed in alternating order (sometimes they're not!), install a .010" diff shim on one side. Usually that's enough to bring a dead one to life.
I have two .010 in the car right now, I also have two tubes of limited slip additive and the thing still "talks" when it slips, which is rarely. One of these days I'll grow a pair and just put a welded diff in there, a shimmed-up diff is basically a spool anyway. Breakaway torque is north of 200ft-lb.
EvanB refreshed one this summer and had a thread about it on here somewhere. The externalcombustion miata challenge car thread also had some info on it.
cghstang wrote: The externalcombustion miata challenge car thread also had some info on it.
Found it. Beer can shims FTW!
http://grassrootsmotorsports.com/forum/grm/team-external-combustion-miata-build/19145/page1/
Yea I used the beer can shims for mine, two on each side took the diff from completely open to 100+ lb ft breakaway.
Anything that be fixed with beer is good in my book.
Also when you take apart the clutches and plates I believe that they are stacked so that 2 clutches are against each other meaning that only 2 of the 4 sides are doing anything. (plate-clutch-clutch-plate) Restack them so that both sides of the clutches are against a plate. (plate-clutch-plate-clutch) Just make sure that there is not a clutch against the end of the cast housing if you can help it.
More or less off topic on here but does anyone know of different gear ratios that you can put in a FC? I either have 4.1or4.3 gears way to tall for the T5 I have! I know I can get 3.9 but im looking for 3.75 or close to it.
I'm giving up on the RX7 unit and putting in a Ford 8.8 IRS so I can get better gear ratios.
That's what iv been seeing but more then likely I will never get around to putting one in. I did see if you can find a MPV they will fit into the FC.
There's actually a bunch of info on miata.net about rebuilding and shimming the S4 diff, as it was a popular for autocross among some people at least. I recall at least one thread where a guy was shimming his and measuring pre-load, then testing, then re-shimming and so on.
I think the tallest stock gear ratio you can get is 3.9, BUT, in order to get the 4.88 and 5.12 gears into FC race cars, people have been making hybrid gears, cutting off the long pinion shaft from FC gears and welding them to similarly trimmed shorter, Miata/FB size pinion gears. You could presumably get that sort of thing done with some taller gears, but the availability still isn't great, but I do believe that there is a 3.6 is out there, somewhere, if you can find it. At that point it might just be cheaper and easier to get an 8.8 though.
Man I really wish there was a easy fix to this... Guess I will have to put up with 3,000rpm and 60mph... I could put a longer 5th gear but I just got the trans back into the car!
Aren't the guts of the FC diff and the Miata diff interchangeable? I know there was a 3.9 option for the Miata.
In reply to rodknock:
Yes and no, the differential, ring gear and rear case are interchangeable, but the pinion on the FC is significantly longer. The auto FC's have a 3.9, most manuals had a 4.1 and there were a few 4.3's, but other than that and you have to cut and weld the long pinion shaft onto a trimmed pinion gear that would fit a Miata housing. There is some limited information online how to do it, but I'd recommend farming that out to someone whose done it before and knows what they're doing. Mazdatrix sells modified gears, so that's one place you could look, but they're seriously expensive.
Well I walked to the spare parts pile and spun the two spare rear ends that I have. One is open that came out of the car the other is LSD that I got with a lot of other parts. The LSD rear end will not let one side spin while holding the other, maybe welded? The open dif does all things open difs do. By spining the LSD it looks to be a 4.1 gear. The open dif looks to be a 3.9. After running the number at 60mph aka around 3000rpm the 3.9 gears will only lower the rpm's to 2853rpm... not worth the trouble of swapping the LSD into the open gears. Maybe that along with taller tires will drop the RPM enough for me to consider swapping them in.
What's the final drive of your T5? Should be in the .79/.78 region right? Edit: just did the calculations for what mine will be as well. rats. Taller tires should help you pretty considerably, depending on how much you up it.
If you are going to rebuild it anyway it isn't too much harder to swap the LSD into the 3.9 open. You can test the breakaway torque on the LSD to see how healthy it is. Make some way to hold one flange stationary and make an adapter with a large nut on the side to put a torque wrench on and see how much torque it takes to move it.
Was not planning on rebuilding my dif. If the LSD that's in my car now is bad I have a back up. I will have to run the numbers and see what final gearing is on the trans its out of a 85-86 mustang. And I just rebuilt the trans and I could have put a longer 5th gear in the car that that would have been perfect! oh well. I will drive the car and see how it is on the road then go from there. I will need new suspension in order to fit taller tires, my car is on the ground right now...
Well maybe I have other issues. Just ran my my numbers T5 5th gear of both .68 and .79, tire size 205-50r16 (24.1"), 4.1 gears and it says I should be doing 76mph at 3000rpm... maybe I have the wrong speedo drive gear? Wish I had the car and I could tell!
I tried two calculators and im still getting the same thing so I just downloaded a APP to tell me my MPH and I will run it in the car and see what happens. Im hoping I was going much faster then I though I was! That will also mean the car is much faster then I thought it was!
This one is a bit old but iv got some new questions now that iv done some miles in the car. Something in the drive line is very loose. You can feel it jerk when going on and off the throttle fast. Up under the car I can hold both wheels so they don't move and spin the drive shaft while in natural and the drive shaft shins about 1/2 to 3/4" at the flange. Don't have a way to test it in the car but does this seem like way to much play?
I have the stock open diff as well as another LSD dif and they feel like they have no play off that car.
There is usually some play, I never measured it, but that does seem excessive.
Another thing to check if you're hearing a thunk and feeling a jerk, make sure your front differential mount isn't cracked.
As a side note, I have a turbo transmission, driveshaft and clutch type LSD from an S4 TII sitting in my garage that are for sale. You know, if you're looking for a spare.
sounds like front diff bushing or said mount.
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