ITSWILL

iTrader: (12)

how many degrees of play should there be in the driveshaft?

My TII started to feel very loose between shifts and I figured it was just from launching it. It will thud between gears and when I let the clutch in and out.

Now my 86 turbo drivetrain swap is doing the same thing. I have been very gentle with this car and I cant imagine why it is doing the same thing now.

In both cases it was just fine then eventually I noticed this.

Any ideas?

TitaniumTT

U-joints or backlash. Maybe tranny starting to go south.

There should be ZERO slop in the U-joints. As for degrees of backlash, I couldn't tell you but you could probably do a shitton of math from the FSM as to what the backlash is at the ring and work it down to the ujoints and measure it there. Or I could just say none to very little at the driveshaft

ITSWILL

iTrader: (12)

The u joints are tight. I would say I get a good 10 to 15 degrees of driveshaft rotation before the wheels start to turn.

If its the ring and pinion, would it be possible to tighten a pinion nut and crush a crush washer to tighten things up?

I've only ever messed with 10 and 12 bolt gm rear ends.

toplessFC3Sman

iTrader: (1)

if its the ring and pinion you'll need to adjust the clearance between the two until its within specs in the FSM. They give a pretty good example of how to do this in "front and rear axle" here:

http://www.wankel.net/~krwright/cars/rx7/88_manual.htm

ITSWILL

iTrader: (12)

yeah, ive been reading it.

And I think by tightening the pinion nut it would just loosen things up.

Does that sound like to much play 10-15 degrees, What is acceptable?

TitaniumTT

Yeah, that is WAAAAAAAAAAAAAAAAAAAAYYYYYYYYYYYYYYYYYYYYYYYYYY too much. The FSM specs backlash to be 0-.1MM or .004" or basically nothing. Your backlash is way outta specs and sadly, the diff needs to come out and be broken apart to adjust it. If its that bad I would pay close attention to the ring an pinion as those are most definately worn.

What brand/weight oil are you using?

ITSWILL

iTrader: (12)

I think one has the redline stuff in it and the other I have no idea. I haven't personally touched either diff.

To be honest I think I have a differential phobia. I am willing to mess with any part of an engine but when it comes to the diff that just seems like it is somewhat of an art to do properly.


On that note there is only one way to get over my fear...

I'm guessing maxdatrix sells everything I need.

As for rear gear ratios, are there any others available that anyone would recommend? I would like this thing to do a decent 1/4 mile and I really don't need to do 160mph anyway.

TitaniumTT

Setting up a diff isn't as hard as it sounds. It's just time consuming. I think I spent 60 minutes setting the backlash/load when I swapped my Torsen in. Small turns on the bearing cap adjustments make big differences in backlash. By big differences I mean .003" (which is the difference between in/out of spec) It's not that hard but there are some special tools required that can be had relatively cheap.

If the pinion looks good, I would start by adjusting the backlash. If you cn't get good contact, the pinion may need to be pulled and the height reset. That would be a tremendous pain.

I would thoughouly inspect both the ring and pinion though. They might not need to be replaced. IFF they need to be replaced than I would look into different gears. Or just find a used rearend. Although I found that the TII rears are hard to come by. I got lucky when I found mine local. I got the diff, subframe, 3 axles, 3 swingarms for $200. Guy didn't know what he had basically. This is also the same guy that threw out 3 manual racks the week before soooooooooooo

ITSWILL

iTrader: (12)

well it looks like mazdatrix only sells the 4.30 for the turbo anyway.

But, wow that is ridiculously expensive $550 for just a ring and pinion. Then on top of that I would redo all the bearings and seals and most likely rebuild the lsd.

I could see this costing over $1000.

So anyone know anything about cobra IRS...



*you find another deal like that let me know ill give you $500

TitaniumTT

You don't know whta it's going to cost until you crack the ****** open. It could just be a simple adjustment.

If you're talking about rebuilding the LSD you're obviously running an S4. What are you using the car for? What kind of power are we talking about here? Ever thought of upgrading to a torsen? I got mine for ~$125 shipped IIRC

TitaniumTT

Oh, you do NOT want to increase the lockup on the clutch pack unless you only plan on driving in a strait line.

ITSWILL

iTrader: (12)

Well I am shooting for 500whp, I should be deep in the 400s by this spring until I do an S5 rear iron and oversize stud the motor. Then I'm going to push it for everything it's got.

Basically I don't really even plan on this car being street legal, but I definitely plan on hitting the streets with it at least once a week. I love the way the car handles now I cant see myself doing anything to sacrifice that. Also I would like to bring it to the strip and run low 11s maybe even high 10s.

What is torsen? Isn't that just a brand? what specifically are you referring to?

toplessFC3Sman

iTrader: (1)

torsen is a brand, but its also a different type of differential. Instead of using clutches or a viscous fluid to prevent slip, its all gearing. For the turbo rear ends, they cant hold as much power (especially on launches) as the clutch-types, but dont wear out and are better suited to track/auto-x.

ITSWILL

iTrader: (12)

ok Then I think the clutch type would be more my speed as I dont really plan on taking hair pin turns with this thing for extended amounts of time, but I can definitely see myself launching it pretty hard.

TitaniumTT

WRONG - Torsen doesn't hold up well to launching. The FD guys gnerally swap them out for S4 rears which is how I got mine

ITSWILL

iTrader: (12)

thats what he said???

you just confused the hell out of me man.

What are you saying? rephrase please. The way you say wrong then make a statement could be interpreted either way, to me at least.

TitaniumTT

I'm assuming there was either an edit on topless' part or his lack of a " ' " made me read it as "can" as opposed to "can't"

S4>Torsen for drag
Torsen>S4 for everything else

ITSWILL

iTrader: (12)

probably the lack of '

ITSWILL

iTrader: (12)

so what do you think is best?

I'm worried that if I rebuild my rear end its just a matter if time before I destroy it with me new turbo setup.

I have read a little about the cobra IRS and am kind of hot and cold about it. It would be a ton of work but it would be stronger. I am also unsure of how it would effect handling.

TitaniumTT

I don't think you really need a Cobra IRS. The stocker rear end can hold a ton of power but if abused it will break just like anything else.

This is all theory though. You won't know anything until you drop the rear and crack it open

Turblown

iTrader: (12)

Almost every Rx-7 on the road needs its driveshaft replaced and its rear-end rebuilt. I have never seen a oem rx-7 driveshaft without bernelled u-joint bearings. I replace those all the time....

ITSWILL

iTrader: (12)

What do you consider abuse? I plan on launching this thing at 4000-5000 rpms with a set of Mickey Ts on it.

I have heard that they hold a ton of power as well. But anything does, it's just a matter of how many times they can.




Yeah there is definitely more inspection required before I can make any conclusions. It's getting pretty shitty cold here and its bad enough working on the topside of the car, I'm really trying to avoid having to get under this thing for now. I wish I had a garage like you fellows.