fstfwd

iTrader: (1)

Hey guys... I have a 5 speed FD with a little over 100k on the original tranny and differential. Since I have owned it, I have replaced the clutch and 5th gear syncro at 68k or so... but nothing else on the rest of the drivetrain. It still drives pretty strong, but is definitely NOT as smooth as my dad's FD with only 45k on it... and that kind of sucks. I test drove an Rx8 not to long ago... and I think one of the things I liked the most about it was the fact it shifted so smoothly... it was really a joy to drive.

SO - begins my mission to get my FD feeling as close to "new" as possible. I know that I have to get my motor mounts replaced - that will probably help alot with miss shifts and vibration... but other things need to be done from the clutch back.

Now on with my question... I'm doing some research to determine pricing on rebuilding my existing tranny... or just replacing it with a used one ( I imagine a new one is ridiculously expensive, but I don't have figures on that). I also want to replace/rebuild the differential... and need some options on that. I've heard some things about aftermarket LSD's that make me think I'd like to just keep a stock one in there, used or rebuilt.

I just called up Mazda Recycling... they are expecting a used 5spd tranny in soon, not sure on mileage and price... but the guy said between $1100-1300. They did have a used differential with only 45k on it for $400. Is that a good price?

I'm not an expert on this stuff (which is of course why I throw these questions out there), but my gutt tells me that things like trannys and differentials should never be openned up once they are put together... and it might be good to just find a used one that WORKS fine.

So I hand this over to you all... what sayest thou?!

Thank you in advance...

alberto_mg

You can try to find a new tranny by calling Ray at Malloy Mazda, but I think they stopped making them. Search on a thread by Zerobanger.

I think that if you want to be 100% certain that it's going to work properly, I'd go with the option of having your tranny rebuilt by a *good* tranny rebuild place or, preferably, a rotary specialist. A used tranny is a crap shoot. It might feel the same as yours so why go through all the expense of buying a used one, having it shipped, then paying for the installation.

You can probably find a low mileage used JDM tranny for ~$400-500 dollars. $1100 is way too much for a used tranny in unknown condition. Search on JDM tranny. I think John Magnussen (spelling?) had posted a thread about that a while back. The later trannys also had a shorter 5th gear which is desirable.

For motor mounts, if vibration is not something you want to tolerate buy new stock ones from Ray at Malloy Mazda. Your next best bet would be the Gotham Racing Urethane mounts for half the price of stock new, but urethane will always give you a little more NVH (noise vibration and harshness) as well as decreasing the amount of engine flex which can improve shifting feel. I've read that they transmit some vibration early on but eventually it smooths out.

I probably wouldn't touch the diff unless needed. I'd just change the oil with some Redline or Neo. I would however, replace the diff bushings which cause slop in the drivetrain. Search on diff bushings for some threads on that. I think Pettit sells a set of nylon diff bushings that when combined with less compliant trailing arms reduce wheel hop. I personally would get the Pettit ones as the factory ones don't last and you don't want to have to do them over. I wouldn't do an aftermarket LSD as they tend to be noisier.

Of course, while the tranny is out you should do a clutch and replace the clutch fork. Might want to also consider a lightweight flywheel. RX7store has one by ACT that is a bit heavier than the 9.5lb Racing Beat. The extra weight of the ACT street one will make it easier to drive.

dgeesaman

iTrader: (7)

I concur with TurboJeff.

Rebuilding your own tranny is time consuming and messy, and it's easy to rack up $500 in parts cost. For that price you can get a low mileage JDM tranny and install that. I think you'll also get the better 5th gear ratio.

Worst case, if the JDM doesn't work much better, your tranny is sitting there ready for a rebuild on your schedule, or to be sent off to a reputable rebuild shop.

Rebuild notes here: www.davidgeesaman.com

Diffs do occasionally go bad, and finding a used replacement should not be expensive or difficult. But I wouldn't do that unless I was convinced something was wrong (the case I know about, the dyno was showing major drivetrain losses).

You can inspect or replace the motor mounts and/or diff mounts easily while the tranny is out.

Dave

fstfwd

iTrader: (1)

Thanks for the feedback guys...

I hadn't planned on rebuilding it myself. I was going to have that done professionally, if that is the route I decide to take. Dave at KDR said he could rebuild it for $1100... which is probably a fair price. But, again, I don't know if that will have the desired results.

As far as the Diff. goes... there are a few symptoms I have experienced that lead me to believe it might be on it's way out. For one, when I am driving around, I get a vibration/grinding noise if I go around sharp turns.. or even gradual ones. It just doesn't feel smooth if I get on the case while I am trying to push myself out of a turn. As soon as I straighten the wheel out, the noise goes away. I also wouldn't be surprised if I am getting overall drivetrain losses on the dyno... as Dave mentioned... I should be putting down around 340-350 to the wheels based on all my mods, and friends with almost identical cars (in fact, I up them on a few things)... and they are consistantly putting down 340 - 360. I don't get much past 290.

I just saw a Jspec 5 speed tran forsale on ebay for $400... though, the owner is unsure about the exact mileage (20k-40k???)... and again, what am I going to be stuck with.

alberto_mg

that sound that could be a wheel bearing.

what mods do you have?

fstfwd

iTrader: (1)

Street port 13b
'99 J-Spec twin turbos
1300cc secondary injectors
Racing Fuel pump
A'PEXi Power FC ECU
A'PEXi Dual intake system
A'PEXi Twin Chamber BOV
Greddy Intercooler
Koyo Radiator
Manual Boost controller
ACT Street Clutch
3" Downpipe
Bonez High-flo Cat
Tanabe Racing Medalion Exhaust
Cusco Strut bar
A'PEXi Power FC Commander
M2 Performance Toelinks
M2 Performance Trailing Arms

and a few other cosmetic things...

fstfwd

iTrader: (1)

The thing I might add is... it only makes that noise when I'm on the gas if... if I take my foot off, and coast into the turn... it's fine, until I get on the throttle... then it makes a low vibrating/grinding noise... until I start to straighten the wheel out.

fstfwd

iTrader: (1)

^

Image Performance

you can get a full rebuild, with synchros bearings seals, and everything else for like 1100 bucks. including labor. KD Rotary in PA. And yes, ray at malloy can find anything

fstfwd

iTrader: (1)

Hey guys - someone recently asked me about this thread, so I thought I would update things... since I actually have some useful information.

My car has been down at KD Rotary in PA for the past month, and the "grinding" noise was one of the issues I had Dave look at.

Dave was able to reproduce the problem regularly (which means I'm not crazy)... and narrowed it down to my exhaust. It turns out that when going around turns the top of my cat is hitting my subframe and causing that obnoxious grinding noise. I was saying to Dave, that it almost feels like you can't get on the throttle sometimes because of the vibration - but that is probably more of a psychological effect... and he agreed with that. The car throttles fine - so it's not the Diff.

I just put in a use '95 JDM 5-Speed tranny... which smoothed things out a bit... but at least i don't have to do the differential.

The solution that we breifly discussed was to possbily have someone tigweld the leadin piping on the cat, and reposition it enough so that when the exhaust is tightened up, it will pull away from the frame enough.