4 replies to this topic

[Jamz14]

Hey All,

 

I just finished rebuilding my trans from a 97 car this past week end and thought I'd share some thoughts on the experience.

 

The trans I rebuild is from our 97 that I purchased with 107K on it. We raced it for 5 weekends and a handful of test days last year. I decided to rebuild it becuase I had noticed some miss shifts from the on board camera and the driver was reporting that 3/4 shifts were becoming more difficult.

 

I would have never have attempted doing this unless I had a very good manual to follow, and after looking here and talking to various people here, I purchased the Miata Enthusiaists Handbook by Grainger. Excellent book. A proper how to manual that will come in handy for other jobs too. Dave Wheeler from Advanced Autosports was kind enough to provide me a list of rebuild parts that would be needed. This service saved me numerous days in the rebuild and I want to thank Dave for doing this. Dave's list is very comprehensive but it is missing a few items like replacement drift pins for the shift forks. Do not worry about the few missing items as you will most likely need to stop the build at some point and order various spacers and you can order the pins and other small parts then. You should also know that though the book is an excellent step by step, they are some small differences I found between the book and my trans. Most notably, there are no longer C clips on the shift rods at the central bearing carrier. The 94-97 now use the 99 rods that do not have these clips.

 

Even with a great book and a comprehensive parts list, be prepared to take two steps forward and one step backward the first time doing this. The clutch hubs, keys, springs, and syncro slots were the leading cause of redoing steps. If you are not careful to keep the clutch hubs in neutral and accidently engage the gear without holding everything in place while you are rebuilding, the keys and springs will come loose. Also keep an eye out for the interlock pin. The interlock pin goes in the 3/4 shift rod. The 3/4 gears reside on the input shaft which can drift fore and aft a bit. If you test shift before recasing the trans, the input shaft can drift forward fractionally and when shifting into fourth, if the input shaft does drift forward, the interlock pin slot can move forward of the cetral bearing carrier and drop down onto the 5/rev shift rod and lock the trans in 4th gear. You can avoid that by ensuring that the 3/4 gears are not engaged when recasing the trans and keeping the input shaft from drifting forward while recasing.

 

Costs: I spent aprox $450.00 in new parts that were described in Dave's list. This included new syncros, shift rods shift forks, and seals. It did not include gears or bearings. More than likely you will not need to replace the gears or bearings.

 

If you highly value your time and you have the need to replace your trans, you should strongly consider having Saulspeed rebuild it for you, or to purchase a rebuilt one from Dave Wheeler or Jim Drago. I decided to do this because I wanted to have the ability to do it and to ensure that if I needed to rebuild the trans, I could do so in between race weekends and not have to worry about a shop schedule and whether they could fit me in before the weekends race. However, if my budget would allow it, this is one area that I would gladly outsource to Saulspeed. He has the expertise to do this work and the price he would charge or that Jim or Dave would charge for a rebuilt trans is a bargin compared to the amount of time and effort you are going to spend doing this this for the first time. I would estimate the job took aprox 16 hrs. Im sure it would be less the second and third time around. Count on some down time as you order proper spacers that can't be determined until you begin the rebuild.

 

Lastly, I wanted to thank Saulspeed and FTodaro for all their help in doing this. These two guys have built many of these and their guidance was crucial and comforting as I was doing this. This job is very doable as a DIYer. But go into it knowing that you will be frustrated at times. And that the time you spend in doing it is not recovered with cost savings by not outsourcing it. Do it because that is the type of person you are and that you like knowing that there is nothing on the car that you can't do and knowing that the job is done with the care that an owner puts into it. For me, sending the driver out on a test drive and him coming back and saying the trans shifted sweetly was priceless.

 

I know I am missing some things. Feel free to ask if curious about something.

 

PS. - I forgot to mention what I found inside the trans that was leading to the shifting problems. No broken springs or syncros. There was wearing on the syncros that was causing the bad shifts. Also wear on the shift forks  and rods that was making the shifts sloppy.

[Bench Racer]

"There was wearing on the syncros that was causing the bad shifts."




Are you refering to the teeth? Did you measure the gap/clearance between the syncro and the clutch hub teeth?




I have a good installed transmission and a pro backup, but am thinking about rebuilding the original that came in the car, for knowledge/gray area experiences/grinz/because I have time. I also want to gain more wear knowledge of the syncro syncro springs that I do not believe are broken and other internal stuff.



Jim, I love the site, but why the smell when one leaves paragraphs spaces doesn't the post show paragraph gaps? These are 4 space gaps.

[Jamz14]

Yes, there was wear on the syncro teeth and some teeth that had some small bits missing. Nothing too drastic.

 

I didn't measure the gap you are referring to either before rebuilding or afterwards. But I didn't notice a huge amount of wear on the syncro in the area that would account for differences in the gap between the gear. I only casually inspected that area though. Focused more on the teeth. Will go back and look tonight at that part of the syncro.

[FTodaro]

The more times you rebuild them the easier it gets. I can do it now by memory. I want to learn how to lash a diff next.

Congrats, I know how satisfied I was with myself the first time I did it. youn accomplished something, not many have the nerve to try it. .

[SaulSpeedwell]

Yes, there was wear on the syncro teeth and some teeth that had some small bits missing. Nothing too drastic.

 

I didn't measure the gap you are referring to either before rebuilding or afterwards. But I didn't notice a huge amount of wear on the syncro in the area that would account for differences in the gap between the gear. I only casually inspected that area though. Focused more on the teeth. Will go back and look tonight at that part of the syncro.

 

Just catching up here.  What did you find on the gap from the synchro to the gear versus how worn the forks were?  Wear on either or both slows/delays the shifting, but grind-free shifts will still be possible if you take your time.  Perpetual grind is almost always a spring or synchro breakage.

 

The teeth never contact hard except when you miss a shift - so wear on that side will come from "missed + grinding" shifts versus "missed but no grinding shifts".