Scenario is second gen rx-7 S4 engine setup for chumpcar, mainly stock except for radiator. The transmissions have been described as being like glass. If that is true what is some preventative maintenance or a way of strengthening them? How many hours can you get before rebuild? Can they last a 24 hour race? My concern is that I will be renting two seats, just want to make sure we can finish the race.

 

I have raced a number of enduros , but not 24 hours straight...I think the trans could easily last that amount of time , but no transmission will stand abuse that long , it is extremely difficult to govern rental drivers to shift it properly that is the risk....consider adjusting the clutch to engage about one third of its travel toward the floor , that can help a little with your renters

 

Tell them not to speed shift the car. It is a 24 hour race, there is no need to beat on the car. The trans should last just fine if it is in good shape behind an NA engine.

 

They say the definition of insanity is doing the same thing again and again and expecting a different result....

I did the VIR 13 hour race 3 years in a row and the trans broke 3 years in a row...My suggestion is to start with a fresh build and BABY EVERY SHIFT. Ignore the red mist and slow your clutch and shift to allow a smooth transition.

Bring a spare or two.

 

I mean you could have the gears cryo treated and/or DLC coated to help but we've found in my cousin's old Prelude and now his miata that deliberately slowing down your shifts is enough. Granted I have not done a 24hr yet but we've done plenty of 12 and 14 hr events. Also, avoid the curbs as much as possible. The shock loads sent through the drive line when you hop on and off curbing is also a tranny killer

 

its a 24 hour race, not a sprint. you will want to start with a rebuilt transmission, and you will want to have a back up. if you can get the drivers not to beat on it, it will be totally fine

when the drivers get excited they will break the 3rd gear synchro first

 

My endurance race FD3S
Come with Trans cooler , what unique is instead of pump back to transmission sump , we have pump it back top of transmission with 3 fiting
To cool the gear direct

 

I find this to be such an interesting topic. I have an 84 GSL-SE that has seen 12 Lemons and Chumpcar weekends, so conservatively about 150 hours of race time on it. It's still working fine. In this space of time I have had to rebuild the motor once and the differential 3 times.

I really think it has more to do with the driver(s), than the rx7 having a "glass transmission". I have always run redline fluid in my trans as well, that may make a difference.

All that being said, if you would please excuse me.... I am going to go find some wood to knock on.

 

Once you can convince your drivers that just being consistent, staying out of trouble, and not having any mechanical failures is usually much more likely to get you the win versus shifting like it's a sprint race the life of the transmission goes up considerably lol. That's been my experience so far at least

edit: also not wasting time in the pits. That's a big one that a lot of people don't immediately realize

 

After nearly 15 years of racing 2nd gen cars in ITS and rebuilding Transmissions for about a dozen different people.......

If you have a solid disc clutch, be gentle with clutch release on downshift. a sprung hub is a little easier, but not a guarantee. If you pop the clutch hard enough to upset the car, you are also stressing the input shaft and counter shaft teeth. Do this too often and you will eventually have a catastrophic failure. This will not usually show until upshift out of a corner, but is usually fractured/broken on the downshift. This will leave no forward gears working except 4th.. This transmission is now more expensive to fix than replace....call the local scrap guy

Redline fluid always worked for me. No problems with Mobil1 either though. I changed mine after 5-6 hours of track time religiously. (pre-chumpcar days).

NO SHORT SHIFTER..never..nada..there is no reason to have one. You will constantly be pounding synchros due to the increased ratio. Shift these with a flick of the wrist, not like an old mustang with a Top-loader and a hurst T-handle. The more abused the synchros get, the slower they work. If you try to shift at the same speed, you will damage them further, or break them. This will also damage hard parts such as sliders and hubs.

Do not rest hand/arm on the shifter....shift, then return to the steering wheel. Even the light weight of your hand can pre-load transmission part due to the lever effect of the shifter. (hands belong on the steering wheel in a race care anyway. )

I hope this isn't too much...I'm not trying to preach, just sharing what I have seen, learned, and rebuilt over the years. If you are going to race these, you will need to have some spares and/or become proficient at refreshing them. new synchros are good preventative measures for long endurance races. If I can help, pm me. There are some special tools needed, I can tell/show how I made mine for much less $$$ than expected.

 

A couple points of note here.

1. I have always raced a stock clutch. I know it's tempting to throw an upgraded heavy clutch in there, but assuming you are running an NA motor that isn't too crazy, it doesn't slip or burn up.

2. Stock shifter. Yes, there is a bit of throw, but I beleive it probably does do a lot to save the syncros and so the transmission.

Neither of these things are fun, but neither is changing a trans on the ground in the paddock.

 

Ok I am a little confused about the short shifter comments. How would decreasing your leverage by changing the ratio to get more movement below the fulcrum and less movement but less mechanical advantage on top of the fulcrum be bad for the syncros?

 

It has to do with quickness of the shift. Less throw in the shifter means a quicker shift between gears means less opportunity for the syncros to do their thing.

 

A syncro doesn't do anything until you start pushing against it so the "quickness" has nothing to do with it. It's the amount of force you are applying while it's trying to get up to speed or down to speed that wears out the friction material in the conical section.

 

If you have to use "force", you are shifting to fast. Again, it's not an old Muncie or Top-Loader 4 speed.. As the friction material in the conical section wears, the teeth of the synchro get closer to the teeth of the gear. Since they are closer,, the "time" that is present between gears is decreased. This gives less time for the teeth to all align while you are shifting. This leads to worn teeth on the gear, and on the slider. Not to mention what happens to the softer brass synchros. When you add a short shifter to the mix, you have even less time between these shifts.

If I were renting out a 2nd gen RX7 for any length of race, there is absolutely no way there would be a short shifter in it.

Do what you want with this info. I don't have a horse in this race, and only offer help. A race car that's on jackstands during a race isn't winning....or racing even

 

Fair enough. Your practical experience is certainly appreciated. One other potential pitfall is that it's much easier to miss a shift or accidentally go from 5th to 2nd with a short shifter. Took me a decent amount of time to get used to it on the street so someone who is renting out a seat certainly might struggle which would be a huge negative as well.