Driver_WT

iTrader: (1)

I had my 93 RX7 (around 400 hp at crank, single turbo) to a track day. On the front stretch, when the car got hot (after about 7 or 8 laps) it would not shift into 4th gear at 6500 rpm. No grinding, no noises, it just would not go into gear. On the back stretch I tried to shift into 4th at 6000 rpm and no issues. When the car cooled down it would go into 4th at 6500 rpm with no issues. Any ideas on what could be causing this?

I hope to be back at the track in another couple of months, and would like to get this figured out.

Thanks.

Wade

HalifaxFD

iTrader: (18)

Wade, possibly a syncro. What tranny oil are you using?

Driver_WT

iTrader: (1)

Good question John. The tranny oil that it came with (whatever that is)
I shall have to change it when I get back to NS.

Any recommendations on tranny fluid?

JDK

iTrader: (8)

Change your fluid, I got best results from Red-Line MT 75w90 and Motul Motylgear (check spelling) 75w90, i tried using Royal Purple once and found I was getting the same problem your having now....

Driver_WT

iTrader: (1)

Thanks Jim. I will give that a try.
Wade

HalifaxFD

iTrader: (18)

I've always used the redline 75w90 as well with good results.

23Racer

I used to use the Redline 75NS90 but I found out that after about 60 minutes of race time the car wouldn't like to shift and I could smell gear lube. I installed an oil temp gauge and saw sustained temps over 250 degrees. Talked to some long time racers and all of them recommended that I install a tranny cooler. I ended up just replacing the gear lube after every race weekend as it would just be cooked.

Last year a local oil company engineer asked me to try some of there race lube in my box based on a 120 weight base stock with friction modifiers and anti oxidants. Dropped oil temperatures about 30 degrees and allowed me to shift gears at over 8000 rpm for 3 hours without a cooler.

Either add a cooler or get used to changing gear lube after every track weekend. And I agree with Jim Redline or Motul are the best choices.

Eric

sctRota

iTrader: (2)

I used royal purple and it caused a similar problem with 3rd gear. It would suddenly get REALLY stiff and worrisome.
Switched to AMS syncro-mesh and never had an issue since

23Racer

I used Royal Purple Synchromax in my Cougar Houseman Race box. It was the trick oil to use in that setup. It allowed me to run 55 minutes of a 1 hour race in second place, then locked up the box in second gear coming out of Turn 5B at Mosport. I had to go all the way up the back straight in second gear and cross the line and I lost 7 places. Later when it all cooled off, I could move it out of gear and get all the gears, but the box had a vibration in it and it felt like it would bind and release in gear when the car rolled.

Pulled the box and took it to a tranny shop and found out that the third gear had almost welded itself to the countershaft. The bearing surface was destroyed on the shaft and the bearings had torn themselves to pieces. A number of the other rotating areas had turned blue from the loading. The shop owner confirmed to me that it was a breakdown of the lube from the heat and loads and strongly suggested that I look at a thicker gear lube for on track use or a cooler. That is why I tried out this other stuff and it has worked great in both the RX7 and the Cougar with quieter boxes, easier shifting when hot and cooler temps. The only issue is that you cant use it in daily drivers as when the temps are colder, it will be too thick to work properly and you will get metal to metal wear.

If it was me and I had a double duty car, I would put a temp sender in the box and make sure that you pull in or ease off the power when you exceed the max recommended temps for the lube you are using. Its way cheaper and easier than replacing a gearbox.

Eric

sctRota

iTrader: (2)

^^ I double duty and use syncro mesh now. It hasn't messed with me since

Driver_WT

iTrader: (1)

Thanks guys. Great information. I have ordered some synthetic trans fluid 75W90. I will give that a try at the track (if the snow in NS ever disappears).
Wade

JDK

iTrader: (8)

Do the diff while your at it

Driver_WT

iTrader: (1)

Yes, thanks Jim. I have ordered enough to do both trans and diff.

Driver_WT

iTrader: (1)

OK, so I changed trans fluid to Idemitsu synthetic and right away on first start I have a strange growling noise in the trans. It goes away after the car warms up, but sounds really bad when cold. Noise goes away when I put the clutch in. Sounds like lots of bad bearings or maybe a bad throwout bearing. Took the car to one track day and it did not want to shift into reverse or first gear easily when hot. Any thoughts?

23Racer

Other than you may have hurt the box the last time? Had you run the car after your last track day with the old lube in it and it was quiet? For example, was everything quiet and you were driving the car, then changed the lube and now it rattles. Any big metallics in the old oul when it came out? Lots of guys have and are using the 75NS90 with no issues.

The only other easy thing I can think of is that your clutch may not be fully disengaging when hot. In all the other gears the synchro cover the weakness, but not into reverse. Try bleeding the clutch again. If not that then I think more work required like visual inspections with a flexible scope to see if there are issues with the clutch disc breaking a spring.

Eric

Driver_WT

iTrader: (1)

Thanks Eric. the trans was quiet after the last track day. It was also quiet when I put it on the ramps to change the trans fluid. There was a small amount of small metallics on the magnetic drain plug when I changed the trans fluid. I did bleed the clutch again and it made no difference. So now I am down to visual inspection of the clutch. I appreciate the questions and advice.