Premature Transmission Failure

[NoDOHC]

I have been having far too many transmission failures for the power my engine is making and the type of driving that I typically do. I have some theories, but I thought that I would run them past all of you.

There is a long history below, this is the executive summary:
NA and turbo transmissions failing
Suspect advanced ignition timing / misfiring.
Problem did not occur with factory ECU/tune/flywheel.
Also think that the lightweight flywheel is contributing factor
Shifter has small vibration (can only be felt if held in hand, does not shake visibly).
Shifter vibration gets significantly worse if timing is advanced further.
Shifter vibration goes away if timing is retarded 15 degrees.
Vibration does not occur above 4,000 RPM or below 1,500 RPM.
Engine pre-ignites in vacuum if AFR is richened past 15:1 with existing ignition timing.

If you want further details, read below:




In the last 3 years and 30,000ish miles, I have put 5 transmissions in my '86 GXL. To give a summation of the failures:
The original transmission was replaced before I owned the car.
The transmission that was in the car when I got it had no synchros in 2nd or 5th, but otherwise was fine for almost 30,000 miles of my ownership.

I found that advancing the timing about 10 degrees past stock greatly improved my fuel economy. Leaning the fuel out by tweaking the AFM helped power, but made no mileage difference (running on the O2 sensor either way). Then I replaced the ECU with a Haltech E6x. I replaced the transmission at the same time because I had no synchros in 2nd or 5th.

With the Haltech ECU, I advanced the timing as far as I could go (which was about 65 degrees BTDC, as I ran a base advance of 15). This improved my average fuel economy from 26 MPG to 34 MPG (19x,xxx mileage 6-port). I was also able to eek an additional 17 Whp out of it (per the G-tech - from 138 WHp to 155WHp, from 95 WLb-Ft to 101 WLb-ft).

Unfortunately, this was the beginning of the transmission woes.

The 1st transmission that I put in (when I replaced the ECU and wiring harness) was a $50.00 special I got on eBay - it seemed to be Ok when I put it in. This transmission lasted for about 6 months (5,000 miles). The synchros were all fine, but the bearings went out of it (I let it go until it would squeal in 5th gear under throttle). I also installed a light-weight flywheel at this time.

Transmission 2 was a 'known-good' transmission from a friend. It lasted for about 6 months (3,000 miles) although this was more spirited driving than before. The failure was the same, good synchros (except 2nd, which I killed drag racing) but bad bearings (I replaced the transmission when it started howling in neutral). I had this transmission in the car when I dynoed at 155 WHp.

Transmission 3 was installed when I upgraded to a 4-port engine. I had a hunch that I would need to upgrade the drive train too, as I was going to install a turbo on the 4-port, so I bought another $75.00 eBay special. This transmission was making noise after 750 miles back of the 4-port. I ran it for about 3,000 miles until I smoked the clutch on the dyno. That dyno run I made 160 WLb-Ft with the 8.2:1 CR 4-port (I was starting to be concerned for my drive train after the clutch gave out).

I should also note that I broke a side seal when I assembled this engine, so it had a side seal that was 1 inch short in the front rotor. It made good compression on two faces of that rotor, but one face was weak. This made the engine shake at idle. I put it down to the porting and never thought another thing of it, until I pulled the engine down to steal the apex seals for another build (it was sitting in my garage) and found the broken seal, with the rest of the groove full of carbon and that rotor face nearly black, while the other 5 were very clean.

The next transmission that I installed was a Turbo II transmission, J-spec. This transmission appeared to be in good shape when I put it in the car. It lived for 10,000 miles back of the 8.2:1 4-port. After about 5,000 miles, the synchros on 5th gear actually broke, they didn't wear out, as they worked fine one shift and the gears ground on the next shift. In addition, I lost the ability to get the shifter into reverse. I eventually got reverse working again, but there were no synchros in 5th or reverse. This transmission started making noise while I was still tuning the 4-port, but made significantly more noise after the dyno run (to make sure that the drivetrain power loss was the same from NA to turbo drivetrain - it was identical). The bearings got so bad toward the end of that 10,000 miles that I had trouble shifting.

The next transmission I installed was from a guy in Minnesota, who said it was in good shape (it appeared to be). This was a US spec (0.72 overdrive instead of the nasty 0.8) turbo transmission. I installed the 9.2:1 4-port engine at the same time (no miss/shake at idle). I also installed a Haltech E8, so I had to redo my fuel and timing curves (although I started and broke the engine in on the old E6X, as it is unpleasant to start a freshly-rebuilt rotary with a new ECU).

My timing curves were conservative for about 4,000 miles, until I ran the engine at the dyno, when I advanced the timing to peak power. I had overheating issues, so I couldn't go past 6,000 rpm, but made 162-182 WLb-ft (I think that the speed reading on the dyno was incorrect, although the dyno reported 182 WLb-ft@5400 rpm, my trace from my ECU showed that I had run to 6000 RPM). I had no trouble with the transmission.

I ran the engine for another 2,000 miles and installed the Defined Autoworks Headers and my own custom exhaust. This netted over 10 WLb-ft on the g-tech, but it was too late in the season for another dyno run by the time I figured the overheating problem out.

Anyway, I put about 4,000 miles on and I noticed this transmission making noise, but only at full throttle/high speed in 3rd and at heavy throttle and any speed in 5th gear. It was still quiet while idling. However, I made some adjustments to idle ignition timing to allow me to run the engine more lean at idle and it occasionally misfires at idle now (I am running on the O2 sensor, 14.8:1). Just Yesterday, I noticed a whine at idle when the transmission is hot. Obviously this is concerning, as this is Transmission #5!

I decided that it can't be torque that is killing the transmissions, as this engine probably only makes 180-185 WLb-ft max - even with the Defined Autoworks headers - and most turbo guys are breaking that, even with relatively stock setups (that is only about 225 Lb-ft at the engine - about 275 Hp in the turbo world of 7,000 RPM red-line). There must be something else.

Here is my theory: I think that it is advanced ignition timing and a light-weight flywheel (old-school racing beat, 12lb) that is killing the transmission. I think that the early ignition is generating negative torque and that this is putting the gears and bearing through reverse loading, causing the roller and ball bearings to lose their oil film and to wear out prematurely. I am going to put the chamber pressure transducers back in as soon as winter breaks (had to park the car yesterday for winter) and see how early the pressure spike is reached. I had the timing advanced on the old stock ECU, but I had a stock flywheel.

The Racing Beat flywheel (which I have had for a long time) came off a turbo build from a while back, it was significantly heavier than the Fidanza NA flywheel that I had on while the NA transmissions were dying like flies.

The vibration can no longer be felt with the engine spinning above about 4,000 rpm and it is no longer noticeable below 1,500 rpm (the timing is running about 18 deg BTDC @ WOT at that speed). Shaking starts again at high throttles while under 900 rpm, but it is normal lugged engine shaking.

I tried taking timing out at 2,000 rpm and the vibration went away at this speed, then started again as the engine accelerated towards 2,250 rpm. I retarded the ignition about 15 degrees to make the vibration stop, but the range was about 300 rpm, so 10 degrees would probably have been sufficient if I had taken it out across the board.

Sorry about the LONG post, but I wanted you to have the same information I have. I won't be able to test any theories for a while, as the salt trucks are out, which means the car doesn't leave the driveway and the vibration doesn't happen unless I have been driving for a little (oil in transmission warmed up?).

EDIT: I should add that I have 2 >6,000 RPM WOT trigged Data logs in my ECU in the last 3 Months. I have not been driving this car hard lately - certainly not in 5th gear (which makes the most noise).

[RETed]

The consensus seems to be that non-turbo 13B putting down close to 200hp at the wheels will shorten the life of the (FC) non-turbo transmissions.
200 at the wheels is typically 150 lb-ft at the wheels...
You're at this level right now...and then some.
So, with the non-turbo transmissions, it's no surprised you're killing them.

As for the turbo transmissions...
Hard to say...
Used units are not a very good baseline - same goes with the non-turbo transmissions.
To have good data, the transmissions need to be inspected and rebuilt.
Even a turbo trans with a problem area internally will let go quickly.
Did you tear down the turbo transmissions to verify it was the bearings / synchros that were damaged?

I don't think you mention what kind of clutches you're using?
Unsprung, puck clutch disc can cause damage unless you're very good as synchronizing your shifting.
Speaking of shifting...bad, slopping shifting can also damage transmission quickly.
Do you rev match often?
How about on the downshift?
What kind of fluid are you running in them?


-Ted

[Whizbang]

have you thought about just going to a T5?

[Rotarydave]

Got another thought for your too. What about have a tranny built for your application. I think that if you had spent the money to have one tranny rebuilt with new bearings etc then you may not have had as many problems. You also don't talk about other things which are just as important, what driveshaft are you using, how old is it? when you went to the turbo tranny in a NA chassis did you also replace the rear end if not who built your driveshaft and what RPM and balance spec did they use? Another thing you didn't mention, you talk of engine vibration but what motor mounts are you using, what tranny mount and what about the rear end mount as well. Used/worn out rubber ones will then put something in the drivetrain in a bind usually the tranny or driveshaft. I have plenty of "good used take out trannys" that I know absolutely nothing about car looked good, looked like it was taken care of but the motor was blown..... hmmm its really easy to say it ran fine when it was put away. Another problem we have seen is that trannys stored on their noses for a long time with little or no oil tend to corrode the gear sets and internals due to natural condensation and water getting in the tranny. I have esp seen this problem with JDM engines/trannys. It isn't a great crisis but enough to shorten the life esp when used heavy. You mention drag racing so I am going to say it, how many times have you missed a shift or speed shifted or power shifted, don't bother to deny it I race to and have a passel of trannys to prove it. Using a used stock tranny for racing application I expect to lose one about every 6 months just a fact of life If I don't want to do that I need to upgrade and then something else will break that is how the system works.

[NoDOHC]

Originally Posted by RETed

The consensus seems to be that non-turbo 13B putting down close to 200hp at the wheels will shorten the life of the (FC) non-turbo transmissions.
200 at the wheels is typically 150 lb-ft at the wheels...
You're at this level right now...and then some.
So, with the non-turbo transmissions, it's no surprise you're killing them.

With the 4-port, I agree, but I killed two transmissions with a 6-port, barely clearing 100 WLb-Ft.

Originally Posted by RETed

As for the turbo transmissions...
Hard to say...
Used units are not a very good baseline - same goes with the non-turbo transmissions.
To have good data, the transmissions need to be inspected and rebuilt.
Even a turbo trans with a problem area internally will let go quickly.
Did you tear down the turbo transmissions to verify it was the bearings / synchros that were damaged?

No, I should do that. I have some experience with ruining transmissions, the symptoms all pointed to bearings. I intend to rebuild this US spec transmission, as they are hard to come by these days.

Originally Posted by RETed

I don't think you mention what kind of clutches you're using?
Unsprung, puck clutch disc can cause damage unless you're very good as synchronizing your shifting.

I have a sprung Spec Stage 3+ Clutch (major overkill - rated at 505 Lb-Ft). I have soaked it with ATF to get a reasonable launch, as the stock condition was way too grabby. However, it is relatively mild now.

Originally Posted by RETed

Speaking of shifting...bad, slopping shifting can also damage transmission quickly.
Do you rev match often?
How about on the downshift?

I typically shift about 2,000 rpm and do so very gently. I will occasionally rev to 10,000 rpm in 1st gear and then go straight to 5th, but I let the clutch up in neutral as the engine is spinning down and then disengage it just to go for 5th when the tach drops below 2200 rpm. This is a daily driver and I don't want trouble with the police.
Bear in mind that the only synchro trouble that I have ever had was on the transmission that I drag raced with and the one that abruptly lost 5th gear synchros and reverse.

Originally Posted by RETed

What kind of fluid are you running in them?

Mobile 1 75W90 Synthetic

Originally Posted by RETed

-Ted

[NoDOHC]

Originally Posted by Gravity Fed

have you thought about just going to a T5?

Many times... Unfortunately I don't want another fabrication project right now and I am unsure if a T5 (which are not bullet-proof) will withstand what is killing the turbo transmissions. I am also concerned about the bearing lubrication at 10,000 rpm.

[NoDOHC]

Originally Posted by Rotarydave

Got another thought for your too. What about have a tranny built for your application. I think that if you had spent the money to have one tranny rebuilt with new bearings etc then you may not have had as many problems.

I think I will do exactly that, with the best bearings that I can afford.

Originally Posted by Rotarydave

You also don't talk about other things which are just as important, what driveshaft are you using, how old is it? when you went to the turbo tranny in a NA chassis did you also replace the rear end if not who built your driveshaft and what RPM and balance spec did they use? Another thing you didn't mention, you talk of engine vibration but what motor mounts are you using, what tranny mount and what about the rear end mount as well. Used/worn out rubber ones will then put something in the drivetrain in a bind usually the tranny or driveshaft.

I have full Turbo Drivetrain, the NA Diff was not a fan of my 245/40/R17s and I was not a fan of the noise that it was making under throttle. The driveshaft is not new, but it is in good repair, I ran over 165 MPH on the dyno without vibration.

I have 1 year old Mazda Engine mounts and the transmission mount was replaced with the US spec transmission (about 10,000 miles/1 year ago).

The Front Diff mount broke again about 2 years ago, it was replaced with a new Mazda one.

Originally Posted by Rotarydave

I have plenty of "good used take out trannys" that I know absolutely nothing about car looked good, looked like it was taken care of but the motor was blown..... hmmm its really easy to say it ran fine when it was put away. Another problem we have seen is that trannys stored on their noses for a long time with little or no oil tend to corrode the gear sets and internals due to natural condensation and water getting in the tranny. I have esp seen this problem with JDM engines/trannys. It isn't a great crisis but enough to shorten the life esp when used heavy. You mention drag racing so I am going to say it, how many times have you missed a shift or speed shifted or power shifted, don't bother to deny it I race to and have a passel of trannys to prove it. Using a used stock tranny for racing application I expect to lose one about every 6 months just a fact of life If I don't want to do that I need to upgrade and then something else will break that is how the system works.

The transmission that died at the drag strip was not in great shape when I went. The synchros in second gear died completely (there was barely anything left). I did miss a shift, but it was going for 3rd. I only went the one time, as I am worried about getting thrown out for not having a roll cage. I was running high 13s with the 6-port at 155WHP. I am now well above 200WHp and have removed about 100 pounds of unnecessary spare parts, which I think will put me in the low 12 second region. 12 is the cutoff for a roll cage around here. (G-tech gave a 12.05@123, my data log which indicates more like 12.4 seconds to 123.)

Okay, so I occasionally beat the car pretty hard, but for the most part, I drive like a Grandpa. My total Average fuel economy with the 9.2:1 4-port is 27.3 MPG, that includes tuning and breakin.

I never speed shifted second while drag racing, as this just causes tirespin. I did speed shift 3rd (kinda cool, the tack barely nudges below the redline). Either way, I have only done that a couple times ever on this transmission and that was only right after installing the Defined Autoworks Headers - almost 6,000 miles ago. Would it take this long to show up?

If this is par for the course, I will accept it. I think that the failures are a little bit too frequent. I posted this to see if any others had similar experiences. If completely rebuilding a transmission doesn't make it last any longer than 10,000 miles, I might try the RX8 6-speed or the T5 next (I would prefer a WC T5 as I would love to have 0.625:1 overdrive - the 45 kPa of vacuum I pull while cruising does not sit well with me).

[RETed]

Originally Posted by NoDOHC

I have a sprung Spec Stage 3+ Clutch (major overkill - rated at 505 Lb-Ft). I have soaked it with ATF to get a reasonable launch, as the stock condition was way too grabby. However, it is relatively mild now.

I gotta ask why the overkill on the clutch?
You have other plans later down the line that will significantly raise power levels?

I would try and stick with an organic face clutch disc is possible.
This will soften the drivetrain shock.
No need to go metallic puck clutch disc unless you're making over 300 lb-ft.

Mobile 1 75W90 Synthetic

Would it be possible to go thicker on the trans oil?


I think what's killing your transmissions is the brief episodes of 10k RPM's.
No OEM trans is rated to handle revs that high...
This explains all the bad bearings.


-Ted

[NoDOHC]

Originally Posted by RETed

I gotta ask why the overkill on the clutch?
You have other plans later down the line that will significantly raise power levels?

I would try and stick with an organic face clutch disc is possible.
This will soften the drivetrain shock.
No need to go metallic puck clutch disc unless you're making over 300 lb-ft.

Yeah, the clutch is not ideal for a daily driver (although it is pretty smooth when soaked with ATF). The clutch is sprung, so the shock is not as bad as it could be.



When I bought the clutch, I had just ruined a cheap clutch on the dyno and didn't want that to happen again. I had a 8.2:1 polished-rotor 4-port engine, a 3 bar map sensor and cobbed-together exhaust. My only intention in that dyno run was for a baseline. What I had in mind was a Turbo and about 14psi boost (>400 WHp). I still may do that, but I would have to put the 8.2:1 engine back in, as I think 9.2:1 is a little heavy for a turbo rotary.