Random Transmission Failures

[Steve Hoelscher]

There always seems to be some interest in some of the odd things I find with X1/9 transmissions. So I though I would start a thread for that instead of posting this stuff elsewhere.

With this winter's round of transmission builds I have run across a couple of common issues I see regularly. I mentioned to Jim during his 128 4 speed build that a core he sent me was somewhat interesting and that I might post some pics on what I found.

First up is a somewhat common problem. One of the cores I got from a customer was in better than average condition and had never been apart. This is usually a good thing because I often find that the biggest problems I have to correct are errors from previous builders. And given the frailty and age of these transmissions a very high percentage have been apart before I get them.

In this instance, the unit hadn't been apart, I know because the driver's side (left) stub shaft would not come out of the case. This is not uncommon. I have an 8 lbs slide hammer setup specifically for pulling stub shafts. Now these can be quite stubborn to remove but I can typically get them out. Occasionally I can't and this was one of those times. I have an alternative means of using bolts to jack it out but even that failed. When this happens you can't get the case apart because the stub shaft has to come out to split the case. The only option then is to break the case. And given that good cases are becoming scarce, I hate to do that.

I use an air hammer to break the case between the diff housing and the stack housing. I can then remove the part of the case with the gearset and pull the two shaft. See above photo. Now I can pull the diff with the case and stub shaft.

I would like to salvage the stub shaft and diff assembly if possible so I rig the assembly in my press and press out the stub shaft. In this case, I maxed out my 20 ton press and it still wouldn't come out. So the entire diff carrier and case where scrapped.

In the photo below you are looking at the empty diff carrier, the bearing, the seal carrier and stub shaft. They won't come apart. And by now, even if they did they have been so highly stressed that I would never use them.

So, what should have been a great core to build produced only a rebuildable gearset and no case or diff. Fortunately, I have diff carriers but cases are scare now.

If you haven't seen a stub shaft this is what they look like. The snap rings fit in the grooves on at the end of the splines.

The above issue isn't due to an assembly error by a rebuilder. It was a retaining clip that was probably sprung when installed at the factory and fouled the shaft when I tried to remove it. Usually, once a stub shaft has been out they are quite easy to remove again and I seldom see this problem on units that have been rebuilt.

Another odd problem I run across is somebody improperly installing the speedo drive. One of the cores that Jim sent me had been rebuilt previously. The gearset was in reasonably good condition with no specific assembly faults but the case itself was another matter.
I found several minor issues with the case due to errors by a previous builder but the speedo drive had the potential for ruining the case.

When the drive was installed they didn't correctly clock the unit so that the allen screw retainer pin fit cleanly into its hole on the speedo drive. Because it didn't match up the hardened allen screw forced a new hole in the speedo drive body.

When I went to remove the drive it didn't want to come out. Now I had no way of knowing why and its not uncommon for these to be stubborn due to corrosion buildup. In this case it was the deformed steel speedo drive body dragging against the side of its bore in the aluminum case. If it had seriously gouged the bore it would be difficult at best to reseal and would cause a consistent leak.

This is what its supposed to look like.

This is the installation:

 

[Dr.Jeff]

Steve, thanks for sharing this.

The only option then is to break the case.

That sucks.

This picture of the broken case reminds me of what happened to one of mine.
I typically wouldn't do this but due to circumstance I used the clutch slave cylinder mounting tab as one of the anchor points to lift the engine/trans assembly off a stand. Got it a few inches up when this happened:

I guess a cast aluminum housing can be brittle.

the hardened allen screw forced a new hole in the speedo drive body

That's surprising. I would think the hardened bolt would strip the threads out of the aluminum case before it would bore a hole in the steel speedo drive.

 

[Steve Hoelscher]

Yep. I was surprised too. My only conclusion: There are a lot of threads, the allen bolt is very hard and the speedo drive must be softer than I thought.

I have seen aluminum cases break for all kinds of strange reasons. People often crack bellhousings trying to pull them into position against the block with the bellhousing bolts. Not a good idea.

A very common problem is having the driver's side CV allen bolts back out and the CV axle smack the case right beside it. Always cracks the case.

 

[Conda]

A very common problem is having the driver's side CV allen bolts back out and the CV axle smack the case right beside it. Always cracks the case.

I had this happen but absolutely lucked out. I was rolling at about 5mph when the CV let go and while it scarred the side of the transmission it did not crack it. It has a few gouges but no cracks thankfully.

 

[dcioccarelli]

I can add another one to the list, although I'm not sure how common it is. Years ago I had a small oil leak in my 4 speed gearbox which I stupidly ignored. I ended up losing so much transmission oil that the bearings started making noise. At this point I topped up the oil but it was too late. I continued like this for several hundred kilometers but at one point when I was driving home from work, accelerating from the traffic lights, I heard a slight thud and then lost all power, as if the car was in neutral. I pulled into a V in the road, just before the onramp to a very long bridge (I was lucky there!) and needed to get towed home. Putting the car in any gear only resulted in some strange metallic gurgling noises.

Closer inspection when I opened the gearbox revealed some broken gears on the input shaft cluster and a broken 4th gear. More surprisingly, though was that I completely sheared off the outer CV joint (right hand) at the point indicated below:

I suppose the gear box must have locked up and the weakest point gave way? Once I lost drive on one wheel the diff wouldn't drive the other?

Cheers,
Dom.

 

[Steve Hoelscher]

When I was racing my '74 I broke quite a few outer CVs as noted above. Its a common failure on those.

 

[myronx19]

Once I lost drive on one wheel the diff wouldn't drive the other

Correct - this is how many axle disconnects work for 4WD/AWD and some E-motor+hybrid systems. I mean, they have a coupling device.


Agree with Steve, my friend's race car with 4spd axles kept breaking the outer splined stub (the original 5spd PBS transmission used a 4spd case & shaft arrangement). Oh, my other friend ran his X1/9 race car with no transmission oil for two laps (at Mosport) before it went BANG! it was completely seized, lol... He forgot to fill it after draining it! But, the splined outer stubs were fine!

 

[Steve Hoelscher]

More random fun. This time an all too common failure, and easy to identify the cause.

You have probably noted I tell people to be gentle with reverse, both selection and clutch engagement. And NEVER, EVER roll start the car in reverse. This is why:

Input shaft:

Reverse Idler gear:

Now the sharp eyed members will note that the teeth are broken away on the side opposite the normal engagement. Reverse engages from the tapered side of the teeth and do not overlap 100%. What happens when you roll start the car in reverse, and the shock load hits the gearset, the entire assembly and case flexes enough to for the engagement to overrun and then finally break the teeth off the components.

The result of the flex is a bent reverse idler shaft and cracked case:

That input shaft is a $350 part. The reverse idler another $140. The case is $250, if I can find one.

This unit was a core that was sent by a customer. These two failures make it 60% junk. Then there is this:

All of that nasty stuff stuck to the case is varnish, mixed with sediment. Varnish is what happens to old gear oil that is allowed to sit for extended periods of time without use. It collects moisture and breaks down. Then when used it doesn't provide adequate lubrication and begins to slowly eat the internals. The lack of proper lubrication ruins the synchros and their components. The bearings, forks, differential, etc... Every wear item gets eaten at an alarming rate. In this unit, the synchro hubs on both 1st and 2nd gear were worn to nothing. Completely non-functional. The synchronizers did nothing. The 3/4 slider was toast along with its synchros, although they did 'something', as opposed to 1st and 2nd. But the lack of synchronizer performance meant it chewed the engagement teeth off both 3rd and 4th. Then there was 5th. 5th was very close to welding itself to the pinion shaft due to the lack of lubrication needed to keep the gear sleeve cool.

So evaluating this core: the case is bad, all 5 gears in the gearset are bad, both sliders are bad, the forks are worn out and the reverse idler is bad. Even the pinion shaft's pinion gear shows enough wear to be noisy so I won't use it. The only usable components are those that a few parts that are not wear items and therefore don't fail. I have plenty of those. So the core is basically 99% useless.

My point was not to make a big deal out of a bad core but do demonstrate the effects of both direct and indirect abuse. CHANGE YOUR GEAR OIL!!!! And use the good stuff (Redline MTL). This unit had GL1 in it. Even if you only put a few hundred miles/year on your car, change the gear oil every other year, unless you live in the desert. It may look new but I promise its not. If the owner had changed the gear oil and not roll started the car in reverse, this unit would likely have nothing more than normal wear. Oddly, it doesn't appear to have had a lot of miles on it.

 

[Dr.Jeff]

All of that nasty stuff stuck to the case is varnish, mixed with sediment.

Same typical stuff often seen in engines that also had improper maintenance.

Thanks for sharing. Nice example of what a 40 year old gearbox can look like.

In another recent thread discussing significant engine upgrades/swaps, it was mentioned the stock X gearbox is sufficient to handle the increased performance (if I recall the example was a upgraded Uno Turbo engine on a X trans). I disagreed. Not necessarily because of the inherent design of the trans, but because of the usual condition of them...even after the typical rebuild (e.g. as done by many owners or average shops, not a 100% proper rebuild like Steve does). The X is considered a sports car by most owners, and typically it gets thrashed accordingly. Given the underpowered nature of the engine, the gearbox is often overly abused to try and make up for the lack of performance. Much like the tendency to always drive it at redline. And the problem with doing a proper gearbox rebuild is the expense, as noted in the above example by Steve. Just to be clear I'm referring to adding a significant increase in power (i.e. engine swap) to a stock X1/9 used/"freshened" gearbox, not a stock or mildly built X engine on a properly rebuilt stock X gearbox (hope that made sense). Naturally there are exceptions, like the purpose built race X that must retain the original engine/trans to meet class rules. But it was noted by one of those individuals that the gearbox requires regular rebuilds to keep it going...not what I'd want to do on a street driven X with a high output Uno Turbo engine.

 

[myronx19]

Steve - saw a NOS late model case on facebook this morning, no price but super interesting! Probably very rare!

 

[beezee]

Nice... I could really use that. My gearbox casing has a few issues.

Brian

 

[Steve Hoelscher]

Yep, very rare would love to know where and how much.

 

[DanielForest]

The Fiat X19 Registro Storico is a Fiat X19 Facebook group from Italy. I guess it's from Italy, or at least from Europe.

 

[Ulix]

Steve,
You showed pics of the broken teeth from bump starting in reverse (I also did this 30 years ago and paid dearly for it).
My buddy just broke a tooth on 5th gear (!) in a trans that had been rebuilt a year ago by a guy who knows what he is doing on X1/9 transmissions.
Is this common at all or super rare?
(The engine is a 1.9 L with big torque).
Is there a special cause for this, or was the gear just overloaded by the engine power?

 

[myronx19]

overloaded by the engine power

In 5th gear? I doubt it. Pictures of the breakage would be interesting to see.

 

[Steve Hoelscher]

Steve,
You showed pics of the broken teeth from bump starting in reverse (I also did this 30 years ago and paid dearly for it).
My buddy just broke a tooth on 5th gear (!) in a trans that had been rebuilt a year ago by a guy who knows what he is doing on X1/9 transmissions.
Is this common at all or super rare?
(The engine is a 1.9 L with big torque).
Is there a special cause for this, or was the gear just overloaded by the engine power?

Ulix, its actually not that uncommon, especially if the car makes significant torque.

Jeff raised an interesting point with regard to X1/9 transmissions and performance, that applies directly to this failure. "How much power will an X1/9 transmission take?" is a common question. The answer is "it depends". It depends on the use. A turbo motor being used for an occasional sporting run up through the gears for a weekend outing isn't much stress on a healthy transmission. A hard launch, at full power, is extremely stressful. I have exploded numerous differential carriers launching my DSP X1/9. The motor made a great deal more torque than stock and the shock loading to the diff carrier easily exceeded its capacity after numerous launches.

But by far the most common failure on most high output SOHC motors is a 4th or 5th gear failure. This is due to the engine's torque working against the taller gear ratio and the car's weight and aero drag. It puts a tremendous load on the pair of gears. A turbo SOHC can easily double the HP/TQ numbers of a stock 1500 X1/9. That additional torque not only is a direct load but generates a considerable amount of heat. Already 5th gear has an issue with lubrication and cooling. Now double the torque load and the heat and lubrication issue will greatly shorten the life of 5th gear if the car spends a considerable amount of time making boost in 5th. Broken teeth are the first point of failure. Its not uncommon for a tooth failure to almost instantly cascade into a stripped gear.

 

[GregS]

Steve, I am wondering if it would be feasible to have the fragile diff carriers manufactured out of billet mild steel? Would this even be possible? If so, could it be made significantly stronger than the cast 5 speed diff carrier. I have stopped entering events that require fast launching because I am scared of exploding the trans.

 

[Steve Hoelscher]

Steve, I am wondering if it would be feasible to have the fragile diff carriers manufactured out of billet mild steel? Would this even be possible? If so, could it be made significantly stronger than the cast 5 speed diff carrier. I have stopped entering events that require fast launching because I am scared of exploding the trans.

That would be expensive but a good digitizer and CNC could certainly make one.

I solved the problem of exploding the diff carrier with two relatively minor modifications. 1) I had the diff carrier cryo treated. 2) I studied the engine mount system and devised a torque suppressor that completely eliminated a number of driveline motion problems. Most importantly it made it much easier to spin the rear tires at launch, which significantly reduces the load on the diff carrier. After implementing these, I never blew up another diff.

The torque suppressor was a major part of this. The lower motor mount is way too soft and permitted a massive amount of fore/aft movement. Not just the normal wind-up that is checked by the dog bone. That movement made it very difficult to break the rear tires loose at launch. Engaging the clutch and giving full throttle would just bog the motor in most cases. With the addition of the torque suppressor, and even with a stock dog bone, the wind-up was minor and the rear tires could be spun for about 10 to 15 feet on most launches, even with 225 Hoosiers on 13x8.5 wheels.

 

[Ulix]

Thanks Steve.
Regarding the torque surpressor, is that just like another dogbone mounted down low by the lower mount?

Here is the 5th gear.
Interestingly, the matching gear shows zero damage.

 

[Dr.Jeff]

The torque suppressor was a major part of this. The lower motor mount is way too soft and permitted a massive amount of fore/aft movement.

If I read your description correctly, you devised a stiffer lower mount to reduce the shock load. Interesting, I might have thought a soft mount would soak up the shock more while a firmer one would transfer that load to the diff more. In other words a bit of the opposite effect. However I see where allowing the tires to spin would allow the load to essentially pass through the driveline altogether. But it seems the moment before they spin, when the shock first hits the system, is when things would break. Obviously your experience showed otherwise, curious to hear more details on how this worked to prevent failures.

By the way, I assume you still have a open diff? So we're talking about spinning one tire. Or do you have a limited slip diff?