Another Diff Bites The Dust…

First the good news: my 1988 Testarossa won first place (in the 12 cylinder Ferrari category) at the 2013 Bella Italia Concours d’Elegance in San Diego, California.

Then the bad news: soon thereafter my differential exploded.

I thought this would never happen to me. Before I bought my car I was aware of this potential problem as I had been reading the entries here on F-Chat. I steered clear of any TR that had been tracked or raced. I examined the repair records of any potential candidate, looking for signs of a hard life or abuse. My car had just a few owners and lived a pampered life.

It had only 20,503 miles on the odometer when I bought it and it had been maintained by the dealer for the last ten plus years. He even worked on it personally and vouched for it as a solid example, both mechanically and aesthetically. I felt confident that I had found an exceptional TR and drove it home.

Owning a Ferrari is the fulfillment of a boyhood dream, and I give mine the red carpet treatment. I always do a low speed lap around the neighborhood in first gear to warm up the gearbox before attempting second gear. I still have no problems with the second gear synchromesh. I never rush the up-shifts and make sure the lever is in the gate before releasing the clutch. I always match RPMs for downshifts and don’t slip the clutch. No burn-outs or power slides. Everything is nice and smooth until one day….

I was taking a friend along for a drive when it happened. We were cruising along at about 30 to 40 mph when I noticed the clutch felt a little odd stating off from a stop light. No bangs or clunks or other noises. We drove along normally for a few more miles and I dropped off my friend when I noticed in my rearview mirror that the heat waves coming off the rear deck had some density to them. It looked like light smoke. I figured some fluid from cleaning the engine had gotten onto the exhaust and was cooking off. All gauges were normal. No indication of elevated oil or coolant temps. No trouble lights on the dash. I was almost home so I kept on going.

I made it onto my street and was rolling along at less than 5 mph when I noticed a cloud of white smoke coming off the engine. Now I heard noises for the first time: loud groans from the rear as I turned the wheel. I had enough momentum to roll onto my driveway and immediately shut off the car. Fluid was pouring out from the engine bay like a waterfall. At first I thought it might be coolant since there was so much pouring out onto the driveway. The puddle was growing larger by the second. Testing it with my finger I realized that it was some kind of oil and the odor indicated gear oil. Following the drip trail I saw that it began just a few hundred feet from my driveway down the street.

The oil was leaking from the bottom rear of the engine somewhere and dripping onto the cats and exhaust pipes, which explained the smoke. A quick call and some emailed pix to the shop confirmed that the car would need to be towed. I hoped it was something simple and easy to repair, like a loose transmission filler plug. It wasn’t.

The mechanic tried to pull the diff casing off to examine the interior but it wouldn’t budge. Something was locking it in place. We would later discover that the outer bearing was demolished and that was jamming the cover, preventing it from being removed. The entire engine sub-frame, including the engine, gearbox, differential, rear wheels and suspension, would have to be removed just to diagnose the problem.

The casing was removed and the damage was severe. The welds at the top of the differential ring gear holder, which connected the end plate to the cylinder of the differential body had failed and the end plate was forced out toward the rear wheel with explosive force. The outer bearing race was in pieces and the roller bearings were smashed and distorted like melted tootsie rolls. The bearing cage was torn and twisted. These broken parts were forced into the aluminum casing like a battering ram and cracked it into three big pieces, releasing all the differential oil.

Luckily this happened when the car was being driven at relatively low speeds. The damage was limited to the drivers side of the differential and the gearbox was completely unharmed. If the diff had blown at high speed the shrapnel could have penetrated the gearbox casing and even the engine itself. It could have been much worse.

A little good news emerged from the gloom; the pinion and ring gear were completely undamaged and could be re-used. Now all I needed was a new diff ring gear carrier. The factory unit for the 512TR (which they wisely redesigned to eliminate the welded end plate) would fit my TR and cost about $6K. I opted for an identical spec aftermarket part for half the price from Forza Motorsports in England. Phil Worrell from Forza was very helpful with technical info and gave the mechanics detailed guidance on how to set up and shim the assembled diff. His part is a one piece cylinder open at one end and CNC machined from high strength billet steel. No welds anywhere. It’s rated for up to 1,000 HP and comes with a lifetime guarantee. Since the TR develops just 390HP I don’t expect any problems.

While the engine was out we did the timing belt service and replaced a few seals and gaskets as well. I was allowed to hang around in the shop with the mechanics when they worked overtime and so I completely cleaned and detailed all the mechanicals and the engine bay. It was a unique opportunity to access all those usually inaccessible surfaces. When the engine went back in the engine bay it was in showroom condition.
Was the failure related to harsh treatment from a previous owner? I have no idea how the car was treated before I got it. I know that I treat it with great care. It gets driven fast at times but I don’t abuse it. I drive with mechanical sympathy and am able to get impressive mileage out of clutches and gearboxes.

One thing that is clear to me is that welding the end plate onto the cylindrical housing of the diff is just a bad idea. The diff casing contains shims and plates that place powerful tension forces on the ends of the diff carrier. Welding on the end plate is just asking for trouble, and the factory probably realized that early on. If the welds themselves don’t break, the metal near the welds , in the heat-affected zone, can. There were probably enough failures under warranty to trigger the redesign. Otherwise the 512TR and 512M would be using the same old welded design. There would be no reason to change it if it worked just fine. Obviously it didn’t work and Ferrari fixed it for the later models. This is a design flaw and a ticking time bomb for TR owners.
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What was the final bill?

I used the Forza Components carrier. The price was just under $3,100, including S&H. The part is sold in UK pounds and the cost varies according to the exchange rate. Total bill was $16,650, which includes the carrier and all the other parts & labor. I had the timing belt service done as well as some other improvements.

 

Good idea. I got lucky and had no collateral damage in the gearbox or engine. Good thing it didn't happen at speed on the freeway.

 

Yeah, I remember reading your post before I bought the car and thinking "Boy, I hope that never happens to me."

Bottom line is that the car now runs better than ever and I shouldn't be looking at another engine out service for a few years. Maybe by then I'll be able to fix it myself.

 

Sure, add me to your list. Maybe someday Ferrari will have pity on us and reimburse us all for these diff repairs! It would be great PR, showing support for their legacy models.