ZFQ Transaxle failure

[Tom Leonard]

Unable to post this in the ZFQ specific thread, inhibited for some reason.

Fellow had some parts for sale but was unable to post pics of the failure.

Thought it might be of interest and promote discussion. Curious regarding other failures of this type or any with ZFQ.

To Chris Melia: Any light you could shed on this would be appreciated. Was there a change made to distribute thrust elsewhere vice the end cover? If so, how does one find out if they have the improved box?

 

[Jac Mac]

Would need to know what if any accidents or incidents had happened to the car in question while in use prior to the failure.

My first thoughts are that it might have suffered a 'huge' torque reversal after a spinout or engine failure; example.. spinout, gets airborne while going backwards, lands heavily with car still in gear & motor now stalled, lots of grip as car lands on rear wheels... ring gear literally drives pinion rearwards due to tooth angle etc & blows rear cover of transmission case.... or as we had with JO in the TVR a couple of years ago, spins out, selects low gear while rolling backwards @ about 30mph after spin & pops the clutch @ about 5k to turn it around again....worked that time...but next race standing start resulted in a snapped half shaft... & he wondered why!!!!!

*****Whoops, I just read Davids ( the original parts for sale poster ) description of what happened just prior to the failure... sounds like a bit of wheel hop/tramp during hard acceleration in 2nd gear with some sticky tires.*****

 

[Tom]

I remember Wanni caught some serious flak for asking about the development process on this 'box.

 

[Jac Mac]

The car in question has a KC 427 ( Keith Craft - bored & stroked 351 w ).

Just speaking generally it seems to me that these type motors will all produce more torque than say an old FE 427 of the sixties was ever capable of. The longer stroke virtually assures that, sticky tires add a bit more pain... if Ford worked out that the FE 427 was pushing the limits with the ZF back then, what makes us think that we can up the torque & grip now and get away with it.

I know that the ZFQ 'worked' in the car that was at Road America? a couple of years back so that would suggest that maybe that driver had a bit/lot more mechanical sympathy in his driving style.

 

[Trevor Booth]

The cover has failed in tension at a vertical plane level with the spot face, making the boss longer will just move the plane further rearward. Needs thicker casting and or more ribs to provide a larger area to resist the tensile load induced by pinion thrust.

 

[Cliff Beer]

Agree with both JacMac and Trevor (aren't they saying the same thing??) - more housing material (likely require longer studs) by the stud holdes to spread the loads around and also strengthen the overall design. Some external/internal ribbing would be good too (as suggested). Or, that housing should probably be made from high grade steel...

 

[Jac Mac]

Agree with both JacMac and Trevor (aren't they saying the same thing??) - more housing material (likely require longer studs) by the stud holdes to spread the loads around and also strengthen the overall design. Some external/internal ribbing would be good too (as suggested). Or, that housing should probably be made from high grade steel...

I think we are both thinking along the same lines...though Trevor probably would be reluctant to agree on that purely out of 'Seasonal' mischeviousness:thumbsup:...

 

[David C. Treichel]

I was driving the car when the failure occured.

No wheel hop, no dropping the clutch, just a smooth roll on of full throttle in 2nd gear on a straight road out in the farm country of Wisconsin. When it hit around 5k rpm, just as I was about to put the clutch in and shift into 3rd, she went BANG!

Before I put the sticky tires on it would just burn them, so I'm guessing the stress went into pushing the pinion shaft out the back.

Any opinions are welcome,

Dave

 

[Darnel A.]

The cover has failed in tension at a vertical plane level with the spot face, making the boss longer will just move the plane further rearward. Needs thicker casting and or more ribs to provide a larger area to resist the tensile load induced by pinion thrust.

Lengthening every other boss so the stresses are no longer in a single plane in order to spread the load. Also, bosses should be raised and then spotfaced, not spotfaced into side of housing. This created stress risers at each boss where the cracks propagated from.

Darnel

 

[Trevor Booth]

both thinking along the same lines not saying the same thing. -
speed quest has a good idea also

 

[flatchat(Chris)]

While some housing improvements maybe obvious, it looks to me that pinion shaft bearing retainer is the weak link--it'd be interesting to see all the bits that aren't shown

 

[Trevor Booth]

FC,
only if the pinion bearing is taking the thrust. In a ZF the pinion bearing is a parallel roller bearing and thrust is taken by a ball bearing in the rear cover.
ZFQ appears to be similar

http://www.lotus30.com/Resources/Articles/ZF_Manual/ZF-5-DS25-Manual.pdf

 

[Mike Pass]

Hi Dave,

What power and torque was your motor putting through the box? Some UK users are putting quite high power/torque motors onto ZFQs so it would be very helpful to compare the loading.

Thanks
Mike

 

[David C. Treichel]

Mike,

520 hp, 490 ft lbs @6ooo

 

[Mike Pass]

Thanks Dave,
A good stout motor but not excessive. Also quite top endy for a biggish stroker.
Cheers
Mike

 

[Tom Leonard]

what makes us think that we can up the torque & grip now and get away with it.

Well, nothing other than the manufacturer assured us that we could because this box is supposedly stronger than the original ZF.

 

[Jac Mac]

I see the ZFQ only uses Eight bolts on the rear cover attach.... The RBT appears to have about 12 or 13 doing the same job, plus the cast iron housing mentioned before.

 

[Seymour Snerd]

Well, nothing other than the manufacturer assured us that we could because this box is supposedly stronger than the original ZF.

As stated in several places,

"The helical synchromesh ZFQ is rated in standard form at 600BHP and 550ftlb we have many cars in this region of power."

Also:

"When testing the ZFQ we destroyed two sets of CV joints so you have to ask yourself about limiting factors. (Drive shafts, CV joints, Clutches, tires, wheel strength ect.)"

(post 326 at http://www.gt40s.com/forum/vendor-m.../20751-zfq-new-proposed-gt40-transaxle-4.html)

 

[Seymour Snerd]

David --

Have you communicated any of this to Chris Melia or Quaife? If so how did they respond?

 

[David C. Treichel]

Alan,

No I did not.

After I took the transaxle apart we were looking for a stronger box. I didn't like the fact that the pinion thrust was contained by the lightweight rear cover.

I had heard that Quaife added a thrust bearing/clamp design right next to the pinion gear in their later designs. This is the design that Porsche has always used and we are putting a LOT more than 520 hp through a G50/50 that has never given us any issues. However I was informed that our box could not be retrofitted with the new design so I looked elsewhere for a solution.

After talking with Oliver Ring and expressing my concerns, he assured me that they beefed up the case and also the rear cover in the RBT to be able to handle the torque. There is no doubt about that.

Also we wanted a box that was available NOW. The RBT bolted right in with only a few very minor linkage changes. Plus the support was great. There was a small leak on the shift shaft seal causing the linkage box to drip gear lube, I was sent a new seal promptly.

Dave