ZF failure? - Page 2

Paul Fleming · 02-23-07, 04:00 AM

For someone who admits to no hands on experience jac mac, why do you think that the bolts have a course thread? in fact it is the opposite, they do have a fine thread. The lockwire is as you say only a safety net, I would never rely on it alone. I always Loctite the bolts as well. The other factor to consider is that the standard ZF bolts are not the highest quality, I always replace them with higher grade ones. With over 150 transaxle unit rebuilds and no failures I do feel as though I can speak with a little bit of experience! As we always say, it is the nut behind the steering wheel that is the biggest problem. remove that and you will eliminate all the problems!!

Ian Anderson · 02-23-07, 04:17 AM

David

I was referring to a pair of motors and gearboxes I located for John.
They were complete and a bargain! The wirelocking on them was beautifully done.

I cannot say the same about the connection of the wiper shaft to the spindle!

But that's another story - back to ZF failures

Ian

Ross Nicol · 02-23-07, 07:09 AM

Hey Paul - Do you think that nut behind the wheel forgot to put oil in the box, thus causing the pinion bearing failure. That bearing is a very formidable tapered roller and I can't believe it failed causing all this damage without a human being involved.I bought upgraded crown wheel bolts but they proved softer than the originals. I ended up drilling the original bolt heads and lockwiring in pairs as per Jac Macs description.I did use loctite as well.
Ross

John W · 02-23-07, 09:20 AM

Okay,
I can see from the pictures and the descriptions that the lockwire is in a Z shape (i.e. top of left bolt to bottom of right bolt) such that any movement is immediately under tension.
Pauls picture would allow the bolt to move maybe 10 degrees before it came under tension as the wire tightened.
I don't see this as being a real big problem, as it still stops full rotation, and that small a movement would likely still see the bolt head under tension from its threads (I guess that relates to the comments about thread pitch).

The wire on the wiper motor still only has a single strand of wire going throughthe head of the bolt, and does not only do 2 screws, it does 3 on the motor in one go, and 4 on the wiper arm geaerbox in one go..

Dave, the arm is on a spline with a bolt in the end (not a pinch bolt) so someone forgot the locktite

Paul, how many other boxes have you seen that have failed ?
(fingers crossed my one doesn't !)

Scott Calabro · 02-23-07, 10:16 AM

If You guys really want to learn how to safety wire correctly, go to the FAA's website. FAA.GOV, search AC 43.13 1B. There you will find out how A&P's do the real thing. Use good quality stainless wire, good saftey wire pliers if space permits, and ALWAYS FILL 50 % of the hole with wire, i.e. if you have a .050 hole use at least .032 wire.

25 years A&P I/A exp. at your service!

S

P.S. If the saftey is done correctly, with the proper wire locktie IS unecessary!

Richard Timte · 03-07-07, 02:05 PM

Here is the picture I was talking about a couple of weeks ago when I introduced my Transaxle.

Bill D · 03-07-07, 03:58 PM

A newbie here on the workings of a ZF, but what causes such catastrophic failure? Too much power?

Scott Calabro · 03-07-07, 04:20 PM

Bill,
There was a disscussion on this issue not too far back. I'll probably get corrected, but I know the fact that the gears are helical cut, causes them to push away from each other. Under high torque loads this can exceed the gears ability to withstand the load causing a gear or somtimes a case failure. I'm sure someone with ZF specific knowledege will chime in.
S

Probably the short answer, all else being equal, is abuse !

Richard Timte · 03-07-07, 04:32 PM

Bill,

Paul will need to comment on what happened to to his box. But the picture I posted I believe is 4th gear. It was sent to me by a GT40s forum member that was racing his pantera. It happened when he was rolling on the throttle coming out of a fast corner (estimated HP was 550 to 600 HP) per his letter. I got the letter over a year ago in regards to the LG600 I had and straight cut gears. He stated that this happen 3 times (each time he had the box rebuild by RBT). After the third time he had them put straight cut gears in the box.

Bill D · 03-07-07, 04:37 PM

Thanks guys!

Scott Calabro · 03-07-07, 04:47 PM

Bill,
You're -40 has a 331 cu.in. SBF ? I dont know specifics, cam grind, comp. ratio etc., but I figure 1.25 HP per cu. in. .... 414 HP... You should have no problems, unless you get excited on cruise night! Whatever you do DON'T get those Avons to hook. Thats when you will be even more intimate with RBT !
S

Bill D · 03-07-07, 04:56 PM

Engine should make around 475HP. I'll be doubly carful with those AVONS

BruceLambo · 03-09-07, 09:31 PM

Quote:

Originally Posted by RTIMTE

Bill,

Paul will need to comment on what happened to to his box. But the picture I posted I believe is 4th gear. It was sent to me by a GT40s forum member that was racing his pantera. It happened when he was rolling on the throttle coming out of a fast corner (estimated HP was 550 to 600 HP) per his letter. I got the letter over a year ago in regards to the LG600 I had and straight cut gears. He stated that this happen 3 times (each time he had the box rebuild by RBT). After the third time he had them put straight cut gears in the box.

It sounds to me like the gears that were replaced at each rebuild were of the same quality as the original one that stripped. Perhaps an option if its too consitant is to have a new one made of a different material?? Helical cut gears are stronger that straight cut gears. As was mentioned above, about the gears pushing each other apart, yes, the helical ones, as well as pushing away from each other, also want to move in opposite directions to each other (sideways). At what position is the 4th gear on the shaft of a ZF box? Perhaps its in the middle of a shaft between the bearings, and shaft flex is the culprit, judging by the breakoff point on the gear teeth?? The closer the gear to a bearing the less shaft flex.
This is also reminiscient of gear stripping on Renault boxes used in the Lotus V8s, except their issue is with 5th gear - come off the throttle at high revs, then back on and whammo! Instant teeth removal. The higher gears (4th and 5th) are the most loaded in the gearbox.

Sandy · 03-10-07, 12:55 AM

The Pics that richard posted were the main reason that I went with the 930 box. To me, and this is just a feeling on the way it looks, the ZF box is not a super strong looking box. Before the flames start, I'll say it again, just my opinion and it has not much basis. The information here really does indicate the opposite is true, with all the Pantera folks running them with crazy hp and they really do seem to work well. When I looked at the ZF that was out of the Petersen MK3 a while ago while at the shop of a friend I was glad I didn't go that route. I think the key is first understanding what your doing with the car and if not a crazy hp motor or track abuser with some sticky tires most all the boxes will work well. I am really excited to see the new boxes come to market (Quife, Richard's, etc) so we are all able to pick a box that suits our needs be from ZF, Porsche, etc.

Did anyone ever get gear width and other dimensions for the ZF's for comparison to other boxes?

Sandy

Russ Noble · 03-10-07, 01:33 AM

Quote:

Originally Posted by Sandy

Did anyone ever get gear width and other dimensions for the ZF's for comparison to other boxes?

Sandy

Not so far Sandy, we may have to wait til Ross Nicol has to strip his one after "rolling on the throttle coming out of a 4th gear corner".

He'll be a fix it himself man - no sending it back to RBT - and I'm sure he'll enlighten us.

Cheers

Russ Noble · 03-10-07, 01:42 AM

Quote:

Originally Posted by RamboLambo

Helical cut gears are stronger that straight cut gears.

Rambo, did you not see this post of Richard's (reproduced below) after your similar statement on the TRT thread?

Quote
"I was going to respond to RamboLambo comment:

"but helical cut gears are in general stronger than straight cut gears."

I don't know where you got your information, but its just the opposite (less teeth which equals more root in the same ratio of gear, plus the contact patch is a lot bigger which means more area to transferring the power). Also, not one race box has helical gears, because it takes 1.5 to 1.75 times the weight to transfer the same amount of power (wider or bigger diameter gears)." Unquote

Cheers

BruceLambo · 03-10-07, 02:35 AM

Quote:

Originally Posted by Russ Noble

Rambo, did you not see this post of Richard's (reproduced below) after your similar statement on the TRT thread?

Quote
"I was going to respond to RamboLambo comment:

"but helical cut gears are in general stronger than straight cut gears."

I don't know where you got your information, but its just the opposite (less teeth which equals more root in the same ratio of gear, plus the contact patch is a lot bigger which means more area to transferring the power). Also, not one race box has helical gears, because it takes 1.5 to 1.75 times the weight to transfer the same amount of power (wider or bigger diameter gears)." Unquote

Cheers

Ahh ok, always open to constructive information and criticisim, but this is my take on it.
First, the Auckland based gear machining company that I deal with confirms that helical is more stronger than straight cut. The other thing is the effective contact area is greater on helical gears. Measure along the length of a helical gear tooth to that of a straight cut. As with the less tooth idea, have a look at the Chev Corvette transaxle unit. There are many fine teeth per gear than I have seen on any other box. In general there is always 3 teeth meshed with this box. Most others I have seen have only had 2 mesh at any time. blah blah ..... etc etc
Yes, there is a power loss because of friction from helical gears wanting to push each other aside as well as apart, and this friction is taken in the thrust bearings and sliding tooth contact. This is a case for straight-cut where in the search for the every last bit of hp is used to propel the vehicle not waste it in heat.
Perhaps there is a point at which straight vs helical in strength comes in when tooth size vs profile etc crosses?
Or perhaps there is a difference in manufacturing materials of gears, OR a build up of metal fatigue of stressed gear teeth over the years of use??

Ross Nicol · 03-10-07, 04:53 AM

Hey this ZF failure heading should be changed.Am I correct in assuming people are making gearbox selection away from ZF based on one failure? It is most likely the ham fisted useless driver caused it himself.I'm rolling on the floor with laughter, not rolling on the throttle after a 4th gear corner.How much torque are you likely to have available at this time, not enough to destroy a gearbox, nowhere near it so forget that one and start thinking the abuse the driver gave it on the previous lap. How about dodgy repairs too like selector interlocks being left out and 2 gears going in together.I don't go for the sticky tyre thing either Sandy. It only takes 2500 revs to light the hell out of mine off the start so I won't agree with sticky tyres causing gearbox damage. Remember it's not a heavy car even though 50% of the weight is over the rear axle.I have fairly wide 300 slicks on the rear and I've got 4 years of racing under my belt, all standing start races, not one rolling start thats for the whimps in their fragile F5000s. So forget even thinking a ZF is fragile and next time someone says they broke one 4 times start asking how many others they've broken.

I don't think I flamed you did I Sandy?PS Going to Phillip Island Historic meeting tomorrow ubelievably 500 cars entered, too many real cars for them to accept my fake.Not sure if any GT40s entered, I will report with times if theyre quick.
Ross