Jlaa

Hi all --

This question is about TBDifferentials and not really about LSDs ---

My 993's G50 transmission is open right now and my original transmission has an open differential. I keep on thinking it is a shame to put the transmission back together without putting in a *something* --- like an Torque biasing differential a la Guard TBD, Quaife, Wavetrac, etc.

Note --- I'm not actually trying to solve for any problem. I occasionally drive in a spirited manner on winding roads, but i do not forsee autocrosses or driver's events any time in the near future (I got that out of my system 20 years ago).

I read about:

--- LSDs provide some lockup under trail-braking which helps steady the rear end at "big track" events (at the cost of slow speed understeer)

--- TBDs do not provide any lockup under non-load conditions, but have the benefit of being virtually maint free (no clutches to replace) and no low-speed understeer.

I read about Quaifes, Guard TBDs, etc. which all perform like regular TBDs
I also read about Wavetrac TBD - which claim to provide some biasing even when one wheel has no traction (which is different from regular TBDs)

.... and I've rationalized a Guard TBD or Wavetrac TBD in my head.

(Obviously Matt's product has the reputation of being the strongest and of the highest quality....)

Any thoughts on either? Or is this a fool's endeavor - a waste of money?

Thanks!

BTW some reading reference

Guard FAQ on TBD vs LSD
Wavetrac TBDs
Positive experience with wavetrac on rennlist with a 987
Some of Matt's thoughts on Pelican
PCA San Diego region discussion on TBD

Bill Verburg

You seem to have a good handle on the benefits of each type.

I'd go w/ either a GT 40/60 or GT TBD

For street use you don't really need either one 99.99% of the time but for that last .01% it sure is nice

pp000830

[QUOTE=J thinking it is a shame to put the transmission back together without putting in a *something*[/QUOTE]

I think the biggest advantage to replacing the standard diff is rarely discussed. I have a theory that when a 911 is pushed to the point of wheel spin it jackhammers the standard differential gears and may be the cause of the common gouging chips from the diff's gear face showing up at the lubricant drain plug. From what I understand this doesn't happen with a limited slip diff and may explain in part why the Turbo, I believe, comes with a limited slip arrangement.

Can someone tell me what the difference between a torque biasing diff and a limited slip is? Seems intuitively that are the same thing??

Andy :-)

Jlaa

Thanks Bill. You are always direct with dispensing wisdom in such a non-threatening way.


Hmmm. PP, are you the author of the 20 page "IF the 993 has these characteristics THEN you may want to check this" Tome of 993 repairs? I read that theory in that tome as well. Frankly I suspect if a previous owner of your car was lighting up the rear tires on a naturally aspirated 993 driving around on the street then that person was either being a hooligan (993s don't make that much torque to do that without a clutch drop really) or driving exceedingly aggressively!

Hi PP --- this provides a good primer.

LSD vs TBD on Rennlist
and here below is an even more succinct primer
Super Succinct on Rennlist

The thought that I am really mulling over in TBD-land for my street-driven-car is GT or Wavetrac. Matt's stuff has such a peerless reputation for quality that I think the question I'm really trying to answer is:

"does the "biasing under zero traction conditions" part of the Wavetrac device REALLY work for REAR ENGINE REAR DRIVE cars ABOVE AND BEYOND a regular TBD like a Quaife or Guard TBD?"

I'll report back if I connect w/ Matt too.

Thanks everyone.

mcipseric

I have had the Wavetrac for the past few years and I am very happy with it.

Jlaa

Thanks Mcipseric -- I have ready several of your posts from days past about your wavterac and your earlier thoughts have intrigued me to start this conversation.

BTW folks - I ran across this incredibly detailed teardown and analysis of Guard vs. Quaife from a Cayman form ---- my goodness, 85% of this is over my head.

Awesome analysis of Guard vs Quaife TBD

The conclusion that this poster came up with is that, verbatim - "I am sure of one thing: The design of the Quaife unit causes less thermal stress on the transmission oil."

Whether or not that additional thermal stress is meaningful --- I have no idea.

BTW --- the technical depth of this article reinforces my decision when I was a young'un that mechanical physics/engineering is NOT a field of study that I should try to master!!! :-)

GTgears

Never had a G50 tbd fail. I don't think the competition can claim the same.

And you will never have a zero traction situation with your car the way you drive it.

That Cayman article is a joke. I provided the tbd for that "test". The guy just took them both apart, speculated about what he thought was going on with no real technical expertise, and then published it. I chose not to argue with him and let it be published because at the time Quaife was doing a $1000 group buy on Planet9 and people were going to buy just on price anyway. I knew that in a couple year they would start breaking them and figured any warning I issued would be assumed to be me trying to sell something.

I was in this business for 7 years before I bought GT. I only sold GT to my customers. I never had an issue. I'm the Norelco guy. I like the product so much I bought the company.

And now I'll let you get back to the input of your peers.

Juha G

I'm with Bill on this one...what do you need the LSD for? If for track driving, go with a proper disc type unit, if for street. You don't really need it for ****.
The 993 has very good traction even with open diff.

With regards to which unit/maker to choose, I'd skip all the marketing BS/hype and get a proven product, such as GT.

Jlaa

Thanks Matt for that balance! There are always multiple views to a story, and I appreciate your input.

I think, BTW, you mean that you're the Remington guy? (that liked the shaver so much that he bought the company?).

My father was a norelco guy. He liked those floating discs. Those floating discs always creeped me out so when I became of age, I used the "Steel mesh thing" from remington! :-)

GTgears

You are right. Though I prefer a blade to electric when I do actually shave. I'm mostly a beard guy.

pp000830

Thanks for the feedback and guidance. Yes I am the author of the 20 pager. I added the comment about the diff because on my vehicle, purchased with 40K some odd miles on it, needed 1st and 2nd gear synchros at 80K. When the technician opened the box up there were good size gouges in one of the diff's gears. My local technician who had 3 g50 transmissions on his bench at the time said the gouging is not that uncommon. I did not qualify if that was on Turbos or with Carreras as well. I am a conservative driver but I can't speak for either of the two previous owners style of driving so your point is well taken in that I do not see too many examples of 993s needing a rebuild at 80K miles for street driven cars.
Andy :-)

GTgears

As the age and mileage on the 993s go up, this is becoming a problem. It has long been a problem on the 996TT, which not only got an open diff, but originally only had 2 spiders instead of 4 in the diff. It was a big enough problem that Porsche upgraded the turbos midway through production. And they also passed it over to the 996 Carreras because they were doing a bunch of warranty boxes for 2nd gear popout and felt it appropriate to mitigate any future problems on the NA cars as the mileage went up.

bw993

Take a look at the OS Giken LSD (clutch based) for your 993.

KaiB

As opposed to the Guard unit? Why?

bw993

The Guard LSD is good. I'm just sharing information. The OS utilizes 24 friction plates and supports 100% lockup. Recommended to me by the engine builder for Singer 911s.

Here's their website: http://www.osgiken.net/products.php?product=lsd