Weak manual transmission, how to strengthen?

Transmission to Rear-end

Moderator: Team

peejay
Guru
Guru
Posts: 1588
Joined: Tue Aug 10, 2010 9:16 pm

Re: Weak manual transmission, how to strengthen?

Post by peejay » Mon Aug 27, 2018 8:05 pm

Is this a Porsche designed trans, or a variant of the Audi 016/01E box?

I will admit to having never once seen a manual trans 928, all have been automatic.

Commentary upthread about the nature of case spreading gave me a kind of eureka moment. I have an aluminum Ford 9" housing and one of the major issues with it is that setup is a huge pain because all of the bores/journals have massive amounts of interference fit. Makes adjusting backlash and gear pattern an interesting experience.

The Mazda transmssions that I blow up on a regular basis (draining gear teeth out, sometimes but not always preceded by bearings that go sloppy) have an almost slip fit in the housings.

The part where I am thinking, and this is sometimes where I get into trouble, is that I wonder if I can drill and tap the case sections so that I can "post" the bearings on the center-center axis, kind of like how stock car guys used to do with Cleveland heads to support the combustion chambers.

There IS no turd that I won't try to polish.

Keith Morganstein
Guru
Guru
Posts: 5433
Joined: Sun Feb 19, 2006 10:19 am
Location: MA

Re: Weak manual transmission, how to strengthen?

Post by Keith Morganstein » Mon Aug 27, 2018 8:22 pm

ptuomov wrote:
Mon Aug 27, 2018 7:11 pm
Keith Morganstein wrote:
Sun Aug 26, 2018 8:42 pm
If the “shafts are spreading”. Clearance increasing between the gears, there will be evidence. The tip of the driving gear, will be making contact in the face of the driven gear. Look for unusual contact in the face of the gear teeth.
Do you have a photo of what this sort of damage looks like?
I have a book of all different kinds of gear damage and failures, and the causes. I’ll have to dig it out and scan some photos.
Automotive Machining, cylinder head rebuilding, engine building. Can't seem to quit #-o

Keith Morganstein
Guru
Guru
Posts: 5433
Joined: Sun Feb 19, 2006 10:19 am
Location: MA

Re: Weak manual transmission, how to strengthen?

Post by Keith Morganstein » Mon Aug 27, 2018 8:38 pm

This does look good, but expensive.
AFB8D3F0-1D36-464F-8D83-AE64196F35F3.jpeg
Automotive Machining, cylinder head rebuilding, engine building. Can't seem to quit #-o

User avatar
MadBill
Guru
Guru
Posts: 13712
Joined: Tue Nov 15, 2005 10:41 am
Location: The Great White North

Re: Weak manual transmission, how to strengthen?

Post by MadBill » Tue Aug 28, 2018 10:49 pm

Probably not cost-effective but the gears appear to be all separate pieces, so custom parts are not out of the question:
o Low helix or straight cut gears.
o Better alloy, e.g. https://www.questek.com/ferrium-c64.html
o Tighten up shaft spacing and bearing interference fit via thin wall sleeves to counter shaft spread/gear tooth disengagement.
o A pal of mine built up a close ratio box for his 375 HP Buick-powered Fiero via a selection of factory bits and a custom input shaft and gear by Houseman Autosport: https://www.racegearbox.com/. He does a ton of specialized automotive gears, e.g. custom final drive ratios for Honda-converted Minis and could be a great technical resource.
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

n2xlr8n
Expert
Expert
Posts: 556
Joined: Tue Jun 28, 2005 9:01 pm
Location: Bama

Re: Weak manual transmission, how to strengthen?

Post by n2xlr8n » Wed Aug 29, 2018 12:44 pm

If it were me, I'd send it (and all samples) to my trusted tranny company and let them tell me how to solve it.

Tapered roller bearings? Case not rigid enough? Heat treat? It could be all of the above. A really good transmission guy could help you out there (of which I am certainly not).
He who is in me is greater than he who is in the world.

User avatar
Caprimaniac
Expert
Expert
Posts: 722
Joined: Fri Nov 18, 2011 1:17 pm
Location: NORWAY

Re: Weak manual transmission, how to strengthen?

Post by Caprimaniac » Wed Aug 29, 2018 4:35 pm

OK, you don't want to og to a Corvette transaxle.

How about the Quaife, UK, transaxle? https://shop.quaife.co.uk/quaife-6-spee ... -transaxle or https://shop.quaife.co.uk/zf-transaxle- ... rn-gearbox Or maybe Porsche, as mentioned.

A hell of alot easier than go through the process of strengthening case, then shafts, then gears, then shifter,..... etc
How to turn GURU in an instant.....

Ken_Parkman
Pro
Pro
Posts: 496
Joined: Sun Jan 02, 2005 11:30 pm
Location: Ontario, Canada

Re: Weak manual transmission, how to strengthen?

Post by Ken_Parkman » Wed Aug 29, 2018 5:26 pm

Completely different question - what are you doing when the failures happen?

While not a perfect solution one comment is type of clutch. You need a tremendously strong tranny to withstand shock loadings. Drag race type abuse (launch, shifts) with a hard grabbing diaphragm clutch that grips the hardest at lock is a really good way to bust stuff. Borg & Beck style pressure plates are not as harsh but I don't know how much you will gain in a street clutch if it will hold the power. And the pedal effort will get a lot worse. For real abuse a sliding clutch is way easier on the driveline and faster as well, but that is certainly not designed with street in mind.

Keith Morganstein
Guru
Guru
Posts: 5433
Joined: Sun Feb 19, 2006 10:19 am
Location: MA

Re: Weak manual transmission, how to strengthen?

Post by Keith Morganstein » Wed Aug 29, 2018 5:53 pm

Keith Morganstein wrote:
Mon Aug 27, 2018 8:22 pm
ptuomov wrote:
Mon Aug 27, 2018 7:11 pm
Keith Morganstein wrote:
Sun Aug 26, 2018 8:42 pm
If the “shafts are spreading”. Clearance increasing between the gears, there will be evidence. The tip of the driving gear, will be making contact in the face of the driven gear. Look for unusual contact in the face of the gear teeth.
Do you have a photo of what this sort of damage looks like?
I have a book of all different kinds of gear damage and failures, and the causes. I’ll have to dig it out and scan some photos.
I have not yet found my book on gear failures with photos. However, if you google search “ gear failure modes “ you will find quite a bit.
Automotive Machining, cylinder head rebuilding, engine building. Can't seem to quit #-o

peejay
Guru
Guru
Posts: 1588
Joined: Tue Aug 10, 2010 9:16 pm

Re: Weak manual transmission, how to strengthen?

Post by peejay » Wed Aug 29, 2018 8:21 pm

Ken_Parkman wrote:
Wed Aug 29, 2018 5:26 pm
Completely different question - what are you doing when the failures happen?

While not a perfect solution one comment is type of clutch. You need a tremendously strong tranny to withstand shock loadings. Drag race type abuse (launch, shifts) with a hard grabbing diaphragm clutch that grips the hardest at lock is a really good way to bust stuff. Borg & Beck style pressure plates are not as harsh but I don't know how much you will gain in a street clutch if it will hold the power. And the pedal effort will get a lot worse. For real abuse a sliding clutch is way easier on the driveline and faster as well, but that is certainly not designed with street in mind.
The reason I ask about what the transmission is, is that certain Audi transmissions are known to fail at the 600hp level by simply hitting a bump.

Shock loads work both ways. When you feel a bump in the road, so does the drivetrain. (The reason I go through so many Mazda transmissions at only 170ft-lb when people run essentially the same transmission at 250-300ft-lb in turbocharged Miatas)

ptuomov
Guru
Guru
Posts: 2140
Joined: Fri Aug 07, 2009 3:52 am

Re: Weak manual transmission, how to strengthen?

Post by ptuomov » Wed Aug 29, 2018 8:24 pm

peejay wrote:
Mon Aug 27, 2018 8:05 pm
Is this a Porsche designed trans, or a variant of the Audi 016/01E box?

I will admit to having never once seen a manual trans 928, all have been automatic.

Commentary upthread about the nature of case spreading gave me a kind of eureka moment. I have an aluminum Ford 9" housing and one of the major issues with it is that setup is a huge pain because all of the bores/journals have massive amounts of interference fit. Makes adjusting backlash and gear pattern an interesting experience.

The Mazda transmssions that I blow up on a regular basis (draining gear teeth out, sometimes but not always preceded by bearings that go sloppy) have an almost slip fit in the housings.

The part where I am thinking, and this is sometimes where I get into trouble, is that I wonder if I can drill and tap the case sections so that I can "post" the bearings on the center-center axis, kind of like how stock car guys used to do with Cleveland heads to support the combustion chambers.

There IS no turd that I won't try to polish.

This 928 transmission is a Porsche design. Not the same as the 944 transmissions that were Audi variants.
Paradigms often shift without the clutch -- https://www.youtube.com/watch?v=cxn-LxwsrnU

ptuomov
Guru
Guru
Posts: 2140
Joined: Fri Aug 07, 2009 3:52 am

Re: Weak manual transmission, how to strengthen?

Post by ptuomov » Thu Aug 30, 2018 7:48 am

Caprimaniac wrote:
Wed Aug 29, 2018 4:35 pm
OK, you don't want to og to a Corvette transaxle.

How about the Quaife, UK, transaxle? https://shop.quaife.co.uk/quaife-6-spee ... -transaxle or https://shop.quaife.co.uk/zf-transaxle- ... rn-gearbox Or maybe Porsche, as mentioned.

A hell of alot easier than go through the process of strengthening case, then shafts, then gears, then shifter,..... etc
The physical envelope that the transmission needs to fit in is limited, so there’s no freedom to fit just and transaxle in there. The Corvette transmission can be made to fit, but almost all other transaxles are a no-go.
Paradigms often shift without the clutch -- https://www.youtube.com/watch?v=cxn-LxwsrnU

ptuomov
Guru
Guru
Posts: 2140
Joined: Fri Aug 07, 2009 3:52 am

Re: Weak manual transmission, how to strengthen?

Post by ptuomov » Thu Aug 30, 2018 7:51 am

Ken_Parkman wrote:
Wed Aug 29, 2018 5:26 pm
Completely different question - what are you doing when the failures happen? While not a perfect solution one comment is type of clutch. You need a tremendously strong tranny to withstand shock loadings. Drag race type abuse (launch, shifts) with a hard grabbing diaphragm clutch that grips the hardest at lock is a really good way to bust stuff. Borg & Beck style pressure plates are not as harsh but I don't know how much you will gain in a street clutch if it will hold the power. And the pedal effort will get a lot worse. For real abuse a sliding clutch is way easier on the driveline and faster as well, but that is certainly not designed with street in mind.
My transmission failed on a gently loaded dyno experiment #500. It wasn’t loaded when thevclutch was dropped. It wasn’t that pull that broke it, though, it was much more likely the cumulative damage.

These transmissions seem to break the easiest when racing in slicks and going over curbs violently catching air. I’m not planning to do that, though.
Paradigms often shift without the clutch -- https://www.youtube.com/watch?v=cxn-LxwsrnU

ptuomov
Guru
Guru
Posts: 2140
Joined: Fri Aug 07, 2009 3:52 am

Re: Weak manual transmission, how to strengthen?

Post by ptuomov » Thu Aug 30, 2018 7:54 am

n2xlr8n wrote:
Wed Aug 29, 2018 12:44 pm
If it were me, I'd send it (and all samples) to my trusted tranny company and let them tell me how to solve it. Tapered roller bearings? Case not rigid enough? Heat treat? It could be all of the above. A really good transmission guy could help you out there (of which I am certainly not).
Do you think that someone could make an aftermarket synchronized transmission rated for say 700 lbf-ft at factory reliability while keeping the torque tube and rear axle interfaces the same as in the stock box and fit it in the same space envelope?
Paradigms often shift without the clutch -- https://www.youtube.com/watch?v=cxn-LxwsrnU

n2xlr8n
Expert
Expert
Posts: 556
Joined: Tue Jun 28, 2005 9:01 pm
Location: Bama

Re: Weak manual transmission, how to strengthen?

Post by n2xlr8n » Thu Aug 30, 2018 8:27 am

ptuomov wrote:
Thu Aug 30, 2018 7:54 am
n2xlr8n wrote:
Wed Aug 29, 2018 12:44 pm
If it were me, I'd send it (and all samples) to my trusted tranny company and let them tell me how to solve it. Tapered roller bearings? Case not rigid enough? Heat treat? It could be all of the above. A really good transmission guy could help you out there (of which I am certainly not).
Do you think that someone could make an aftermarket synchronized transmission rated for say 700 lbf-ft at factory reliability while keeping the torque tube and rear axle interfaces the same as in the stock box and fit it in the same space envelope?
Realistically, no. Maybe with a F1 budget.

I think I mis-communicated my suggestion- I've had one off trannies where my guy performed a failure analysis based on a single unit and made changes that were not widely known at the time. Not to me, anyway, and I grew up in a MT/AT tranny shop.

Edit: I just read the posts after mine-

If a Corvette transaxle could be made to fit, that's what I'd do; it would save headache and money in the long run (and you may like the ratios better anyway).
He who is in me is greater than he who is in the world.

ptuomov
Guru
Guru
Posts: 2140
Joined: Fri Aug 07, 2009 3:52 am

Re: Weak manual transmission, how to strengthen?

Post by ptuomov » Thu Aug 30, 2018 8:35 am

n2xlr8n wrote:
Thu Aug 30, 2018 8:27 am
Does the car hook? Is it more of an example of regardless of tractive force, the transmission can't withstand the power going through it?
Some people break transmissions randomly on the street with stock power. This may just be 30 years of age and neglected maintenance.

Other people systematically break these transmissions racing on slicks. That I think is overheating and shock loads.

John Kuhn breaks these at ideal operating temperature on a load-holding dyno running a relatively gentle program but up to 750 lbf-ft of torque.

From this, I'd say that, like many engineering efforts by a marketing company called Porsche, the transmission suffers from multiple design problems. Like the engine, it took a long time to understand the 928 S4 engine and make it run reliably on street, but now those problems are solved.

Until recently, almost nobody gave a rats a$$ about these 928 cars so there are virtually no competently designed aftermarket alternatives. The "aftermarketed" products for the 928 are almost always worse than stock pieces (but usually also cheaper).
Paradigms often shift without the clutch -- https://www.youtube.com/watch?v=cxn-LxwsrnU

Post Reply