Weak manual transmission, how to strengthen?

Transmission to Rear-end

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ptuomov
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Re: Weak manual transmission, how to strengthen?

Post by ptuomov » Wed Sep 12, 2018 7:04 pm

weedburner wrote:
Wed Sep 12, 2018 7:03 pm
ptuomov wrote:
Wed Sep 12, 2018 4:22 pm
Thanks for the clutch info. This transmission gave up without being shifted particularly hard. In fact, it was on the fourth gear for about a month as John run various hub dyno experiments.
I don't know much about your transmission, but dyno experiments are often performed in a direct gear. That means power may not actually flow thru a set of transmission gears, as direct is a coupling of the input/output shafts.

Grant
Unfortunately, can’t do that with this transaxle and dyno, as the dyno would overspeed on the fifth gear. The redline on fifth is 210-225 mph from memory.
Paradigms often shift without the clutch -- https://www.youtube.com/watch?v=cxn-LxwsrnU

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Re: Weak manual transmission, how to strengthen?

Post by peejay » Wed Sep 12, 2018 8:39 pm

Would a transaxle even have a direct gear? Most don't. Doing so would require the input shaft to be inline with the pinion shaft, which would require rather a lot more fussing around than merely using the "countershaft" as the pinion shaft.


Really, I am kind of surprised that nobody ever picked up on this for regular rear drive transmissions. You could get the driveshaft lower in the chassis. This was probably never done because you would need to get your machining really spot on since the input shaft would run the whole length of the transmission instead of ending just past the bellhousing. That kind of precision would never have flown in Detroit in the 40s/50s/60s. I have seen factory bellhousing/engine combos with .020" of radial offset, you can only get away with that kind of sloppy work when the input shaft has only one bearing and relies on the pilot bushing for support.

And now I just had an epiphany of why some of those old transmissions didn't have any kind of input seal. Why bother when you expect the input shaft to get all cockeyed?

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Re: Weak manual transmission, how to strengthen?

Post by ptuomov » Thu Sep 13, 2018 7:43 am

Would filling the webbing there with belzona help with case stability?
959E173A-88E1-4924-BE0C-59B2EAB565BA.jpeg
Paradigms often shift without the clutch -- https://www.youtube.com/watch?v=cxn-LxwsrnU

Kevin Johnson
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Re: Weak manual transmission, how to strengthen?

Post by Kevin Johnson » Thu Sep 13, 2018 2:16 pm

Coefficient of thermal expansion of typical Belzona product appears to be about 35 ppm/degree C. Aluminium is about 24 and iron 12. Be careful.

Perhaps scan the volumes and additively manufacture plugs to be cast in alloy and cemented into place. $^n

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Re: Weak manual transmission, how to strengthen?

Post by ptuomov » Thu Sep 13, 2018 3:00 pm

Kevin Johnson wrote:
Thu Sep 13, 2018 2:16 pm
Coefficient of thermal expansion of typical Belzona product appears to be about 35 ppm/degree C. Aluminium is about 24 and iron 12. Be careful.
Anyone know what the thermal expansion coefficient of cured Belzona 1511 HT is?
Paradigms often shift without the clutch -- https://www.youtube.com/watch?v=cxn-LxwsrnU

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Re: Weak manual transmission, how to strengthen?

Post by Kevin Johnson » Fri Sep 14, 2018 3:27 am

ptuomov wrote:
Thu Sep 13, 2018 3:00 pm
Kevin Johnson wrote:
Thu Sep 13, 2018 2:16 pm
Coefficient of thermal expansion of typical Belzona product appears to be about 35 ppm/degree C. Aluminium is about 24 and iron 12. Be careful.
Anyone know what the thermal expansion coefficient of cured Belzona 1511 HT is?
viewtopic.php?f=1&t=54611

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Re: Weak manual transmission, how to strengthen?

Post by peejay » Fri Sep 14, 2018 9:20 pm

Interesting thought, if that area is where the failures happen.

Speaking from Mazda xsperience, the standard "type M" (aka "smoothcase", the trans used in '79-92 nonturbo RX-7s and '90-14? 5-speed Miatas) has gone through many revisions. The original trans had 4.5mm thick aluminum in the bellhousing/front case area, the Competition transmission had the whole area upped to 6mm. All transmissions starting in '89 or so had large concentric ribs around the bellhousing, even the 100 ft-lb early Miatas.

These transmissions are generally considered to be strong enough up to 250ft-lb with the Miata gearset, less so with the RX-7 higher countershaft ratio gearsets. Just like T5s, a higher countershaft ratio means the whole trans is weaker. (With only 170-180ft-lb, I have sheared 2nd gear, 3rd gear, and/or the input shaft gear leaving nothing but 4th available. A fun thing to happen when powershifting to 5th at 85mph while passing a truck on the way to work)

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Re: Weak manual transmission, how to strengthen?

Post by ptuomov » Sat Sep 15, 2018 2:47 pm

peejay wrote:
Fri Sep 14, 2018 9:20 pm
Interesting thought, if that area is where the failures happen.
I have no firm idea about why and how the failures happen. One hypothesis is that case is too weak and allows the shafts to pull apart, especially when it heats up. Another is that the shafts are simply too long, or the gears simply too weak. Belzona rep recommended their 1111 for aluminum alloy transmission cases. The front end of the case could be reinforced from the outside by pouring / injecting Belzona 1111 between the ribs. The rear end of the case needs to be reinforced from the inside of the differential compartment of the case, but one should be able to pour / inject 1111 between the ribs in there relatively easily as well.
Paradigms often shift without the clutch -- https://www.youtube.com/watch?v=cxn-LxwsrnU

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Re: Weak manual transmission, how to strengthen?

Post by Kevin Johnson » Sat Sep 15, 2018 4:02 pm

I am guessing that the transaxle does not currently have a cooling circuit and depends upon airflow. I question whether the typical dyno-blower fan setup reproduces what happens on the road (??? -- maybe it does in your case). If the lubricant temperature was not monitored (???) then the earlier information about gear failures at high lubricant temperatures might be responsible.

Here is an aftermarket solution to a problem that might have been occurring unnoticed because of 4th gear being constantly used for lengthy time periods under heavy load.

https://928motorsports.com/parts/transaxlecooler.php

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Re: Weak manual transmission, how to strengthen?

Post by peejay » Sat Sep 15, 2018 5:35 pm

High internal temps will also make everything shift around and grow in different directions! Don't miss the forest for the trees.

This was the big problem (well, one of them) with Mazda's 323GTX transmission. When they got hot, proper gear mesh would go away. Band-aid solution was a transmission cooler.

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Re: Weak manual transmission, how to strengthen?

Post by Kevin Johnson » Sat Sep 15, 2018 5:37 pm

Transaxle Cooler Kit For The Porsche® 928
this part is Pikes Peak tested this part is Bonneville Tested
Stops hard shifting on hot transmissions!
Application: 1978-95 Porsche® 928 with Manual Transmission

Background: Racers and performance drivers of the 928 often experience hard shifting the hotter it gets. The heat that binds the transmission can be any combination of high ambient temperatures and the heating effects of a long race and dual exhaust. In extreme cases, the 928 5-speed can become nearly impossible to shift if it gets hot enough.

This is not unusual for single-casing transaxles the world over, whether in a Porsche® or a Pantera. The heat causes the case to expand, binding the shifter rails and synchros within.

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Re: Weak manual transmission, how to strengthen?

Post by ptuomov » Sun Sep 16, 2018 7:25 am

Kevin Johnson wrote:
Sat Sep 15, 2018 4:02 pm
Here is an aftermarket solution to a problem that might have been occurring unnoticed because of 4th gear being constantly used for lengthy time periods under heavy load.

https://928motorsports.com/parts/transaxlecooler.php
The transmission temperature was not logged but it's obvious that it didn't overheat on the dyno. The dyno itself overheats a lot easier and therefore there was ample time between experiments for the transmission to cool down.

We're adding a transmission cooler system. One can do the transmission cooler system a _lot_ better than what's shown in the link. We'll be using a spray bar engineered with some rhyme and reason, a thermostatic control, a pump that has a chance of lasting with hot oil, etc.
Paradigms often shift without the clutch -- https://www.youtube.com/watch?v=cxn-LxwsrnU

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Re: Weak manual transmission, how to strengthen?

Post by ptuomov » Sun Sep 16, 2018 12:12 pm

Here's an example of a more logically designed transmission cooler for the 928:
OttCooler.jpg
Paradigms often shift without the clutch -- https://www.youtube.com/watch?v=cxn-LxwsrnU

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Re: Weak manual transmission, how to strengthen?

Post by Leftcoaster » Sun Sep 16, 2018 12:25 pm

What's the approximate root diameter of those shafts and length between (radial) support bearings?

I'm no tranny guru and the photo may be deceptive, but - - :shock:

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Re: Weak manual transmission, how to strengthen?

Post by ptuomov » Tue Sep 18, 2018 7:47 am

Leftcoaster wrote:
Sun Sep 16, 2018 12:25 pm
What's the approximate root diameter of those shafts and length between (radial) support bearings?

I'm no tranny guru and the photo may be deceptive, but - - :shock:
It’s like two long tooth picks suspended between two big marshmellows with life savers hanging on the toothpicks
Paradigms often shift without the clutch -- https://www.youtube.com/watch?v=cxn-LxwsrnU

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