Our 6-speed Project
03-01-2013, 05:12 PM
#31
Also note that the trans and the diff use different fluids now. IMHO that's always been a problem for those who want to race the current trans. The viscosity needed to protect the ring and pinion from wear is too heavy for the trans if performance shifting is your goal. It probably didn't matter to the OEM 'cause the 928 was a touring car.
But now, with Dexron III in the trans (synthetic, slim film, quick and easy shifting) and hypoid only in the diff - the T56 is going to shift quicker and more easily than the G28-13
Then there is the "hard to shift when hot" issue that the racers encounter that should be also solved by this.
...and the drive-shaft breakage on the racers and/or the high torque cars. This upgrade would also address that issue as well.
But now, with Dexron III in the trans (synthetic, slim film, quick and easy shifting) and hypoid only in the diff - the T56 is going to shift quicker and more easily than the G28-13
Then there is the "hard to shift when hot" issue that the racers encounter that should be also solved by this.
...and the drive-shaft breakage on the racers and/or the high torque cars. This upgrade would also address that issue as well.
03-01-2013, 05:46 PM
#32
Drifting
03-01-2013, 06:09 PM
#33
Nordschleife Master
03-01-2013, 09:07 PM
#35
You would have to run TWO separate ones for the transmission and diff we are talking about here. I'm sure that two of those with modified fittings would work though.
03-03-2013, 01:41 PM
#36
Developer
Thread Starter
Will you be offering a new shifter setup with the kit?
Are there a lot of threads about shifter upgrades for the 'vette?
If yes, then I would also bet someone already makes an "improved" shifter....
03-03-2013, 04:17 PM
#37
Race Director
great thread......I just got off the phone with a friend and we worked out a deal were I get his C6 Z06 transmission-torque tube + clutch.....all it needs is the rear end!!!!! So I will have it up for sale shortly.....mostly since I don't need it with my brute 257ftlbs...
03-03-2013, 04:52 PM
#38
Brian,
The C6 transaxle does mount slightly differently than the C5 stuff. Just an FYI. One mount in the rear for all C5 and first year C6, two mounts on each side from '06 onwards for the C6. Generally the swap requires a C6 cradle for use in a C5. For instance, my C5Z uses an RPM C6 trans, and uses special mounts and a C6 cradle.
I would think that these swaps should take that into consideration.
The C6 transaxle does mount slightly differently than the C5 stuff. Just an FYI. One mount in the rear for all C5 and first year C6, two mounts on each side from '06 onwards for the C6. Generally the swap requires a C6 cradle for use in a C5. For instance, my C5Z uses an RPM C6 trans, and uses special mounts and a C6 cradle.
I would think that these swaps should take that into consideration.
03-04-2013, 01:15 PM
#39
Developer
Thread Starter
The C6 trans is larger in almost every dimension than the C5 transaxle.
It can be done, and I know it has been done - but it required alteration of the 928 floor pan to make it fit. Fine for a race car - but not OK for most DIY installs.
The C6 in stock form is stronger than the C5 in stock form, that's true. But the C5 has after-market parts available if the owner should need that takes the C5 up to handle the same torque levels as the C6.
I selected the C5 trans for my project because we do have an eye for putting together a shippable bolt-in kit. The C6 trans requires cutting and welding of the floor pan + some hammering - so not the trans that I thought most 928 owners would want to mess with.
Its a great trans, Brian, you will enjoy it.
It can be done, and I know it has been done - but it required alteration of the 928 floor pan to make it fit. Fine for a race car - but not OK for most DIY installs.
The C6 in stock form is stronger than the C5 in stock form, that's true. But the C5 has after-market parts available if the owner should need that takes the C5 up to handle the same torque levels as the C6.
I selected the C5 trans for my project because we do have an eye for putting together a shippable bolt-in kit. The C6 trans requires cutting and welding of the floor pan + some hammering - so not the trans that I thought most 928 owners would want to mess with.
Its a great trans, Brian, you will enjoy it.
03-04-2013, 08:17 PM
#40
Race Director
I am not planning on installing the C6 transaxle.....no point to add all that weight given my low power point....even my 5.0L engine won't push enough power to justify all that extra weight....keep in mind...I weighed my G28-03 transaxle at it came in at 122lbs dry.... I have been told the later boxes weight at least 30lbs more.....the C6 transaxle is approaching 200lbs....
03-05-2013, 04:42 PM
#41
Developer
Thread Starter
Yes, your are right - it is at least that much heavier than the C5. Some think the C6 would be better for racing because of the integral cooling pump. Just hook up the lines to a finned cooler and let it go, they think.
When I looked at the weight of the pump we use to move the hypoid to cool our present transaxle, the C5 with an external pump was still lighter and more compact than the C6.
The C6 was built to handle about 600 lb ft of torque - so in stock trim its quite a bit stronger than the C5, there is no doubt. But like I said, the parts are everywhere to make your C5 handle just as much torque as the C6, and it will always be lighter.
When I looked at the weight of the pump we use to move the hypoid to cool our present transaxle, the C5 with an external pump was still lighter and more compact than the C6.
The C6 was built to handle about 600 lb ft of torque - so in stock trim its quite a bit stronger than the C5, there is no doubt. But like I said, the parts are everywhere to make your C5 handle just as much torque as the C6, and it will always be lighter.
Last edited by Carl Fausett; 03-05-2013 at 06:09 PM.
03-05-2013, 04:43 PM
#42
Developer
Thread Starter
Progress on the 6-speed trans-axle kit: The Torque-tube adapter from the C5 6-speed to the 928 bell housing was drawn up yesterday and this morning I gave it to the engineers for CAD modelling and quoting. I have a meeting scheduled Thursday to discuss the design and manufacture of the rear cross-member for the C5 transaxle.
03-05-2013, 10:59 PM
#44
Shameful Thread Killer
Rennlist Member
Rennlist Member
I thought the idea of the low axle ratio and 1.00 - 1 fifth gear was so that there was less drag through a lay-shaft in the 928 trans and shaft?
I drive a 968 with a factory six speed regularly, and take it from me, the cars don't need the extra gear. I think the torque curve of the 928 with the resonant intake in 85 and later provided for a good power band with 5 gears.
Not a fan of putting BW/Tremec Mexico built parts in place of the factory stuff, which is pretty robust.
I'm guessing this whole project is to replace the auto trans found in so many cars. I guess if you gotta row, you might as well row for 6. Sorry for the urine in the corn flakes. I'm sure it will sell but if you want a stick 928, buy a stick 928.
I drive a 968 with a factory six speed regularly, and take it from me, the cars don't need the extra gear. I think the torque curve of the 928 with the resonant intake in 85 and later provided for a good power band with 5 gears.
Not a fan of putting BW/Tremec Mexico built parts in place of the factory stuff, which is pretty robust.
I'm guessing this whole project is to replace the auto trans found in so many cars. I guess if you gotta row, you might as well row for 6. Sorry for the urine in the corn flakes. I'm sure it will sell but if you want a stick 928, buy a stick 928.
03-05-2013, 11:06 PM
#45
Three Wheelin'
But isn't the beauty of it the fact that you actually can replace things without spending an arm and a leg? Who cares if a diff goes... just learn from your mistakes and slap a new one in.