Road race modifications to 951 transaxle
07-21-2018, 12:49 AM
#1
Instructor
Thread Starter
Road race modifications to 951 transaxle
Hi All,
I recently attended a tech seminar with some of the old Chrysler racers from the 1960s known as the Ramchargers and they got me interested in transmission modification. While they were mostly focused on drag racing, some of their ideas could be useful for road race applications. They were discussing how to improve shift speed for their manual transmissions and developed a technique which was furthered by Liberty gears. Essentially, they modified the synchro, dog rings and sliders to a more coarse design, making it a “looser” fit. I found an article on the Hamb illustrating this technique, in particular from post #32 onwards https://www.jalopyjournal.com/forum/....671771/page-2
I wonder how this could apply to the 951 transaxle and improving shifting to make an almost sequential box. The article states that Liberty gear in Michigan can machine the gears and modify them. Also, the split collars are somewhat of a liberty trademark. I remember reading. One time ago about Patrick looking for a sequential transmission option for his time attack car and thought this would be an interesting idea as it would all be internal modification in the existing transaxle for class rules where stock appearing is a must.
I would be interested to hear some experts thoughts. Kevin Gross, Dimi, and others ?
Steven
I recently attended a tech seminar with some of the old Chrysler racers from the 1960s known as the Ramchargers and they got me interested in transmission modification. While they were mostly focused on drag racing, some of their ideas could be useful for road race applications. They were discussing how to improve shift speed for their manual transmissions and developed a technique which was furthered by Liberty gears. Essentially, they modified the synchro, dog rings and sliders to a more coarse design, making it a “looser” fit. I found an article on the Hamb illustrating this technique, in particular from post #32 onwards https://www.jalopyjournal.com/forum/....671771/page-2
I wonder how this could apply to the 951 transaxle and improving shifting to make an almost sequential box. The article states that Liberty gear in Michigan can machine the gears and modify them. Also, the split collars are somewhat of a liberty trademark. I remember reading. One time ago about Patrick looking for a sequential transmission option for his time attack car and thought this would be an interesting idea as it would all be internal modification in the existing transaxle for class rules where stock appearing is a must.
I would be interested to hear some experts thoughts. Kevin Gross, Dimi, and others ?
Steven
07-21-2018, 02:40 AM
#2
Burning Brakes
While I'm familiar with the modifications (old Mopar guy) I don't think it will make a very streetable transmission.
Also the shock load on the rest of the drivetrain from the powershifts is not going to be kind to the rest of the mechanicals. And these mods are made for powershifts. And the design of the 944 gearbox is not that similar to the Mopar gearbox synchronizer internals.
If you want sequential shifting, get a sequential box. Sorry.
Also the shock load on the rest of the drivetrain from the powershifts is not going to be kind to the rest of the mechanicals. And these mods are made for powershifts. And the design of the 944 gearbox is not that similar to the Mopar gearbox synchronizer internals.
If you want sequential shifting, get a sequential box. Sorry.
07-21-2018, 11:13 AM
#3
Race Car
Custom parts, out of realm of 99.9% of anybody racing a 944.
Heck, it's an arm for a custom ring and pinion and a leg for custom ratio 2-4 gears as it is.
In slow motion, as you make a shift, the fork begins to move the sleeve towards the gear engagement teeth as the synchro ring (which is really a clutch) has to speed or slow the intended gear to match shaft speed for the sleeve to make full engagement.
The logical thing to do is to lighten the mass of the floating driven gears, on input/mainshaft, 3rd and 4th and 2nd gear on pinion/countershaft.
Back cutting the overhang on the side opposite the cone and teeth and/or a hole pattern and rebalance on the same side will lighten the gears, allow them to be speed matched faster and make synchros last longer.
Truth be told though, our transmission live in 2nd, 3rd and 4th with rare tracks using 5th once per lap. 1st only used for tooling around the pits and loading onto the trailer.
The better you get at heel/toe and mechanics of your arm movements, the less there is to gain.
T
Heck, it's an arm for a custom ring and pinion and a leg for custom ratio 2-4 gears as it is.
In slow motion, as you make a shift, the fork begins to move the sleeve towards the gear engagement teeth as the synchro ring (which is really a clutch) has to speed or slow the intended gear to match shaft speed for the sleeve to make full engagement.
The logical thing to do is to lighten the mass of the floating driven gears, on input/mainshaft, 3rd and 4th and 2nd gear on pinion/countershaft.
Back cutting the overhang on the side opposite the cone and teeth and/or a hole pattern and rebalance on the same side will lighten the gears, allow them to be speed matched faster and make synchros last longer.
Truth be told though, our transmission live in 2nd, 3rd and 4th with rare tracks using 5th once per lap. 1st only used for tooling around the pits and loading onto the trailer.
The better you get at heel/toe and mechanics of your arm movements, the less there is to gain.
T
07-22-2018, 04:16 PM
#4
Burning Brakes
Speaking of lightening the mass of the gears/shafts to improve shift speed, the easiest way is to use a lighter clutch disc such as an unsprung clutch disc, or even better would be a small diameter twin disc clutch. Of course this would work great for a track car, but the improvements would compromise driveability if it's used on the street.
Last edited by Dave W.; 07-22-2018 at 07:21 PM.
07-22-2018, 05:22 PM
#6
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07-22-2018, 11:05 PM
#8
Race Car
