1st gear problems

[neilca]

Since I have been racing a 901 box, three years now. I have killed 4 first gears. Ironically, I do not use first gear on the track except when I screw up and have to restart.

Two of the gears were my fault. I was running Redline MTL in the box and I think it was too slippery for the synchros. I tore all the dog teath off of these gears.

Two other failures where the synchro stops located under the synchronizer ring. First gear has a unique set up where it only has one reaction bar. See in red on my diagram. The other gears have two bars.

I am thinking about changing to the two bar set up for my first gear.



The failure this past weekend was both lugs sheared, the circlip came off and all that stuff ended up in the transmisson. Luckily, I tore it apart before the garbage got to the other components.

Is it just me or have you guys seen problems here?

Thanks,

neilca

[Grady Clay]

neilca,

Yes, you can install the 2-3-4-5 syncro components (includes the 2-5 gear dog tooth ring) on 1st gear. This is a very desirable mod as it increases the synchronization when you ‘up-shift’ into first gear (from neutral).

You should be very careful when taking off in 1st gear. The cantilever design of the input shaft can lead to it braking off with ‘jackrabbit’ starts in the heat of racing. In fact the input shaft can simply break off for no apparent immediate reason.

There was introduced a ‘reinforced’ input shaft with the ’68 model 901/902 transmissions. This increased the size of the threaded stub at first gear. The ‘reinforced’ shafts still break.

I assume you are using a LSD in your 901. The 904 LSD is very fragile casting and is known to fail under the roller bearing (ring gear side). There are stronger aftermarket differentials.
If legal in your class, the type 911 transmission uses the substantially stronger LS differential common to the 915 and 930 transmissions (with 917 clutch plates).

If there is an ‘open’ differential, make sure it has the update for the ‘simplified’ differential.

Best,
Grady

[neilca]

Thanks Grady,

I am running an open diff. What is this "simplified" differential?

So far my engine doesn't produce enough HP to hurt the input shaft (126 hp). I hope to have an engine built soon that will ring that thing off : )

[john walker's workshop]

with the two band first, it's easier to downshift into 1st while moving and harder to get into 1st when stopped, from neutral.