901 trans shifting question

[Hotrod911T]

Hi All,

I need some opinions from the tranmission experts on the board regarding a "new" magnesium 901 trans built for my '69 911T Street/Autocross car. It has a Guard billet aluminum midplate and side cover, all new bearings, new 930 dog teeth, 930 syncros, 930 energizers and 930 sliders, and a rebuilt late ZF 915 LSD. The gear ratios are A-F-M-S-X. I have a Rennshift shifter with a Wevo coupler. My old 901 trans shifted very smoothly until it ate up a bearing and needed to be replaced. With the same shifter setup, it is now sometimes difficult to get into 1st gear from a stop. Sometimes it is impossible to get into 1st without touching 2nd and then going down into first, other times it just goes right in. I don't want to start a debate here, but I was advised by a trans builder not to use Swepco with the LSD as it was too slippery and would reduce the life of the friction plates, so I went with Lucas 80w-90 and a bottle of GM friction modifer.

I have no issues with the trans other than it is difficult to get into first gear. Once going, you can "slam" it into 2nd as fast as your arm can move and it is as smooth a silk and the reverse lock out keeps it from touching reverse. It shifts into the rest of the gears smoothly and as fast as you can move the shifter. The trans is so good that I can live with this problem by first touching 2nd gear before going into 1st, but my wife does not like this. You know how it goes, sometimes if your wife is not happy, nobody is happy.

Now my question, do you think this first gear problem is related to the all new parts (930 syncros) and a setup that is a little tight (harder when the trans is hot) that will go away as the new parts wear a little? We've run one autocross (two drivers) with it and have about 250 (mostly freeway) miles on the trans. There is no change yet. I was told by others that with the 930 parts, the shifting will be the best yet for a 901. I've played around with the fine adjustment of the Rennshift and it doesn't seem to be a problem with the shifter, besides everything worked great on the old trans.

Any thoughts and ideas will be greatly appreciated.

Thanks,

Rod

[304065]

Your trans builder is wrong. Swepco 201 is what you want. I have used it for five racing seasons with my ZF 901 LSD and it's not a problem. However, I used synthetic in my AFMSX-geared '66 and it WAS a huge problem, wouldn't shift properly into second, forget about griding first.

Start with that and wait for the synchros to break in. Do not "slam" it into second, a baulk-ring has to move at a certain speed which is constant no matter how urgent the need.

All the gizmo shifters are useless IMHO. I have the lovejoy coupling and weltmeister springs in my 901 and I wouldn't trade it for any race shifter sold. (Well, maybe the one Jim Newton put in Hamblin's car.)

[Hotrod911T]

John,

Thanks for the comment. My first thought was to go with Swepco because that's what I had in my old trans before it ate itself up (hope there was no connection there, probably my hypo 2.7). Naturally, I don't "slam" it into 2nd and was only using that as a poor example of how fast you could get it into 2nd if you wanted to without any hangup on the part of the transmission.

Thanks again,

Rod

[Hotrod911T]

John,

By the way, if I swap back to Swepco, do I need to add any limit-slip modifier with the gear lube or use as is with the ZF LSD? I used the GM additive before but don't know if it is really necessary with Swepco. There is nothing on the label that even mentions use with a limited-slip.

Thanks,

Rod

[304065]

Rod,

If you search the archives here you will find plenty of people, not just myself, who say that a friction modifier is not necessary. I have never used one and don't intend to, I don't know what they do anyway.

Why don't you send an email to SWEPCO and ask them directly and post the result here? That would settle the question once and for all, but I bet that none is needed.

Remember that the 201 was developed by SWEPCO in conjunction with the Porsche Engineers, it actually kept the 935's gearboxes from failing during a race.

I also recommend that you search under the name "Grady Clay" and read everything he has written about shifting technique-- with your newly rebuilt box, if you use two fingers and your thumb to shift and delicately work it, you'll get a lot more miles out of the box and be just as fast. It's not easy during the heat of battle but with enough practice it becomes second nature.

Good luck!

[Scott at Pelican Parts]

Originally posted by Hotrod911T
Sometimes it is impossible to get into 1st without touching 2nd and then going down into first, other times it just goes right in.

I was taught by Otto (Otto's Venice -- a premier 901/911 transmission builder) to first put the car into 3rd gear, then 1st. Unfortunately, I forget the details of the logical explanation he gave me at the time as to why this will give your 901 more longevity. But I do know that my shifts into 1st (from 3rd) at traffic lights are much smoother and more consistent now.

[Hotrod911T]

John,

Thanks again. I did check the Swepco website and talked with a few suppliers and it appears that no additional additives are necessary when using Swepco 201 with a ZF limited-slip. I am going to take your suggestion and put in Swepco and wait for the syncros to wear in. If the limited-slip starts to chatter, I will add just enough additive to solve the problem. Our next AutoX is in a couple of weeks so I will see how the trans performs with the Swepco.

Rod