911/01 Disassembly and Post Mortum - Comments Welcome

[denniso]

Hi All,

I purchased a core 1971 911/01 5-speed transmission (S/N 771xxxx) from an Early S member for my '70 Targa project that I plan to rebuild. The seller didn’t have any history on the trans, as it was from a parts car that was parted out a long time ago.

I had hoped that the trans had not been previously opened, but probably wishful thinking for something 50+ yrs old. Anyway, I started the teardown yesterday and unfortunately started seeing a few things that did not look correct to me. I’m hoping the experts on the forum can provide some guidance on what needs to be replaced and what can be reused. I am on a limited budget, so I want to make smart decisions on which parts to replace, but avoid stupid one that save me a few bucks.

I drained the fluid which looked very clear, but upon opening the transmission I saw a black film/slime over some of the internal parts and inside the case. The magnetic plug was filled with sludge and magnetic fur, but no solid particles. I have not started to clean the parts yet, so the pictures below are not very good. My plan is to start cleaning the parts as my time allows over the new few day to better determine the state of the parts and start taking measurements.

The Transmission:



Intermediate Plate and Gear Clusters








Items that Caught My Attention

Marks on 1st Gear Sleeve


Chipped Tooth


Score marks on Bearing faces - this seems very odd to me. what would cause this?




Broken Bearing


Main Shaft is stamped "FB" and PET stated it should be "GA". If GA is correct, then mainshaft was swapped out.



Thanks for input and more to follow....

[ajwans]

Can you post more pictures of the pinion gear. There seems to be some damage but hard to tell exactly from the end picture posted.

andy

[denniso]

Hi Andy,

Thanks for taking a look.

I'm having a hard time taking pictures of the pinion gear, as I keep get reflections that make it appear there are bad spots on it. I've looked at the pinion gear with a magnifying glass and it looks perfect to me. There are no signs of galling or even scratches. Here is another attempt at a picture:




Both sides of the differential around the bearings have wear makes which seems odd to me. Here is a picture of the wear marks (it's the same on both sides of the differential).


Also I see some wear marks on the outside of one of the gears - also seems odd to me:



Does anyone know if a 911/01 came with "FB" Mainshaft? I only see "GA" in PET.

Any recommendations on a good bearing supplier for these transmissions? I'm real concerned about getting counterfeit bearings. I may need to but at Porsche unless someone has a solid recommendation.


Thanks for the help!

-Dennis

[edmayo]

There is no FB, count the teeth, 18/32 is GA.

[denniso]

Hi Ed,

Hard to get good pics, but it looks like "F B" to me. I counted 18 teeth on the gear.

[catelluseng]

Your 1st/reverse spider and shift sleeve should ideally be replaced. Your pinion looks fine in the photos. I would not be terribly worried about any of the wear marks you note, it's 52 years old, stuff rubs. The ding to the input shaft 2nd gear in one of your later photos is a bit of a surprise. If the damage is just to the edge as shown in the photo and nowhere else, you should be fine cleaning it up with a honing stone.

Just rebuild the transmission properly, fresh bearings and factory set-up, should be ducky.

[Richy]

!st gear sleeve is usable , chipped tooth on reverse 1st gear slider would work but would be noisy , the important part is the wear in the inside of the slider . Broken ball bearing is fairly normal . If money is an issue , buy new ball bearings and use the existing roller bearings and use the 2nd and 3rd gear synchro components for 4th and 5th and vice versa .

[denniso]

Thanks all for the continued comments.

I'm wondering if the broken bearing caused the shaft to move and contributed to the wear marks??

Yeah, this rebuild is going to be pricey. My current plan is to replace:
4-5 synchros
4 dog teeth
2 Shift Sleeves
Maybe 1st gear slider and shift sleeve. I need to clean and look more closely for wear
4-6 bearings. I need to clean and look at rear shaft bearings, but suspect they will also need to be replaced. This would make all 6 replaced :-(
I'm not sure about the stop bands and blocks yet, as I haven't inspected yet. There are threads about upgrading to the later design for these transmissions.

-Dennis

[Richy]

If you are concerned about money , why would you replace 4-5 synchros ? Shifting to 5th is never an issue and 4th is rarely an issue . Also , do not replace 4th 5th shift sleeve , spend money on 2nd ,3rd and 1st .
Why spend money on new roller bearings ? You definitely need some guidance . Who's checking the ring and pinion specs or wear pattern ? You are not inspiring any confidence in the rebuild .

[catelluseng]

If you are concerned about money , why would you replace 4-5 synchros ? Shifting to 5th is never an issue and 4th is rarely an issue . Also , do not replace 4th 5th shift sleeve , spend money on 2nd ,3rd and 1st .
Why spend money on new roller bearings ? You definitely need some guidance . Who's checking the ring and pinion specs or wear pattern ? You are not inspiring any confidence in the rebuild .

Dunno how you can give this advice without seeing what those synchros look like, and how they and their dog rings measure. Same goes for the bearings.

Just for an example, I just rebuilt a 902/1 for a customer upgrading his 912 from a four to five speed. Although the replacement five-speed was sold to us as low mileage and looked great, the years had taken their toll on everything inside. All bearings, dog rings, synchros, and shift sleeves needed replacement. Some of the bearings were corroded (it had been sitting for many years), others were pitted from use. Except for first gear, the dog rings all looked great... but measured well out of spec with new synchros. As you probably know, with the Porsche-design balk ring synchros, the sleeves wear with the synchros, so they were also replaced. Bottom line is that 901-series transmissions are all fifty or more years old, and unless they've seen some TLC in the meantime, they need it now. Cheers,