Top-Gun

I've had to dig into my 65K mile G50/20 due to a shifting issue that I predict is from a shift spindle/tensioning plate issue.

Other than this mechanical problem preventing access to R/1/2 after a shift into 5/6, the gearbox did not exhibit any other issues (no grinding or popping out of gear). I did notice a considerable amount of brass metallic specs in the gear oil when I drained it indicating the synchros may be well worn.

This box is an early serial number (G5020 1 001964) so it should have the early steel caged needle bearings and loose 2nd gear (yay!). Its also an open diff.

I'm wondering what all I should replace/upgrade while the box is apart without getting crazy as I don't want to spend a fortune on it. I've considered re-gearing and adding steel syncho's but the parts cost alone (with me being in Canada) is pretty much insane.

I figure on the following;

- New Porsche brass syncro rings and cones
- Upgraded shift spindle (probably the GT gears steel one)
- Upgraded Porsche 3/4 fork 950.303.113.04

Is there anything else I should consider keeping in mind that I'm trying to not get carried away and this car is 90% weekend toy and 10% DE?

Thanks.

NP993

Get a worn stock LSD, rebuild with Guard plates, install. Cheap and a great mod (what I did on mine).

Top-Gun

Was the diff plate swap a DIY or did you send it to Guard? I presume theres some messing with side to side shimming if the diff is swapped but pinion depth (the truly hard part) would remain intact?

chaoscreature

When you open up the transmission case you will really get a better idea of what needs to be replaced.
Not sure what the shift spindle is... is there a PN for it?
Check your dog gear teeth, you can replace the shift sleeves pretty cheap but the actual gears are pretty expensive. You lucked out if you have the loose 2nd gear. You obviously have more options than most to replace the whole gear set, or gears of your choice but plan on a big budget increase if you go that route.

If you take all the gear stacks off the shaft I would replace ALL the synchros since they don't cost much and that way they will all be at the same wear point. I skimped on this and regret it now.
You will need a few nuts for the input/output shafts that are single-use only (deform with chisel items) so get those ordered. Skip the gasket set and ask Gbox for a tube of their gasket maker, It's not cheap but it works great!

Top-Gun

Thanks for the tips.

This may be a dumb question but do you only replace the Synchro rings or do the cones get replaced at the same time?

The shift spindle is also known as the reversing lever. Its the component that transfers the shift rod motion to the forks (has springs at the top and bottom and a pin that follows a detent plate). I predict something in that mechanism is binding after a 5/6 shift. The part number is 95030303506.

M. Schneider

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chaoscreature

This is not specific to your question but I took a bunch of pictures from my G50 rebuild.
Feel free to browse them for reference
http://s1292.photobucket.com/user/ch...?sort=3&page=1

pipingken1

Did anybody respond to this question. I'm refreshing a 50/21 box and assumed I could change to steel sychros only without changing the cones.

Paul902

When I did this on mine, Guard tried to figure out what plain plates and friction plates would fit in mine over the phone, with me taking measurements. Some stuff wasn't adding up so I sent it in. Now I have a recipe on file with Guard. When my plates wear out, I just need to request those thicknesses.Guard told me they have seen many variations of housing sizing, and internals sizing, so every one is not the same.

On mine, I reused the same housing and bearings so no shimming. I would think with a new diff but original ring gear that the pinion would not need to be reshimmed, but it is just a guess.

Edit note: my diff already was an LSD being a 4S model. I presume now, that yours is non-LSD, not sure if Guard could do this over the phone or not. Give 'em a call to find out.

pipingken1

I was trying to confirm that when changing to a steel synchro on 2nd gear (950 304 611 11) you also need to change the Cone (950 304 613 11) and the Ring (950 304 617 11)

But on the 3rd 4th and 5th you can simply change the synchro (928 304 211 30)

Any help out there ???

pp000830

For street use and after a very close inspection of all the parts I would consider
just the 1st and 2 gear synchro & cone assemblies as the upper gear sets should show little or no visible wear.
I would not bother with a new shift spindle unless you know you have an issue. If you still feel compelled to replace it ask a reputable transmission re-builder how many and under what user conditions has he seen one fail or have tolerance problems.
I would not replace the porsche 3/4 fork 950.303.113.04 again unless you have an issue.

I would very closely inspect the main sets of ball bearings for bluish discoloration suggesting exposure to excessive heat and replace them is this bluing is present.

I would never put a steel "racing" replacement for a soft metal original part in a transmission for road use as racers have the intent to strip down and rebuild stuff every few races. In the road application involves some part sacrificing metal with age and the parts that are soft metal are soft for a reason.

Last but not least have a guy that works on these transmissions all the time do the work as there are likely fit issues related to longevity that only a guy who has seen multiple failure modes knows how to deal with.

I am not a mechanic but I had my transmission serviced and the guy walked me through his thought process in detail while the box was open and laid out on his bench.
Hope this helps,
Andy

Top-Gun

For reference after opening up my trans we found the following;

- Shift spindle was sheared off right where the diameter necks down, this was causing the binding preventing access to R/1/2 after a 5/6 shift. After it broke it wore the upper brass bushing on the reversing lever completely through. Installed a stronger Guard spindle and new upper and lower bushings in the lever.
- All synchros checked out within spec with the exception of 2nd gear. 2nd received a new brass syncro/cone/ring and I left the rest alone. 1st had some measurable wear but I rarely downshift into 1st gear and opted to leave it be (the 2nd gear parts were $450).
- Bearings all looked fine.
- Differential spider gears (open diff) were chewed up pretty bad. I've seen pictures of other diff's with similar wear on the spiders. Looks to be shock induced, the spider gears actually "shale" metal off and deteriorate. For the time being I refreshed the open diff with new spiders.

So in summary, I would replace that shift spindle if you're in there. Judging by the failure on mine it looks to be very weak and prone to shear where the diameter changes. Also if you have an open diff and have found metallic flakes on your magnetic drain plug, its likely from your spider gears.

pp000830

I saw this on the gears in mine as well. My gut tells me that when one makes a hot start to the point that one of the real wheels breaks loose it hammers the hell out of the Differential's gears resulting in damage that looks like some one scooped some metal right out of the gear. Kind'a an odd looking damage.
Andy

96PCarrera993mg

Any pics?