915 3rd gear grind

[Tooth911]

Hi everyone
I have a 915 trans with 23k on rebuild with cheap gate shifter.Also all bushings done 1k ago.3rd gear shifts fine at below 3000 rpm but seems to grind when shifting under spirited driving if iam not careful to nurse it. there is a lot of for and aft play in 3rd and 4th about 1 inch.1rst and 2nd do not and any advice would be great .Thanks Chuck car is a 77 911s 2.8l hot rod.

[john walker's workshop]

grinding is generally worn syncro/worn shift sleeve. slop is generally bushings. stock coupler bushings have built in slop. use the ones from pelican with the round hole for the pin. if you hold the shifter against 3rd and get shifter movement on and off throttle, the mainshaft may have end play from a worn 4 point bearing or a worn tensioning plate.

[Tooth911]

Thanks John I will check that out and post again.Thanks Chuck

[turbochad]

Also, make sure you don't have synthetic fluid in it. It is too slick for the pre G50 transmissions.
Chad

[dave 911]

My car is starting to do the same thing every once in a while. Spirited driving getting a slight grind going into 3rd, fine if I baby it a bit, no grind at all if downshifting from 4th into 3rd.

Just thought I'd ask to see if you fixed yours Tooth, and what the fix was? Sounds like another item possibly to add to the eventual engine rebuild list....

Any other thoughts since this is a relatively old thread?

[Peter Zimmermann]

3rd gear is the often overlooked gear at 1/2 synchro repair time. When the 915 is partially disassembled, almost always to repair a 1st/2nd shifting problem, it's relatively easy to repair that problem and not take apart the M/S, measure the 3rd/4th synchro rings, and examine the 3/4 slider.

Third gear is used almost as often as 1/2, and has a smaller synchro ring, which makes it susceptible to wear. Most of the 915s that I've done over the last fifteen years had a 3rd synchro at minimum allowable wear, or was out of tolerance. 3rd gear, and the possibility of a loose pinion bearing, are two issues that should never be ignored when repairing a 915 transmission. I'm about 98% sure that the OP's car has a badly worn 3rd gear synchro ring.

[zippy_gg]

I have a similar issue with my 3rd gear, both when upshifting and downshifting.
I have no problems shifting from 1st to 2nd gear.
The car has 133+K miles, and the clutch disc was worn down to the rivets. The tranny is now out so I'll read up again Peter's tutorial and dig in...

[Tooth911]

Paul Zimmerman's post pretty well covers it.

[Peter Zimmermann]

Link for Tutorial:

Welcome to Red Line Porsche Wiki - Porsche Wiki

Scroll left side of page; click on "915" under "page tags"...

[midnight911]

Cool... time for a cross ratio and an LSD! :-)