Reverse gear crunch?!

[moazam]

I just bought a 1986 Carrera about 1 week ago. I'm finally getting used to shifting the Porsche 915 transmission.

I was shocked and horrified earlier today when I went to start my car and as I shifted in to the reverse gear, I heard a nice loud CRUNCH'ing! I tried this again, CRUNCH...

This was NOT happening all the times I shifted into reverse before....whats going on?! I always have the clutch pushed all the way down, so I know it's not that...any ideas?

-M

[john walker's workshop]

reverse is not syncronized. go slow when engaging it, and/or touch another gear before engaging. a high cold idle speed will make it worse, so engage even slower.

[moazam]

Hmm...OK. So then this is normal? *sigh*

Maybe I shifted too quick or something into reverse...I did notice that if I do it slowly there is no crunching.

Still quite a bit disconcerting :/

I guess I'll go to 1st gear and then reverse from now on.

-M

[Early_S_Man]

NOT NORMAL AT ALL!

Check your freeplay at the clutch pedal ... if it is too much you may not be fully disengaging the clutch, hence some torque on the transaxle input shaft AND grinding into reverse. If your clutch pedal engagement was 'lazy' or not full ... the clutch adjustment may have been marginal, and responsible for the grinding.

Freeplay should be 5/8" to 3/4" ...

[Formerly Steve Wilkinson]

It's always normal. A simple gearbox--which is what a 915 is, dispensing for the moment with the fact that it's a compact, lightweight wonder-- is a bunch of rotating parts mushing around in a bath of oil, revolving, meshing, turning...we're so used to moron-proof transmissions that the fact that you can't just cram the gear lever into a speed and select it with everything miraculousy coming to an instant halt is something that we in 2003 forget about a gearbox designed in the 1950s. Be nice to it.

Stephan

[david914]

It could be a couple of things. Like John said, if your idle speed is high you can grind reverse if you don't give it a couple of seconds after depressing the clutch before you put it in gear. Also, if your clutch is not adjusted properly, it may not be releasing all the way and you'll grind going into reverse. Combine the two scenarios and you're guaranteed a "grind"!

[david914]

Warren and Stephan slipped in while I was typing. I need to learn to type faster...

[Alan Cottrill]

when your trans is in neutral and your foot is not depressing the clutch, the trans main shaft is spinning.

when you depress the clutch your main shaft will continue to spin.

when you try to engage reverse while the mainshaft is still spinning it will grind... because as JW pointed out it is non-syncro.

to test this, start the engine with the clutct depressed and engage reverse, if no grind the clutch adjustment is probably not to blame.

you should still check and adjust your clutch as needed, and maybe even look into an gear oil change with some swepco. and since you'll be under there look into a new cable and helper spring. and since you're doing that...

[GrindingGears]

Read your Porsche manual. Mine states to press the clutch down for a second or two before shifting into reverse. Mine does the same when I rush to shift. No worries.

-Grind

[moazam]

Originally posted by john walker's workshop
reverse is not syncronized. go slow when engaging it, and/or touch another gear before engaging. a high cold idle speed will make it worse, so engage even slower.

Yuhp, this worked. Shifts smoothly now. A little disconcerting, but oh well.

-M

[moazam]

Originally posted by moazam
Yuhp, this worked. Shifts smoothly now. A little disconcerting, but oh well.

-M

I've noticed though...when the car is parked on an incline, its much more difficult to get into reverse. Suppose I could just roll backwards...

-M

[john walker's workshop]

reverse gears are straight cut, and if the teeth happen to bump into each other tooth to tooth, rather than tooth to groove, reverse won't engage until you either roll the car a bit, or let the clutch out a bit to spin the mainshaft, depress it again, and try reverse again. you usually have to "feel" it in.

[fogcity]

Put the clutch in , blip gas, put it in reverse.

Speaking of: whenever I start the car I have it in neutral AND put in the clutch, thinking I'm being "easier" on the tranny this way instead of leaving the clutch out when I start the motor. Is there any sense to this?

[FrdzRed]

I always shift into first than put it in reverse. Guess this stops the spinning of the main shaft enough to engage the gears.

[vesnyder]

I have a similar issue. When I fist put it into 4th gear and then into reverse it never happens.

[Rick Lee]

I thought I read a while back that this could also be a weak pressure plate, not wanting to come all the way off the disc. My '96 Mazda truck makes this reverse crunch every single time I forget to touch another gear first. I usually throw it into 2nd real quick before going into reverse.

[john walker's workshop]

yes, dry, rust-dusted mainshaft splines can cause the disc to drag on the p/plate or flywheel, and make shifting difficult.

[mwbaum]

"I always shift into first than put it in reverse. Guess this stops the spinning of the main shaft enough to engage the gears."

Thats how I do it too...

[agabriel]

I touch the second gear synchro and never have a grind. It gets me to slow down and get everything in happy place.

Enjoy your '86 - I love mine

[Wayne 962]

Not normal (as Warren said). Wait 10 seconds with the clutch pedal to the floor before shifting into reverse. If it still grinds, your clutch cable is misadjusted, and you are wearing out *all* your synchros prematurely. Or, the clutch is dragging like John said...

-Wayne