Gearbox about to die?!?!

[deez]

It's been happening for about a month now. Every once in a while I'm double clutching, or downshifting quickly, there's a sharp, loud, and scary crunching coming from the gearbox This happens even when I had the clutch fully depressed, and seems to happen more often on the 4-3 downshift. More so than the 5-4 although I have had that happen before as well

Any ideas? Is the gearbox about to..... DIE?

[Sheck]

Why are you double clutching? You may have muffed the sequence. other wise i'd say it is syncros.

See if the sound still happens if you just single clutch and change gears really slow. It should be better or if your syncros are completely shagged then you'll be able to hear that about 15-30 teeth on the gear skip making a disgusting sound and then finnaly it engauges with a crunch.

Check the oil for any metal.

Hope that helps a little as i'm out of ideas both of my previous stuffed gearboxes whined like they were in reverse which meant that the gears were worn/stuffed.

Dave

[timk]

I hope this isn't off topic but I try to double clutch around a downshift blip whenever possible just to make the synchros and gearbox last longer. It's just interesting that you questioned it, do you think it has a negative impact of some sort?

[AJ]

sab, double clutching is just a waste of time with modern gearboxes, all you're doing is wearing your clutch components out prematurely by doing it mate

[Inf3ct0R]

sab. my clutch hose leaked because i heel/toe and double clutched too much, i think! LOL

[timk]

So it's better to let the synchros spin up the input shaft?

[zoomzoom]

As far as I understood double clutching with a bit of a hit of the throttle to match revs should both match the speed of the engine, input shaft and mainshaft to the speed of the output shaft to take some stress off the syncros, and also prevents a compression lockup. This should all be taking from the stress on the car, and the extra wear on clutch would be very minimal if at all as it is not under load at the time, and is not having to take the load of getting the engine speed up to the output speed.

[AJ]

So it's better to let the synchros spin up the input shaft?

a simple blip on the throttle while downshifting is sufficient, rev matching is as old as time itself........however, double clutching is only necessary in a gearbox that has no syncromesh.......ie: getting a three on the tree EH holden back into low gear whilst still moving.......most truck gearboxes in the old days were crash boxes, so double clutch with a rev match throttle blip was the ONLY way to change gears, but even that has gone by the wayside, most modern trucks have syncromesh g/boxes, usually with air assistance.....once again, in a modern car, double declutching is just a wasted effort, it doesn't do anything but wear out components from overuse

[zoomzoom]

the throttle blip will only match the engine speed to the output but still leaves the synchros and clutch to spin up the main and input shafts. I still dont see how double clutching is going to prematurely wear components, if anything it should be making them last longer

[zoomzoom]

I do think it really isn't necessary for normal road driving though.

[deez]

Sorry guys I may have misused the terminology. By double clutching I don't mean *really* double clutching. All I'm doing is blipping the throttle between the downshift

[EGG80X]

Sorry guys I may have misused the terminology. By double clutching I don't mean *really* double clutching. All I'm doing is blipping the throttle between the downshift

heel and toe

[JBT]

heel and toe

Only applies if your "toe" is on the brakes and you use your "heel" to blip the thottle at the same time.

[JBT]

the throttle blip will only match the engine speed to the output but still leaves the synchros and clutch to spin up the main and input shafts. I still dont see how double clutching is going to prematurely wear components, if anything it should be making them last longer

Rev matching on downshift will absolutely reduce clutch, transmission and drivetrain wear and strain.

Double de-clutching will prematurely wear the clutch hydraulics because you're making two clutch operations when only one is needed.

[Mick93]

AJ is wrong if you are blipping the throttle on a doulble declutch it wont wear things out as long as it is done properly. The Blip should be done whilst the gearbox is in Neutral then clutch and put back in gear. If you do it whilst just having the clutch in you are wearing out the clutch. And I am sorry AJ but you are very wrong about syncro boxes. Porsche used them for 15 years at Lemans before they moved to paddleshift gearboxes. They still double declutch though to keep the the car in gear at the correct rpms. You could never be quick on the track if you could not do it and if done correctly you should not wear your syncros. However like anything it is practice that gets it right and it dose take time to do it correctly. Its up to you wether you think the skill is worth aquiring.
Good Luck