Double clutching because of worn synchro?

[bulwnkl]

On the up-shift, the engine and input side of the tranny need to slow in order for rpm of input & output shaft to match. Just waiting, even with the clutch constantly depressed, allows that to happen anyway. On the down-shift, however, the input shaft needs to be sped up in order to match the rpm of the output shaft in the gear you're trying to get into. That means you must RELEASE the clutch pedal while you're in neutral, blip the throttle (which speeds up the input shaft only because you're _not_ pushing the clutch), then push the clutch pedal again and make the shift into the lower gear.

You can actually shift the tranny completely without the clutch pedal if you always match revs, but do NOT do this regularly. To do so will cause a specific wear type which will eventually result in the tranny popping out of gear on its own. OTR semi-truck transmissions can be shifted without the clutch at all times because they're designed & built a little differently than synchronized car/pickup trannies.

You're only experiencing this issue when down-shifting into one gear, correct? But not at any other time? That means it's the synchro, just like you're thinking, and double-clutching (with a throttle blip in-between) will help you avoid the crunching & grinding. It takes a little experience to know how much extra rev you need, but that comes with practice.

 

[Drew99GT]

If you can get it shipped or it's available locally, try throwing a bottle of Ac Delco or Pennzoil Synchromesh manual transmission fluid into your transmission. If it specs 80 weight, you might be able to use just that fluid (it's pretty thin), but if it specs a thicker fluid, mix 1 bottle to the recommended fluid so it's not too thin. I do this on my Corolla with worn 2nd and 3rd synchros and it works wonders. The synchromesh fluid has additives that help synchros work easier.

 

[jacobsond]

I quit downshifting a while ago. No point in a little vehicle. IMHO brakes are cheaper to replace in a passenger vehicle than a clutch or transmission. So downshifting to save your brakes is [censored] Brake repair is cheaper than trannie problems.

 

[SHOZ]

Originally Posted By: jacobsond
I quit downshifting a while ago. No point in a little vehicle. IMHO brakes are cheaper to replace in a passenger vehicle than a clutch or transmission. So downshifting to save your brakes is [censored] Brake repair is cheaper than trannie problems.
Are you saying downshifting will cause transmission problems?

 

[Popsy]

Originally Posted By: jacobsond
I quit downshifting a while ago. No point in a little vehicle. IMHO brakes are cheaper to replace in a passenger vehicle than a clutch or transmission. So downshifting to save your brakes is [censored] Brake repair is cheaper than trannie problems.

I totally agree with that. I only downshift to gain rpm if needed, but I prefer to use brakes to slow down, cheaper and easier to replace than clutch.
Engine braking is another thing but I don't need engine braking very often.

 

[DeafBrad]

[/quote]Are you saying downshifting will cause transmission problems?[/quote]

Downshifting will not necessarily cause transmission problems. Think of a synchronizer as little brakes in transmission. When you go to upshift, the next gear is spinning at a different rate. The syncronizer makes the gears match in speed. Then they will not grind because they are going at the same speed.

Rev matching does the same thing as a synchronizer. Done correctly, there will not be grinding because the parts are spinning at the same speed. On upshifts, the engine needs to slow down a little. On downshifts, the engine needs to speed up a little.

What wears out synchronisers quickly? Quickly slamming the transmission into the next gear. Example: if you slam on the brakes hard every time you stop, you will need to replace your brake pads often. The trick is to not be in a hurry when shifting. That will prolong the life of the synchronizers. 1st to 2nd is where a lot of wear is. People leave a light quickly, and slam it into second.

Synchromesh is worth looking into. Make sure it is compatible with the metals in your transmission. I am sure other guys on this site could help you determine that.

 

[FCD]

Ah ok i understand it now
And no i can't really get AC Delco or Penzzoil anywhere in Europe as those brands aren't sold here and shipping from the US would be expensive.
And yes it ONLY happens downshifting from 3rd to 2nd.
But how long do you think i could go by double clutching until i get it fixed? could i do a lot of damage by not having it fixed on time? i'm not a rich person by any means..., i don't do more than 5000 Km / 3000 Miles a year ( usually even less than that ) with it and most of that is just highway cruising and not driving aggressively really.
And this noise is not recent by the way, it's been there for quite some time i will try to film it if i can.

 

[Popsy]

Some cars/trucks were not fitted with synchro at all, so I guess if you keep double shifting you can get it running like forever

That's I thought with one of my car, and then I came across a relatively low mileage gearbox, so I replaced it. Maybe look for a used compatible gearbox, so you'll have time to take a peak inside and restore it yourself for cheap, while you can still use the car.

 

[FCD]

The problem is i'm in Spain, parts here are scarce for these cars, and my particular model wasn't sold here so i have to buy all my parts from Germany or the UK, i might be able to get a reconditioned gearbox for about a grand but not sure

 

[xfactor9]

Originally Posted By: FordCapriDriver

But how long do you think i could go by double clutching until i get it fixed? could i do a lot of damage by not having it fixed on time? i'm not a rich person by any means..., i don't do more than 5000 Km / 3000 Miles a year ( usually even less than that ) with it and most of that is just highway cruising and not driving aggressively really.
And this noise is not recent by the way, it's been there for quite some time i will try to film it if i can.


You probably don't need to fix it. My previous manual tranny car developed grinding synchros only a few months after I bought it used, and I kept driving it with double-clutching until I sold it, 60k miles later. I never fixed it. I made it a habit to always double-clutch, even in gears whose synchros worked fine. It becomes subconscious after a while

If the repair is disproportionately expensive relative to the car's value, just leave it as is. Synchros are like power steering -- nice to have but not necessary as long as you double-clutch. The only reason to fix it is if, even with lots of practicing, you still can't eliminate the grinding. In that case you're wearing down your tranny so it's worth fixing

 

[eljefino]

Originally Posted By: xfactor9

You probably don't need to fix it. My previous manual tranny car developed grinding synchros only a few months after I bought it used, and I kept driving it with double-clutching until I sold it, 60k miles later. I never fixed it. I made it a habit to always double-clutch, even in gears whose synchros worked fine. It becomes subconscious after a while



Pretty much me too. Drove enough junkers that the habit carries over to newer cars with working synchros. This also preserves the synchros, possibly forever!

 

[Silk]

I had a '93 Ford Telstar SW (Mazda 626/Capella), 330,000km when we got it, 450,000km when sold. It always had a crunchy 2nd gear...not worth fixing, just live with it...anyway, the son in law was driving it so I didn't care. One day I had it in the shop and put some Pennz synth 70/80 (can't remember, it was 13 years ago), and it was still the same. A couple of months later I had it again, and after I gave it back to the SIL, he asked if I'd fixed the gearbox...ah, no. But it was fixed, no more crunch for 100,000km. Strange it took so long to make a difference.