For the (probably newer) drivers that have never heard of it, double clutching is a technique whereby after shifting to neutral on an upshift, the cluch is let out and the engine is revved up a bit before being depressed again to go for the next gear. In the case of the FD where they syncros go bad, it helps with shifting and can eliminate grinding when going into 5th.

In the case of my red '93, it does not matter how long I hold the clutch in, the trans grinds going into 5th using regular shifting. If I shift from 4th to neutral, let out the clutch, rev the engine past the matching revs, push the clutch back in and then go for 5th, it almost always goes in just fine, no grind. I have a replacment trans, but this works to carry me until I can schedule the other one to go in and helps reduce wear on parts so fewer of them need to be replaced during a rebuild.

 

Just float shift it.

 

Just change the syncro....HAHAHAHAHA

 

"double clutching is a technique whereby after shifting to neutral on an upshift, the cluch is let out and the engine is revved up a bit before being depressed again to go for the next gear. "

You don't rev up on an up shift. And if you are good at what you're doing, you don't even use the clutch on an up shift. Sounds like you "power shifting" into 5th is what's doing the damage.

 

you're going to destroy the syncro pretty soon doing that method, as that IS NOT how you double-clutch. At all...... stop watching fast and furious.....

you can't save the few hundred bucks to buy the replacement syncro and pay for one day's worth of labor to have a tranny shop do it?

What about the few hundred bucks it would cost to buy a known good used tranny that doesn't have the 5th gear grind and do the install over the weekend?

 

In the case of normal driving with this FD, the technique that prevents grinding is what I described. With the syncro issues rev matching does not work well, I have used it in other cars, and first learned about how to do it when the clutch cable broke on the first car I ever owned while on a long distance trip.

Actually re the "power shifting"; I bought the car 3 weeks ago with the syncro issue, it's a common '93 FD issue.

 

Please read my thread:

"I have a replacment trans, but this works to carry me until I can schedule the other one to go in and helps reduce wear on parts so fewer of them need to be replaced during a rebuild."

FYI, I bought car 3 weeks ago and located a local trans last week.

The syncro was shot long before I bought it, what I described is what works for this car to go into 5th without grinding.

 

I'm pretty sure double clutching is for downshifts only. The purpose is to speed up the rotation speed of the gearsets to aid in meshing for a downshift. If you are Upshifting, (4th to 5th) you want to reduce the rotational speed of the gears. I double clutch almost every downshift... A habit that started in '95 when I bought an '82 with bad synchros.

You can time shift up, but it's difficult and very damaging to the synchros if botched.

I can't see any way that double clutching an uplift has any merit. I recall hearing that on Fast and Furious and thinking "morons."

 

You're talking about heel-toe.....

you dont have to double-clutch anything...... thats why we have syncros......

 

Sorry, i didnt read that part.....

It seems your have another car you can use by looking at your sig..... why are you even driving the FD if the 5th gear syncro is as bad as you say?

 

No, I'm talking about double clutching. Heel toe is a form of double clutching or can be used just to rev match to prevent driveline shock when pudding deep into a corner.

You are correct, you don't HAVE to double clutch anything because we have synchros, but if you read my post, you will see that it is a habit I got into when mine were shot. Double clutching is easier on the syncros than traditional downshifting and our cars aren't getting any younger.

 

+1

Double clutching and heel-toe are completely different. You can one or both at the same time.

Double clutching is simply used to speed up the transmission internals on a downshift. Transmissions with straight cut gears (no synchros) or with a band clutch (read - a band around the flywheel that just slowed the engine down to jam it in to gear) required double clutching.

 

In my original post I mis-stated the double clutching is used for upshifts, of course it is used for downshifting. Theoretically it shouldn’t do anything on an upshift since the input shaft of the trans is spinning at a higher RPM. With this FD, a normal upshift from 4 to 5 makes a grind every time, doing a double clutch through neutral on the upshift allows a grind free shift. Hope it helps someone else until they can get their trans fixed or replaced

 

What's the different between double clutching and holding the clutch down and rev it up before engaging it?

 

Double clutching involves a momentary shift to neutral. You release the clutch, blip the throttle, clutch in, and drop it in the lower gear. Blipping the throttle spins the transmission internals up to the speed they need to be in the lower gear. Sometimes a brief rev match blip is necessary if you have a super light flywheel.

 

I understand that, but wouldn't holding down the clutch and just rev it before engaging it does the same thing? I guess my question is what's the propose of clutching it twice?

 

Revving the motor while the clutch pedal is depressed does nothing for the transmission.

As long as the clutch pedal is pressed in, the motor and transmission are two separate entities and thus increasing the RPM of your motor does not increase the RPM of your transmission.

 

Ok got it, thanks

 

I always double clutch to get into 5th, if I don't the gears grind

5th gear syncro is gone, and I'm too lazy to change it. Learning to double clutch was easier and cheaper :P

 

MIBagentQ, thanks for the post, good to know I'm not the only one to use this. I've seen pictures of FD 5th gear syncros that were broken into 2 pieces and still (sort of) working, not sure how bad the one in this trans is, but I want to have all parts on hand to do other work while swapping it out, things like seals, input shaft bearing, maybe a lightweight flywheel and automatic counterweight, different clutch, new slave cylinder, 3" midpipe etc. etc. etc. you know how these things go, as long as it's on the rack.....

 

I don't know why we're having this discussion. You have synchros so you do not need to do what was done in the age of Troy. If the synchro is gone, fix the transmission.

 

It's a good discussion, not every RX-7 owner will have the mechanical competency or facilities available to dismantle and replace the 5th gear syncro or have the available funds or sufficient reasons to justify simply paying shop to replace it for them. We all come from various walks of life and while some of us do have deep pockets to spend on our cars, some aren't as fortunate and will need to make do with what is available to them.

Members should know that there is another way, without simply grinding the 5th gear each on every shift which could lead to even larger more expensive problems. If you double clutch (which is FREE to learn), you can get away with not having a working 5th gear syncro.

I've been double clutching 5th gear since 2006 and at this point it's become so habitual that I have no plans on ever replacing that syncro.

 

LOL a lot easier said than done

I do somewhat of the same thing when shifting to 5th only I rev-match after letting the rpms drop 1200-1500 rpms:

usually rev out to 4000 rpms in 4th
pop the tranny in nuetral
rpms drop to say 2500
light rev to 3000ish
usually goes into 5th with little to no grinds