Garage Project: Is Your Clutch Pedal Slowing You Down?

Want lower lap times? Right now, you can spend a few minutes dialing in the action of your clutch pedal. It’s an easy garage project.

When trying to trim down lap times, explains James Clay, president of BimmerWorld, properly timing the clutch engagement is very important. 

“And …

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This was cool. And informative. 

In reply to _ :

Thank you, thank you. James knows a lot about stuff. 

Yeah I thought this was going to be about how "automatics are faster now blah blah blah".

I was happy to be wrong.  Good stuff.

Great article!

BMW clutches definitely have a unique feel, especially coming from Japanese stuff.  The initial breakaway is a little stiff and then very light, with a long pedal throw.  I put these clutch stops in both my E46 and E36 and it made a world of difference.  

One of the biggest advantages to the wide stop is that the OE stop is so flimsy, if you put any lateral force on the pedal while its on the stop, it will slip past the stop and stick to the floor.  Never fun to have to reach down and pull the pedal back up in the heat of things.  Had that happen with both the E46 and E36 before adding a meaty stop.  

Truly one of the best $20 upgrades you can do to any BMW.  

I too expected this to be a pro-auto trans piece. Neat stuff!

I can think of a simpler solution, if your clutch is allowing slowing you down, quit using it altogether. Get a dogbox, quit wasting valuable time either being gentle with your synchros or rebuilding a gearbox with them because you're not gentle. An auto-manual/dual clutch can speed you up incrementally from there, but a dogbox is the ultimate for purist cred.

My e36 came with one of these installed. First modification I made to the car was removing it. It couldn't be adjusted far enough to let the clutch fully disengage. I still have to tell people, "clutch bites at the floor" and that's without the clutch stop.

Headed to the garage to investigate the clutch stop on my Miata.  Great article, thanks for posting.

Matt B said:

Yeah I thought this was going to be about how "automatics are faster now blah blah blah".

I was happy to be wrong.  Good stuff.

Ha, didn't even think about that when writing the title. Glad you're all digging the piece. Major props to James for the help. This piece actually started out as something very different, but what we all wound up with is way better. 

buzzboy said:

My e36.... I still have to tell people, "clutch bites at the floor" and that's without the clutch stop.

Would that be improved with a new throwout fork or something? Biting at the floor seems like a problem that I have experienced in other e36 as well. 

In reply to Durty :

Sounds lke there was something wrong with buzzboy's clutch. I have made this great, cheap mod to many of my project cars.

I would not have guessed that shift speed would make that big of a difference.  It makes perfect sense and I have no trouble believing the data.  I guess I heard, or read somewhere that shift speed isn't very important in road racing and accepted that at face value.

I'm going to bump fixing the soft 5th\reverse gate detent on the Miata up on my to do list.  I've adopted a slow, shift with my wrist, technique on my 2-3 shifts to avoid 2-5 shifts.  If that gate detent was firmer I could speed up my shift time significantly. 

I don't think I'm pushing the clutch pedal beyond the disengagement point but I'm going to take a close look at the data to see what my shift times are in the other gears. Perhaps I could benefit from a clutch stop.

In reply to David S. Wallens :

Or you can skip using the clutch pedal completely  except to get rolling. 
Use dog ring gears.  ( non syncro )  

Your  shifts become massively faster.  Basically  you just slam the lever either up or down. ( more detail in a bit) 

For decades race cars have used these.  
 

No you can't use this on the street unless you intend to drive like a jerk  If you try using dog rings while using the clutch pedal plan on replacing gears very frequently.  
A normal transmission has syncros. They are tapered brass ( usually)  cones that speed up a gear to match revolutions and allow the gears to slide together.  ( without the crunch you hear when the syncro is worn out) 

dog rings are straight cut gears with a notch on the side that catches the next gear to match speed and then lock in.  If you shift it as slow as you shift a syncro gear the notches bounce off each other and won't engage.  Persist and you'll round out the notch Possibly enough so it won't stay in that gear and spread a lot of metal through the gear box. It's worse if you have the clutch disengaged. 
 It works best at full throttle, say shifting from 2 nd to 3rd  you slightly hesitate for a nano second. As you slam the gear lever forward. The faster and more brutal you do it the better the gears look after  the race. No clutch 
Downshifting  is a little different,  when you are ready to shift for that same Nano second  you floor the throttle and jam the lever down a gear. No clutch  

Actually  on downshifts  if you know the transmission there is a certain revolution you can jam the lever down a gear and it snicks together so sweet  you'll want to pat yourself on the back. Still don't use the clutch 

One other advantage to a lot of dog rings. Like a quick change rear end you can just take the back end off. Slide the whole stack of gears out, mix and match them and slightly change ratios very quickly.  Let's say you come out below the power curve in one corner. You change change it to be exactly where power is best. 
 

Using that approach you can over cam your engine to gain peak power but over a narrower power band.  
 The result is faster lap times. 
Most 5& 6 speed transmissions have 5 & 6 th gear as over drives not useful gears on the race track. Without losing the time syncro's cost you on a shift  you can shift so fast it's a continuous surge of speed.  

In reply to buzzboy :

I still have to tell people, "clutch bites at the floor" and that's without the clutch stop.

Yeah, that's a  problem with your clutch somewhere. It shouldn't be doing that. 

It bites just off the carpet and has for 50k miles since I've owned it. I don't want to mess with it.

I've done this to both my MK2 Cortina's.Mainly because on the one the original carpet padding has gone away and that made the pedal go in to far and the other because there is no carpet.It's a fix that really did work for my cars.And being hydraulic clutches the pistons cab go in to far and bottom out.A stop sets things right.

frenchyd said:

In reply to David S. Wallens :

Or you can skip using the clutch pedal completely  except to get rolling. 
Use dog ring gears.  ( non syncro )  

Your  shifts become massively faster.  Basically  you just slam the lever either up or down. ( more detail in a bit) 

For decades race cars have used these.  
 

No you can't use this on the street unless you intend to drive like a jerk  If you try using dog rings while using the clutch pedal plan on replacing gears very frequently.  
A normal transmission has syncros. They are tapered brass ( usually)  cones that speed up a gear to match revolutions and allow the gears to slide together.  ( without the crunch you hear when the syncro is worn out) 

dog rings are straight cut gears with a notch on the side that catches the next gear to match speed and then lock in.  If you shift it as slow as you shift a syncro gear the notches bounce off each other and won't engage.  Persist and you'll round out the notch Possibly enough so it won't stay in that gear and spread a lot of metal through the gear box. It's worse if you have the clutch disengaged. 
 It works best at full throttle, say shifting from 2 nd to 3rd  you slightly hesitate for a nano second. As you slam the gear lever forward. The faster and more brutal you do it the better the gears look after  the race. No clutch 
Downshifting  is a little different,  when you are ready to shift for that same Nano second  you floor the throttle and jam the lever down a gear. No clutch  

Actually  on downshifts  if you know the transmission there is a certain revolution you can jam the lever down a gear and it snicks together so sweet  you'll want to pat yourself on the back. Still don't use the clutch 

One other advantage to a lot of dog rings. Like a quick change rear end you can just take the back end off. Slide the whole stack of gears out, mix and match them and slightly change ratios very quickly.  Let's say you come out below the power curve in one corner. You change change it to be exactly where power is best. 
 

Using that approach you can over cam your engine to gain peak power but over a narrower power band.  
 The result is faster lap times. 
Most 5& 6 speed transmissions have 5 & 6 th gear as over drives not useful gears on the race track. Without losing the time syncro's cost you on a shift  you can shift so fast it's a continuous surge of speed.  

My dog box is based on a T-5, and the builder told me specifically not to shift fast without the clutch. There is no intermediate bearing, that the forces involved would cause problems. 
 

That said, my Fairmont has a cable clutch, so it has no "free play" the engagement distance is set completely by the condition/material of the clutch disk, and the distance off the floor is set by adjusting the length of the cable. 
 

Shifting quickly involves putting a little preload on the shift handle, then moving the clutch until the shifter moves (usually about half way through its travel). As soon as the shifter starts to move, MOVE IT NOW to the next gear. "Snick!"  The clutch is already on the way back out. 
 

Watch the first two seconds of this video for one of my early attempts at shifting fast. It *can* happen faster, if everything goes right. 
 

Sorta related, but today I'm expecting a box from Dublin, Virginia. 

snailmont5oh said:

frenchyd said:

In reply to David S. Wallens :

Or you can skip using the clutch pedal completely  except to get rolling. 
Use dog ring gears.  ( non syncro )  

Your  shifts become massively faster.  Basically  you just slam the lever either up or down. ( more detail in a bit) 

For decades race cars have used these.  
 

No you can't use this on the street unless you intend to drive like a jerk  If you try using dog rings while using the clutch pedal plan on replacing gears very frequently.  
A normal transmission has syncros. They are tapered brass ( usually)  cones that speed up a gear to match revolutions and allow the gears to slide together.  ( without the crunch you hear when the syncro is worn out) 

dog rings are straight cut gears with a notch on the side that catches the next gear to match speed and then lock in.  If you shift it as slow as you shift a syncro gear the notches bounce off each other and won't engage.  Persist and you'll round out the notch Possibly enough so it won't stay in that gear and spread a lot of metal through the gear box. It's worse if you have the clutch disengaged. 
 It works best at full throttle, say shifting from 2 nd to 3rd  you slightly hesitate for a nano second. As you slam the gear lever forward. The faster and more brutal you do it the better the gears look after  the race. No clutch 
Downshifting  is a little different,  when you are ready to shift for that same Nano second  you floor the throttle and jam the lever down a gear. No clutch  

Actually  on downshifts  if you know the transmission there is a certain revolution you can jam the lever down a gear and it snicks together so sweet  you'll want to pat yourself on the back. Still don't use the clutch 

One other advantage to a lot of dog rings. Like a quick change rear end you can just take the back end off. Slide the whole stack of gears out, mix and match them and slightly change ratios very quickly.  Let's say you come out below the power curve in one corner. You change change it to be exactly where power is best. 
 

Using that approach you can over cam your engine to gain peak power but over a narrower power band.  
 The result is faster lap times. 
Most 5& 6 speed transmissions have 5 & 6 th gear as over drives not useful gears on the race track. Without losing the time syncro's cost you on a shift  you can shift so fast it's a continuous surge of speed.  

My dog box is based on a T-5, and the builder told me specifically not to shift fast without the clutch. There is no intermediate bearing, that the forces involved would cause problems. 
 

That said, my Fairmont has a cable clutch, so it has no "free play" the engagement distance is set completely by the condition/material of the clutch disk, and the distance off the floor is set by adjusting the length of the cable. 
 

Shifting quickly involves putting a little preload on the shift handle, then moving the clutch until the shifter moves (usually about half way through its travel). As soon as the shifter starts to move, MOVE IT NOW to the next gear. "Snick!"  The clutch is already on the way back out. 
 

Watch the first two seconds of this video for one of my early attempts at shifting fast. It *can* happen faster, if everything goes right. 
 

https://www.youtube.com/embed/izFbe9qo0mA?rel=0

 

A. T5 gearbox still has the syncro cones. What has been done  is the old hot rodders trick of grinding out every other tooth in the  slider.  It's not a true dog ring. 
Seinz and Hewland are two dog ring gear boxes. And at least Seinz tells you not to slow shift .  ( I haven't called anybody at Hewland ) 

I had to replace gears after every track session when the original owner  insisted on using the clutch to shift. luckily with a Seinz you can do it like a quick change rear end,  take the back off slide the gears out clean out the metal shavings etc and slide in a fresh set of gears.  Laying on the grass in the pits it's about a 15-20 minute job. On the bench it's about 5 minutes. 
Look at the engagement method.  Basically there are open "boxes" where the gear slides over and catches the next gear. The sides of the "boxes" are back cut at an angle to hold the gear in. Lifting the throttle like you do with a normal syncro has the effect of speeding up one gear relative to the other making engagement more difficult. down shift you "floor it" to speed up the lower gear in the micro second the dogs are apart. 

Once he gave up and gave me his old box I had One fresh set of gears  in the box. And a few spare gears. Instead of  replacing the gears every session I raced using that gear box for decades. Still shifts very crisp and stays in gear. On the original set of gears. 
One other advantage to a true dog ring gear box is you only ever use the clutch to get rolling. I have a triple disk 7&1/2 inch Tilton clutch it's been used for more than a decade at somewhere around 40 races without replacement. I'm tempted to reuse it. In my next race car. While there is some wear about 1/2 of the friction material is still there and the floater disks still look usable 

In reply to frenchyd :

Here's a pic of the inside of my G-force T-5. It's a true dog box.

In reply to snailmont5oh :

Yes it is. Didn't know anyone was doing that. 

noddaz said:

 

 

 

 

I think every single one of us understands scope creep. 
 

BimmerWorld order has landed.