What IS engine braking anyway?

[Rick Murchison]

Anyone want to guess how long before the Mods move this thread?

Oh, 'bout 28 minutes...
Rick

 

[Thalassamania]

You know... you can learn the most arcane things on this Board. For those of you who THINK you know clutches, tell me what a Marcel cushion is without using Google or the like. These are in danger when you power/engine brake with a gasoline car with a manual transmission.

Marcel’s are the little kind of leaf springs that “cushion” the clutch’s engagement and disengagement thus reducing both chatter and the requisite driver skill (my AC Cobra had no torsion damper, no marcel, and sintered iron pads).

If have Marcels and you synchronize the clutch plates before engaging what’s the danger?

 

[meekal]

WOW - i KNEW the good folks that patrol this (wonderful) board would know and i figured that i'd put it in the CAVE section since a lot of folks that patrol here have also seen the sign and might have asked a buddy or two what it meant.

thanks folks!

 

[Teamcasa]

You know... you can learn the most arcane things on this Board. For those of you who THINK you know clutches, tell me what a Marcel cushion is without using Google or the like. These are in danger when you power/engine brake with a gasoline car with a manual transmission.

Every clutch disk (short of racing) has marcel cushions. The term rarely used anymore, you are dating yourself. It’s the wavy flat spring that cushions the clutch friction material from the actual (metal) clutch disk. Clutch/power braking causes the clutch friction material to generate extremely high temperatures. This extreme heat will anneal the thin springs and render them useless.
After this happens, the friction material may become loose on the disk and clutch. This is a bad thing.


There are a million term's used in the automotive industry, some are very - very arcane and useless to most. After thirty five years in this industry, I find it fascinating to hear older terms used by the up and coming, their not knowing how they originated.
Dave

 

[eclipse785]

Just FYI: That's not engine breaking, that's wearing out your clutch. When downshifting you need to clutch, blip the throttle to match speeds between the plates and then come off the clutch pedal with the plates spinning at similar speeds, else all you do is transfer wear from the brakes (easy and cheap to renew) to the clutch (expensive and dificult to renew).

Actually it is. Using the compression of an engine to slow down a vehicle is by definition engine braking. And while I understand the premise of your point (using the brakes is cheaper than replacing your clutch), it's really not an accurate comparison since you don't "ride the clutch" to engine brake. Once you drop the clutch, it creates no more wear than normal.

One question though,.. why are people so quick to ask a relatively simple questions like this on a forum like Scubaboard, when there are so many references online? That's what Google or Wikipedia is for.

 

[The Chairman]

If have Marcels and you synchronize the clutch plates before engaging what’s the danger?

Once bent, even just a smidgen, disengaging the clutch becomes problematic. This is why I would never install a rebuilt clutch disc as this is SOOOO common. The reverse torque applied to these thin wafers of metal on deceleration often causes more than enough deformation to accomplish this even on a brand new disc. This causes hard shifting (especially to first gear while stopped), an inability to synchronize (grinding) and vehicle creep while at a stop with the brakes disengaged.

In our next section we will discuss how worn long timing chains, like those found on older overhead valved engines and even some timing belts can skip a tooth doing the same maneuver. However, I might point out that this never stopped me from having fun in a sports car. Vroooom, Vroooom!

 

[The Chairman]

The term rarely used anymore, you are dating yourself.

Can I wax long and loud about the dumbing down of mechanic certifications now a days? I did my 30 years from 1969 until 1999, saw the advent of the first anti-polution device (can anyone guess what that was?), the first electronic ignitions and of course, the computers that have rotted the mechanic's brains. If you want to tune an old Brittish car equipped with SU or Stromberg carbs, you need to go no further than my garage. However, my computer diagnostics don't go beyond 1998 (OBD II).

BTW, I do not miss being an automotive technician.

 

[Teamcasa]

Once bent, even just a smidgen, disengaging the clutch becomes problematic. This is why I would never install a rebuilt clutch disc as this is SOOOO common. The reverse torque applied to these thin wafers of metal on deceleration often causes more than enough deformation to accomplish this even on a brand new disc. This causes hard shifting (especially to first gear while stopped), an inability to synchronize (grinding) and vehicle creep while at a stop with the brakes disengaged.

In our next section we will discuss how worn long timing chains, like those found on older overhead valved engines and even some timing belts can skip a tooth doing the same maneuver. However, I might point out that this never stopped me from having fun in a sports car. Vroooom, Vroooom!

Too true regarding the clutch disk. After replacing hundreds of pistons, valves and sometimes the head on engines with interference valve/piston clearance, timing belts or chains should be replaced on a scheduled basis, or after they have been abused by excessive power braking.
We are not going so far back in time that we will cover Arden or Mill-Offy’s are we?

Dave

 

[The Chairman]

One question though,.. why are people so quick to ask a relatively simple questions like this on a forum like Scubaboard, when there are so many references online? That's what Google or Wikipedia is for.

Because they get to learn a LOT about what they didn't think to ask. Also, they might trust the wisdom gleaned from our collective intellect more than a wiki which can be changed at a whim.

 

[Karibelle]

Can I wax long and loud about the dumbing down of mechanic certifications now a days?

You may. Please speak in generalities, and never mention an agency.

kari