Friday, April 7, 2006

Double Clutching

I thought I understood double-clutching the transmission. You just let the clutch out (in neutral) on the way from first to second gear, and then when going into second gear it doesn’t grind.  I thought it was just some kind of magic.

On Sunday I took my dad for a ride to Home Depot in the 900, and I learned the story behind the “magic”. Turns out it isn’t magic at all, it’s just a mechanical speed-matching between the speed of the parts in the transmission and the speed of the crankshaft on the other side of the clutch (or something close to that).

I had wondered why I could always double-clutch on the 1-2 shift, but could never do it on the 3-2 shift. It always ground terribly. Dad explained that before the 1970s, most cars (at least the ones he drove) didn’t have synchromesh transmissions, at least not full synchromesh. To shift between gears that weren’t synchromesh, you had to double-clutch, or heel-and-toe shift.

I’ve ready about heel-and-toe shifting in car magazines, but never really understood the technique or the purpose. Turns out it’s all about not being abusive to the synchros- and to driving more smoothly.

My dad explained that in order to shift from 3rd to 2nd without grinding, I had to double clutch shift, but while in neutral I needed to rev the engine, so that the engine revs are where they would be if I was already in 2nd gear at that speed. He said that when he was learning to drive, his family had a Renault Dauphine. I’m not even sure what that looks like, but mechanically it had a very small engine as well as a transmission that wasn’t synchromesh into 1st gear. He had to double-clutch shift into 1st gear if the car wasn’t fully stopped, which happened quite often because the car would lug in 2nd at relatively low speeds. It required use of the heel on the gas pedal and toe on the brake (or the other way around) to be slowing the car while revving the engine.

We stopped and switched my dad into the driver’s seat for a demonstration, because I wasn’t having any luck trying to do what he was explaining. Sure enough, he was able to shift from 3rd to 2nd without grinding by doing just what he had explained. Way cool.

I finally did some practicing yesterday. I had gone to Bellevue to meet James (the guy whose wheels I bought) to trade him the payment for the last 2 wheel cap retaining bolts. James and I had a good lunch at Burgermaster after finally parking; we were in the parking lot for several minutes watching this woman try to park her big Mercedes with very little driving skill. She essentially got herself sideways to the driveway, similar to when Austin Powers tried to turn that cart around in a hallway in one of his movies. Except the lady in the Mercedes had more room and a much more expensive cart.

In any case, in my driving around Bellevue I did practice the double-clutch shifting, with a middling degree of success. It’s somehow opposite to the way I learned how to drive, to shift into a lower gear while racing the engine. But I’m getting better at it.

Because I already had the 900 in Bellevue, with its cool wheels on, I decided to stop by Barrier Volvo after lunch and show it off to Sue. I didn’t know it was supposed to be her day off, but it didn’t matter anyhow because she was there delivering a really nice looking S40 T5 AWD to a guy about my age. The S40 was in the showroom, similar to the way our V70R was in Jim Fisher’s showroom, but the car was parked far from any fire alarm control panels, so that in his excitement the guy couldn’t bump into the alarm control panel and set off the alarm (which is exactly what I did when we picked up our Volvo).

Sue hurriedly finished off the delivery of the S40 and brought her client out to show off my 900. I hope the client doesn’t feel badly about that. Sue thought the wheels really helped the car out.  I agree that they do. She had the great idea to put some Barrier plate frames on the car so it could get a free car wash (it was pretty dirty). So she brought out the frames, and I began installing them. Some of the salesmen who work with Sue came out to check out the 900 too. It was a proud moment for me to show off the 900. She insists I can’t put the racing stripes on it. I am intending to put them on, it’s one of those things I just haven’t gotten to yet.

I thanked Sue and headed off to the car wash, using the lane for “Barrier Preferred Customers” rather than the “Barrier Vehicles Only” lane. The car wash attendant asked if this was my first visit, then he explained the free and optional pay services. As he was going through his explanation, he stated that the highest level of wash service ($75) includes a lot of attention to the surfaces of the vehicle, but that such a service is no substitute for a hand waxing of the paint, which on an older vehicle such as mine would be required to take the dullness out of the paint. I think this guy who is used to seeing new Audi, Saab, Volvo, Porsche, and Mercedes vehicles was pretty much rolling his eyes at my 14 year old Saab with visibly oxidized paint and rusty trim, wondering why I would feel entitled to run my old car through his nice carwash. He dutifully brushed the wheels and sent me in to the wash bay, where I was afraid some trim pieces might come loose by the abrasive wash brushes and pads.  The car came out of there just fine, and much cleaner when I entered. Thanks, Sue.

I’ll definitely need to keep practicing the double-clutch shifting. But now that I understand exactly what it is I’m doing, I’m in much better shape. So I owe my dad thanks for the driving lesson. At age 32, I’m still learning new tricks. And like they say, practice makes perfect.

Posted by KR at 16:13:11
Comments

6 Responses to “Double Clutching”

  1. inzane says:

    i have given up on double clutching and have sold my soul to the heal toe. why, u ask? because when the lights are on, i have to heal toe, just to keep the engine in the FC from dying because the TPS is hosed and there’s some impedance somewhere i have yet to fix.

    also proves useful when driving =)

  2. SexyArmo says:

    Hey, Kevin. This is George in Arizona. I was directed to your blog from Zane’s (he and I went to highschool together).

    I’m really enjoying your posts. Fun stuff - keep up the great work!

    A question: what compelled you to enlist a ‘92 SAAB 900 into auto-x service (besides the cost of acquiring one)? I know virtually nothing about SAABs (I own Audis), but my guess would be that the 900 is probably not the most nimble machine on the track. What is your suspension setup? My initial guess (and you’ve probably covered this somewhere already) is that you have coilovers based on this line in a previous post: “It looks like I need to lower the car a bit now”. The ability to adjust ride-height points to a coilover setup. Anti-sway bars?

    BTW, I took a closer look at your bumper-sticker set-up, too, because, as Zane will tell you, I am a bit of political animal. :-) Anyway, did you go to Middlebury College? When I interned in Congress, one of my roomates attended Middlebury. If that car originated in Vermont, it has come a long way, eh?

    Well, good luck with everything. I will be checking in on the progress regularly. (Zane’s blog is dead anyway! Besides, I refuse to get involved in his political hackery anymore.) :-)

  3. Kevin says:

    Thanks for reading George. Looks like I need to update the photos of the 900. I scraped all of those Vermonty bumper stickers and replaced them with two from the Rat City Rollergirls, our local roller derby league. All of those bumper stickers (including the Middlebury one) were included in the $800 sale price when I bought the car in January.

    The reason I chose a ‘92 900s for autocross is because I found this one for sale on craigslist for $800. No joke. I’ve always been a saab nut, this is my third black saab (and my oldest). It’s not the most nimble… part of the suspension setup currently includes “OEM rear shock absorbers and springs”. I’ll have to add a suspension diagram or two in a future post.

    The 900 is a well-engineered car. It just happens to have been engineered in the late 1970s based on a components set from the early 1970s, yet it was produced until 1993. So some of the solutions seem a little nonconventional based on the more modern cars we’re all accustomed to.

  4. SexyArmo says:

    Check out this link for some great renderings of suspension schemes: http://www.carbibles.com/suspension_bible.html

    BTW, did I read it correctly - are you a safety engineer? As in occupational safety and health? Or are you involved in safety sytems of, say, aircraft? My current career pursuit has me heavily involved with occupational safety and health. In fact I am a member of ASSE (American Socitety of Safety Engineers).

    Or are you in some other aspect of safety?

  5. Kevin says:

    I’m a safety engineer as in Electrical Safety/Product Safety. I work for a Intertek, a Nationally Recognized Testing Laboratory. I evaluate and test equipment to national standards to ensure compliance with those standards. Fun, fun, fun. It’s actually really interesting most of the time, as I get to see a lot of different types of products and take them apart.

    Your suspension comment cause me to make a post about the 900’s suspension design. Check it out.

  6. inzane says:

    political hackery?? lol!

    yeah i know… sorry… all i do is write what i happen to be thinking about that day. ususally it’s because i’m listening to the radio.

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