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Synchromesh, Dogbox, Autoblip: grinding the gears


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#1 Nemo1965

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Posted 15 March 2021 - 10:09

This is a thread-topic which borders on the Technical Forum or the Racing Sim-Forum, but I will leave it here.

 

Recently I bought a wheel with stick-shift and three pedals, and in rFactor I've installed several mods to make stick-shifting with clutch as realistically as possible (for example: a neutral-stall when you depress the clutch insufficiently).

 

While I am enjoying this (and trying to learn heel-toe), I kind of get confused about the technical history of stick-shifting in racing. Playing realistic F1-mods on rFactor (for example the exemplary F1 1991 historic mod), I was led to believe that synchromesh gearboxes only left F1 after the semi-automatic flipper-wheel operated gearboxes of the mid-90's. (About which Nigel Mansell said he thought it was slightly inconvenient to have to go through the gears instead of just selecting the gear he needed).

 

Then again, I read somewhere that Colin Chapman already secured synchromesh gearboxes for his Lotus F1-cars in the early sixties... and then I read this quote from Mark Donohue's book: The Unfair Advantage: 

 

Walt drove the first two-hour stretch. When it was my turn, he came in and told me that the clutch linkage was out. It wasn’t possible to disengage the clutch at any time. I thought, “Oh ****! Now what?” He must have seen the panicked look on my face, because he got right to work explaining how to drive without a clutch. I could get going by using the starter with the car in gear. From then on I had to shift by matching engine rpms with the throttle. To upshift, I put pressure on the lever while still at full throttle, then let up on the throttle for just an instant, and it would slip into the next gear. The three-four shift was a little harder, because I had to move the lever laterally in the gate and match engine rpms better. Downshifting was somewhat like double-clutching without the clutch, with a little blip in neutral.

 

That would indicate a Dogbox, and not synchromesh, right?

 

To cut a long story short: when did double clutching become unnecessary in most race-cars? And did, say Jim Clark, go through the gears or did he just, as Dear Nige, just select the gear he wanted to be in for the next corner? And perhaps did not even use the clutch?


Edited by Nemo1965, 15 March 2021 - 10:09.


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#2 mariner

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Posted 15 March 2021 - 11:45

Put simply most purpose built  racing gearboxes were non-synchro e.g. Heweland.

eThe snchro cones take up space, can wear and break and given teh close ratios and a focused driver you do'nt need synchro.

 

Two big exceptions ZF and, I think, Porsche

 

Lotus used  ZF boxes instead of Hewlands and they had fixed ratios and synchro.- plus a lock out gate so the driver had to go down through each gear.

 

The other big user of the ZF was the Fiord GT40 in endurance racing where synchro and interlocks probably stopped tired drivers mis-using the box.

 

I think Porsche always used synchro in the racing cars but  that probably had something to do with Porsche owning the key patents on synchro so good advertising.

 

You can double de-clutch and make clutchless changes on synchro and non synchro boxes - its just easier with synchro until you wreck the synchro cones!


Edited by mariner, 15 March 2021 - 11:59.


#3 Nemo1965

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Posted 15 March 2021 - 13:08

Put simply most purpose built  racing gearboxes were non-synchro e.g. Heweland.

eThe snchro cones take up space, can wear and break and given teh close ratios and a focused driver you do'nt need synchro.

 

Two big exceptions ZF and, I think, Porsche

 

Lotus used  ZF boxes instead of Hewlands and they had fixed ratios and synchro.- plus a lock out gate so the driver had to go down through each gear.

 

The other big user of the ZF was the Fiord GT40 in endurance racing where synchro and interlocks probably stopped tired drivers mis-using the box.

 

I think Porsche always used synchro in the racing cars but  that probably had something to do with Porsche owning the key patents on synchro so good advertising.

 

You can double de-clutch and make clutchless changes on synchro and non synchro boxes - its just easier with synchro until you wreck the synchro cones!

 

Thank you, wonderful answer. About the Hewlands, that would explain a lot. Drivers of historic cars I have spoken (or read interviews with), contradicted each other. For example: I had a nice conversation with Gijs van Lennep once and he told me the 917's were beasts to drive but changed gears like a dream. While Frits Kroymans (the Dutch Ferrari-importer) admitted he wanted to put his teeth in his wheel sometimes when he drove historic cars, so cumbersome were the gear-changes to make. 



#4 404KF2

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Posted 15 March 2021 - 22:41

I've driven a 1967 Peugeot 404 with no clutch - linkage broke on a drive in Vancouver many years ago - and it's a synchromesh box (late C3 type) with Nardi floor shifter (which is bolted directly to the gearbox and has no linkages).  It's dead easy to drive and shift without the clutch, doing exactly what the Donohue quote above says.  The exact workings of the gears and when to snick it into the next one is dead obvious due to excellent feel through the lever.



#5 Kelpiecross

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Posted 16 March 2021 - 04:00

All (that I know of) motorbikes have constant-mesh synchro-less gearboxes.   



#6 Charlieman

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Posted 16 March 2021 - 09:56

If you go back to the 1920s and earlier, most cars had sliding mesh gearboxes which require an even more sensitive touch than dog engagement and constant mesh. Does anyone recall when GN first used their chain drive transmission with dog gear selectors?



#7 Allan Lupton

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Posted 16 March 2021 - 11:40

Thirlby has 1913 for the first use of the GN multi-chain transmission.

It was not developed as an easy-change system but as a way of using chains for a multi-ratio transmission.

The contemporary sliding-mesh gearboxes are not difficult to drive by the standards (and speeds) of the time, particularly if you have a clutch-stop to help up-changes and know how to double-declutch down.

 

Like 404KF2 I've driven many clutchless miles in unlikely cars such as an AlfaSud and a Daimler SP250 - the latter was dead easy to start in gear from standstill, provided you had some throttle which did make it take off a bit smartly!


Edited by Allan Lupton, 16 March 2021 - 11:48.


#8 Lee Nicolle

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Posted 27 March 2021 - 02:11

All of my racing for 50+ years has been with sychro boxes which are more fragile when used racing. But far nicer on the street cars they came on.

I have driven dogboxes in private testing and had to modify my driving a little on down changes.

Plus in that case getting out of my RHD car with a 4 speed Muncie to a LHD car with a 5 speed dog box. Interesting!

I was fairly easy on gearboxes and did not kill many, whereas another racer who used the same gearbox bloke smashed them!!

Though late 90s better gearoils became available and made changes far nicer. That was just as well as between the two of us we broke most Muncie and T10 parts available locally. Ofcourse the gearboxes were rated far less torque than our engines. and 7500+ rpm as well for boxes designed with about 5000 rpm limits.

You can drive any gearbox without a clutch once moving, rpm and feel the next ratio in. Up or down. 

Heel and toe though is the only way to come down when racing however. Apart from all these modern 'gearboxes' that are designed [or not] to be driven without. I have seen Hollinger Supercar boxes destroyed by a driver not using the clutch.

I had to learn all of this very early,, I learnt to drive [in paddocks] in a 1932 Dodge truck. Or a Vanguard ute with no syncro on first. And for a period no clutch either!