Slowing down down hill

Clem Clement

Clem Clement

Well-known member
At the GWC meeting last night Jim Cross mentioned that to slow a Model T going down hill, he retards the spark and throttle.

Do folks regualrly do that on a Model A? Seems smart. I never thought about it before. Both handles need to be full up during this procedure. Thanks Jim.

clem
 
Well, retarding the throttle is a no-brainer, but the retarded spark while pushing the engine will certainly foul plugs, raw-gas wash the cylinders, and pump a lot of incomplete combustion fouling over the exhaust valve stems and out the tailpipe. If anything, an engine being pushed should have the ignition advanced farther than normal running. A Model T has only two whimpy brakes on the rear axle, the axle that is the least effective in braking. An A has four wheel brakes that should do the job at any speed as long as the throttle is closed. I would never use my advance lever to do that.
 
MikeK: The rear brakes, unless modified, on a Model T are cast iron on steel drums. They are parking brakes only and are not to be used while moving unless one is really in a panic mode. Gar Williams
 
Jack '29 Sport Coupe said:
On a Model A you can simply downshift like on a modern car. Model T's do not
have the type of transmission that allows that option.
Click to expand...

It's a LOT easier to down-shift on a Model T: you just mash that left-side pedal down... of course doing so might launch you over the windshield...

But there's no double-clutching, no grinding of gears....

And if things really get out of hand, you mash all three pedals down at the same time and hold on tight... this will lock-up the ****** and rear wheels and stall the engine.
 
Special Coupe Frank said:
It's a LOT easier to down-shift on a Model T: you just mash that left-side pedal down... of course doing so might launch you over the windshield...

But there's no double-clutching, no grinding of gears....

And if things really get out of hand, you mash all three pedals down at the same time and hold on tight... this will lock-up the ****** and rear wheels and stall the engine.
Click to expand...

It's been about 20 years since I drove a Model T, but doesn't pushing ANY 2 pedals stop the car?
 
The Model T brakes are in the transmission and if descending a long or steep hill and brakes must be used you could easily wear out the brake band by constant use. To avoid this you can alternate using the brake pedal for a brief time, then the reverse pedal for a brief time, then back to the brake pedal, etc.
This allows heat to dissipate and eliminates extreme wear on the brake band. The brake band in the rear wheel is a parking brake only.
 
MikeK said:
Well, retarding the throttle is a no-brainer, but the retarded spark while pushing the engine will certainly foul plugs, raw-gas wash the cylinders, and pump a lot of incomplete combustion fouling over the exhaust valve stems and out the tailpipe. If anything, an engine being pushed should have the ignition advanced farther than normal running. ... .
Click to expand...

I'm pleased to agree with Mike on this, although don't know if our reasoning is the same. Two reasons I see for ADVANCING the spark when running downhill. First, the pistons are probably moving fast, especially if you have downshifted, so the combustion process and flame front need more of a head start so they don't meet the piston on its way up. Second, since the only fuel charge being supplied is the measly amount coming from the idle circuit, and since the combustion process is slower at low fuel charge, combustion needs more time, again, so it doesn't meet the piston on its way up.

A better thing to do than fiddle with the spark is to open the GAV a turn or so to help get a little more fuel in and minimize the backfiring.

Steve
 
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