VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 Down shifting in the 1930 Roadster

Up shifting is a breeze, but like the 28 Model A... I had, this Roadster is a bear, downshifting from 3rd to second. So far on my maiden voyage, I was unsuccessful, and of course didn't want to grind the gears. Double clutched it with a slight hesitation in neutral, tried tapping the gas a bit, to no avail. Any secrets here?

That does take a bit of practice and is still difficult. Some times it falls right in to place and other times it seems impossible. Make sure you have the right oil or its equivalent in the transmission, I believe it is 600W. The thickness should help slow the gears down when you push in the clutch.

Dave

In a word it takes "practice".

To help reduce practice time and gear grinding: To downshift it is necessary to coordinate the engine speed with the transmission gear speed. As an example if traveling at 10 mph it will be necessary to have the engine speed ~ 1000 rpm to downshift into second. If you pay attention to the sound of the engine at different speeds in each gear it will help in the learning process. Note that the sound changes if accelerating, maintaining a speed or slowing in a given gear.

After driving these non synchromesh Chevrolets for over 50 years it has almost been grind free even if each one has its own sounds.

I'll first change out the tranny oil....did the engine a few days ago. It needed it. 600 w must be as thick as molasses. Any particular brand?

On the engine speed to gear ratio, is the actual speed of the car matter? Obviously we don't downshift into a gear that will cause a lunge of the car....but is there a speed range that would match the shifting process, to some degree anyway?

I got mine from The Filling Station. The 600w sounds thick but it is a steam cylinder oil and the number does not equate to our modern numbers. There is a modern equivalent , something like 250 but I have not tried it. Maybe someone that has will advise.

Dave

Mobil 600W. Yes, it is quite thick. I use it in my tranny, u-joint area, and differential.

Since I have two vehicles that use it, I bought a 5 gallon bucket of it from a local oil dealer (Western Oil) a number of years ago. It was cheaper than buying a bunch of quarts from one of the regular old Chevy Parts vendors.

Dean

Hi there old72er

Just to elaborate a little on what Chipper said...

While in NEUTRAL with the clutch ENGAGED, you have to match the engine rpm to what it would be if you were in the gear you are down shifting to, with the car at it's present forward speed
Then push in (release) the clutch and QUICKLY shift into gear with no hesitation.

If you hesitate with the clutch released, it gives the input and countershafts time to slow down and de-synchronize.
With this in mind, a thicker oil can actually make down shifting more difficult.

To make it easy...
Let the car coast down to idle speed in high gear.
Dis-engage the clutch and shift into neutral.
Engage the clutch and bring the engine up to the rpm you would have been at when you up-shifted into high.
Dis-engage the clutch and immediately shift into second.

You may get a little grinding until you learn to fine-tune your shift, but it shouldn't be much.

Hope that helps. 🙂

PS
Heavy oil helps on the up shift of course.
In this case there is no need to double-clutch.
Just shift into neutral, wait the appropriate amount of time for the input and countershafts to slow down the appropriate amount due to oil drag, and up-shift.

There is one trick I use to "learn" how a vehicle sounds when you properly match the engine speed to ground speed in various gears.

I take the vehicle out into a large level and empty parking lot. One I get moving in first gear I hold it at a steady speed (maybe 10 mph or less). I slowly let off the gas while putting some pressure on the shift lever to taker it out of first gear. It will come out of gear when there is no load on the transmission. I then gradually let off the gas so the engine slows down while I apply pressure to shift into second. When the engine speed matches the transmission speed it will easily slide into second gear without pushing in on the clutch.

This is the technique you also use when the clutch linkage fails and you need to get a vehicle home.

With practice you can learn to upshift and downshift with no clutching.

Hi Rusty

That works well when you are "applying pressure" to a synchronizer.
A lot of care and experience is required when it's spur cut teeth on spur cut teeth.
It tends to put a few chips and sometimes the ends of a few teeth in the bottom of the case. 🙂

Downshifting in a Chevy is easy.

A 600 weight Transmission oil is much too heavy. Get any standard transmission oil used in normal three speed cars and use that.

Down shifting is easy. From 3rd to second, give it some gas in neutral (with the clutch depressed) before shifting to second.

I just replaced the old tranny oil with 600. Stuff is not cheap. Hate to drain it and use 90. There seems to be some opposing opinions here on what to use.....as far as shifting.

I tried your method without success, BTW. had a few old non-synchro trucks and cars with better success on the downshift. The 28 Model A and this old girl, not so much.

Double clutch with some gas in neutral is the good solution, as mentioned above.
BUT! Very importantant to reduce the speed of the car BEFORE you start the process. The amount of the gas in neutral depends on the speed of the car. Low speed = little gas and very low speed = NO GAS in neutral.
More difficult to downshift if the road leads uphill, because the car needs the speed and you have less time.

Mihaly