MTFCA Forum

When my 27 shifts into high gear it starts luging and bucking. ????????

Mike

Michael, This has been discussed many times in the past and the first thing to look into is your shifting technique. Have you driven Model T’s in the past? Is this a new T to you or one you have driven before and it is now shifting differently?
Give us some details so we can veer towards something mechanical or shifting technique.

Details on what your doing when your starting out with your T and what your doing when you shift into high would help.
Also remember your T is about 20 HP and isn’t like a modern vehicle. Even when your T is in top condition your shifting, stopping and starting technique is very very important for getting started on a drive.

As mentioned above, technique is often the issue. Also, look for misfires. With the engine running fast in low gear, misfires are not always noticed, but after shifting to high, with the engine turning much slower and depending on each cylinder to do its work, misfires are far more pronounced and can cause the car to buck & lurch.

Also, at what speed do you shift to high? Normally between 5 & 10 mph is about right.

Another consideration is the rear axle ratio. If it is a 3 to 1, the shift speed should be higher.
With std rear gears, I prefer to shift into high at 10 mph, which results in the engine speed of 400 rpm.

Art Mirtes

A very important thing. I notice you live in Colorado. If you are starting on a hill, you might not even be able to use high until you get to the top of the hill. Some hills can be climbed in high if you get a running start, but when the engine starts to bog down, you will need to shift down. A Ruckstell or other auxiliary axle helps a lot in hill climbing. Also the weight of the car is important. The Roadsters and Tourings will climb hills better than sedans . Also it even makes a difference how many passengers you have aboard or what other loads you carry. I have a hill I can climb in high with a running start, but with passengers, I have to shift down. My dad told me of a trip to Yosemite back in the 1920's. They had camping gear and 5 people in a T touring. When they came to a hill grandpa would say," Time to get out boys" and his 3 sons would get out and walk up the hill or even get out and push.
Norm

I am familiar with driving a T. I think my problem might be a miss Fire under a load. I will check on that.

Thanks everyone

Michael

your additional info is instructive...if it is in fact a misfire, then I'd be inclined to thoroughly investigate for a vacuum leak at the manifold. If the carb is a Stromberg or any accessory carb, I'd investigate the high-speed setting. Finally, a leaking intake valve can cause havoc with proper intake air flow.

The compression on each cylinder should be checked. It is easy to do and will tell a lot about the condition of the engine.

Art Mirtes

Having a carb set too lean can also produce what you describe. Easy enough to check, start the car normal, open carb adjust 1/2 turn above your normal setting, do for a drive, see if it bucks...

Also, if you have a gas line filter, take out the cartridge and try again...I learned that one the hard way working on a guys car 'for lunch inclusive' as the only fee...and he was about to declare me a dependent...lol

Too much advance on the timing is another consideration, try reducing and see if the bucking goes away...Robert

Any weakness in the ignition system will be emphasized when pulling either on a steep grade, or at low speeds with the throttle. Under those conditions the engine compression will be highest and it will take a stronger spark to jump the gap in the spark plug. I would start with the spark plugs and to see if each is clean and looks like it has been firing. A fouled plug will be oily and black. Or could be sooty and black or just soaked with gasoline. If you have good plugs, next would be the coils. They should each be tested to see if they spark at 1.5 amps. They should be even and through a good strong spark. Next would be to be sure the timer is working correctly and you can turn over the hand crank on battery at a very slow speed. and see if each coil is firing in proper order. Also check the initial timing to be just after the crankshaft passes top dead center with the spark all the way up.
Check these and all of the above posts. Eventually you will find the true cause of the problem.
Norm

Thanks everyone.

Mike

Michael Davis wrote: ↑

Sun Mar 27, 2022 9:50 am

Thanks everyone.

Mike

??? So did you get to the source of your trouble? If so, let us know...

I will address a problem I had with my T a few years ago. We were at Big Bear, CA in high altitude. A few years before, I had won for a door prize a "High Volume Intake Manifold".
I decided to install it on my car. My engine is stock. Only modifications I have are a Skat counterbalanced crankshaft, standard T stroke and journals. I also have a Stipe camshaft. The block has been sleeved to standard with aluminum pistons, standard bore. The head is a stock high head except it has been resurfaced the minimum to be straight. I run an Anderson timer with magneto and coils. I use a sandard NH carburetor. The engine ran very well at high speeds on level ground, but was slow on hills and in starting out from a stop and when going slow in high. I also have Ruckstell, but the gear ratio is standard T in high range.
Anyway, going up hills it was very sluggish. I put the stock manifold back on and it runs much better. The high volume manifold is like trying to blow out a candle with your mouth open wide. The standard is like puckering the lips to blow out the candle.
I believe the high volume would work well if there were other modifications to the engine and exhaust system, but the stock one works better with everything stock.
Anyway, not knowing much about your car, and whether it ran fine and then just recently started having problems, or if this is a different car than you are used to driving, I can't diagnose your problem, but I can tell you about similar problems I have had in the past.
Norm

Thanks Norm. I had an intake leak fixed solved. My wife is from big bear. Her Mom and Dad where William and Casey Patterson. Family members are Sa;zers, Stratigers, Savilles

Mike

Scott,
You identified the problem being the vacuum leak.
Congratulations

Art Mirtes

Good! I'm glad you were able to fix it.
Norm