Low speed jerk and no I'm not talking about myself!

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Model T Ford Forum: Forum 2014: Low speed jerk and no I'm not talking about myself!
Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Santilla on Sunday, May 11, 2014 - 07:14 pm:

Since I brought my car a 1926 roadster pickup out from its Winter long sleep, I have had a number of problems getting it running as well as it was when I parked it last Fall. All problems have been solved except the jerking motion I get at low speed when slowing to a stop. I have installed a new timer, new spark plugs, and four new coils yet the problem continues. Any help will be greatly appreciated.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Hal Davis-SE Georgia on Sunday, May 11, 2014 - 07:21 pm:

Can describe the jerking? Is this while in low gear or just low speeds in high gear? Is this while you are applying the brake or just coasting to a stop using engine braking only?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Sunday, May 11, 2014 - 09:54 pm:

Bands too tight and it's trying to stop and go at the same time? Clutch maybe needs to be adjusted, not releasing all the way? Not pushing the low pedal down enough to release clutch? Not using the throttle and spark to slow the engine and speed down?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Val Soupios on Sunday, May 11, 2014 - 10:06 pm:

Is it just before you stop and while the brake is being applied or is it when you let off the gas and the car is slowing down without the brake on but while it is still in high?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Santilla on Sunday, May 11, 2014 - 10:22 pm:

The jerking occurs when I am slowing down in high gear at low speeds using no brake. It gets violent enough that I have begun to go to neutral rather than put up with it.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ted Dumas on Sunday, May 11, 2014 - 11:21 pm:

Have you made any panic stops? Have you been thru the rear axle and replaced the babbitt thrust washers? How does it behave on a hard pull forward?

It could be you are slowing down with the spark to far advanced at low speed in high. You might try it with both spark fully retarded and throttle closed.

If the engine is trying to pull it forward in high gear at a very slow speed it will jump around pretty good.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dan B on Monday, May 12, 2014 - 04:40 am:

Bob,

Did you have the handbrake set all winter? Doing this releases tension on the clutch discs and I'm wondering if they didn't pick up some corrosion that causes them to bind at slower speeds. It always a good idea to disengage the handbrake (all the way forward) during long term storage so that the clutch discs are compressed. Maybe someone else can weigh in on this theory and help provide you a fix. The only thing I can think of would be to pull the drain plug and flush the assembly with some kerosene.

In any event, it is not a good idea to let it stay in high gear at low speeds. You're just asking for a broke crankshaft.

Dan


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Santilla on Monday, May 12, 2014 - 09:12 am:

I am pretty new at driving my car. Last year I probably put two hundred miles on it. One of the guys in my club told me that after the engine started pull the advance all the way down and forget it, so that's what I have been doing. No panic stops. I am VERY careful not to put myself in a situation where I have to do that. I am getting ready to run to town and will try retarding the spark to see if that helps. I did park the car last Winter with the hand brake on. I have read many time about guy's breaking crankshafts due to engine problems so I am really appreciative to all of you for your input.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Monday, May 12, 2014 - 09:17 am:

Sounds like a fuel mixture adjustment problem or too high float level. As you are slowing down, a drop of gas gets into the engine and it burns causing it to speed up and then slow down. Have you tried closing the fuel mixture needle slightly? Actually, the throttle does not close completely unless you have the idle adjustment set to completely shut off the throttle, then you run the risk of killing the engine when you come to a stop with the throttle closed. So when you slow down you are still getting a little gas through the idle system. This is too rich causing intermittent firing. similar to the popping you hear in the exhaust, only yours is popping inside the cylinders.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Santilla on Monday, May 12, 2014 - 10:48 am:

I have had the carburetor off and apart more times that I would like. This year after waking the car up from Winter the carb was flooding over. I found the float to be too heavy and re-placed it. The car runs well with no flooding but sounds like it is running rich. Tried adjusting the mixture in but the engine does not sound "happy" there. The float level is at a 1/4". I am in the habit of slowing the car using a closed throttle. The brakes aren't much anyway but they do work and once the car is at just a creep I apply the brakes.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem on Monday, May 12, 2014 - 04:24 pm:

Bob,

This is somewhat normal if you're going too slow to be in high gear. Maybe you have some other driveline wear/slop, and maybe you've got a slight miss as well. All these conditions will be highlighted when you run down too slow.

Try driving without getting down so slow in high.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Val Soupios on Monday, May 12, 2014 - 06:41 pm:

I had that problem and believe it or not the solution was to change the carburetor. I don't know why but right after I changed the carburetor because it was leaking the problem went away. It was purely by chance as the carburetor seemed to be fine except that it often dripped gas after I shut the car off. Obviously, if you let the car really slow down in high it will buck a bit and eventually stall but doing that is going to cost you a crankshaft eventually so it is not a good practice.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Santilla on Monday, May 12, 2014 - 07:28 pm:

I drove the car today and while doing so tried a variety of timing positions. It had no effect. While I was going threw my preflight (Tire pressure, oil level, etc.) today I noticed the carburetor had a drop of gas on the drain cock. I tightened the nut a little more and waited a while and it remained dry. However, upon my return home the drain cock was wet again. Now I am VERY SURE all the settings on that carburetor are CORRECT. I am retired auto mechanics teacher and have rebuilt hundreds of carburetors in my time. Compared to most the carburetor on my Model T is by far the least complicated. So I am completely baffled as to why it is still leaking. But maybe as some of you have pointed out the jerking is coming from a carburetor malfunction. Maybe some of the parts are not correct. I have at one time or another replaced everything but the shell. I will try a new carburetor and see what happens.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Jablonski on Monday, May 12, 2014 - 07:49 pm:

Check the sediment bowl screen filter for partial blockage.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dennis Seth - Ohio on Monday, May 12, 2014 - 07:58 pm:

If fuel can get out then air can get in. Perhaps your sucking air. Be sure your gaskets haven't dried out over the winter or have a hair line crack in one of them. Double check to see if the full bowl is seated properly.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Monday, May 12, 2014 - 09:05 pm:

There are several things which can make a carburetor drip. High float level, plugged air vent at the bowl, leaky gaskets, cracked body, leaky needle and seat, dirt in the fuel. etc.etc. It is sometimes hard to find and fix. I like to park with a tin can under the carb to catch drips. Even a leaky shut off valve can cause some gas to get through. Sometimes the can doesn't get any drips and sometimes quite a bit. Keep trying, and eventually you might be lucky and find out what is wrong. If you have a Holly NH, they sometimes run lean at high speed and rich at idle, so you will need to monkey around with the mixture adjustment to see if it corrects the bucking.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Jablonski on Tuesday, May 13, 2014 - 04:01 pm:

Bob:

Slowing down you stated you close the throttle then apply brake near end of stop..... do you also retard the spark as you decelerate ?? Try it.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Quigley on Wednesday, May 14, 2014 - 08:43 am:

Bob, try checking the rear wheel tightness and wear on the rear wheel key and key way. Sometimes the wear causes a jerk when these components are not snug.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Seth from NC on Wednesday, May 14, 2014 - 08:56 am:

Howdy Bob - pretty much any of the Model T carbs are extremely sensitive to any trash in the gas line. If you let it sit all winter, try draining the sediment bulb and making sure it's clean and fresh. I'd pull the carb one more time and make sure that the needle and seat for the float are clean and there's no tiny pieces of junk in the bowl.

Once carb is back on car, screw the choke adjustment needle all the way down (gently) and then back it off about 1 & 1/4 turns. Once you crank the car you may can lean it out (tighten) a little from there.

At approximately what speed does this happen? If you are cruising at 35 mph, and then slow down by closing throttle and retarding spark, when it starts to buck and jerk what speed are you going?

If you close the throttle and spark all the way while cruising you should get a pretty smooth but noticeable engine braking effect. It's amazing how hard it is to diagnose some of these things with only the written description. I'm sure more than half the guys on here responding would have a way better idea if they could just be in your car when it happened.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kevin Holland, Utah on Wednesday, May 14, 2014 - 08:36 pm:

I had the same problem last year. I ruined a good New Day timer. It turned out to be the crap gas with alcohol. I drained it out and put in fresh gas and a new timer, and all was well. The jerking and sputtering at low speeds went away.


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