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Old 01-23-2017, 01:01 PM   #1
Dick Carne
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Default Car jumps out of gear

On our recently restored sedan, I am finding that the car will often jump out of high gear when I have let off the gas and it is in a continual coasting pattern (usually downhill). All of the transmission gears, bearings, shafts, seals, etc. were replaced; in the shifter housing, the detent springs and posts were replaced, the forks inspected and flipped; and the flywheel housing was properly shimmed against the back of the engine block. I am at somewhat of a loss in terms of what to do next. Any suggestions and guidance is most appreciated. Thanks guys.

Dick
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Old 01-23-2017, 01:15 PM   #2
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Default Re: Car jumps out of gear

I would take the cover off and take a hard look at those detents again. Sure sounds like the problem would be there. Not a big job just to check.
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Old 01-23-2017, 01:21 PM   #3
Mitch//pa
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Default Re: Car jumps out of gear

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Old 01-23-2017, 01:32 PM   #4
H. L. Chauvin
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Default Re: Car jumps out of gear

Mr. Carne,

As a start,

1. Please go to Bratton's catalog to read his warning note in the rectangle, under transmission plungers.

2. Then try inspecting "everything" a second time.

3. In addition to having two (2) "un-worn" forks, and a "round" ball in lieu of a worn square ball at the end of the shift rod, Mr. Bratton's note is there for a definite reason often overlooked over and over.
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Old 01-23-2017, 03:12 PM   #5
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Default Re: Car jumps out of gear

Chief made a FORKED stick, to hold his '35 International P.U. in HIGH gear.
Chiefs' Son
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Old 01-23-2017, 03:25 PM   #6
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Default Re: Car jumps out of gear

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I know your not going to want this on your restored car but I used a lawn mower we would mow the 5 acres at my dads with. It had a bungee cord that you hooked onto the shifter to hold high gear in.
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Old 01-23-2017, 03:57 PM   #7
H. L. Chauvin
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Default Re: Car jumps out of gear

The Model A transmissions, new and restored, performed extremely well for more Model A's than I care to count for 80+ years.

Usually every time a Model A mechanical item is restored twice within a short period of time, the term "Good enough for a Model A" is thrown out of the window, totally out of sight ..... and it becomes time to dismantle and get serious.
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Old 01-23-2017, 04:32 PM   #8
Ron in Quincy
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Default Re: Car jumps out of gear

According to Mitchell, who builds Overdrives and Overdrive Transmissions, the problem is the bearings retainer castings; if they are too thick by a few thousands, the gears do not fully engage. Steve said customers, when rebuilding their transmission, send the front and rear bearing retainers to him and he machines them to the proper thickness.

I have the same problem as you, jumps out of high gear when going down hill under compression. so I am sending my front and rear bearing retainers to Steve Mitchell for machining.

Ron
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Old 01-23-2017, 06:25 PM   #9
Dick Carne
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Default Re: Car jumps out of gear

Thanks to all of you for your kind and informative recommendations. Given all of the variables at play, I think that I may go back and take a second look at the detents. Even though they were new, along with a new spring, this seems to me to be more indicative of a problem within the shift tower. I'll try to remember to let folks know what I find when I have a few minutes to pull the tower.

Once again, thanks to all of you for your thoughts and suggestions.

Dick
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Old 01-23-2017, 07:49 PM   #10
Tom Wesenberg
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Default Re: Car jumps out of gear

If everything is right, it shouldn't take too much detent pressure to hold a straight cut gear in place.

First the flywheel cover must be shimmed to within .006" at 9, 12, and 3 o'clock positions.
The pilot and front tranny bearings must be snug so the shaft can't have any sideways movement.
The center bearing and rear tranny case bearings must be snug to keep the output shaft from excess side movement.
The gears on the shaft must be a snug fit so they can't move side to side.
The cluster gear bearings and shaft must be good to prevent side slop.
None of the gear teeth should show wear in a V pattern. In other words the edges along the length of each tooth should be perfectly parallel, even though the leading edge has a bevel to help with a smooth engagement.

I have a 1949 Chevy 1 1/2 ton truck that will walk out of granny gear after about 30 feet, but I'm never in that gear more than 10 feet, so I never investigated the cause.
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Old 01-23-2017, 07:53 PM   #11
Jerry Kzoo
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Default Re: Car jumps out of gear

Dick,

Good luck on your investigation.

You might try reading this for other ideas:

http://www.santaanitaas.org/wp-conte...ut-of-Gear.pdf

Tom is very good at explaining technical issues.

Also, we were talking at our club's seminar about the shifter plungers and spring that go into the detents might have an incorrect shape and not fully engage the detents. You might check those against the ones you pulled out when you get it apart.

Jerry
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Old 09-13-2020, 03:19 AM   #12
H.Colledge
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Default Re: Car jumps out of gear

Quote:
Originally Posted by Dick Carne View Post
On our recently restored sedan, I am finding that the car will often jump out of high gear when I have let off the gas and it is in a continual coasting pattern (usually downhill). All of the transmission gears, bearings, shafts, seals, etc. were replaced; in the shifter housing, the detent springs and posts were replaced, the forks inspected and flipped; and the flywheel housing was properly shimmed against the back of the engine block. I am at somewhat of a loss in terms of what to do next. Any suggestions and guidance is most appreciated. Thanks guys.

Dick
Hi Dick Carne - did you solve the issue of your car jumping out of gear and if so, what was the root cause of the problem and how did you solve it?

I have the same problem having rebuilt the gearbox twice. Jumping out of gear lets down what is otherwise a great car.

Thanks

Harry
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Old 09-13-2020, 06:15 AM   #13
McMimmcs
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Default Re: Car jumps out of gear

This is another case of person not updating post when a solution was found !
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Old 09-13-2020, 11:11 AM   #14
rotorwrench
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Default Re: Car jumps out of gear

The model A transmission is about as simple as they get. The gears are all straight cut so they don't thrust as much as the later Ford transmissions when the unit changes from load to engine braking but they still move. It's just the nature of gears. The second gear gas to dog onto the main input shaft for high gear so those splines (both internal and external) have to be in good condition. Shift fork slop doesn't help if there is any.

Some of the new reproduction bearings that fit between the input shaft and the main shaft have been known to have problems. If there is looseness there, it's almost as bad as a worn out pilot bearing. Clutch housing alignment is very important as well.

Don't be afraid to start a new thread. It will generally get better responses. A lot of folks don't report on results of problems and some aren't regular posters.
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Old 09-13-2020, 11:43 AM   #15
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Default Re: Car jumps out of gear

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Originally Posted by McMimmcs View Post
This is another case of person not updating post when a solution was found !
Could be he hasn't found a solution. But I agree it is an on going problem along with PMs to those of us that come on here to learn.
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Old 09-13-2020, 11:48 AM   #16
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Default Re: Car jumps out of gear

I once had a problem with my 1929 A transmission slipping out of high gear while coasting against compression. Turned out the needle bearing I had used between the input shaft and out put shaft was the longer needle bearing cage instead of the shorter one. I put the correct shorter needle bearing in and it has worked fine for years.
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