Change in brake behavior

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Model T Ford Forum: Forum 2017: Change in brake behavior
Top of pagePrevious messageNext messageBottom of page Link to this message  By Rob Patterson. Australia. on Wednesday, October 25, 2017 - 12:55 am:

Hi,
My 21 has just developed a change in its braking.
When the car comes to a stop, it momentarily (a split second) goes backwards, and then stops. Its never done that before.
Also, the pedal dropped suddenly on its last outing, requiring a bigger than usual band adjustment.
Kevlar bands with only about 1,000 miles of use.
Cracked brake drum? There are no signs of lint in the screen or oil.
Any advice welcome.
Cheers,
Rob


Top of pagePrevious messageNext messageBottom of page Link to this message  By Alan George Long on Wednesday, October 25, 2017 - 05:20 am:

Hi Rob

To me, the rolling back us a sign of excessive driveline backlash. This could be anything from a worn square in the transmission output shaft, Uni Joint or any number of differential items, keys etc. . Was the brake band fully applied
when it rolled back? Suggest you take a peek at the drums and the items that apply the band then readjust it
Alan in Western Aus.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Wednesday, October 25, 2017 - 11:24 am:

It is normal to need to adjust the bands a few times after re-lining. Look carefully at all the drums while someone rotates the engine in high gear with the rear axle raised. Look for any cracks. If not and you don't have a lot of lint the problem is not very likely to be in the bands. Looseness anywhere from the rivets which hold the driven plate to the brake drum or slack in the universal joint could cause the rolling back. also slack in the gears of the rear axle or looseness in the thrust washers could also cause the problem. One thing you could do would be with the transmission inspection plate off and the rear wheels on the ground and the parking lever forward in the high gear position have a friend rock the car front to back while you look into the transmission. If nothing at the back of transmission moves back and forth the looseness is very likely in the rear axle or U joint.

If you decide to open the rear axle, be sure to check first the universal joint. You might get lucky and replace the joint only. If not the joint check the nut which holds the pinion gear. If the key is loose and the gear moves on the driveshaft.

Good luck in finding the source of the problem.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Rob Patterson. Australia. on Wednesday, October 25, 2017 - 03:34 pm:

The momentary backwards is powered/driven.
The 1000 miles is not just on the band linings, its for the whole car since restoration, which included a complete engine and gearbox rebuild.
Anyway, "Thank You", I figured that there may have been a well known reason, but obviously there isn't, so now the diagnostic fun begins.....%$#@*&
Cheers,
Rob


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Strange - Hillsboro, MO on Wednesday, October 25, 2017 - 03:41 pm:

My speculation - the "shoulder" on the brake pedal shaft has ridden up into one of the brake band ends, making the band seem much looser than before. Not sure of the cause of the momentary reverse action.

Remove the inspection cover, take a well-lit picture of the innards, and post it here, thanks. :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Rob Patterson. Australia. on Wednesday, October 25, 2017 - 07:26 pm:

Norman,
"Thank You". I'll take your advice, do a thorough inspection and go from there.

Mark,
Its not so much the low brake that is the problem. Its the momentary backwards motion of the car that is the problem. As I mentioned in my first post, there is no lint in the screen, or the oil, which should indicate that I have already removed the cover and made an inspection. Had I found anything obviously wrong, I would have just gone about fixing the problem.

Thanks,
Rob

(Message edited by rob patterson on October 25, 2017)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger - Wyoming on Wednesday, October 25, 2017 - 08:22 pm:

I'd check the 6 screws that hold the output shaft to the brake drum. I bought a car that did that and all 6 screws were loose. Tightened them 1/2 turn each and safety wired and all was good to go.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Rob Patterson. Australia. on Wednesday, October 25, 2017 - 08:39 pm:

Thanks Scott,
I'll look closely at that when I start work on it tomorrow.
Rob


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dick Fischer - Arroyo Grande, CA on Wednesday, October 25, 2017 - 09:28 pm:

Rob,

I am probably more dense than most people, but please clarify one thing. In your original post, you said, "Also, the pedal dropped suddenly on its last outing, requiring a bigger than usual band adjustment".

Which pedal dropped ? I'm thinking you meant brake pedal, but not certain.

Dick


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