Brake pedal clearance desapears

Don

Don

Well-known member
Went for a drive today after replacing all wheel cyl You and MC this summer,good brakes but the further I drove ,about 20 miles,the brake pedal play was going away,had a full pedal with no play,thought the brakes might lock up , but they didn’t
Got home after about a 70 mile trip ,let set for awhile and pedal was back to normal,with about 1 1/2 inch play,what’s goin on,MC rod to long???
 
Don said:
Went for a drive today after replacing all wheel cyl You and MC this summer,good brakes but the further I drove ,about 20 miles,the brake pedal play was going away,had a full pedal with no play,thought the brakes might lock up , but they didn’t
Got home after about a 70 mile trip ,let set for awhile and pedal was back to normal,with about 1 1/2 inch play,what’s goin on,MC rod to long???
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Master cylinder rod is adjusted incorrectly. There's a fine line between not long enough and too long. Yours is presently too long.

To keep as much pedal as possible, I'd suggest you shorten the rod perhaps but one full turn at a time. Drive it, see what happens. If necessary, reduce the length another full turn.
Yeah, a little time consuming but you'll end up with a nice "feeling" pedal.
 
Also, just making sure you remember that you need a pedal return spring to pull the pedal all the way up every time. DD
 
Recently had similar experience. 39 Standard coupe. hydraulic brakes been fitted with auto bleeders. Car was running ok went for short run and no brake pedal clearance and brakes did lock up also return spring fitted hydraulic level ok.
Had to get under car and bleed a rear brake to release brakes and give some travel.
Drove home ok and went round all brakes and recheck bleed. Presently travel is ok approx 1.5". Could this have been caused by the MC non return of oil?
A new experience as car certianly reveed high in this condition with brakes locked.
Phil NZ
 
One more thing that CAN cause such a condition is if you have something causing extreme heat near a brake line, or a pair of brake shoes dragging so tightly as to heat and expand the fluid in the system. When you park and let it cool down for a bit, the fluid cools, returns to a normal state, and the brakes feel and operate normally again. Cracking a bleed valve at a wheel cylinder momentarily can relieve pressure and get you back on the road in an extreme emergency. DD
 
My '50 Coupe did similar. I noticed after short trips the pedal would get hard. Other times, the car would be sluggish. That time, I noticed the brakes were hot. After it cooled off, it was back to normal.
I drove it to the Firehouse to work, about 3 miles. I parked the car and somebody stopped saying the lights were left on. Sure enough the brake lights were on.
46509846891_45e6fcf8e4_z.jpgUntitled by Travis Brown, on Flickr

The master cylinder casting was flawed. The hole for the by pass port was spotted but not drilled through. On a Shoebox master cylinder, you can see this port with the cap off. The fluid was clear as the brakes were new.

I was able to drill that hole out through the cap. I did not have to take the cylinder out of the car. It did not take much as the hole was spotted. It's been over 20 years. I cant remember if it was a 1/16 or 1/8 bit.

Clearing that hole did the trick,
 
Possible a blockage at my MC bypass port could have been the problem.
Not sure if it can be viewed via filler cap. A 39 Coupe MC.
Phil NZ
 
Don, I'm with Kube. Start with the rod and see if that doesn't solve your problem. Happened to me on my '39. Betting you've done everything else correctly and that your new parts are all good.

Dick.
 
When I bought my '39 p/u the PO had redone the brakes including a new off shore M/C. The brakes would lock up after a short drive. I replaced the M/C with a new USA made Wagner and the problem went away.
 
Shortened the MC rod and that fixed the full pedal problem,good hard pedal and down to normal position,,,always good to get a second opinion!!! Tks,,
 
just a thought check the seal of the dust boot i had one fail and unknown to me had crap build up under the pushrod not much but enough.
 
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