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MC operating rod length

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jmwuva05

jmwuva05

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I have a question. On the 948 Master cylinder are the brake and clutch push rods the same length. I ordered new ones from moss and they are the same even though I ordered one as brake and the other as clutch they are listed as the same part#. Anyway I was looking at the old rods from my MC and noticed they were two different lengths. The brakes didnt function correctly when I bought the car so I have an idea someone jimmy rigged it with an illfitiing rod. Any ideas greatly appreciated.
 
I can't remember is there's a difference, but providing you can adjust the length (using the 2 nuts) so that there's some play between the rod and the piston, the brakes will be working OK.
 
They are the same.
 
Well shucks, you mean the full top to the full bottom?

Why would that be of intrest?

Brake will never go all the way down, and the clutch has a stoper welded on it.
 
I have not set the stopper yet. Still working on the bleeder. I hope I cut the rods correctly for the larger master. It just seems that the pedals don't have much travel.

Maybe a better question would be how far do the pedels measure away from the floor when they are at "rest"?
 
The free-play between the pushrod and the piston should be 1/32"nd which should result in a 5/32"nd free-play at the pedal. The lower the pedal is adjusted to the floor, the shorter the effective throw of the piston, and the piston must travel fully. Pedal-stop adjusting bolts and rod length can be adjusted in sync. to achieve correct free-play and an acceptable pedal height! I.e., if you lengthen the push-rod, to achieve the acceptable free play, the pedal will have to be further from the floor and vice versa!
 
There were 2 different size push rods over the years.
Drum brakes used a 7/8 bore master with LONGER rods.
These rods without the end fittings are 4-3/16" long.
Later disc brake cars (up to 1966) used a 3/4 bore master with SHORTER rods. These rods measure 3-11/16" with out the end fittings.
As stated the lengths can be adjusted for a higher pedal, to much length and the brakes will stay locked on. The fluid has no way to get back to the bleed back hole if the rod is too long. So if you adjust it to a nice high rock hard pedal, try steping on the brakes a few times and then roll the car, if it doesn't move, crack a bleeder and reduce the length of the rod. I like mine high and tight but there is a fine line between high and tight and locked up.
 
Sure enough one of my MC rods the one on the brake side is shorter 3-11/16" and is a little smaller in diameter than the other. No wonder the brakes didnt work right! Maybe someone just tried a quick fix and didnt realize it was the wrong part. Anyhow the new rods from moss fit nicely. I suppose I can get on with the rebuild now.
It seems I have been working on a lot of mechanicals lately. I hope I can get everything sorted out soon as the body tub should be painted in the next 2-3 weeks. I cant wait to see that nice dark green paint. I took the chrome bits to the polish shop the other day and man is that stuff expensive.
 
I had a horrible time with brakes that would lock on and could only be freed by breaking a bleeder until I finally resolved that problem!! A DPO had "rebuilt" the master with an assortment of parts and had mismatched the rods!!!
 
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