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My 88 IIa has started losing brakes and I have to restore by pumping pedal with satisfactory results but it consistently loses all stopping power with the pedal to the floor! I checked and did not find any leaks in the cylinders at th individual wheels or lines. Was told my MC was probably letting fluid by a seal and was a dangerous situation. I have a dual system with booster and in looking for a replacement is there a difference in the dual MC's for 109 and 88? And is there a way to test MC while in truck? Thanks.
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A usual telltale of a failing MC is leaking down the firewall and/or pedal slowly falling to the floor once it is depressed and held there. Pumping a pedal a couple of times to get firm brakes may mean it might be a sign to adjust the shoes at the wheels. There is no self adjusting feature on series brakes and have to be kept adjusted manually. The large nut on the back plate can be tightened until it locks the wheels. Apply the pedal a few times. Then back off adjuster a couple of notches or until the wheel rotates freely. This is not an exact science as drums can be slightly out of round, etc.
If it is a failing master cylinder, The fluid can bypass causing the pedal to lose pressure and bypass fliud internally. It will not lose any fluid, but will push to the floor eventually, as you have found. -
The way I understand it a 109 MC has a slightly larger bore so it moves more fluid. I'm running a 109 MC in my 88 and have had no issues doing so.
JimComment
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The 109"cylinder has a larger diameter bore to account for the two wheel cylinders on the front brakes of the LWB. It is actually the rear port on the MC.Jason
"Clubs are for Chumps" Club presidentComment
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I seem to be experiencing this phenomenon right now: I adjusted my brakes a few months ago and got good pedal pressure and good stopping power (for a Rover); Now I am experiencing loss of pedal pressure (at a stop light, for instance), especially when holding the brake - and no apparent loss of fluid.Last edited by TedW; 08-20-2012, 10:17 AM.Comment
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Yep. Classic MC failure. It happens to many an old vehicle this way. I forgot about it going down at a stop light. A perfect way to test for it.Comment
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So Gudgeon: Here's a twist to throw in: In my case, the problem only seems to happen when I'm driving: My truck is shut off in the garage, and I just pumped the brakes and stood on 'em - and they held. I didn't get the same fade that I experience when I'm driving / when the motor is running.
What do you think?
TedComment
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Running with the booster on when the MC is activated amplifies the power of the MC. If it is starting to fail, it is likely that the wear or internal bypass shows up first when running. Not leaking down when not running may mean the wear hasn't progressed to the point of it showing up under non-assisted depression of the pedal. Leaking down at a light usually points to worn MC, barring any other leaks, assisted or not.
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Thankfully I have a brandy new Genuine master cylinder in the basement and ready to go - anticipating this type of situation.Running with the booster on when the MC is activated amplifies the power of the MC. If it is starting to fail, it is likely that the wear or internal bypass shows up first when running. Not leaking down when not running may mean the wear hasn't progressed to the point of it showing up under non-assisted depression of the pedal. Leaking down at a light usually points to worn MC, barring any other leaks, assisted or not.
The MC I have is at the moment is a used one that was installed as a stop gap in '93. I think I got my moneys worth!Comment
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Mine is running a 109 MC with front brakes having 2 cylinders per wheel. Gonna adjust drums and check the holding power on a hill and see if the pedal and brakes give way with sustained pedal on incline. Also gonna check cylinders with drums off as I have only checked visually under vehicle and have not removed drums. Thanks, will keep you all posted.Comment
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My MC must be an 88 as my 109 is longer with the spacing between the lines being 3 1/4 inch versus mine has 2 inches. The Front lines are connected to the front opening. Can I switch MC without brake pedal adjustment? Gonna adjust brakes in am and see what that does for them. THanksComment
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