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Double line master cylinder problem.

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EastBoundJoe

EastBoundJoe

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I have been trying to fix the rear brakes on the 1972 Midget. While exploring I notice a lack of fluid at both rear wheels, then followed the line back to the pressure differential switch and followed the lack of fluid all the secondary reservoir on the master cylinder.

I have not taken the master cylinder apart yet. Would it be better to buy a repair kit to replace the seals and cups, or would it be wiser to just buy a new Master cylinder?
 
Thanks for the advise, I'll make sure that there is no scoring before anything is replaced.
 
Actually, rebuilding the dual line MC is a real bear. There are a few tricks to it, which make all the difference.

If your secondary resevoir is dry, but the front brakes are still working, it seems to me the leak is down stream somewhere... most likely at the wheel cylinders. Pull your hubs and have a look for leaks.
 
The rear wheel cylinders where both dry and they remaind dry while trying to bleed. the line from the master cylinder to the pressure differential switch was dry too.

I filled both reservoirs then pumped the master cylinder on the bench, and noticed fluid squirts out of the primary hole (for the front brakes) and dose not squirt out of the secondary hole (for the back brakes). It seems the fluid will not move from the secondary reservoir into the cylinder. While pumping the master cylinder on the bench there is no pressure felt coming out the secondary hole.

I'm thinking that maybe a cup seal has twisted around or something along those lines... I'll have to take it apart today to find out.

Thanks for the input fellas :^)
 
The thing is, all that seperates the the front from rear in the MC is a cup. If you have a bad cup for the rear, it would affect the performance for the front. If the front is working, it is unlikely, though not impossible, that the MC is broken. You may have several compound problems going on. First thing I would do is loosen one of your rear bleed fittings, put a hose on it that runs into a catch can, then with the resevoir cap removed, pump the brakes a few times to get things moving. Then take a long break. If you don't get any fluid at the bleeder after fluid has been allowed to run down for a few hours, odds are you have an obstruction.

Seriously, rebuilding the dual MC can be a horrible ordeal. It's worth it to run down every possible problem before tearing into the MC.
 
I'm heading on vacation tomorrow for 5 days, but when I get back I'll be installing my "new" dual bore MC. It's actually a rebuilt unit by cardone that I ordered for about $40 + shipping but does not come w/ a reservoir. I'll let you know how it works out for me once I get it on. Definately a bit cheaper than $165 minimum for a new one.

- Drew
 
By the sound of your posts Morris, I have the feeling that you don't have a circlip tool (# 18G 1112). Without this tool it can be difficult to remove the circlips down in the inside of the bore.
It's a snap ring pliers with a tall cylinderical working end at 90 degrees from the handles and pins at the bottom.
Also, the nylon bushing, drill a small hole in it and use a wood screw to pull it out.
 
I made a circlip extraction tool for mine as I was unable to find one with long enough pins. As for that nylon bush, the wood screw method is the surest way to scar up your bore and plunger (I learned this the first time I rebuilt my MC). Another BCFer suggested (and I can attest that it works perfectly) melting the nylon ring out with a propane torch.
 
Melting the nylon ring, I like the sound of that. I hope a new one comes with the repair kit. The manual I have says to move to piston up and down until the nylon rig comes loose, I don't think that will work though.

P.S.
That tiny metal ring that holds the retaining spring on was a B**** to get out.
 
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