Leaking Master Cylinder Grommets
Thread Starter
Race Director
Joined: Mar 2003
Posts: 11,608
Likes: 780
From: Eustis ( Area 51 Bat Cave ) Fl
Leaking Master Cylinder Grommets
I have a problem with the rubber grommets that go between the master cylinder and the reservoir tank,
About a year ago I replaced the master cylinder and it didn't come with a new tank,
I had to reuse the old one, I had the new grommets and the fit was super tight it was hard to keep from distorting the grommets when putting the tank onto the reservoir,
Now they both are seeping one pretty bad,
I bought a couple new grommets from GM today,
So what is the secret to putting these things on without them distorting and leaking?
Do I start with them in the cylinder or on the reservoir?
Last time I did lube them them which may or may not been right,
Thanks for the help.
Cheers,
P.
About a year ago I replaced the master cylinder and it didn't come with a new tank,
I had to reuse the old one, I had the new grommets and the fit was super tight it was hard to keep from distorting the grommets when putting the tank onto the reservoir,
Now they both are seeping one pretty bad,
I bought a couple new grommets from GM today,
So what is the secret to putting these things on without them distorting and leaking?
Do I start with them in the cylinder or on the reservoir?
Last time I did lube them them which may or may not been right,
Thanks for the help.
Cheers,
P.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
I think I put mine on the MC and pressed the resevoirs over them. I used a 2x4 under the MC a socket over the bottom of the resevoir and a huge C-clamp to force the resevoir down over the gasket. It was still difficult with a little distortion but no leaks in nearly a year.
There is a tool shown in the GM Shop Manual specific to this task.
There is a tool shown in the GM Shop Manual specific to this task.
Race Director
Joined: Sep 2005
Posts: 13,269
Likes: 0
From: Sharpsburg Georgia
GA Events Coordinator
start out with them on the reservoir, lubricate with clean brake fluid, just twist slightly and push and they will go on there with out much problem. I just did one two weeks ago. I tried doing it with them on the master cylinder and it was a no go. pull the rubber grommets off and look at the angles and you will see why it is better to start them on the reservoir
Thread Starter
Race Director
Joined: Mar 2003
Posts: 11,608
Likes: 780
From: Eustis ( Area 51 Bat Cave ) Fl
Thanks for the feedback and here is an update that might help others,
I noticed the reason the rear tank was almost impossible to get over the nipple on the master cylinder was the nipple was far bigger on the rear port that the front port,
I assume this is a casting flaw, I used a power tool (dremel) to grind the rear nipple down to the same OD as the front nipple, after doing this both grommets were still a tight fit but the rear one didn't deform and screw up,
The shoulder or "nipple" on mine are 3/4"
Of course if you went too far and ground off the nipple nothing would hold the tank down.
Now for the other thing I learned, the tank or reservoir is a two part thing made on a angle to set level when on the car, the tank sits over the rear port with a tube running to a cap that goes over the front port, where this tube slides together is an "O" ring which was messed up in fact that was in my case where most of the leak was, the fluid would come out there and run to the front port and appear that the front grommet was leaking.
Cheers,
P.
I noticed the reason the rear tank was almost impossible to get over the nipple on the master cylinder was the nipple was far bigger on the rear port that the front port,
I assume this is a casting flaw, I used a power tool (dremel) to grind the rear nipple down to the same OD as the front nipple, after doing this both grommets were still a tight fit but the rear one didn't deform and screw up,
The shoulder or "nipple" on mine are 3/4"
Of course if you went too far and ground off the nipple nothing would hold the tank down.
Now for the other thing I learned, the tank or reservoir is a two part thing made on a angle to set level when on the car, the tank sits over the rear port with a tube running to a cap that goes over the front port, where this tube slides together is an "O" ring which was messed up in fact that was in my case where most of the leak was, the fluid would come out there and run to the front port and appear that the front grommet was leaking.
Cheers,
P.
Drifting
Joined: Jan 2001
Posts: 1,970
Likes: 21
From: Denville NJ
I just went through this a few weeks back and I ended up going with a whole new mc with a new resevoir already attached. I tried putting the old resevoir on the new cylinder but it was a royal PITA. A little more expensive but I feel worth it.
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Thread Starter
Race Director
Joined: Mar 2003
Posts: 11,608
Likes: 780
From: Eustis ( Area 51 Bat Cave ) Fl
Worth the trouble?
I don't recall the price of the complete unit over the way I did it reusing the old tank,
But I do recall it being very pricey to get the whole thing,
I guess it depends on how bucks up the person is, I have this 86 and my c3 makoshark motion car the only way I could afford to drive vettes is to save every penny I can on things like this,
After I ground down the nipple on the bigger of the two ports the grommet went on tight but fairly easly I have driven the car about 100 miles since then and the MC is dry so no leaks yet,
so For me it was worth it,
In case someone runs into this problem the nipples on mine are 3/4" and this seems idea, only one of mine was oversize I imagine if both were oversize then it would be a holy hell to try to get it together.
But if u got a MC that both were 3/4" then you would be wondering what I was fussing about.
Cheers,
P.
I don't recall the price of the complete unit over the way I did it reusing the old tank,
But I do recall it being very pricey to get the whole thing,
I guess it depends on how bucks up the person is, I have this 86 and my c3 makoshark motion car the only way I could afford to drive vettes is to save every penny I can on things like this,
After I ground down the nipple on the bigger of the two ports the grommet went on tight but fairly easly I have driven the car about 100 miles since then and the MC is dry so no leaks yet,
so For me it was worth it,
In case someone runs into this problem the nipples on mine are 3/4" and this seems idea, only one of mine was oversize I imagine if both were oversize then it would be a holy hell to try to get it together.
But if u got a MC that both were 3/4" then you would be wondering what I was fussing about.
Cheers,
P.
