Grommet installation in Master Cylinder

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Ken King
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Grommet installation in Master Cylinder

#1 Post by Ken King »

I bought two grommets from Stoddard for a dual master cylinder that I purchased about 10 years ago from Klasse. The only one they list for a 356C is listed as 901-355-929-00 Master Cylinder Inlet Grommet Fits 911 1965-89 930 912 914 90135592900. The diameter of the large end is about 2mm larger than the hole in the master cylinder. Is this the correct grommet? Is there a way to install that without removing the master cylinder from the car? Can I use silicone paste for a lubricant?
Ken King

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Vic Skirmants
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Re: Grommet installation in Master Cylinder

#2 Post by Vic Skirmants »

The diameter of the large end has to be larger to fit into a groove inside the master cylinder. The groove prevents the grommet coming out easily. I have ALWAYS had problems inserting the metal tube completely into the grommet after installation of the master cylinder. I find it practically impossible while it's in the car. My most successful installations have been on the bench after cutting the metal line. Then re-installing the master cylinder and connecting the cut line with the correct blue hose that is compatible with brake fluid.

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Ken King
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Re: Grommet installation in Master Cylinder

#3 Post by Ken King »

The diameter of the hole in the cylinder I have is 15mm, while the grommet is 17mm and the ring that goes in the groove is nearly 18mm. Is that really the correct grommet? If all I had to do is get the ring in it would be easy. I've made a tool from a 7/8 dowel and drilled a 1/2" hole in it to hold the grommet. Then I tried soaking the grommet in brake fluid and heating it with a heat gun. No success. Now I'm trying to bore out a washer with a taper to help direct the bushing into the hole. Shade tree mechanic stuff.
I think the flare is at least 10mm and the hole is about 6.5mm. I was hoping that my heat gun would help there, too. Sure need a better rubber lube than brake fluid. I have some tire mount rubber lube, but it is not all that slick. Maybe a thin coat of grease?
Ken King

Edward Pugh
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Re: Grommet installation in Master Cylinder

#4 Post by Edward Pugh »

Finally getting this thing back together! 64 SC. I have rebuilt the brakes and for now am reinstalling the original (but rebuilt) master cylinder; have bench bled the M/C and have it installed. But.. the inlet line from the reservoir concerns me. I have a new grommet, and the flared metal fitting going through the grommet and into the M/C seems to be in good condition. But.... I just can't seem to get a seat that suits me. Any movement of the metal brake line or movement at installation at the reservoir causes some seeping of fluid at the grommet. The brake lines are not connected; nor anything bled beyond the M/C. Am I doing something wrong at the M/C grommet? I appreciate any input anyone might provide. Thanks, Nick

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John Lindstrom
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Re: Grommet installation in Master Cylinder

#5 Post by John Lindstrom »

Don’t get going too fast the first time you check your brakes

Dan Epperly
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Re: Grommet installation in Master Cylinder

#6 Post by Dan Epperly »

I use silicon spray when inserting those things.

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