VCCA Home Forums TECHNICAL - 1945 AND NEWER 1949-1954 brake line leak at mast cyl jct. block

Hey Folks,
Put in a new master cylinder, but can't stop a leak from the hollow bolt in junction block to my new brake line. Replaced the copper gaskets and re-centered the brake line fitting in the hollow bolt and tightened. Still leaks. Anybody got a fix out there? Nobody seems to sell the hollow junction block bolt at the master cylinder. My guess is the fitting is shot.
Am using the old junction block also but replaced copper gaskets there too.

Is it possible to substitute the convertible junction block? It looks a bit different and doesn't use the same hollow bolt. My car is a coupe. This seems like a strange contraption. Is there another substitute??

Thankshttps://vccachat.org/images/icons/default/confused.gif

Rick

I'd make sure that the bolt is not bottoming in the hole and keeping the washers from tightening. Also make sure that the replacement washers are at least as thick as the originals, that would also cause the bolt to bottom and not allow the washers to seal. I'd also check and make sure something didn't get stuck in the sealing surface for the copper washers either on the fitting or the master cylinder. The bolt needs to be pretty darn tight to seat the washers, but be cautious so you don't ruin the threads in the master cylinder. Goog luck Don

Thanks Don,
I'll check that out. My washers were actually a little thicker than the originals but maybe I can add another in just in case?
Not sure why the line is leaking where it screws into the bolt head.
I wish I could replace the hollow bolt and block . Maybe someone out there knows a source or can suggest a jury-rigged substitute that'll work.

Thanks

The washer needs to be soft copper. It can be soften by heating and quinch in cold water.

If the washers are not the same diameter inside and out as the originals they will leak as they will slide one way or another. Most washers found at parts houses are now metric and are not a perfect fit.

Thanks Gyn and 1937 Truck for the feedback.
Guess I'm up the creek. I'm surprised that despite everyone selling new/rebuilt master cylinders, brake lines, etc. that nobody sells/makes the special fittings we need to hook up the repro parts. I preferred to use all new fittings and this is what happens when ya hafta use the old junction blocks/fittings--they leak. Yet you can buy the rear brake junction blocks. I even called Inline Tube--nothing.

I may have plumb up something from Ace Hdwe to replace this tee set up. What a dumb design. I guess not everything old was better.
Enough ranting. Back to the challenge.

Check with National Chevy Association in St. Paul MN. They should be able to help you. Don

Thanks Don. They don't carry the bolt, only the block which I've ordered. I also ordered the convertible block so maybe I can adapt it, but I think the problem is with the hollow bolt.
Anybody got an NOS bolt they want to sell??

update on the master cyl block:
I got the new block from Chevs (convertible block). It has the banjo bolt with a retainer nut, but the bolt is solid going into the block. The block has three outlets for std brake line flare fittings. What gives?? Do I have to drill out the bolt?
Waiting for an answer from Chevs also.

Meanwhile, my old block still leaks despite new gaskets which are probably metric.

The saga continues.... Strange.

Does the bolt have step down areas on it?

I don't think so. Not sure exactly what you mean by "step down," though.

It looks like a regular bolt except the end is hollow and there is an opening on the side which lines up with the brake line fitting holes on the block. The bolt uses a thin copper gasket where it enters the block and another at the end which screws into the master cylinder. At this point, my current leak appears to be between the block and the master cylinder. I'm reluctant to put any more tightening torque on it for fear of stripping the bolt thds.

As I said the new block I just received has three holes and a banjo bolt protruding which is solid, so maybe Chevs of the Forties sent me a dud or I'm expected to drill out the bolt going into the block?? The Chevs part no is #3692044 (gm pt#04.686-0)

Thanks Don.

rr

I just looked at the part that you are trying to use. If it was me I wouldn't use it. I would look for the correct copper washers for the block that you have. I'm thinking that the copper washers you need are 2 different sizes. Take some time and make sure they fit good. When I did my '50 a couple years back I remember that the bolt into the master cylinder needs to be darn tight. Once you get it snugged up pretty tight stop, then tighten it just a bit more. Check for a leak, if it drips give it a bit more. I would guess it will take 60 -70 ft lbs to have it tight enough.
Good Luck Don

Good advice, I'll stick with my original unit and try some other copper gaskets.

Thanks Don.
Happy Easter!!
Best,

You might try this place...They show a drilled bolt. It may work for you...americanclassic.com....on line
Company name....American classic truck parts inc. GOOD LUCK..ED

Thanks Ed.
Will check it out.

Cheers,

Hi Folks,
Well, finally--SUCCESS!!
After hitting every parts store in my area, I found some 1/2 inch copper oil drain plug gaskets. They look like o-rings as they're rounded. The first fit snug but leaked. I put the second on top of it, cranked down the bolt and it leaked at first, then held.
I pumped up the brake pedal, held it and no leaks!! I guess the copper had to form against the sealing rings on the block and master cyl..

So I think this is the solution. For all you folks changing out your 50-52 master cylinders, don't throw away those old copper gaskets and especially the junction block/bolt assbly.
Try the copper o-rings--they seem to work.

Thanks to all for your good ideas and support!!
Cheers,