Brake master cylinder combination valve (Page 1/2)
stevep914 FEB 09, 03:24 PM
My 1986 Fiero/ F40 replica has developed a brake line leak on the rear brake line coming out of the bottom rear outlet from the combination valve below the master cylinder. The leak is somewhere right where the line passes through the trunk to the bottom outside of the car, right where all this foam is located. I had to remove some of the foam to expose the line. I would suspect this line is one of the originals on the car, and the connection to the combination valve is on the bottom rear of the valve, in a pita of a place to get at. I would love to not have to dissasemble the master and combination valve, trying to loosen all those old rusted up connections. Any ideas how to get that one line under there disconnected without having to take all this apart? I can see what has to be done, but would appreciate any input from someone who has had to do this, and then, of course, what has to be done to get brake fluid everywhere after the whole assembly has run dry when getting everything reconnected. Thanks in advance! Steve
Patrick FEB 09, 04:10 PM

Steve, I don't know if this is of any help to you... but this shows where the brake lines run when the tub is removed.
olejoedad FEB 09, 06:17 PM
You should be able to break the fitting loose without removing the prop valve or master.
Be sure to use line wrenches, and a touch of very localized heat could be beneficial.

[This message has been edited by olejoedad (edited 02-09-2025).]

stevep914 FEB 09, 10:01 PM
Thanks to both of you! I am going to give this a go. Of course it is a little more cluttered and difficult without stripping all that stuff away. I dug a lot of foam out just find the line and where it leaks.will repost after my attempt. Steve
Patrick FEB 09, 11:03 PM

quote
Originally posted by stevep914:

Of course it is a little more cluttered and difficult without stripping all that stuff away.



Steve, removing the tub is actually pretty simple, and makes access to everything so much easier. It's mostly held in place with plastic Christmas tree clips that just pull out, plus two rivets that need to be drilled out that hold a brake line to the bottom of the tub.

82-T/A [At Work] FEB 10, 08:28 AM

quote
Originally posted by Patrick:

Steve, removing the tub is actually pretty simple, and makes access to everything so much easier. It's mostly held in place with plastic Christmas tree clips that just pull out, plus two rivets that need to be drilled out that hold a brake line to the bottom of the tub.




On both tubs (my daughter's 85, and my 87 SE V6), the brake line was held on by tree clips. I don't know about the 85, but my 87 was an all-original car that had been unmolsted.
stevep914 FEB 11, 10:48 AM
Well I have tried heat, and the correct wrench, which just stripped the edges of the fitting. ( lots of bruises and swear words came with this), and still no luck. Can’t use PB blaster because the fitting is underneath and upside down. By the tub, I assume you are referring to the front trunk bottom. So I would remove all the carpet, and then remove all these clips, and would get a scenario like the picture you sent me, Patrick? The only other thing I can think of is using a small pipe wrench, destroying the fitting, and hope it does not break off. Steve
olejoedad FEB 11, 10:59 AM

quote
Originally posted by stevep914:

Well I have tried heat, and the correct wrench, which just stripped the edges of the fitting. ( lots of bruises and swear words came with this), and still no luck. Can’t use PB blaster because the fitting is underneath and upside down. By the tub, I assume you are referring to the front trunk bottom. So I would remove all the carpet, and then remove all these clips, and would get a scenario like the picture you sent me, Patrick? The only other thing I can think of is using a small pipe wrench, destroying the fitting, and hope it does not break off. Steve


Were you using two line wrenches, one one the hex that's part of the prop valve and one on the line fitting?

If you rounded off the edges of the fitting, you were not using a line wrench, or you were using the wrong size, or an inexpensive one that did not fit snugly.

[This message has been edited by olejoedad (edited 02-11-2025).]

Patrick FEB 11, 03:30 PM

quote
Originally posted by stevep914:

By the tub, I assume you are referring to the front trunk bottom. So I would remove all the carpet, and then remove all these clips, and would get a scenario like the picture you sent me, Patrick?



Steve, I don't know exactly what else might be different with your non-factory Fiero (ie carpeting in the front trunk)... but yes, with a minimal amount of work, the entire area opens up when the plastic tub is removed. Besides the clips and the two rivets holding the brake that I earlier mentioned, there's also a bracket or two which hold the jack in place that need to come off, and the cowl drain tubes need to be detached from the tub as well. Here's a wide shot of the whole area taken years ago of my '86 GT. With the tub removed, it's also an excellent time to adjust the pre-load of the steering rack.
stevep914 FEB 11, 04:51 PM
Guys, Thankyou for your input! Now, here is what I have discovered: I took the carpet out, and there is no plastic tub- it has been customized with what appears to be a solid 1inch thick fiberboard that has been foamed in all around with no visible way of removing it. However I can now see the bottom of the cylinder the brake lines go up into. Yes, I used a line wrench, albeit maybe not an expensive one. And there are not two nuts to put wrenches on, there is only the line and one fitting going into the cylinder. I MIGHT, be able to get some blaster in there, and try to break the corrosion that obviously is preventing this from backing off. Had enough today-will get at it again tomorrow.