OK I'm restoring my car, got a good rebuild kit for the master cylinder. Got to removing the valve cap screws and no luck, I broke a 29mm box end wrench. Before I put that amount of force on the part and it would not budge, I tried in a vice, penetrating oil, then a little heat, then I decided to put the part in a tub of just penetrating oil for one week, then heat again till it starting to get red put some dry ice on the valve cap and turned, no luck. tried wrench and hitting the wrench with a hammer for one hour, then i tried a little heat and then some force, wrench brakes. all parts are not cracked, does anyone have an idea?

Been there, done that, same results. I put those parts back in the box and replaced everything else. It's been fine ever since.

Sorry, I can't help, but just wanted to let you know you aren't alone.

Good to know that this is not uncommon. I had a slight give in the peddal, I think I be ending up doing the same thing. If I find one for a spare, you better bet I'll take it apart and when I put it together I'll use some anti-seize on that. Their is a hole in the wall from the broken wrench snapping, glad it didn't go at the car or me.

I'll give you they are tight. Clamp the m/cyl tight in a vice (with flat protection plates), use a 3/4" drive socket (1 1/8" in my case), long rachet wrench, mine around 18", and they loosen in seconds.

You can never have enough tools!

Edited October 8, 201014 yr by Nigel1943

Yep, I viced mine up, long wrench, then the 4 ft cheater bar, a buddy keeping the bench from moving, then it broke loose. It didn't go back on that tight. Inspect the copper washer before installing.

Bonzi Lon

I used a pneumatic impact wrench and a vice. I started off around half pressure and increased it until it broke free.

I got it off last week nothing like letting parts sit for over a month in penetrating oil

Congrats! After reading about it in another thread awhile back, I've been using the 50/50 acetone/automatic trans fluid concoction for penetrating frozen parts. The acetone evaporates before long though, so more has to be added to get the desired penetration. The acetone really thins the trans. fluid and allows it to "wick" to the deepest, tightest areas that are locked together.

The age old problem of removing frozen/galled brake drums without damaging them, is a thing of the past, with the help of this mixture (as long as you have at least a decent two finger puller to apply the pressure). Its a great feeling to finally triumph over situations like that, when it seems hopeless at first.

I found a soak in Gibbs penetrating oil can work wonders. My grand father showed me the trick you do, it works with the 50/50 mixture, but the Gibbs seems to be a little thinner and seeps in nicer. However with big parts transition oil and acetone are cheaper so I'll use that on bigger parts.