cuda2k

So I have a Mongoose Mtb that I use for light trails, gravel trails, etc etc. The rear brake was a ProMax POS V-Brake that I couldn't keep adjusted to save my life. So I get on ebay and I find myself a pair of used Shimano XTR brakes that have been thoroughly used but decently taken care of (cheap).

So they arrive in the mail today and I eagerly open the box, decide that they need a good cleaning of the surface dust and dirt on them, a bit of oil and I'll be ready to install them. Well, I got about as far as pulling one side of the Promax brakes off to realize I had a problem... The screw that attaches the brake arm to the frame is all one piece, and there's no way to remove it from the Promax brake arm. So I dig up the tech document for the XTR brakes and it shows the brake arm slipping over a brake boss post that raises off the frame mount location - and then a screw being screwed into that to secure the brake lever arm.

So here I sit, wondering what I've gotten myself into this time (I knew it couldn't be this easy to upgrade to xtr *sigh*) and if there's a reasonably easy way out. I can't just screw straight down to the frame with a single screw because that will keep the brake arm from moving (obviously not good). Here's the exploded view of the brakes in question with the boss illistration on the lower left area.

https://bike.shimano.com/media/cyclin...9830538683.pdf

Any suggestions, ideas, saving graces? please...

sydney

Are you overthinking this without really thinking? The V brakes I have all attach like the XTRs. A bolt into a threaded stud. Im assuming you didn't get the bolts with the v brake arms?

cuda2k

Correct, I got a couple of lever arms and that's about it. I attempted to get the screw and stud apart off of the ProMax brakes, but an allen wrench on the screw and a vice-grips couldn't get them apart. Seems like everything on this bike is put together with JB Weld on the treads when I really need to get something apart. (Don't get me started on the pedal threads...)

sydney

Thought you had it apart.The retaiing bolts are typically loctited.Suppose anything is possible on a mongoose,but the brake arms and bolts are not typically one piece.

cuda2k

let me see if I can describe a bit better what I have -

The promax brake arm that I unscrewed from the bike apparently unscrewed what I suppose you would consider the boss and the retaining screw together, out of the frame of the bike. Thus, I can't attach the new brake arms with them to the bike as they are still firmly attached to the original brake arm. I've attempted to seperate these two pieces (screw and lower boss bolt) from the arm but only managed to scar what little non-threaded exposed section of the boss bolt I could get a wrench on. I'm going to assume that these just aren't going to seperate and on the search for new boss bolts that I can attach to the frame and mount the brake arms to.

One would think that easier than it seems to be... maybe if I got some liquid wrench on those retaining screws and boss bolts... blah... who knows.

sydney

got it.The bosses are often loctited in too,even tighter than the bolts. May be simpler to get new bosses,and bolts.

cuda2k

Agreed - if I could locate some online. Guess I'll stop by the LBS tomorrow as I'm headed there anyways for their Saturday morning ride. Everyone sells the boots to put in the hole left if you REMOVE the bosses, but no one apparently thought someone might need a new one apparently.

As always sydney - thanks for the input even if we went around in circles a bit to get there. If you have a magical source for brake bosses and screws I'd appriciate any suggestions.

sydney

Another idea.....What happens if you put the whole mess back together,then hold the brake arm while trying to loosen the retaining bolt? No extras, in fact I need a set of bosses too.

Retro Grouch 

Do you know exactly what kind of bosses you need? They come in a couple of different threads. What do you have for tradeing stock? Maybe some stainless steel stem bolts would be fair? I've got a few spare bosses in my workshop.

sydney

Threading??....hadn't considered that angle.Have a set scavanged from a too big Raleigh MTB frame, but someone might need Raleigh and it's in real good shape. The ones off the Raleigh that fit the GT rear measure about 9.5mm