i have a 79 chevy on 35s there was cracks behind the gearbox and the front crossmember had poped the rivets off i welded all the cracks up and put it back together i was wondering if i should ad some braces has anyone ever had the crossmember break  

First did you drill stop the cracks? It is a wise idea to do this before you weld/repair it. Next sometimes when you weld frame like that is can crystallize grain structure and make it more prone to crack around repair. Getting back to your question though, the damage you saw was because of steering forces being applied beyond its design specs. I would gusset/reinforce frame rail with a plate that goes under steering box mount and spans crack for several inches for starters (you want to bolt this one too) On cross member, I have seen the rivets there loosen up before. It would replace them with grade 8 bolts at both ends of cross member to stiffen it up a bit. I would not beef up cross member itself at this time as this can apply even more stress to rails and they need to be able to flex a little too.  

thats a very common problem on that era even without large tires, especially factory equipt dual shock versions, there used to be a reinforcement fitted frame braces available for that purpose, haven't seen any in a while, I may have a couple that never got used.

ya can just weld em up and get rid of all the rivots in the crossmember like snoman suggested, it's generally a temporary fix for the box mountig surface though.  

ord sells the repair plate and a steering box brace never to late to put them on  

I had a '77 Bonanza and the gearbox ripped off the frame.  I welded it back together and the thing ripped off again, right behind the weld.  I was just running 33's just some FYI, be carefull.  

You have to be careful welding truck frame especially if you stick weld it because it can change carbon content of steel and make it more brittle and cause it to fail right next to weld as above.  

Drill stop your cracks weld up the cracks. Add a doubler plate on the opposite site of fram rail, or if you can box the frame in this area. If you can avoid beefing up the crossmember do so because you will lose alot of your flex. Most Important is before you start welding make sure metal is clean. There is alot of aftermarket braces for steering boxes out there as well, but a brace really isn't necessary if you box or reinforce with a doubler.  

It happens. Weld it and plate it and call it good till it happens again... lol  

check this out. they also have an engine crossmember replacement, too. go through their site, most of it is reasonably priced. they have the best stuff for older chevy's. for $200 and some welding your truck frame is fixed.

http://www.offroaddesign.com/catalog/steeringkit.htm

also try to find a solid tierod with no stabilizer from an 80's 3/4 ton in a junkyard. it will save you money, and is stronger than the slim tierods with the stabilizer mounts.  

go to you tube and search for "1973 chevy bends tie rod" to see what I mean. If you're running 35's or bigger, it's going to happen eventually.  

another way to save money is to use an older model engine crossmember like a 73 or 74, sometimes they are a little bigger, and if you grab one from a junkyard, you can beef it up on your workbench with some welding and bracing before you install it.

or just buy the one from offroad design. i have helped a club member install one and he likes to jump at glamis. so far, no cracks!  

oh my god! you mentioned the great GlAMIS  which reminds, GLAMIS SEASON IS UPON US!!!!!