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Re: Transmission Crossmember Bolts Are Stripped out
Those things are too weenie to bother with trying to Heli-Coil...
They're a little chinesium "nut" captivated in a little sheet metal "cage". Alot of the time, the reason they "strip", is because they are actually SPLIT. No amount of tapping, larger bolts, Heli-Coils, or ANYTHING ELSE will EVER fix that.
Best thing to do is to hole-saw through the floor from the inside; put an actual NUT in there, that's some kind of actual HARDWARE grade material; and put a plastic hole plug or the like over the hole.
Re: Transmission Crossmember Bolts Are Stripped out
The "nut" portion on the inside of the frame is a stamped piece of thicker sheet metal thats spotwelded to the inside of the frame. The holes are just punched with a 1/8-3/16ths curled edge for the threads of the bolt.
Not a very user friendly design that strips very easy if over torqued a lil bit or is crossthreaded.
Some people drill the trans side of the frame rail to install the nuts/washers (one man trans removal job),
I think drilling inside the car would make it a 2 man operation unless you use caged nuts which would be hard to weld into place. You would have to remove the interior to set it up with caged nuts but the finished product would be nice.
I removed my flat sheet metal speed nuts from the frame, drilled the holes out and welded proper nuts to the metal, reinstalled the plates then welded the plate back in.
Re: Transmission Crossmember Bolts Are Stripped out
i used nuts i actually welded a small piece of coat hanger on one nut and slid it into the rail not sure if i cut a small hole and it takes a little time but once get the nut in place just screw in the bolt the hanger will act as a wedge so the nut won't spin in there took me alittle while but once it's done its good as new
Re: Transmission Crossmember Bolts Are Stripped out
For those looking for another simple option for this fix using knurled inserts (sometimes known as nutserts) that will work to add another bolt hole, or repair stripped ones. See post here:
Re: Transmission Crossmember Bolts Are Stripped out
Originally Posted by 6speedIROC
For those looking for another simple option for this fix using knurled inserts (sometimes known as nutserts) that will work to add another bolt hole, or repair stripped ones. See post here:
Re: Transmission Crossmember Bolts Are Stripped out
Do not trust nutserts to hold up the transmission, it's not just component weight on there but also torque reaction
Use a M12 spiral flute machine tap to instantly drill and tap it to this size. I do this on all of these cars I work on
The reason I say NOT to use the nutserts is because in all my experience working on C5 and C6 vettes these things are always a problem. For one, the front cradle on those cars (radiator frame/air dam mount) is bolted down into the frame with the frame having nutserts. they strip out real easy or simply spin when trying to remove the bolt. These frames see the occasional scrape and bump on speed bumps etc but nothing like the loading a crossmember sees. There's plenty of meat in the welded nut plates for M12 and that's a whole lot stronger than a thin little ferrule with threads. Yes I do have these nutserts and the nutter tool for them but I only use them for sheet metal and non heavily loaded or dynamically loaded applications.
Last edited by Twin_Turbo; 01-30-2017 at 08:34 AM.
Re: Transmission Crossmember Bolts Are Stripped out
The nutserts depend on their little knurling or splines to hold them in place.
Not a real secure long-term proposition in thin sheet metal like floor pans. Excellent in something thicker like aluminum extrusions, for a one-time put together and forget in an indoor environment; but for something that has to withstand repeated assy/disassy over a long period of time with corrosion water salt rust and general sheet metal aging, ... less than ideal.
I still like the process of removing the factor one-time garbage (whether cast chinesium or stamped sheet metal) and spot-welding in a real NUT.
Re: Transmission Crossmember Bolts Are Stripped out
There are applications well suited for rivet nuts* and they're handy as heck. I use them for mounting speakers in doors, or in radiator supports to mount ATF coolers, etc.
*The type that are similar to pop rivets; not the type where the threads get pulled into the rivet to hold them in place.
No, don't think a transmission cross member is a good application for such fasteners either.
Re: Transmission Crossmember Bolts Are Stripped out
Ok , so if I ever run into this , nutserts are out . The idea of a real nut , welded into the frame is more appealing to me strength wise , and I can easily see where the load the transmission would put on the nutserts may be too much for them .
Years ago when our cars were WAY more prevalent on the streets I was at a good friend's muffler shop picking up some pipes for a project I was doing and he and all the other employees were under a beat up thirdgen on the lift , laughing like crazy . Of course I had to ask "what is so darned funny under that car ?" Come to find out someone's solution to the problem we're discussing here was to weld the transmission crossmember right to the frame , no bolts , nuts , or nutserts under there ! Come to find out the car's owner had no clue that some hack welded in the crossmember and I kinda felt bad for the guy , who checks for a welded crossmember when buying a daily driver beater ?
Re: Transmission Crossmember Bolts Are Stripped out
Hey guys, nice to get some feedback on the nutserts..good or bad. I also agree that ripping up the carpet, cutting the floor and welding in a real nut is a much better solution.
Just to clarify a few things, they are not held in place with the "little knurling or splines", but crush to make a shoulder above the base metal they are installed into, ie the frame and remaining ring of the factory weld nut. The part can't collapse inwards during use as the bolt is installed in there.
The pull-out on these particular threaded inserts is 17KN or 3,800lbs each in 1/8' thick metal, so this is the reasoning is using them.
As for the loading on the cross member, there is the weight of the transmission weight downwards (200-300lbs max), torque arm upwards during acceleration (so no downward load on crossmember), and torque arm downwards during braking. I figure about 550lbs max, using [(tire dia = 26"/2) * (rear tire friction = 2,000lbs {50% car weight on rear wheels during braking being very conservative * friction coefficient of 1.0}) / (torque arm length ~ 48"). Total load would be in the order of 300lbs + 550lbs = 850lbs. This gives a 'safety factor' of about 17X on the inserts.
Re: Transmission Crossmember Bolts Are Stripped out
Vibration, going over bumps, etc. will FAR EXCEED the "normal load" on those fasteners.
The sheet metal in our cars at that point is NOWHERE NEAR 1/8"... at a guess, probably around .075" (14 ga) or thereabouts, AT BEST. Probably less than that but I've never actually measured it.
What happens after a little exposure to road salt? What happens to it as cracks in the sheet metal develop around it?
Looks like a good product and all such as that, but just the same, I'm simply not convinced that it's a solution that will hold up over the long term in this particular application. Probably a very good product for some situations, but just doesn't look to me like the right setup for this one.
For my money, I'll just keep on hole-sawing about a 1½" hole in the interior right above it, NUKE the factory cage/captive/whatever nut garbage, and spot-weld a 10mm flange nut on where the chinesium thing used to be. Maybe even spot-weld a fender washer onto the floor pan before the nut to repair the cracks in the sheet metal around the hole, depending on what I see once I can see it. Then stick a plastic hole plug in over it with a bit of Window-Weld around it, and lay the carpet back down.
Re: Transmission Crossmember Bolts Are Stripped out
1/8" is a conservative estimate at the front subframe thickness plus the flange of the factory trans bolt weld nut that is spot welded in there as this installs into it.. I'm sure it's actually thicker.
Re: Transmission Crossmember Bolts Are Stripped out
Originally Posted by midias
Originally Posted by Twin_Turbo
Originally Posted by sofakingdom
Originally Posted by paulo57509
Originally Posted by 6speedIROC
.....I also agree that ripping up the carpet, cutting the floor and welding in a real nut is a much better solution.
Hi 6speedIROC ,
I gotta admit when I saw your first posting I thought : "Great ! an easy quick pop in solution to a common major PIA problem on our cars !"
I am a Mechanic , a pretty good one with a strong side of electrical/electronics . I am not an Engineer in any way shape or form .
So , along comes four of the guys whose third gen knowledge I trust even more than the General* himself , one of whom I know is an Engineer , and all four of them tell me that a nutsert ain't the way to go here . Now I'm not sure if your statement here I quoted is supposed to be sarcastic or not , but at the expense of someone's crossmember pulling out due to what may be an inadequate repair yes indeed I would rather the big ol nut welded in , in the way Sofa described . It's not an insult to your product which as Sofa said I'm sure has lots of great applications with less "life or death" implications .
* The General did it for profit only and has long since moved on . These guys do this for their love of these cars , each and every day
05-01-2012, 05:03 AM
Very nice tip 6speedIROC , Thank You for that ! 
Ok , so if I ever run into this , nutserts are out . The idea of a real nut , welded into the frame is more appealing to me strength wise , and I can easily see where the load the transmission would put on the nutserts may be too much for them . 
Years ago when our cars were WAY more prevalent on the streets I was at a good friend's muffler shop picking up some pipes for a project I was doing and he and all the other employees were under a beat up thirdgen on the lift , laughing like crazy . Of course I had to ask "what is so darned funny under that car ?" Come to find out someone's solution to the problem we're discussing here was to weld the transmission crossmember right to the frame , no bolts , nuts , or nutserts under there ! Come to find out the car's owner had no clue that some hack welded in the crossmember and I kinda felt bad for the guy , who checks for a welded crossmember when buying a daily driver beater ? 
