torque converter bolts sheared off

stp2136 · **Joined:** Sat Sep 29, 2007 8:30 am **Posts:** 35

Anybody else have this problem? Suncoast T/C was installed about a year ago and probably has 10,000 miles on it including towing a 2500# trailer. The bolts were torqued correctly and I even used Loctite on them. It looks like one bolt came out, then the other three sheared off. The holes in the flex plate are elongated so it will have to be replaced. The bolt holes in the T/C are also distorted so I'm not sure if it can be salvaged. My concern is....what caused the bolts to loosen/shear off? The bolts look awfully small (5/16 or so) for the amount of torque this engine delivers. Bad batch of bolts? These were supplied by Suncoast with the T/C. Should I drill and tap for larger bolts? Appreciate the help/advice.

BlackLibertyCRD · **Posted:** Sun Feb 08, 2009 4:21 pm

Sounds like Suncoast owes you a T/C, bolts and a flex plate. Maybe the bolts were too long and bottom out and wasn't tight enough on the flex plate. Elongated means that they were all loose.

warp2diesel · **Posted:** Sun Feb 08, 2009 4:39 pm

Or did you need to use washers?
Suncoast may have gotten stuck with some junk bolts, it does happen.

Bill.Barg · **Posted:** Sun Feb 08, 2009 10:10 pm

I did a simple shear stress calculation

A 5/16 fine thread grade 8 bolt can take around 6900 psi in shear.
given our 300 ft/b acting on 4 bolts at a radius of about 7", I get a factor of safety of about 3.

If a grade 5 bolt were used, things might be too close for comfort.

Wobbly · **Posted:** Mon Feb 09, 2009 2:29 pm

Bill.Barg wrote:

I did a simple shear stress calculation

A 5/16 fine thread grade 8 bolt can take around 6900 psi in shear.
given our 300 ft/b acting on 4 bolts at a radius of about 7", I get a factor of safety of about 3.

If a grade 5 bolt were used, things might be too close for comfort.

Possibly an impact shear failure: http://www.arp-bolts.com/Tech/T4_WhyPag ... _Why3.html

The formula for impact shear stress is given here: http://en.wikipedia.org/wiki/Shear_stress
I'm not sure how some of the parameters are calculated.

tulsa · **Posted:** Mon Feb 09, 2009 3:30 pm

I had the bolts shear after the front seal was replaced, before f37. Took the Jeep to a different dealer and was told that the bolts were not torqued properly by the first dealer.

007husky · **Posted:** Mon Feb 09, 2009 5:54 pm

I didn`t got any bolts with my Suncoast TC.

Haven`t installed it yet, since is winter and i m waiting for warmer days to do the job myself.

everybody else got suplied with bolts ?

Bill.Barg · **Posted:** Mon Feb 09, 2009 9:26 pm

007husky wrote:

I didn`t got any bolts with my Suncoast TC.

Haven`t installed it yet, since is winter and i m waiting for warmer days to do the job myself.

everybody else got suplied with bolts ?

Yes, my suncoast came with bolts (no washers)

JeepinJarhead03 · **Posted:** Mon Feb 09, 2009 9:34 pm

we were forbidden to use 5's regardless of the diameter anywhere on the allison A\T's on rigs, but on our applications, even the crd's I almost find it hard to believe they would have sheered if either the bolt shaft size was too small for the application to begin with, weren't torqued correctly or were simply faulty. I've seen weaker bolts on passenger TC diesel applications backout and bend, but not sheer.

I think they gave you poop bolts sir

Diggerfreek · **Posted:** Mon Feb 09, 2009 11:32 pm

Thats the problem with bolts, as they become harder in grade, they become more brittle and less apt to bent... a grade 5 or an 8.8 will bend and stretch where as a grade 8 or 10.8 will break. However the higher grade bolts will have a higher sheer psi

Wobbly · **Posted:** Tue Feb 10, 2009 12:51 pm

Diggerfreek wrote:

Thats the problem with bolts, as they become harder in grade, they become more brittle and less apt to bent... a grade 5 or an 8.8 will bend and stretch where as a grade 8 or 10.8 will break. However the higher grade bolts will have a higher sheer psi

Here's a discussion of toughness versus brittleness: http://www.rockcrawler.com/techreports/ ... /index.asp

JeepinJarhead03 · **Posted:** Tue Feb 10, 2009 2:05 pm

thats fairly good explanation, just doesnt cover engineering issues, issues i can only explain by certain examples, i dont know why its like that it just is

certain load bearing bolts in dump trucks are intentionally larger diameter softer bolts to allow them to bend instead of sheer because a bending bolt can be torched and replaced where a sheered bolt will cause a catastrophic failure of the load bearing capibilities of the bed

for whatever reason the harder bolt of same length and diameter will sheer

same goes for the bolts in the tractor trailer models of allison automatics, were forbidden to use 5 or above grade bolts because of allisons experience with using the harder bolts, if and when they sheered you couldnt shut it down before it tore itself apart, with the softer bolts theyed bend throw things out of ballance and it would vibrate horrendously but not tear itself apart, and those bolts were a *#*#& to get out, but it saved the transmission. Not that taking the transmission out wasn't about 30% of the cost of the transmission in labor anyway it was roughly a 20 hr job all starting with a flywheel turnin bar and a 5 foot long extension stuck through a hole in the firewall that was about the size of a half dollar or less

I smile because I don't ever have to touch one again

tjkj2002 · **Posted:** Tue Feb 10, 2009 2:18 pm

JeepinJarhead03 wrote:

thats fairly good explanation, just doesnt cover engineering issues, issues i can only explain by certain examples, i dont know why its like that it just is

certain load bearing bolts in dump trucks are intentionally larger diameter softer bolts to allow them to bend instead of sheer because a bending bolt can be torched and replaced where a sheered bolt will cause a catastrophic failure of the load bearing capibilities of the bed

for whatever reason the harder bolt of same length and diameter will sheer

same goes for the bolts in the tractor trailer models of allison automatics, were forbidden to use 5 or above grade bolts because of allisons experience with using the harder bolts, if and when they sheered you couldnt shut it down before it tore itself apart, with the softer bolts theyed bend throw things out of ballance and it would vibrate horrendously but not tear itself apart, and those bolts were a *#*#& to get out, but it saved the transmission. Not that taking the transmission out wasn't about 30% of the cost of the transmission in labor anyway it was roughly a 20 hr job all starting with a flywheel turnin bar and a 5 foot long extension stuck through a hole in the firewall that was about the size of a half dollar or less

I smile because I don't ever have to touch one again

Every Allison transmission I've ever worked on used grade 8 or metric 10.9 TC bolts.From the GM Durmax's to the Marine Corps LVS(MK48).The LVS used a Detroit 8V92TA diesel engine and I forget the model # of the Allison trans but it was a big one with only 4 speeds,1300lbs+ of torque in 45,000lbs vehicle rated to haul 12.5tons offroad,22.5tons on road and can tow 120,000lbs.Never had a TC bolt issue.

retmil46 · **Posted:** Tue Feb 10, 2009 2:44 pm

As far as the original post - why not just contact Suncoast and get their input as to what happened?

JeepinJarhead03 · **Posted:** Tue Feb 10, 2009 3:10 pm

I don't remember what the model of that allison was, but we were told directly by allison through a bulletin not to put the higher grade bolts in, why, I don't know but I did have first hand eyeball on what happened when you did on two occassions with the same truck

never the less, sorry for the hijack

i think we got a bit carried away

gmctd · **Posted:** Tue Feb 10, 2009 3:13 pm

The wallered flexplate holes and TC holes indicate this had been going on for some time, prolly related to the vibration reported last year - unfortunately, having to remove the starter to get to the plugged port to check the tighen-up prevents most from easily rechecking their work - imo, the bolts did not just stress-shear, they were sheared by flexplate tork\reverse-tork action on the bolt shanks -

As this identical Suncoast TC is used in the 545RFE's in the Hemi SRT drag trucks'n'cars, I really don't see this as a Suncoast problem unless they supplied inch bolts for metric threads, or vise versa (and I do like my vices versa!) - I'd drill'n'tap the torque convertor holes for next size up inch or metric fasteners (I prefer oem GM fasteners scrounged from boneyards, as they meet stated rockwell specs), drill the holes in the new flexplate larger to match the new bolts

stp2136 · **Joined:** Sat Sep 29, 2007 8:30 am **Posts:** 35

Agreed this isn't a Suncoast problem but they have graciously agreed to exchange the T/C for a nominal charge. They also suspect a bolt problem (insufficient torque) as have most of the others on this thread. The supplied bolts are about 8mm, same as OEM. Service manual calls for 270 in-lbs. Suncoast recommends Loctite--I will use the high temp version this time. I thought about drilling/tapping for larger bolts but am concerned about drilling through into innards of the T/C and the fact that standard taps won't cut threads all the way to the bottom of the hole (end of the tap is tapered). Also, I would be concerned about the centering of the T/C with non precision (hand) drilled holes. So I plan on using the supplied bolts again, making sure the torque is correct (what is the general opinion about 270 in-lbs for 8mm bolts?) and using high temp Loctite. I also plan on checking the bolts as part of the regular maintenance (it ain't THAT hard to pull the starter!).

gmctd · **Posted:** Wed Feb 11, 2009 10:55 am

Good deal, then - just FYI: a starting tap is tapered for, guess what? starting - a finishing tap is straight, will tap to bottom of blind holes

Wobbly · **Posted:** Wed Feb 11, 2009 12:43 pm

stp2136 wrote:

what is the general opinion about 270 in-lbs for 8mm bolts?) and using high temp Loctite.

Check out http://www.fandisc.com/tti.htm and note the difference between dry and lubed torque values.

warp2diesel · **Posted:** Wed Feb 11, 2009 1:58 pm

It lubricates the threads, so if Suncoast recommends Loctite on the bolts and prescribes a torque, I will bet that torque is close to the lubricated torque. Unlike generic torque charts, torquing by testing and experience is the best way to go.

To put it into perspective, most generic torque charts are based upon the torque the lousiest bolt in the batch can take with out failing or snapping off. Generic Bolt Torque Charts are like Building Codes so every installation does not need to be engineered.

MY former employer had an application that had to have the 1/4" X 20 TPI 316 Stainless Steel bolts torqued to 10 ft-lb. Generic torque charts called for 8 ft-lb max. We tested and found the stretch torque was 16 ft-lb. Since the applications was through bolted with a nut that had 2760 Loctite applied, we figured that if the bolt twisted off, good grab another. It was better to have the bolt fail in ones hand that fail in the application and cause damage, we shipped extra bolts.
I am sure Suncoast has gone through extensive field testing and evaluation and did not stretch their rectum to get the data.

Save the Generic bolt torque charts for bolting on skid plates and other goodies.

torque converter bolts sheared off

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