Tic,Tic,Tic coming from flex plate

[Preston]

I recently installed a th400 in my 1985 Silverado, I had to use an adapter for this because the transmission came out of a 60’s GTO. All installed and had a driveshaft cut To fit, so I thought, it was a little long but got it installed while the truck was on stands. Test drive all was well trans shifted fine but shortly I noticed a tic, tic, tic, coming from the bell housing area, didn’t drive it too far, back on jack stands removed driveshaft and started the engine ticking was quieter, I let the truck set for a couple days and started the engine the ticking was almost gone. Well I believe the driveshaft is 3/4 to 1” too long and putting too much pressure on the flex-plate question running through my mind have I cracked my flex plate or should I try it again after shorting the driveshaft or just get a new one and install it before I reinstall the driveshaft. I have not been back to The machine shop yet because I did the measurements and subtracted 1/2 “ for play should have been 1 1/2” , just wanted to relay this so that if anyone goes through this can learn from my mistakes. I look forward to comments from you all, also appreciate all the threads on the site that help me so much as I continue to work on these wonderful square body trucks.

 

[HotRodPC]

I've never heard of driveshaft length having anything to do with causing a flexplate to crack. Driveshaft length should not affect the input shaft at all. Unless I'm about to learn something new.

 

[SquareRoot]

Well the good news is, there's no way the driveshaft length has anything to do with the flexplate. Check the torque converter to flex plate bolts and make sure they are tight. It can be hard to tell where the sound is coming from. Exhaust leaks on the manifold flange make similar noises. You can always unbolt the converter from the flex plate and slide it backwards slightly and idle the engine for short periods. If the noise goes away you know it's coming from the trans- if not- it coming from the engine.

 

[Preston]

I replaced the bolts for the torque converter with grade 8 bolts before I removed the driveshaft, it does sound like an exhaust leak it resonates so much it’s hard to pinpoint I have been listening with a stick and just can’t seem to pinpoint where it’s coming from. Thanks for the thoughts, I really don’t want to remove the transmission unless I have to. Also just remembered that there is a gizmo on the right exhaust manifold that could be leaking, but there was no noise until I test drove the truck with the th400 in it.

 

[Michael Wood]

[QUOTE="Preston, post: 479816, member: 17582"]I replaced the bolts for the torque converter with grade 8 bolts before I removed the driveshaft, it does sound like an exhaust leak it resonates so much it’s hard to pinpoint I have been listening with a stick and just can’t seem to pinpoint where it’s coming from. Thanks for the thoughts, I really don’t want to remove the transmission unless I have to. Also just remembered that there is a gizmo on the right exhaust manifold that could be leaking, but there was no noise until I test drove the truck with the th400 in it.[/QUOTE]


Were the new bolts the same length exactly and not a shade longer? Were the heads on the new bolts thicker? The new bolts could be having clearance issues and scraping somewhere.

I just rebuilt an AMC 360 a couple months ago and lost a flywheel bolt somewhere and replaced it with one I had the "same size" ..... the bolt was about 2 threads longer and when I was done
the engine was seized up and wouldn't turn over, after checking EVERYTHING for 2 days I found that the new bolt was hitting the rear of the engine block and actually locked the flywheel from turning...lol Easy fix though. Point is even a couple of threads can make a difference sometimes.

Also, Big Block Chevy engines & small block Chevy engines use different flywheels due to how the engine is balanced. They both have the same bolt patterns and will bolt up but WILL crack and or shatter.....how I learned that is a story for a different day...... Don't want to seem too stupid on my first post!

 

[Preston]

Thanks I will double check the bolts tomorrow

 

[TravisB]

I replaced the bolts for the torque converter with grade 8 bolts before I removed the driveshaft, it does sound like an exhaust leak it resonates so much it’s hard to pinpoint I have been listening with a stick and just can’t seem to pinpoint where it’s coming from. Thanks for the thoughts, I really don’t want to remove the transmission unless I have to. Also just remembered that there is a gizmo on the right exhaust manifold that could be leaking, but there was no noise until I test drove the truck with the th400 in it.

You surely had the exhaust dropped to get that trans in there right? Maybe it's where you disconnected and reconnected the pipes?

 

[Preston]

Found it, the tick, tic, tic is an exhaust leak passenger side the flapper attached to the exhaust manifold.

 

[Michael Wood]

Easy fix!

 

[Preston]

Yes, thinking about putting headers on it

 

[Preston]

Okay update I got my headers and mufflers bolted in today ( no tailpipes yet) that tic tic is back (sounds more like a card in a bicycle spokes now) when I drive or park next to a vehicle or building I can hear it better ( I’m half way deaf anyway) in park the noise increases with rpm’s almost like a bolt on the flex is just a little too long. I’ll get the grinder out tomorrow and see if I can make the noise go away. The truck sounds awesome no exhaust leaks though.

 

[asltrfl]

I had the same exact problem, took me a week to track it down. It was the new flex-plate bolts. The fit perfect, but the bolt heads were .015" taller, pulled them out and put back in the old ones after spending hours finding them, and the ticking went away.

 

[Preston]

Great thanks, I was not looking forward to pulling the transmission again, I’ll go and buy some bolts from a auto store instead of the hardware store size does matter huh!

 

[asltrfl]

Yup, when I found the old bolts and took out one of the new-fangled super-hardened ARP or Edlebrock racing bolts (yes, they make "racing" or heavy-duty flex-plate bolts that I just had to have), I compared them visually and you could see the difference in height. I then put the micrometer on them...couldn't believe that .015-.020 thousandths would make a difference, but it did, especially when under hard acceleration. Like you said, just like a card in the bicycle spokes when we were kids. The stock ones work fine almost 20 years later.

If your buying from the auto parts store aftermarket isle, bring one of the bolts that you have in there now, make sure to compare the bolt-head height. You want a short head, a very obvious short headed bolt. If you can't find any, you can grind them down, BUT, grinding steel will take the temper / heat-treat out of steel. So better to file down by hand or grind a little at a time, letting the bolts cool down before your next pass. Maybe someone has a factory flex-plate bolt from your vintage and can give you the bolt-head height.

Good luck and let us know how it came out.

 

[Preston]

Thanks will do, have a great day