Torque Converter Bolts Backed Off? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

clockdoc · 05-08-2019, 07:42 PM

I've put a little over 600 miles on a newly built 355. I started with an ATI short block and used the top end components from a 327 that ate its thrust bearing and roached the main webs. Early on there was a "chirp" that showed up intermittently, and always after the engine was warmed up thoroughly. I was never able to determine where the noise was coming from. I replaced all belts and corrected one belt alignment issue and there was no change. Following a very long traffic jam last weekend, on an 85 degree day, a much nastier noise appeared. It is a pronounced, knock/rattle that seems to be coming from the rear of the engine. The noise starts as soon as the engine is started and calms down a little after idling for a few minutes. When put in gear, it gets much worse. A light load on the engine quietens it down and, as long as there is a load on the engine, it is quiet. It runs great and sounds good on the road, but gets noisy again at a stoplight unless the idle is held up slightly with the accelerator.

I have concluded that the converter must have loosened up, but have not had time this week to get into it. I plan to get back to it this weekend. Does it sound like I am on the right track? Any words of wisdom?

geezer#99 · 05-08-2019, 08:01 PM

I’d bet on a cracked flexplate.

clockdoc · 05-08-2019, 08:15 PM

Thanks for the response. Would you expect a brand new flexplate to crack so soon? Truck has not been raced or driven hard.

geezer#99 · 05-08-2019, 08:17 PM

Not normally but we live in a time of poor quality replacement parts.

clockdoc · 05-08-2019, 09:42 PM

I just realized that I posted this in the wrong place. Should be in 1973-1987 forum. How can I remove the post from here

geezer#99 · 05-08-2019, 09:49 PM

Ah!
You are in the 73-87 forum!

clockdoc · 05-08-2019, 10:05 PM

Obviously I don't know what I'm doing.

Matt Man · 05-09-2019, 11:21 AM

I just had the same situation in my 81, I would drive mine on the freeway then it would start knocking when I got off the freeway. I checked my converter bolts and they seemed tight or so I thought. I had a shop replace my converter because I wanted a 4x4/towing application with brazed converter fins. Well I also had them replace the flexplate and converter bolts while it was out and sure enough the other shop that rebuilt my transmissions drilled out the flexplate bolt holes because the new 59$ converter didn't like up. Plus the 59$ converter didn't have long enough threaded holes and the screws bottomed out... cheap a**holes. How could you not notice the bolts bottomed out... I should have known better and threw in a higher quality converter but I was moving at the time and was pretty strapped for cash. Buy once cry once.

Tom · 05-09-2019, 06:39 PM

Cracked flexplate. Happened with my new engine too. New TCI plate and it lived happy ever after from that point on.

clockdoc · 05-10-2019, 11:59 PM

The flexplate is cracked and at least two of the flexplate to crank bolts are loosened. The flexplate was from SCAT and the converter was a Summit unit. Both were new 600 miles ago. Guide pins in the block are new (came in the short block). I torqued the crank bolts (ARP) to 65 ft-lbs. The converter was installed by the engine installer. Any suggestions as to what I should do to hopefully avoid this happening again?

geezer#99 · 05-11-2019, 12:17 AM

What did you get for a new flexplate?
Are there any star washers on the crank bolts?

Wikid61 · 05-11-2019, 01:02 AM

Pix would really help the cause.

clockdoc · 05-11-2019, 08:17 AM

I haven't bought a new one yet. Not sure what to buy. There were no star washers on the crank bolts.

geezer#99 · 05-11-2019, 09:10 AM

Like Tom said.
Get a TCI.
And some correct bolts and washers.
https://www.jegs.com/p/TCI/TCI-Heavy...46478/10002/-1

**MikeB** · 05-14-2019, 01:29 PM

Good quality flexplate bolts: https://www.summitracing.com/parts/a...2902/overview/

The T/C bolts are 230-7303 or 230-7304 depending on trans type. Then again, some T/Cs have "nuts" welded on, so you would need only bolts with correct threads.

clockdoc · 05-14-2019, 05:39 PM

Thanks Mike. These are what I had used initially. Turns out they are not intended for this crank/block (1986 and up, one-piece rear seal, Gen l). The correct ones are apparently 200-2906. They are .725 long rather than .680 and have a 5/8 head rather than a 3/4 head. I have ordered a set, along with a B&M flexplate (TCI had only one that could work, but I would have had to drill out the converter holes) and I plan to take the lot to the trans shop Thursday. I really appreciate your response. Looks like I didn't pay enough attention to detail the first time around.

Bloodhound · 05-14-2019, 08:02 PM

Quote:

Originally Posted by clockdoc

Thanks Mike. These are what I had used initially. Turns out they are not intended for this crank/block (1986 and up, one-piece rear seal, Gen l). The correct ones are apparently 200-2906. They are .725 long rather than .680 and have a 5/8 head rather than a 3/4 head. I have ordered a set, along with a B&M flexplate (TCI had only one that could work, but I would have had to drill out the converter holes) and I plan to take the lot to the trans shop Thursday. I really appreciate your response. Looks like I didn't pay enough attention to detail the first time around.

You just made me have a mini-heart attack and go back and check what I recently installed. Fortunately it was the 200-2906. Good luck with yours.

clockdoc · 05-14-2019, 09:39 PM

Glad it was just a false alarm!

**MikeB** · 05-15-2019, 10:50 AM

Quote:

Originally Posted by clockdoc

Thanks Mike. These are what I had used initially. Turns out they are not intended for this crank/block (1986 and up, one-piece rear seal, Gen l). The correct ones are apparently 200-2906. They are .725 long rather than .680 and have a 5/8 head rather than a 3/4 head.

Good catch! Looking at Summit Racing's website, you'd never know there's a difference between ARP flexplate bolts for 1-piece and 2-piece main seal blocks. In the future, I'm going directly to ARP's website.

I installed a 1-piece main seal 350 in my truck four years ago. Just spent nearly an hour looking through paper invoices and on-line orders, but can't find what I used for flexplate bolts. I have a couple thousand miles on the truck since then, so I'm probably OK.

clockdoc · 05-16-2019, 09:00 PM

I'm going to ask what is probably a stupid question but, because I have become so paranoid about overlooking something, I'll ask it anyway. Given the one piece rear seal block/crank, does it make any difference whether I use a 153 or a 168 tooth flexplate as long as it is externally balanced (other than the starter)? The truck went to the transmission shop today.

**MikeB** · 05-17-2019, 10:12 AM

Quote:

Originally Posted by clockdoc

Given the one piece rear seal block/crank, does it make any difference whether I use a 153 or a 168 tooth flexplate as long as it is externally balanced (other than the starter)? .

You can use either. Just make sure the starter and the dust cover work with the size you choose. Many aftermarket starters have two sets of mounting holes, whereas OE starters do not.

In my experience, the 153-tooth flexplate is more header-friendly because it tucks the starter in closer to the block.

Tom · 05-17-2019, 03:39 PM

Quote:

Originally Posted by clockdoc

Thanks Mike. These are what I had used initially. Turns out they are not intended for this crank/block (1986 and up, one-piece rear seal, Gen l). The correct ones are apparently 200-2906. They are .725 long rather than .680 and have a 5/8 head rather than a 3/4 head. I have ordered a set, along with a B&M flexplate (TCI had only one that could work, but I would have had to drill out the converter holes) and I plan to take the lot to the trans shop Thursday. I really appreciate your response. Looks like I didn't pay enough attention to detail the first time around.

Annnnnnnnnnnnd pretty sure you just figured out my intial problem as well. MY setup was a vortec 350 mating to a 200-4R, replacing the original 350 and th350 trans. I re-used the TC bolts. Flexplate cracked, I went TCI with ARP bolts. Bet I ordered the correct TC bolts when I got ARP and hence no more problems....

clockdoc · 05-17-2019, 04:39 PM

Many thanks Mike. I am going with the 153 tooth plate.Probably wouldn't have thought about the headers but it makes sense. Thanks again.

clockdoc · 05-17-2019, 05:02 PM

Sometimes what seem to be non-issues bite the hardest. glad you are back and running well. I think I will be early next week.

clockdoc · 05-21-2019, 10:19 PM

Thanks to all of you who offered advice. I have the truck back now and have looked at the flexplate closely tonight. It is a Scat plate and is either powder-coated or painted black. The six crankshaft bolts were loose enough to remove by hand. I'm not sure the plate is cracked, as I had previously thought, but the black coating has numerous stress cracks radiating from the torque converter holes. I plan to remove coating from one of these areas and see if the plate itself is cracked.

I just found this 2012 post on the Corvette Forum:

https://www.corvetteforum.com/forums...nTiY9sJc.email

The problem described in that post is exactly what happened to me. In addition to flaking under the bolt heads, there had obviously been fretting between the crank flange and the flexplate at the bolted connection. The coating there was basically destroyed.

There is too much similarity between the poster's experience and mine for me not to believe that the coating was the culprit.

05-08-2019, 07:42 PM	#1
clockdoc Registered User Join Date: Feb 2016 Location: Glen Allen, VA Posts: 67	Torque Converter Bolts Backed Off? I've put a little over 600 miles on a newly built 355. I started with an ATI short block and used the top end components from a 327 that ate its thrust bearing and roached the main webs. Early on there was a "chirp" that showed up intermittently, and always after the engine was warmed up thoroughly. I was never able to determine where the noise was coming from. I replaced all belts and corrected one belt alignment issue and there was no change. Following a very long traffic jam last weekend, on an 85 degree day, a much nastier noise appeared. It is a pronounced, knock/rattle that seems to be coming from the rear of the engine. The noise starts as soon as the engine is started and calms down a little after idling for a few minutes. When put in gear, it gets much worse. A light load on the engine quietens it down and, as long as there is a load on the engine, it is quiet. It runs great and sounds good on the road, but gets noisy again at a stoplight unless the idle is held up slightly with the accelerator. I have concluded that the converter must have loosened up, but have not had time this week to get into it. I plan to get back to it this weekend. Does it sound like I am on the right track? Any words of wisdom?

05-08-2019, 08:01 PM	#2
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,731	Re: Torque Converter Bolts Backed Off? I’d bet on a cracked flexplate.

05-08-2019, 08:15 PM	#3
clockdoc Registered User Join Date: Feb 2016 Location: Glen Allen, VA Posts: 67	Re: Torque Converter Bolts Backed Off? Thanks for the response. Would you expect a brand new flexplate to crack so soon? Truck has not been raced or driven hard.

05-08-2019, 08:17 PM	#4
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,731	Re: Torque Converter Bolts Backed Off? Not normally but we live in a time of poor quality replacement parts.

05-08-2019, 09:42 PM	#5
clockdoc Registered User Join Date: Feb 2016 Location: Glen Allen, VA Posts: 67	Re: Torque Converter Bolts Backed Off? I just realized that I posted this in the wrong place. Should be in 1973-1987 forum. How can I remove the post from here

05-08-2019, 09:49 PM	#6
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,731	Re: Torque Converter Bolts Backed Off? Ah! You are in the 73-87 forum!

05-08-2019, 10:05 PM	#7
clockdoc Registered User Join Date: Feb 2016 Location: Glen Allen, VA Posts: 67	Re: Torque Converter Bolts Backed Off? Obviously I don't know what I'm doing.

05-09-2019, 11:21 AM	#8
Matt Man Registered User Join Date: Oct 2009 Location: Buhl, Idaho Posts: 1,438	Re: Torque Converter Bolts Backed Off? I just had the same situation in my 81, I would drive mine on the freeway then it would start knocking when I got off the freeway. I checked my converter bolts and they seemed tight or so I thought. I had a shop replace my converter because I wanted a 4x4/towing application with brazed converter fins. Well I also had them replace the flexplate and converter bolts while it was out and sure enough the other shop that rebuilt my transmissions drilled out the flexplate bolt holes because the new 59$ converter didn't like up. Plus the 59$ converter didn't have long enough threaded holes and the screws bottomed out... cheap a**holes. How could you not notice the bolts bottomed out... I should have known better and threw in a higher quality converter but I was moving at the time and was pretty strapped for cash. Buy once cry once. __________________ 86 c30 crew cab dually 454/400 4/6 drop SOLD 1-8-11 1981 chevy K10 short Bed Scottsdale SOLD 10-26-2020 67 GMC Stepside Straight six/3 on the tree "The Peach" 2020 Silverado Double Cab LT Z71 5.3 8 speed Daily Driver K10 build http://67-72chevytrucks.com/vboard/s...d.php?t=671934 The Peach build http://67-72chevytrucks.com/vboard/s...d.php?t=733903

05-09-2019, 06:39 PM	#9
Tom driving is in my blood Join Date: Dec 1999 Location: Mesa AZ Posts: 5,748	Re: Torque Converter Bolts Backed Off? Cracked flexplate. Happened with my new engine too. New TCI plate and it lived happy ever after from that point on. __________________ -78 c10 short/step: 388cid, M20, 5/5 drop, lots more. Playtoy and first vehicle. -98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes. -02 Suburban 4x4: leveled front -CBR600F4i, CBR600RR, CBR1000RR, and standup skis DISCLAIMER: I cant spell for the life of me.

05-10-2019, 11:59 PM	#10
clockdoc Registered User Join Date: Feb 2016 Location: Glen Allen, VA Posts: 67	Re: Torque Converter Bolts Backed Off? The flexplate is cracked and at least two of the flexplate to crank bolts are loosened. The flexplate was from SCAT and the converter was a Summit unit. Both were new 600 miles ago. Guide pins in the block are new (came in the short block). I torqued the crank bolts (ARP) to 65 ft-lbs. The converter was installed by the engine installer. Any suggestions as to what I should do to hopefully avoid this happening again?

05-11-2019, 12:17 AM	#11
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,731	Re: Torque Converter Bolts Backed Off? What did you get for a new flexplate? Are there any star washers on the crank bolts?

05-11-2019, 01:02 AM	#12
Wikid61 Registered User Join Date: Aug 2013 Location: anamosa iowa Posts: 58,278	Re: Torque Converter Bolts Backed Off? Pix would really help the cause.

05-11-2019, 08:17 AM	#13
clockdoc Registered User Join Date: Feb 2016 Location: Glen Allen, VA Posts: 67	Re: Torque Converter Bolts Backed Off? I haven't bought a new one yet. Not sure what to buy. There were no star washers on the crank bolts.

05-11-2019, 09:10 AM	#14
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,731	Re: Torque Converter Bolts Backed Off? Like Tom said. Get a TCI. And some correct bolts and washers. https://www.jegs.com/p/TCI/TCI-Heavy...46478/10002/-1

05-14-2019, 01:29 PM	#15
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,597	Re: Torque Converter Bolts Backed Off? Good quality flexplate bolts: https://www.summitracing.com/parts/a...2902/overview/ The T/C bolts are 230-7303 or 230-7304 depending on trans type. Then again, some T/Cs have "nuts" welded on, so you would need only bolts with correct threads. __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, recent AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!



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05-14-2019, 05:39 PM	#16
clockdoc Registered User Join Date: Feb 2016 Location: Glen Allen, VA Posts: 67	Re: Torque Converter Bolts Backed Off? Thanks Mike. These are what I had used initially. Turns out they are not intended for this crank/block (1986 and up, one-piece rear seal, Gen l). The correct ones are apparently 200-2906. They are .725 long rather than .680 and have a 5/8 head rather than a 3/4 head. I have ordered a set, along with a B&M flexplate (TCI had only one that could work, but I would have had to drill out the converter holes) and I plan to take the lot to the trans shop Thursday. I really appreciate your response. Looks like I didn't pay enough attention to detail the first time around.

05-14-2019, 09:39 PM	#18
clockdoc Registered User Join Date: Feb 2016 Location: Glen Allen, VA Posts: 67	Re: Torque Converter Bolts Backed Off? Glad it was just a false alarm!

05-16-2019, 09:00 PM	#20
clockdoc Registered User Join Date: Feb 2016 Location: Glen Allen, VA Posts: 67	Re: Torque Converter Bolts Backed Off? I'm going to ask what is probably a stupid question but, because I have become so paranoid about overlooking something, I'll ask it anyway. Given the one piece rear seal block/crank, does it make any difference whether I use a 153 or a 168 tooth flexplate as long as it is externally balanced (other than the starter)? The truck went to the transmission shop today.

05-17-2019, 04:39 PM	#23
clockdoc Registered User Join Date: Feb 2016 Location: Glen Allen, VA Posts: 67	Re: Torque Converter Bolts Backed Off? Many thanks Mike. I am going with the 153 tooth plate.Probably wouldn't have thought about the headers but it makes sense. Thanks again.

05-17-2019, 05:02 PM	#24
clockdoc Registered User Join Date: Feb 2016 Location: Glen Allen, VA Posts: 67	Re: Torque Converter Bolts Backed Off? Sometimes what seem to be non-issues bite the hardest. glad you are back and running well. I think I will be early next week.

05-21-2019, 10:19 PM	#25
clockdoc Registered User Join Date: Feb 2016 Location: Glen Allen, VA Posts: 67	Re: Torque Converter Bolts Backed Off? Thanks to all of you who offered advice. I have the truck back now and have looked at the flexplate closely tonight. It is a Scat plate and is either powder-coated or painted black. The six crankshaft bolts were loose enough to remove by hand. I'm not sure the plate is cracked, as I had previously thought, but the black coating has numerous stress cracks radiating from the torque converter holes. I plan to remove coating from one of these areas and see if the plate itself is cracked. I just found this 2012 post on the Corvette Forum: https://www.corvetteforum.com/forums...nTiY9sJc.email The problem described in that post is exactly what happened to me. In addition to flaking under the bolt heads, there had obviously been fretting between the crank flange and the flexplate at the bolted connection. The coating there was basically destroyed. There is too much similarity between the poster's experience and mine for me not to believe that the coating was the culprit.

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