Dowty (bonded seal) washers vs copper washers - converter housing bolts

thunder550

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I'm chasing a trans fluid leak coming from the converter housing-to-transmission bolts. I pulled the top of the trans apart already, replaced the two stator/pump plate gaskets, new pump o-ring, new seals on the 10 pump bolts, new copper washers on the bottom two converter housing bolts. Put it all back together and it still leaks. On inspection with a borescope through the inspection covers, I am seeing red fluid rings around the bottom 4 bolts inside the converter housing....labeled 1-4 in the pic below (same locations as original leak). Converter itself is dry, area under the pump seal is dry. Pump bolts (with the rubber seals) are also dry.



I found "Dowty" or Bonded Seal washers that say they are typically used in higher pressure fluid applications where copper washers are insufficient for sealing. Any thoughts on using these on the converter housing bolts? NOT the pump bolts with the rubber seals....those aren't leaking...

I'm thinking replacing the two copper washers on the bottom, as well as adding to the rest of the housing bolts.

Here's what these washers look like:


FWIW, I called Allison's tech support line earlier this afternoon to ask about the leaks. They wouldn't give me any info since this is apparently a GM built transmission, just branded as Allison. The guy I was talking to referred me to a local service center, who refused to let me talk to a tech and wouldn't give any recommendations about anything. Called and left Mike L a voicemail, hoping to be able to pick his brain if he calls back.
 
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2004LB7

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Well I'm not savvy with the Allison I do think those washers will work as long as they can handle the clamping force of the bolts.

I did find this in another site for those bolts

"In addition to the copper washers, Allison techs recommend sealing the bolt threads using a dab of Teflon paste, along with a small amount of silicone gasket sealing compound on both sides of the copper washer, before torquing each bolt to 42 ft/lbs"

I've always had better luck sealing copper washers by feel then by a specific torque spec. What torque did you tighten them down to? I've been able to help troublesome copper washers by annealing them before use. Some come from the factory with a little work hardening from the rolling & stamping process so softening them up with a little torching can help them crush and seal easier
 

thunder550

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Well I'm not savvy with the Allison I do think those washers will work as long as they can handle the clamping force of the bolts.

I did find this in another site for those bolts

"In addition to the copper washers, Allison techs recommend sealing the bolt threads using a dab of Teflon paste, along with a small amount of silicone gasket sealing compound on both sides of the copper washer, before torquing each bolt to 42 ft/lbs"

I've always had better luck sealing copper washers by feel then by a specific torque spec. What torque did you tighten them down to? I've been able to help troublesome copper washers by annealing them before use. Some come from the factory with a little work hardening from the rolling & stamping process so softening them up with a little torching can help them crush and seal easier
Good info there about the Teflon paste and sealant, I hadn't read any of that. Thank you. Bolts went on dry and torqued to 42 lb-ft.

I do find it interesting that it's not just the lower bolts that call for the copper washers that are leaking, but appears to be the next ones up as well. Those ones don't call for the washers, and I haven't seen any other threads about these ones leaking.
 

thunder550

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Well after doing more reading on the NBR rubber material that comes on the bonded seal washers, it seems like it's only rated for 225-250 degrees F. I'm thinking that's not sufficient for this use case, and I should try what @2004LB7 suggested above...teflon paste on the threads and some RTV under the washer and bolt heads.

Thoughts? Anyone know what material the factory rubber seals are made of under the pump bolts?
 

PureHybrid

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Sorry, I don't have any other input, never had those leak. But I've had a core trans that someone slobbered silicone around all the bolt heads

I'm surprised that those washers would only be rated for 250F. Did you try a different source? I've always called them a banjo washer or stato seal.

Maybe there's a problem with the case allowing oil up past the bolt threads?
 

2004LB7

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Apparently its from the porosity in the casting causing it to leak. Not all have that issue bit depending on the porosity near the bolts some leak while some don't. Supposedly it was discovered after a bunch where already made and in use so they started adding copper washers to help with the leaking even if it wasn't an issue with that particular casting
 

thunder550

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Sorry, I don't have any other input, never had those leak. But I've had a core trans that someone slobbered silicone around all the bolt heads

I'm surprised that those washers would only be rated for 250F. Did you try a different source? I've always called them a banjo washer or stato seal.

Maybe there's a problem with the case allowing oil up past the bolt threads?
The description on the washers I was looking at says they are "oil resistant NBR". There's no temperature rating on them, but I googled NBR temperature ratings and came up with the 225-250 number.

Another thing I jus trealized...the M10 bolts have a shoulder on them that's about 21mm in diameter. The Dowty washers I'm looking at have an OD of about 15mm, so not really wide enough. Could maybe find a different supplier, but now I'm really considering just doing what you posted above regarding the teflon and sealant.
 
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Chevy1925

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I know no ones uses any special seals there. I would clean the threads thoroughly (bolt and case threads), put a dab or two of rtv on the bolt threads and bolt it back down with the washers.

If it’s still leaking, something is cracked or bad with the case I would think.
 
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Mike L.

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I know no ones uses any special seals there. I would clean the threads thoroughly (bolt and case threads), put a dab or two of rtv on the bolt threads and bolt it back down with the washers.

If it’s still leaking, something is cracked or bad with the case I would think.
^^^^^^^^^^^^^^
 
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thunder550

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Ended up putting thread sealer on the bolts and RTV under the bolt heads. After driving 200 miles there is no new fluid inside the case that I can see. Crossing fingers this is fixed now.
 

NC-smokinlmm

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Looks like you found an lbz! Yea, the epa stuff put the brakes on the diesel performance world. I have a stock 16 LML, I just hang out here bc of the knowledge and people. You going to build up the truck?
 

thunder550

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Looks like you found an lbz! Yea, the epa stuff put the brakes on the diesel performance world. I have a stock 16 LML, I just hang out here bc of the knowledge and people. You going to build up the truck?
Crazy, I've been out of the loop for so long that I had no idea any of that was happening. Just read a few articles on it, explains a lot of what I've seen (or not seen) on several of the vendor sites.

I'm not planning anything for this truck other than to keep it maintained and running...bought it to tow a 5th wheel. It's completely stock down to the exhaust and intake. 254k miles....single owner, looks like he changed fluids religiously every 10k miles. Picked it up for $15k, seemed like an ok deal...unmolested LBZ trucks are hard to find. Just needed a little TLC...every single thing on it leaked when I got it 🤣
 

NC-smokinlmm

<<<Future tuna killer
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I can't stand a leak! I gave up on the diesel performance about 5 years ago and built myself a regular cab LS. It's fun but dosent have the torque of the Duramax. Welcome back! There are still a few of the old crew here just not as much. Hell, I hardly ever post anymore but saw your sig, funny I ran across an old thread of your on performance trucks a couple days ago. Lol
 
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2004LB7

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If it was mine, I would just chamfer the hole and put an o ring on the bolt. Kind of like the transmission cooler line fittings
 

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