#1  
Old 05-12-2021, 09:46 PM
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CraigG. CraigG. is offline
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Default How to locate turbo 400 transmission Leaks

Hey Everybody,

I've got a turbo 400 with a break and a stamped steel deep pan that has worked well in the past. Last year changing the filter and transmission fluid from the pan and this year has started leaking - (possibly leaking last year too?).

I wanted to know the best way to locate the leak.

First time at using a cork a gasket so likely have Over tightened the pan.

Also using the obscenely expensive B and M synthetic fluid.

Thanks again, Craig

  #2  
Old 05-13-2021, 06:04 AM
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I stopped using gaskets ages ago, you just need the time to do it right with a form-a-gasket product and I never had a leak again!

Lay a 1/8" tall bead around a 100% clean and dry pan lip ,going around the inside edge of the pan bolts in a C shape, then let the bead set up for 30 to 40 minutes as it needs to skin over very well.

Install the pan and tighten the bolts enough to see the bead compress some.

Let it sit overnight and the tighten the bolts to the ft lbs needed.

Note. Next time you go to get the pan off it will need to be pryed off slowly at multiple locations so you do not bend it !

Note that 98% of the small weep type leaks that I have ever had when using a gasket where at the pan bolts, and yes your usage of synthetic fluid does not help the weep condition!

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Old 05-13-2021, 07:36 AM
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Most trans builders perfer the cork gasket. Are you sure it's coming from the pan seal? There is an o-ring that seals the shaft that mounts the shifter linkage that can look like a pan leak.

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Old 05-13-2021, 07:56 AM
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Your assumption that you may have overtightened the pan is likely the correct answer. You could do the usual fix of putting a socket in a vise, put the pan on it around the bolt hole, and use the round end of a small ball-peen hammer to take the "pucker" out of the pan around the hole.

When I went to an aluminum pan on my 400, I didnt use a gasket. I put on just enough silicone to see "color" (a truly small amount), then bolted it up directly. Never a leak. When I had it gone thru the last time, the guy put a blue gasket on it. If it starts leaking, I am going back to the no-gasket deal that worked.

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Old 05-13-2021, 08:37 AM
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We try to not use the cork gaskets-too easy to over.tighten by customers . We like the hard fibre gaskets,stuck to the pan side with Grey Abro if it's an old pan.

  #6  
Old 05-13-2021, 10:14 AM
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The Moroso TH400 gasket I used seems to be ok..

https://www.moroso.com/perm-align-tr...n-gasket93103/

  #7  
Old 05-13-2021, 10:42 AM
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I will check the shaft seal.

Is there a dye that helps to locate the leak?
I have a UV light.

Thanks Again, Craig

  #8  
Old 05-13-2021, 02:10 PM
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Quote:
Originally Posted by CraigG. View Post
I will check the shaft seal.

Is there a dye that helps to locate the leak?
I have a UV light.

Thanks Again, Craig
Yes, when I worked in a dealership this is how we would have to find the really stubborn leaks. One type of stubborn leak that has nothing to do with gaskets is case, or casting porosity, not all that common, but is a possibility.

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Old 05-13-2021, 03:10 PM
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can you recommend a dye?

  #10  
Old 05-13-2021, 06:43 PM
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https://www.amazon.com/Tracer-Produc.../dp/B000JFHNTM

  #11  
Old 05-13-2021, 09:03 PM
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Old 05-13-2021, 10:19 PM
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I had a leak around the dipstick tube o ring. Replaced it,still leaked. Cleaned,dried,used new loring and used sealer,forget brand. I have a new seal with short tube from Cliff,its really tight into case. Need to weld it to tube.

  #13  
Old 05-16-2021, 05:56 PM
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I just used a GM 4 to 1 dye - and started car - waiting for the leak over night.
Shifter shaft looks clean with paper towel overnight.
Would a transbrake solenoid leak and where - over 28 years old?
Leaking from both sides of pan - off TB solenoid too.
Vent in trans leak when sitting for a year - drained back from converter?
Thanks Again, Craig

  #14  
Old 05-17-2021, 10:03 PM
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Looks like a leak from the plunger on the Transmission Brake Solenoid - 27 years old?

  #15  
Old 06-07-2021, 09:42 PM
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Hey everybody,
Thanks for your help and per several positive suggestions from different guys the one I remember recently is Cliff - to go with a Farpack Fiber gasket from global transmission parts in Ohio – $3.95 plus shipping!
I also got a new TCI replacement Transmission brake solenoid.
Take care, Craig

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