Turbo 350 tranny leak - Impala Tech
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post #1 of 8 (permalink) Old 11-21-2014, 12:44 PM Thread Starter
 
 
Join Date: Nov 2014
Location: Charlotte
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Turbo 350 tranny leak

Went out to the garage to go for a drive and I've got a decent amount of transmission fluid on the floor. '64 Impala, I picked it up about 2 weeks ago. Previous owner had a transmission shop rebuild the 350, cut the driveshaft to fit. Thats what I know, I made a 4 hour haul with no problems in it when I bought it. Im going to be researching and calling the previous owner to get more info in the meantime about any past leak issues etc, while all you genius's give me the extremely helpful feedback that I know you will.

Thanks guys

"Man is not made for defeat, a man can be destroyed but not defeated" -Ernest Hemingway
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post #2 of 8 (permalink) Old 11-21-2014, 02:18 PM
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There are several places where something goes into or out of the tranny. Any one could be a source of the leak.

The front main seal is a prime candidate because a full sized eleven inch converter is pretty hefty when full of oil. It has to be supported while you twist and turn it to get all three sets of splines to align. That is how most front seals get hurt. In the back if the tail shaft is too short or too long it can either break the tail shaft off or destroy the seal depending upon suspension travel and road condition.

Big Dave

Last edited by Big Dave; 11-21-2014 at 02:51 PM.
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post #3 of 8 (permalink) Old 11-22-2014, 07:34 AM
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Try tightening the pan bolts with a torque wrench. Check the lines at the tranny for leaks. Before you do this clean the tranny so that you can see where a new leak might develop. Put paper under the tranny so hopefully you can see where it began. And good luck you are going to need it.
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post #4 of 8 (permalink) Old 11-22-2014, 09:53 AM
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All previous suggestions are on target. Also, take a look at the detent cable. The 350 trans is notorious for leaking where the cable goes in and also take a look at the top hat. where the dip tube goes into the trans.

If there are no leaks in these areas; I would pull the pan. Often the trans bolts have been over tighten (I believe they should be 12ft pound max torque) thus causing the gasket to leak. Just look at the gasket around the pan and if it's bulging over tighten is probably the issue. Also, if you pull the pan check the bolt holes and if they are pushed upwards toward the trans housing this is likely the issue and you won't get a good seal. You can tap them down lightly until flat and use a new gasket...no sealer put it in dry.

Hope this helps!
msp177
Mike
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post #5 of 8 (permalink) Old 11-22-2014, 10:29 AM
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All GM stamped steel covers (timing chain, valve covers, oil pan and transmission pan) have a raised boss that is stamped into the cover when the lip is formed (after cutting the excess metal off). This embossed ridge applies the pressure to compress the gasket. If any one without a torque wrench or using an unregulated impact gun over-tightens the bolts, then the part is ruined.

It will leak because as you draw the bolt or machine screw down past it's torque specification, you bend the metal bowing the pan at each bolt hole. Oil can then pass through the gap freely or be wicked out by capillary action if not a gaping hole.

In the case of valve covers that seals against a raw cast iron edge you can flatten the bow out on an anvil with a body hammer. You can not do that with a machined surface to seal against as it is the raised boss that forms the seal. Once the boss is beaten flat the lip looses rigidity and will not seal. You need a factory fresh unmolested replacement pan from the junk yard, or buy a deeper finned cast aluminum transmission pan that holds more fluid. The aluminum pan is machined flat to seal with a paper gasket instead of a cork one.

Here is a list of the torque values for the covers on a Chevrolet power train:

Oil pan bolts (1/4-20) 80 in/lbs
Oil pan bolts (5/16-18) 65in/lbs on the SBC
Oil pan bolts (5/16-18) 135in/lbs on the BBC
Transmission pan to case 165 in/lbs
Timing cover bolts 80 in/lbs
Valve Cover bolts 45 in/lbs for the SBC
Valve Cover bolts 50 in/lbs for the BBC

You need an in/lb torque wrench because many of these bolts are below the threshold of a click type ft/lb torque wrench.

Here is one for $40 that works.

http://www.amazon.com/TEKTON-24320-4-Inch-Torque-20-200-Inch/dp/B00C5ZL2EG/ref=sr_1_1?ie=UTF8&qid=1416670112&sr=8-1&keywords=1+4+drive+torque+wrench .

Use Blue Loc-Tite on all threads except where it screws into aluminum then use anti-seize.

Big Dave
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post #6 of 8 (permalink) Old 11-23-2014, 10:06 AM Thread Starter
 
 
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Location: Charlotte
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Thanks for the advice everyone, I got under it yesterday and there was fluid dripping off the u joint. It could have been running down to the joint, it was hard to tell. Nothing obvious like I was hoping for. But I cleaned the spill up tightened the speedo cable and parked it back in the garage with a pan under where I thought it may drip. This morning I was greeted with another big leak. Im going to check the pan, gaskets and all the line connections today. Thanks again guys

"Man is not made for defeat, a man can be destroyed but not defeated" -Ernest Hemingway
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post #7 of 8 (permalink) Old 11-23-2014, 11:57 AM
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Check your dip stick. Given that your rear seal is worn out, there shouldn't be that much oil at the rear seal to continuously drip unless the transmission has been over filled. Or you are parked on a slope? If parked on a level surface the fluid level should be remain below the top of the transmission's oil pan.

Over filling leads to foaming; which leads to both leaks and accelerated wear.

Big Dave
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post #8 of 8 (permalink) Old 11-23-2014, 12:32 PM Thread Starter
 
 
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Thanks Dave, I haven't changed the transmission fluid so it may have been overfilled by the last owner. Ill check the fluid level and the dipstick. Ive only dropped a transmission once so I am by no means an expert transmission guy. Your advice is greatly needed and appreciated, Ill give these things a shot.

"Man is not made for defeat, a man can be destroyed but not defeated" -Ernest Hemingway
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