700R4 Transmisson Leaking

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  #1  
Old 01-21-08, 08:33 PM
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700R4 Transmisson Leaking

I posted this in the Cars, Trucks, RV's, Boats forum and then thought it probably belonged in this forum instead. Here is the problem...
700R4 transmission leaking...but where the hell from?? Rear seal was replaced a while ago and is clean. It was thought to be coming from the front seal or torque converter. Front seal looked good, replaced it anyway. Torque converter doesn't have any cracks or appear to be leaking from any point on it. Put everything back in, started it up and as soon as it started to warm up...drip, drip, drip. WTH? The leak is being splattered everywhere and really making it hard to pin point the exact place it is coming from. So, my question is where else can this transmission leak? Are there known "weak" points on it? We know it isn't the front or real seal or the torque converter. It is transmission fluid. Well it looks like it and smells like it, so pretty safe to say it is tranny fluid. Not the original owner of this vehicle, but pretty sure I saw some papers when we bought it that the transmission had already been rebuilt.

Oh, one other question. After we get the leak fixed. Does this transmission work better with certain types of fluid? We are using Dextron, but just wondering if we need to be using another type.
 
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  #2  
Old 01-22-08, 04:40 AM
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Dexron is fine, just keep it changed according to your owner's manual.

I would be looking closely at the lines running to the cooler. This will be two lines, could be either solid or rubber running from the side of the tranny up forward to the radiator (or a separate cooler).
There are also some other places where it is possible for tranny fluid to exit the case. I had to have a leak on my 4L80E a while back that was coming from where the electrical harness connector went through the case.

You didn't say how many miles are on the vehicle. Did this leak sudddenly pop up or did it start slow and has gotten worse. Both front and rear seals have been know to leak even with brand new seals if you get enough miles on the vehicle to actually wear down the metal surface being sealed. Happens with wheel bearing seals on axles and engine front and rear seals, too. BUT, it takes a lot of miles for that to happen.
 
  #3  
Old 01-22-08, 05:33 AM
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The vehicle has 260,000 miles on it. We bought it about 4 years ago. It had 220,000 on it when we bought it and the transmission had been rebuilt at about 215,000 miles. As you can see we haven't put a whole lot of miles on it, but it is driven daily, about 20 miles a day to work and back. Not much towing done with it. Travel trailer once or twice a year. We replaced the rear seal about 6 or 7 months ago. This new leak is sudden. We had a leak at the intake manifold. As soon as we replaced that (nightmare, broken bolts and such), the transmission fluid started leaking. It was not leaking before replacing the manifold gasket. I realize that the truck has a lot of miles on it, but this is still a very strong running truck. It is just really throwing us for a loop as to why it all of a sudden started to leak and where the heck it is coming from. I did check the lines running to the cooler. I could see one clearly, but not so much on the other. Will recheck them again, but it actually looked like it was coming from farther up. Meaning it didn't look like it was coming from where they screw into the transmission, but it is hard to tell because it is being slung around while the motor is running. Turn off the motor and it is pick and choose which drip to try and follow it's path. Thanks for the suggestions, will be looking at it again later today!
 

Last edited by the_tow_guy; 01-22-08 at 09:27 AM. Reason: Not necessary to quote entire post.
  #4  
Old 01-22-08, 09:31 AM
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A leaking vacuum modulator wil cause of loss of fluid also, but if all the lines are properly connected the leakage would simply be drawn into the vacuum side where it would be sucked into the engine (via the intake manifold - hmmm) and burned. This is often the source of fluid loss when fluid keeps getting low with no evidence of external leakage. I really doubt that's your problem if the vacuum line was disconnected you would have a performance issue and would likely hear the vacuum leak.
 
  #5  
Old 01-22-08, 04:47 PM
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Anyone know of a dye or something that can be used in the transmission to check for leaks? Still not having any luck on finding where this leak is coming from. Watched the truck all day and it didn't leak, so it is only leaking when the fluid is being pushed through it. Is it possible that even though we didn't see any cracks or anything on the torque converter, that it could still possibly be the problem? Meaning it isn't leaking until under pressure? The TC was sitting on a table for 2 days completely full of fluid and never leaked one drop, but it is still looking like the fluid is coming from that area.
 

Last edited by Melitta; 01-22-08 at 04:49 PM. Reason: spelling
  #6  
Old 01-24-08, 06:50 PM
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you should have a tranny shop pull the front pump and check the rubber o-ring around the pump these are known to dry out and fool alot of people into thinking seal ! When we pull a tranny to put a seal in we always put a pump o-ring seal in also !!! Good Luck
 
  #7  
Old 01-25-08, 04:07 AM
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Yes, there are fluorescent dye leak detection kits available. Only problem is that the way you describe the fluid being slung everywhere, I'm not sure it would be helpful.
 
  #8  
Old 01-26-08, 01:52 PM
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Originally Posted by rob24chevy View Post
you should have a tranny shop pull the front pump and check the rubber o-ring around the pump these are known to dry out and fool alot of people into thinking seal ! When we pull a tranny to put a seal in we always put a pump o-ring seal in also !!! Good Luck
We have pin pointed the leak as coming from in between the flywheel and the transmission.
Any chance that is where the pump is?
Is this pump o-ring hard to change out?
Haven't changed out this O-ring before, does this entail taking the pump apart or is the O-ring on the outside of the pump?
Our local parts stores don't have a tech manual for this transmission, so while we have the tools and skill to do this job, we are somewhat going at it blindly also. Any and all help would be greatly appreciated!!
 
  #9  
Old 01-28-08, 05:10 PM
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yes you will have to remove the punp from the transmission. then the o-ring i`m talking about is a big o-ring around the outside of the pump probably around 6-8 inches around, be sure to get the converter locked all the way back in.. good luck!!!
 
  #10  
Old 02-07-08, 06:36 PM
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We finally broke down and took the truck in to the transmission shop, as we figured this was way beyond our mechanical knowledge. Ended up with a pump seal leak and a hair line crack in the torque converter. We are up and running like new again! Thanks to all who gave suggestions!
 
  #11  
Old 02-08-08, 04:10 AM
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Thanks for posting back, Melitta; always nice to know how things turned out.
 
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