Several months ago I had the GM 400 THM in my car rebuilt. Not thinking clearly, I should have had the pan replaced with one that I could drain. Well, I didn't, which is my own fault.

An additional mistake I made was trusting that the shop that did the work was competent (and maybe they were). They have a great reputation and work on cars much older than mine. So, thinking that they did a good job, I had no reason to check the level of the transmission fluid after they were done.

Now is where the mystery begins. About a month or so ago I noticed a leak of transmission fluid. When I checked the fluid level, it was over full....WELL over full. So, I started draining fluid by sucking it out via a plastic hose stuck into the transmission dipstick pipe. So far I've removed 10 ounces and it still shows overfull on both the cold and hot sides of the dipstick. So I'm now wondering about the dipstick itself.

The dipstick is stamped with "400" on the hot side, which may mean that its the correct dipstick for a TH400...but maybe not in a Jag. Given the commonality of this transmission, I would think that there are may different dipstick lengths to fit many different installations.

My dipstick, full length (from the end of the measuring end to the top of the red handle) is 29.5" long. The measuring (coiled part) is 26.5 inches long.

So, I'm left with wondering several things.

Is this the correct dipstick?

When it was reassembled was the dipstick tube properly placed, i.e. could it be a bit higher or lower than where it should be mounted?

What would be a prudent course of action to ensure the thing has the correct amount of fluid in it?

To complicate things I've noticed that since I've started draining some of the fluid that the tranny seems to be slipping at times. But could this be because we are in our cold weather months?

John
1987 XJ-S V12
75,000 miles

 

The TH400 trans is common but the two-sided dipstick is not. You probably have a Jaguar transmission dipstick....but still it may be incorrect. The parts catalog shows two different sticks depending on engine number and two different oil pans depending on VIN. I don't know what the difference is between them.

Plus any number of different non-Jaguar 400 pans could have found their way onto the car in some way or the other.

The possibility of incorrectly matched permutations is there.

It's more possible that the trans was simply overfilled. It is very easy to do.

FWIW my trans dipstick is 30.75" overall and 27.75" for the coiled part.

Anyhow....

Before going too deep into the weeds you are checking the level with the engine running, yes?

And the most accurate method is to check with the fluid HOT (not warm, not cold) after a good 10 mile run. If fluid is added based on a cold or warm reading the likelihood of overfilling is greater.

Cheers
DD

 

Thanks for that Doug.

Actually, I've not been looking at the level with it hot. I've been letting it sit overnight and looking at it cold "assuming" that all the fluid that was going to drain into the pan would have done so in that time period. I'm not a car guy (although I've learned a ton about the engine in particular and the car in general over the last 10 or so years) so now I know better.

I took it for a drive today per your suggestion. I got about 200 yards before the tranny began slipping. So...back into the garage and having no good idea what to do (given the possible with the dipstick and pan) I put in 1/2 quart of new fluid and tried again. It was better at first but when I got it up to speed (which around here is 60 MPH) the tranny started slipping badly. So, I got it on the back roads, limped home and noted the fluid level...it wasn't even touching the bottom of the dipstick. So I added about 1/4 pint then decided to let it go for the day due to other obligations.

Tomorrows plan is to do the same, adding a small amount of fluid until the slipping stops. While I'd like to put a TH700R4 in it if (when) the 400 goes south, rust is becoming a real issue so the car may be nearing the end of its useful life.

Suggestions appreciated.

Thanks,

John
1987 XJ-S V12
75,000 miles

 

John,

Only ever check these boxes when they are hot, and engine running as Doug mentioned. IME, there is no point ever checking the fluid level when they are cold.

Get the box hot, cycle the lever through all the positions a number of times, then ONLY if it's safe to do so, get someone to hold it in Drive with foot on the brake, and then check the level a few times, wiping the dipstick thoroughly between each check. If it's not safe to do it with someone holding it in Drive, then cycle it in all positions, put it in Park and jump out of the car and check it.

Good luck

Paul

 

Guys,

Thanks again for the input.

After yesterday's drive I added about a pint of fluid and let it sit all night in an unheated garage. Inside the garage temperature was probably about 45 degrees.

Today I backed it out of the driveway, (which slopes down) to take it for a drive. Once in the middle of the street I found that it won't go into any forward gears, whereas yesterday it was at least drivable. It would barely go into reverse, and I really had to put my foot into it to make that happen. So I shut it down and came inside to think about it.

So, lacking any better ideas, I let the engine come up to temperature, let it sit for several minutes, then put my foot on the brake, went thru all the gears, pushing on the gas pedal just a bit until I could fee the transmission wanted to come into gear. Did this several times and *poof* all the gears are now active. There is still a bit of slipping and while I didn't drive it at any considerable speed due to a lack of time, It's parked again in the garage. I added a bit more fluid and will hopefully have a chance to get the tranny hot tomorrow before the snow starts and the temperature drops.

So can this behavior be explained by bringing the engine up to temperature, which would in turn increase the tranny fluid temperature? I can't think of anything else that has changed.

Thanks,
John
1987 XJ-S V12
75,000 miles

 

There is no need to check the fluid level in Drive, and it's potentially very unsafe to do so. With it running and in park the pump is turning and the torque converter is full, the only difference between neutral and drive is the forward clutch is applied in drive. That particular clutch doesn't hold a lot of fluid, so while there will be a difference in fluid level between D and P, it's within the tolerance of the hash marks on the dipstick.

I can't ever recall seeing a GM manual that recommends checking the fluid level in D. Doug: does that ring any bells? You've seen a lot more GM documentation than I have.

 

One possible explanation is there is a seal on the neck of the filter, and the neck goes up into the transmission and is above the fluid level in the pan. Occasionally the old seal stays in the transmission when the old filter is removed and that gets overlooked. New filter with new seal is installed and then the seals don't actually seal properly, as you have 2 stacked in the space designed for one.

As this is above the fluid level in the pan, you can then start sucking air into the pump, instead of fluid and the result is you have no drive. Unfortunately, the solution is to drop the pan ( usually getting a bath in transmission fluid in the process), remove the filter and look up and see if there is an extra seal in there ( all the while transmission fluid is dripping on your face - ask me how I know). If there is a seal, pick it out, probably buy a new filter and seal and put that back in correctly, then reinstall the pan and gasket, refill the fluid to the proper level.

In you case, as the fluid heats it expands, maybe that is getting the fluid above the level where it was sucking air and you have drive again. Some GM transmissions had a small adapter pipe between the transmission and the filter, I can't remember if this is one of them or not.

Yet another possibility is you have the wrong filter and it's sitting too close to the bottom of the pan. It can seal itself against the bottom of the pan and again not be able to suck any fluid into the pump. If you can feel any slip, don't drive the car. It's very easy to burn up a transmission if it is slipping. Only a few miles can cook it completely.

 

OK, well...as seems to be the case in the world we live in these days, I'm going to have to do this myself to have a reasonable chance of it being done right.

The mess I don't mind, my problem is getting the car up high enough to be able to safely drop the pan and have a look around. I think this will mean getting it up on "all fours", so I'll have to be able to support the weight of the entire car.

So, thinking of ways to get the car up "that high" invites this question...between the bottom of the pan and the supporting floor how much do I need to elevate the car to make this task not to much of a pain. I'm guessing two feet?

Thanks,

John

 

Your taxing my memory :-). I don't recall any GM specifics but I don't recall seeing "While in Drive" in any manual for any car.

However, I've seen many dipsticks marked "Check at idle in Park".

I follow the same procedure on all auto trans cars with a dipstick. Cold fluid, engine idling, in "P", I add fluid to bring the level half-way into the "safe zone" markings on the stick. Usually hashmarks as you mention. Then drive the car 10 miles. Then recheck. In almost all cases the fluid level will then be at "Max" or close to it. Done.

Heh heh, when I had an XJR/6 the recommendation from Jaguar, via TSB, is that the 'safe zone' be ignored and the level brought up to "MAX" line, exactly. The "exactly" part was a real PITA!

Recently I learned new things. On my S-type there is no dipstick nor filler tube. You add fluid as though you are filling a differential but need to wait until the trans fluid is at xxx-temperature before filling right to the bottom of the fill hole.

Enough rambling !

Cheers
DD