Transmission Noise - it's Coolant in ATF

Suddenly out of nowhere, I think my TH400 transmission is acting up on my 88 XJ-S.

Once I have driven about 20+ minutes, the transmission seems to make a whining noise above 2000RPM, and the pitch is higher as the RPMs go up. In Neutral, the noise does not happen. It happens in 1st, 2nd or 3rd. It is under load or not under load, as long as rpms are above 2000rpm.

I’ve also noticed, the auxillary fan comes on more often now at idle, it used to rarely come on unless it was a very hot day. (There are transmission cooler lines to radiator, correct?) And when I went to check the transmission dipstick, the fluid level was fine, but the actual dipstick was quite hot and I actually saw ‘steam’ come off of it. Fluid is still nice and pink too.

So I assume somehow, my TH400 is running hot!? I changed ATF about 1 1/2 years ago, with a filter change too. I also put in a street B&M Shift kit 1 1/2 years ago. The transmission is shifting fine, btw. Perfect.

What could be going on? If pump were going out, wouldn’t that cause shifting problems? Wouldn’t a clogged filter show up more when cold? Could it be a failing torque converter generating too much heat?

I guess first thing to do is change ATF and filter and see what happens?

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When was the last time you changed the differential fluid?

Last summer I changed differential. The whining sounds like it’s coming from frontish, not rear of car.

And if I coast in neutral, noise goes away. It’s dependent on engine RPM, not speed.

Could be the transmission fluid pump (whine) - low on fluid, clogged filter, leaking internal seals?

Perhaps the filter dropped off the pickup tube. If so, first thing to try would be to overfill it by a quart or so. If that fixes it, that was the problem.

Thanks, I really really hope it’s something as simple as the filter. Would that also cause overheating ATF temps?

I have a spare filter and pan gasket. I was planning on doing an ATF change w/ filter soon, since I’ve only done one since owning the car and that was almost 2 years ago. Perhaps a lot of crud has ‘cleaned up’ and deposited into the filter. I’ll post my findings Saturday.

If it causes the bands to start slipping due to lack of engagement pressure, you betcha!


We’re all getting to know you better. It seems your Xjs is similar to ours, a pile of bad karma.

There should be no steam coming out from the dipstick.
Before you’ll slam the sht out of your tranny past the Event Horizon - check if radiator is not leaking coolant to the ATF section…

Heat in the tranny is a sign of malfunction. Usually related to friction plates / clutches, not torque converter…

Start from the plug, check if there is anything that brakes your tranny, then inspect coolant system.

Thanks guys. I thought the TC does indeed generate a lot of heat?!?

My plan of attack

  • check coolant/ATF for cross contamination.
  • Drop pan and inspect. Ill change filter and fluid.
  • Some other wise advice, disconnect cooling lines and blow some air thru them
  • if noise remains, suspect TC, pull th400 and upgrade to B&M!:slight_smile:

Honestly, forfet about TC or at least leave ot to a very grave end. When TC is failing it gives you all sort of clanks and noises, increases the drag rpms, lowers the perception of power transfer and overheats the fluid which goes amberish in colour, hence shifting problems. I would rather check the temp with hand after longer journey and engine/gerbox mounts to exclude confirm possible source of noise.

It is also worth mentioning that failing alternator bearing will give you similar experience…

I’m with veekay more then likely differential

I would check the fluid level in the Diff first before I did anything.

If i coast car in neutral, noise goes away. If i shift gears, noise changes pitch depending on rpm of engine. I changed diff fluid last year. No leaks. So ???

Alt bearing… noise does not happen when engine cold or revving in neutral.

Ive been getting rattling noise for a year that im quite sure is coming from TC.

Greg, how about this, think about recent changes you’ve done to your car (transmission) .
One of the things you’ve mentioned in recent posts is you’ve changed your modulator.
I would not claim to be a transmission expert, but if you have a faulty modulator all the symptoms you have mentioned, wining noises , overheating etc… will be the symptoms. I believe they are connected and controlled via vacuum and can draw heat via manifold and lower fluid levels as well as overheating.
Maybe start there.

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Be mindful when blowing air backwards through those lines because you’ll be forcing the transmission fluid out of the torque converter and end up with a huge mess to cleanup. It’s also one way to get a complete fluid change in one go :face_with_symbols_over_mouth:

I’ll be disconnecting both lines, so torque converter will not be involved.

Bad modulator would - make whining sound if diaphram is bad, and would overheat transmission due to loss of ATF being sucked into intake manifold. Worth checking out, I guess.

But my shift points are working as expected, there is no transmission fluid in the vacuum line at the intake manifold, and I am not low on transmission fluid. So odds are it’s not that. But with most transmission diagnosis, it’s a list of eliminations. So I’ll double check while under there.

Also worth mentioning, I installed a street B&M Shift kit about 2 years ago. I am pretty sure I got everything back together correctly, with balls in their right places, and I also replaced the plastic modulator shift valve with an aluminum one. If I did something wrong, I would think it would have made itself known a long time ago?

I know the TH400 has a natural whine in 1st gear from the planetary gears. The whine I am hearing now in 2nd and 3rd at 2000RPM (only when fully warmed up) sounds very much the same.

Been reading a lot about transmissions, and I agree, the TC seems like the last possibility.

IMO, I’m hoping it’s just a partially clogged cooling line. It kinda makes sense, as when the transmission is cold, it runs perfect and no whine. When the engine hits 190F after about 10 minutes, still no whine. But after 20 minutes of driving, the whine is heard only at high rpm in gear (2000RPM and up). And at this point, i notice at idle the aux fan is coming on quite a lot, even though ambient temp is cool. Never used to do this, my aux fan only came on during hot summer days. Another symptom I just remembered, when it’s hot enough to cause the whine, when I come to a stop the downshift into 1st is more pronounced. Hot ATF?

So if there were a partial clog in the lines, it could overheat the ATF, causing the TC to whine on load?

I read that the TH400 has a bypass, so if there is too much pressure in the cooling line, the hot ATF is diverted back into the transmission maintaining pressure. Which would explain why it’s still shifting fine.

When I pull both cooling lines from the TH400 this weekend, I will use 50psi compressed air. This isn’t too much, is it?

I’ll of course inspect fluid and filter. Crossing my fingers I’ll have it sorted after this weekend.

Whine from the pump would be aerated fluid; air leak on the suction side (filter or pipe o rings) or cavitation caused by blocked screen. If you installed a deep sump pan, the suction height increases, increasing either issue. If you are pulling the pan anyway, Kirby’s advice of adding a quart or two will probably tell if suction side is at fault.
I think the cooler is just a “S” shaped tube in the radiator tank and is unlikely to be blocked.
Cooler should handle that pressure, especially if other end is open. Be prepared for a mess.

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