[dataway]

My rebuilt TH400 (done myself) and new Hughes converter have started making a strange noise on the test stand.

Imagine an old Pete Jackson gear cam drive ... that's what it sounds like, coming from the pump area. Intermittent, doesn't really do it at idle ... does when I rev the engine up a bit ... mixed in is a kind of sucking sound as if it cavitating or pulling in air. I've got the cooling line looped with clear tube ... no bubbles in the fluid. Has about ten quarts of Vavoline syn ATF. Forward gears, reverse, neutral work as they should ... at least by looking at the yoke spinning. No unusual vibrations. Converter has about 3/16" clearance. Makes the same noise in all shifter positions.

Did not make the noise the first few times I started it up with the tranny attached .... seemed to start when I got the fluid topped up.

I did add a shim on the torque converter bolts to close up the clearance a bit, it was around 1/4" .... but, I can't remember if I did that before I started it the first time ... or before the noise started

Also, I did not replace the pump ... I had installed a new one many years ago before the trans when on the shelf for 30+ years ... looked good during the rebuild but I'm no expert ... and it was likely the cheapest one I could find 35 year ago.

At first I thought it was the flex plate teeth getting close to something, but I don't see anything close enough.

[Sirrotica]

Back in the day the T 400s had a tendency to suck air around where the filter fits into the transmission housing, fairly well known problem back then. The easy cure was to use 2 O rings on the filter neck. I always used the heel of my hand to pound the bottom of the filter in as hard as I could, negating possible leaks on the suction side of the filter.

They also had a tendency to slip down causing an air leak on the suction side if all the attendant filter parts were even off a little bit. If it were me I'd look at these 2 places first. Air cavitation on any hydraulic system is never good for longevity.

It may not be either of these 2 items, but they're easy and cheap to check and fix if that's the problem.

[Half-Inch Stud]

I never found the air-leak to be the reason.


ususal culprit is wrong Pump parts were used; pump halves (895 vs 121) or wrong Reg valve. I think the whine is the Pump regulator banging end-to-end.

[dataway]

It's a pretty high pitched whine, I'll try to get a video of it ... immediately brings to mind a gear-mesh whine. I was surprised the noise only started after some run time and after the fluid was completely topped up. The noise also seemed to quiet down some as the trans warmed up. ... Before I got to far with this ... now that I think about it I topped it to the full mark when the tranny was dead cold ... could over filling cause this?

Also ... the modulator is installed, but no vacuum line installed ... any effect on pump pressure etc?

Could be the pump half ... I vaguely remember when I originally installed the new pump it was only the front half I think.

Now the question would be ... what is the right pump half? Does it depend on what the other half is?

Are there good sources for pumps ... I see it's not a common parts store part anymore.

[steve25]

my experience's have been that it's by far better to be 1/2 pint low the too high!

[Half-Inch Stud]

No vacuum calls for Full Line Pressure. Maybe overfill can cause this, along with a converter that has drained fluid and filled the case to the vent tube.

I don't know, due to lack of experience with the problem

[track73]

My 67 Catalina had a sound similar. Since it had a 50,000 mile warranty (I think) I took it to a dealer and my friend Red Nevens said it was the pressure regulator. Now that was about 48 years ago so I may not have remembered it correctly.

[Formulas]

Filter? Some don't flow as well as others
Only time I ever had a TH400 whine the pump was starving for fluid either low or needed a filter change

[Cliff R]

If it's not related to sucking air at the filter it's going to be "buzzing" at the PR valve in the pump or the pump is not assembled correctly or incorrect components used to assemble it as mentioned.......Cliff

["QUICK-SILVER"]

Originally Posted by dataway

... could over filling cause this?

What does it show on the stick at hot idle in park ?

And while the stick is out....Stick a long plastic funnel in the tube. If it's sucking air in the pan the funnel will be talking to you.

Clay

[dataway]

I've never had it warmed up to temp on the test stand ... I filled it to "full" on the stick when the trans was probably at about 90 degrees.

Since it's freshly rebuilt the filter of course is brand new ... and does have two o-rings on the suction tube.

Pump is a bit of an unknown ... since as mentioned ... I bought it and installed it about 35 years ago ... when I did the rebuild I just reinstalled it. I'm sure it was just an over the counter pump from a parts store.

So ... before I pull it back off I'll ....

1. Remove some fluid
2. hook a vacuum line to the modulator (an old modulator that holds vacuum and appears to function, I do also have a new modern style)
3. Warm it up better and check fluid level again.

That said .... how do I determine what is the correct pump? I thought they were all the same on the TH400. This unit is a 1968 "PX" TH400 that is original to the GTO.

Thanks for the help

[thebuick]

had my 400 rebuilt last month, whines and doesn't shift until its warmed up. then the noise stops and shifts good. Its going back to the shop paid good $$$$ for the rebuild and it should not have any issues

[dataway]

Update:

Fired it up again .... hooked up the vacuum modulator, let it warm up ... whine is gone.

While it was warming up I could I could unplug the modulator and it would slowly start to whine again, plug it back in and it would stop whining after a few seconds.

Still not fully warm ... say 100-105 degrees ... in Park, fluid shows at right between add one pint and full ... put it in Neutral and it shows half a pint ABOVE full.

Considering the pump is a "new" 35 year old part of unknown origin .... what do you guys think ... go ahead and pull it and replace before I put this thing in the chassis. It's not a real expensive part. Buy a full pump with shaft .... or the front half? I definitely would rather do this on the stand than do it later under the car.

[Cliff R]

I'd take the vehicle out and test it everyplace. If it's not assembled correctly, or miss-matched parts, you'll find out in short order. If it works flawlessly in all areas and the whine doesn't come back....good to go.......Cliff

[dataway]

Well, that is kind of what I'm trying to avoid at this point ... I'd rather try to take care of as many potential problem areas while it's on the test stand. I don't have a lift here so I'd basically have to pull the engine on a freshly restored car to get the trans out if I find a problem later.

I can't test it's shifting behavior on the stand ... although I can watch the yoke and see it shifting through all the gears ... I have no idea what it would do under load.

I'm thinking my next move is to replace the filter with a screen type and make sure the o-rings are still in order. It's been my experience with sounds that involve pumps-temps-viscosity that they have more impact on suction side than output side (not trans related, but industrial pumps) .. so kind of an easy next step ... already added a drain to the pan.

Cliff ... do you have a favorite source for pumps should I want to install a new one? OPH mentioned mismatches halves .... any info on that? And where do I find a filter with the brass screen?

Thanks.

[Half-Inch Stud]

I think 1968 was the 1st year for the "121" pump.

1970+ started the 895 pump; 895 pump back NOT compatible with 121 front.
Regulators are different too, for two conflicting reasons: no drill holes to reduce cost and reduce flushing the regulator backside.

[Cliff R]

"Cliff ... do you have a favorite source for pumps should I want to install a new one?"

Since the pump was never a problem with TH400's I just pull them from used cores. 99.9 percent of the time they will be fine and just need a converter bushing and front oil seal......Cliff

[dataway]

Not sure if it will be any help ... but here's a picture of the pump that's in there right now.

Back half is probably original to the 68 trans. Front half was purchased about 35 years ago ... I think it has no miles on it.

[Cliff R]

Without going out and looking at some different pumps for comparison the pics really don't help.

The best thing to do here, IMHO is to obtain a complete pump assembly right out of a good core where both halves have always lived together, put a new bushing/front seal in it, and replace what you have now.

The only thing you may have to do is replace the PR spring and remove any "horseshoe|" springs that you may find under it, IF some sort of shift kit was used in the trans and that modification was part of it.

I also like to restrict the converter feed a bit.......Cliff

[Half-Inch Stud]

So, tell me more about the Pump cast numbers...on each half.