Full Throttle Pump Cavitation

[bkoons]

Spent the better part of my summer free time and $ rebuilding my tranny. BTW much thanks to Bruce and Chris for the willingness to share decades of experience and pointers. Spent a few extra bucks on a good pressure gage and am glad I did. Pressure was fine at min and max TV and driving around under normal to moderate load conditions. However, during full throttle blasts from a standing start the pressure took a dive down to 100 psi at about 3800 rpm. After overfilling it past the curve on the dipstick (over 2 quarts past full) the pressure was able to be maintained. I suspect now that just running it at the full mark is what toasted the thing in the first place.

Just want to share the experience with everyone. A pressure gage is a must before the strip. Cheap compared to a rebuild. Also, do not take the pan/filter for granted. I expect the mods like performance pump, stall converters, drilling holes, etc. probably place a larger fluid demand further revealing the stock pan problems. I ordering an aluminum pan, although I'm sure there are other remedies (i.e. run it over-filled).

 

[brian]

Very good info here.
Thanks for posting.
Brian

 

[A. G. Olphart]

This is a known low gear/hard launch problem. Fluid goes to the back of the pan & tranny sucks air. Overfilling is a quick temporary fix. Long term... special pans & pickups alleviate the problem, and Chris has another remedy in his book.

 

[2quiktocare]

The problem with pump cavitation is a common issue with a 200 4R especially when you start building some power in them. There are some temporary fixes to the issue as well as some other band aids, but the only way to actually fix it is to run a bottom feed pick up that is placed at the very back of the pan. People try 700 filters and many like wise "fixes', but to my knowledge, we are the only ones that have a true bottom feed. With our shallow and deep pans, the pick up is at the back of the trans and is a large feed screen filter pick up. Our pan kit utilizes the entire bolt pattern with 2 1/4"(shallow pan) depth to maintain absolute coverage of the pick up oil. Anything other than this is just a quick fix and not a solution.

 

[turbot2496]

Taking nothing away from 2quicks excellent kit.

If you take your stock filter and cover the intake hole with your hand, you can still suck air through the tube. This air comes from the seems around the filter where the metal meets the plastic. You can take some JB weld and go around that seam to seal it up. Try above test again and no air leak.It will help some with the cavitation because the front of the filter where that seam is is easily uncovered during acceleration allowing air to be sucked in.

 

[2quiktocare]

Taking nothing away from 2quicks excellent kit.

If you take your stock filter and cover the intake hole with your hand, you can still suck air through the tube. This air comes from the seems around the filter where the metal meets the plastic. You can take some JB weld and go around that seam to seal it up. Try above test again and no air leak.It will help some with the cavitation because the front of the filter where that seam is is easily uncovered during acceleration allowing air to be sucked in.

That is a good idea turbot, but it doesn't correct the main issue which is the filter pick up being uncovered during hard acceleration.

 

[bkoons]

Alright, I did the sheet metal baffle per the CK book. Admittedly it did help but did not eliminate the problem... at least not in my car. Instead of line pressure dropping to 100 psi it only dropped to about 150. I still would need to significantly overfill it (aprrox. 2 qts) to maintain line pressure. Did not try the JB weld trick. I think I'll wait for the pan to get here before I try to destroy anything else.

 

[turbot2496]

You should have tried it I think you would have been suprised. I was. Good luck with the pan that should definatly fix the problem.

 

[Russ Merritt]

The PTS pan/filter is sweet.....

 

[chris718]

youve got another problem my friend

 

[turbot2496]

Hey BKoons,

Just how hard does that car launch anyway.. are you doing this pressure testing on the street?

I was diagnosing a wot shift problem today that turned out the be a stuck TV valve. Anyway I made some runs just to see what my pressure drop was when taking off after reading this thread. My car usually pulls 1.70-1.80 short times at the track. My pressure was around 200 and never dropped a bit. I'm kinda with Chris in wondering if theres other issues. Is the filter seated good?? Sounds like your getting air somewhere. Maybe a crack in the filter tube or something??????

Also a question for 2quick or chris...

I've never gotten a trans filter directly from GM. Do you have any experience with the factory filter? I'm wondering if it leaks as much air around the seams as the aftermarket ones do? Doesn't seem like this cavitation was as much a problem from the factory and I'm wondering if inferior aftermarket filters are a part of the problem. I had aftermarket one before that leaked alot around the front seam.

 

[bkoons]

Testing is on a new, smooth street with drag radials. I wish my 60's were as good as yours, but the thing is I noticed the onset beyond 60'. When overfilled pressure is constant around 250 and the shifts are great. After reading Chris's post I was planning on a close inspection of the filter and seal. Possibly a trip to NAPA for a new one (and some JB weld) just to see if this and two filter seals have any affect.

 

[bkoons]

Okay, I got my PTS pan and the problem is gone. However, upon inspection of the old filter there is an extreme amount of leakage past the metal to plastic joint. So much so that I didnt have any problem blowing through the tube with the inlet hole covered. A significant amount of pump inlet flow was clearly coming through this joint. I went and got a NAPA filter. It was much better but if I blew real hard I was able to produce a soap bubble in the joint right where the tube transitions to the strainer housing.

I could see how this could cause my problem and would caution anyone with a stock pan to check this during service.

 

[turbot2496]

Awesome, glad you got her fixed.

Have you ever tried to drink a soda with a straw that has a tiny slit in it. You get alot of air.... When the front lip of that filter was coming uncovered you were probably sucking a good amount of air with that filter, even though the actual pickup hole was still in fluid. With the extra 2qts of fluid you had enough where that front lip wasn't getting uncovered. I've often wondered about whether the quality of different filters wasn't what was causing alot of guys cavitation problems.

 

[2quiktocare]

Sounds like you had a bad filter. We have done numerous test with cars suffering from cavitation using factory and aftermarket filters and found no difference to speak of between the two. When we ship a pan kit, we send two lip seals for the sump, just as overkill. We also checked to make sure the filters were not leaking by and even when sealed completely, they still had cavitation.

There are lots of ways to put a band aid on it as has been discussed, extra fluid helps, but it also allow fluid to be airated by rotating mass, a baffle will just slow fluid transfer, but you end up with the filter coming uncovered. We want to make sure our stuff will not break due to something that can be FIXED.

I'm glad you corrected your problem. thanks, Mark