Yellow Bullet Forums banner

1 - 19 of 19 Posts

·
Registered
Joined
·
1,410 Posts
Discussion Starter #1
Hi Guys,

So I'm doing my research here to try to understand possible causes for thrust failure, and after referring to my trusty Munroe book, I have a question - it seems that powerglide pumps have a built-in valve that opens up when there's more than 27 psi of pressure in the cooling circuit; bypassing the cooler and dropping the pressure. It does seem that thrust failure from excessive cooler pressure is not uncommon.

How are people getting 70-100 psi in their cooling circuits if the bypass is supposed to open at 27 psi? Do some pumps eliminate this valve? If so, why? Or is there just too much volume?

It would seem the keeping the cooler line pressure down would avoid these thrust issues completely, is there a reason why there needs to be over 27 psi in the cooler line? Maybe converter function comes into play...

Thanks in advance!
 

·
Registered
Joined
·
143 Posts
That particular Valve only opens when there is a pressure differential of X psi between Cooler Out and Cooler In. It was designed as a Bypass Valve if the Trans Cooler ever became Blocked.
He's something to think about.
Block the Passage that runs to the Base of the Valve.
Drill a 0.100" Hole at the base of the Valve.
Change the Spring for one that opens at your desired pressure.
And you have an inbuilt regulated Cooler Pressure circuit. Bugger to adjust though.
 

·
Registered
Joined
·
1,410 Posts
Discussion Starter #3
Hmm. Good point - and an interesting idea. So if the cooler pressure goes over 27 psi (stock spring), it'll just open up and start to piss trans fluid into the body of the trans?

I'm investigating a possible thrust bearing failure and possible cures; one of the problems might be too small of a stacked plate cooler in line with the radiator cooler. I've found where more than one guy had a thrust failure because they added a cooler in line or something happened that caused a restriction in the cooling path. But wouldn't the valve prevent that from happening? How are thee people getting such high readings from cooler line restriction? I would still think 27 psi would be max, because the valve would open.
 

·
Super Moderator
Joined
·
19,592 Posts
Are you having a thrust bearing failure? Have you measured your cooler pressure? Does your pump have a converter press relief valve and a cooler bypass valve or just a cooler bypass valve?


Hutch
 

·
Banned
Joined
·
16,597 Posts
OIL OUT of the converter can be restricted in the stator support and result in elevated pressure, however the same circuit can be used to control pressure. Mis-indexed stator tube can cause curious too.
 

·
Registered
Joined
·
1,410 Posts
Discussion Starter #6
Hutch - Possibly. I've got .020" endplay with a max allowable of .012". But with all the other stuff I found (and fixed) on this thing, it's possible the guy built it that way. Either way, I will take some pressure readings (maybe today) and check things out. It could also be my tiny B&M stacked plate cooler causing a restriction. I like to cover all my bases before "j'accuse!"

Hipster - Thanks. That's a good point too. I saw somebody else had that issue too. I guess what I really should do is take the other pump apart so I have a good visual of exactly what's going on. Pictures are one thing, holding something in your hand quite another.

Either way, I'm not blaming anyone. The trans works great, and if the motor wasn't built that way (I measured and checked everything but thrust, of course), and it turns out that I have a cooler restriction, then the onus is clearly on me, and I'm not even remotely upset - in fact, I'm thrilled to be learning so much so quickly. And I have to get the converter tightened up anyway (the motor coming out is not a huge deal) - it's a little loose for the street and I'm only seeing a 600 rpm drop on the shift (at the optimum shift point). And I'm about to add more boost.

But let's assume that the stator support is in correctly, I'm still not clear how can you have more that 27 psi in the cooler circuit? There's that bypass valve...
 

·
Super Moderator
Joined
·
19,592 Posts
You have an aftermarket pump , my mistake. There is no converter relief valve in that pump. I really doubt the motor was built with .020" end play. Check the cooler pressure before you pull it apart.


Hutch
 

·
Registered
Joined
·
1,410 Posts
Discussion Starter #8
Normally, I'd agree with you that it wasn't built that way, but I found six missing freeze plugs, the "degreed" cam was 4 degrees off, the oil pump pickup was 7/8" from the bottom of the pan, the "hardened" oil pump shaft was a stock replacement, the timing cover was a rigged up old piece that wasn't even close to flat with the block rail, etc, etc. I seem to attract screw-itude. Which is why I take it upon myself to learn as much as possible. Otherwise I should be taking up synchronized knitting as a hobby.

I was looking at a photo I took of the bottom end, and look at the thrust bearing - it's doesn't look good, but it's hard to tell anything meaningful from a photo. This was before it went in:



Sorry for the size. It's so you can see it better. Ha! If I had a dime for every time I've had to say that...

But the proof's in the pressure readings. As I said in an earlier post - I really don't want to place blame unfairly. Not my thing.

Thaks for the help (again). Pressure readings coming soon.
 

·
Registered
Joined
·
478 Posts
Alex here is some info on the bypass valve it looks like you have a misunderstanding of it.

It does not dump lube to the inside.
It goes from the out passage to the in passage.
It only opens when there is a difference of pressure in the passages the is more then the bypass valve.
In my drawing you can have 100 PSI on the out passage and 75 PSI on the in passage.
This is a 25 PSI difference this will not open a 27 PSI bypass valve.

 

·
Registered
Joined
·
1,410 Posts
Discussion Starter #10
Thanks Ralph. That does clarify things for me. I did take the measurements today - at idle, I'm seeing 180 psi line pressure in low. It goes up a little with throttle. I see no more than 65 psi in the cooler circuit, most of the time between 40-60 psi. I shot a video, but I'll have to post it tomorrow. It's looking like the BTE stuff is behaving exactly as it should, and not the cause of my potential issues.
 

·
Registered
Joined
·
1,410 Posts
Discussion Starter #13
I didn't try the brake - because I haven't used it. I can't do 3,000 rpm in low gear, unless I drive it, then I won't be able to see the gauge. And yes, it looks like the thrust bearing is going. I also found out I only have about .065" of clearance between the crank and converter. Could that be an issue?
 

·
Registered
Joined
·
1,410 Posts
Discussion Starter #15
Yeah - on jackstands. Witness marks where? The flexplate did hit the block plate a few times - that's what tipped me off in the first place. I did manage to take a picture of the converter/flexplate interface. The adapter moves freely, but it won't go all the way into the crank - only about halfway (.065")

 

·
Super Moderator
Joined
·
19,592 Posts
If your on jackstands you can certainly get it to 3000 rpm in low gear. I thought there may have been witness marks from some part of the converter hitting the adapter or crank bolts etc.


Hutch
 

·
Registered
Joined
·
1,410 Posts
Discussion Starter #17
Oh - lol. Sorry - I had a moment of "stupid." The front of the car was on jackstands when I took the converter clearance measurements - I thought that was an odd question in that context. There's really no way that the converter could be touching any part of the flexplate/bolts - I can practically squeeze my fingers between the two. I've already starting pulling stuff apart. At this point, I'm reasonably confident that the issue is not with the trans itself. Though you can damn well bet I'll be doing proper pressure testing once it's back together. As well as frequent thrust checks, at least until it's proven to be stable.
 

·
Registered
Joined
·
1,410 Posts
Discussion Starter #19
There is a bit of info that might be helpful for you to know. This block had some issue with the number 3 main (where the thrust is) before the machinist assembled it. It had to go back to Dart. When it came back, the machinist couldn't get the crank to rotate freely, even though the bore/journal measured out fine. He struggled with this for a while. In the end, it turned out that Dart didn't re-chamfer the #3 main after cutting it. So when the machinist put the #3 main in, it was sitting up a little, binding it. Finally, he found the problem, and chamfered the main. But it is possible that he over-sanded the thrust surface of the bearing looking for the bind.

I'm just theorizing here, but I'm going with the most likely path. The trans (with your, BTE's and the bullet's help) turned out perfectly, and is performing right up to spec and flawlessly. The engine and crank thrust interface, on the other hand, warrant further examination. I mean, the guy left out six freeze plugs and a balancer bolt. As well as degreeing the cam 4 degrees off, the oil pickup 7/8" from the bottom of the pan, no roller bearing on the cam gear, etc, etc. I caught most of it, but missed a thrust check. I feel good about the trans, but the motor - well, less good. I'll actually be happy if this is the only issue with the motor.
 
1 - 19 of 19 Posts
Top