harp

Does line pressure put added stress on the pump

Gregg Nader

I think you mean ‘does increased line pressure put added stress on the pump’
The simple answer is yes, but there is more to the story. Simple logic says if the pump is doing more work it sees more stress, but in our applications does this lead to premature failure? For that the answer is not as simple, but I will share what I know.
First, an increase in pressure is usually accompanied by an increase in heat (due to the extra work being done). Typically this is small and well managed by the cooling and not a factor, but is worthy of mention.
Most significant in vane style pumps like in the 4L60E family is movement of the pump slide. The pump slide controls pump volume, and pressure too. My understanding of how higher pressure reduces durability is not from the simple stress of making more pressure. For example power steering systems use a small vane style pump and make 2000 to 3000 psi without failing. I believe failures are more from running the pump closer to its limit (seen when at max pressures) when the rest of the pressure regulating system is not in 100% condition. If the pump slide pivot pin, wiper seal, PR valve bore are worn, or if there is a poor fitting boost valve that is loose and leaking, this is when problems occur.
What I am talking about can be seen with a pressure gauge when at or near max pressures. If the pressure gauge needle bounces wildly at high pressures, you will NOT get maximum life because the pump slide is hammering back and forth. If pressures are more steady, then you should be OK.

Gregg Nader
Sonnax Tech

harp

Gregg ive broke 2 rotors and slides in the trans and nobody knows why ive used new gm parts both times the whole pump assembly, and i keep breaking the rotor the converter cheched out fine no run out backspacings good i have a 3000 yank vette servos, should i zero out line pressure

Gregg Nader

One of these deals eh’, sorry to hear.
I had a local shop that went through two in the same trans (different complete pumps & converters), and then a 3rd with a complete different trans. After the first, all the others failed within a few months. I have heard of other similar cases as well. I wish I had some definitive answers for you but I don’t. Put a pressure gauge on it and see how stable the pressure is under ALL operating conditions. Excess needle bounce is a sign of trouble. Are there any other changes to the pump? I can tell you if I had it, this is what I would do after checking pressures. . .

1) Check crank end play (I think specs are usually around .005”).
2) Check flex plate run out.
3) Compare converter pilot outer diameter to bore in back of crank. I do not have the specs, but anything more than .001” is contributing to misalignment.
4) (the important one), check concentricity between engine and trans. I think this can be done with the removable bell housing as long as there is an inner diameter that aligns around the pump area. Remove the spark plugs, mount the bell housing to the block, attach a dial indicator to the crank and set it to read the inner diameter of the bell housing. Rotate the crank/indicator and read any misalignment between the block and trans. If misalignment is confirmed, there used to be off set dowel pins that could be used to dial in the alignment.

Hope this helps,
Gregg

harp

Gregg, thanx so much that's the most use full information I've received! I've spoken to alot of people pros and joe's to no avail, there was one guy who said to check the measurement of the rotor and cover to see if they were matched and they were so thanx to you and him. harp PS ill post my findings