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« on: January 13 2021, 10:34:50 PM »
NOTE: You MUST be logged in to see pictures in this thread. Signing up is easy. I had no way around it.
PREFACE: THIS INFORMATION IS NOT INTENDED TO BE TAKEN AS GOSPEL. THIS IS ONE PERSON'S WAY OF DOING THINGS, SOME WILL DISAGREE WITH SOME OF IT, I'LL TRY TO POINT OUT ANYTHING THAT FALLS UNDER BUILDER PREFERENCE. None of this will be news to any of the veteran builders, but I'm doing this by request to help the average "guy in his garage" get his pump built as properly as can be done without machining the housings. I got good at these back when I worked full time at a trans shop doing 700r4 pumps. Thankfully for us, most parts interchange except the housings themselves, which greatly helps part availability and cost. Let's not forget that the 200-4r predated the 700r4 by three years, so the early build 200s are GM's first use of this style pump. which brings me to the first area of discussion.
What pump castings do you have and what's the difference? Early build pumps and pump covers are 149/150 casting number (ignore the red paint,it's the only early pump I have here), late castings are 082 body/088 cover and then the latest 690 body which used the same 088 cover. Here's the differences:
Early style is the bottom housing in this picture. The cavity that the orange screwdriver is stuck into is line pressure. Note how the early casting has the top land of the pressure regulator valve open for line pressure to exert force on it and uses a solid valve, and the late casting has the top of the valve area closed off. Now note how the late pr valve has a hole in it, EDIT: crap, you can't see the hole in this pic. Anyway, the late pr valve has a hole in it that goes from the area of the 90 degree pick, up through the valve and out the top of the valve into the now sealed off cavity. Still gets the same line pressure to the top of the valve, just through a different route. There's a GM service bulletin on the change, it was done to help isolate the land from pump pulsing in an effort to reduce PR valve buzz. I HAVE read mixed impressions about it's effectiveness. Some claim they won't use early pumps and some claim there's no practical difference. You do, however, need to know about this for interchange reasons. The "proper" way to do it is to use the 149/150 early combo as an assembly with the solid PR valve and use the late 082 or 690 body with the late 088 cover with the PR valve that has a hole through it. However, the only combo that absolutely won't work is to somehow end up with an early solid PR valve in a late housing. If you mix/match the parts it'll work as long as you have a pr valve with a hole in it. However, it'll work the same as an early design with line pressure acting directly on top of the valve and not through the hole.
Next pic shows the early and late pump bodies with the tools pointed at the same holes as the cover in the previous pic. Note how the late casting was revised with a larger flat machined area to fully isolate the valve tip from line pressure and forcing it to go through the hole in the revised valve. If you use an early body with the late cover it will allow line pressure to go around the newly sealed off cavity and negate any gains from the design change. It WILL "work", however.
Next pic is of the pr valve circuit from the manual. My manual only shows the early design, not sure if a later revision bothers to show the late design?? Edit: It doesn't.
Again, if anyone has more detailed info or testimonial from using early vs late pump castings, I'm all ears.
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