Im rebuilding my 700-R4 and I found that the 1-2 spring broke and the combination of spring pieces and the piston being cocked in the bore pretty much trashed the piston and the accumulator housing. There are deep gouges in the bore as well as the piston. Also it looks like the piston almost broke through the spacer plate.

Why did the spring break in the first place? I had problems with the TV valve sticking and the trans would have a very harsh 1-2 shift every once in a while before I unstuck the valve each time. Is this the cause? Also, other then the obvious effect on shift quality, what other effects would a busted accumulator have on the trans?

Pic of broken spring:

 

...and a close-up of the accumulator housing + piston.

 

Thats a VERY common occurance with the stock accumulator spring (even worse on the pre-88 models which used a different shaped spring)...

 

Ok, so its just metal fatigue then? So I guess Ill just buy another accumulator piston and housing then.

 

What thirdgen88 said. No need to replace the accumulator piston and housing unless there are signs of excess wear - just replace the spring.

 

So it can be reused again even though its scuffed? Cool...

 

as long as it moves smoothly in the bore, you shouldn't have any problems... obviously you'll want a new seal..

 

Now that I look at that picture more closely, there appears to be vertical scratches/gouges on both the housing and piston. If that's the case, then they should both be replaced also.

 

Just wondering if I am the same page here, but isnt that the same thing as a "vette servo".

Kevin

 

No. A servo applies a band, while an accumulator helps to soften the apply of a clutch.

 

On that note, to what extent can the damage be before the components have to be replaced? All of them have some scuffing deep enough to catch my nail but none are like the 1-2 accumulator. I assume that if the damage is bad enough the blowby could cause the circuit to begin loosing pressure.

 

The main concern isn't so much the loss of pressure due to "blow-by" (the transmission's pump can compensate for quite a bit of this, so the clutch won't slip), but it's the accelerated wear on the teflon sealing rings.

 

Usually if a few passes with scotch brite wont smooth it out its time to replace the component. In this case its better just to replace the housing, piston and pin since there cheap enough.

Side note: My old 700 that served duity in the bird for a few years had the same broken spring, no damage even shifted real nice. I replaced it with the orange spring, that seemed to hold up much better.

 

Keep in mind that you want to use the updated accumulator piston seals (which are a one-piece rubber design, as opposed to the old style split ring teflon seal)...

 

Well, looks like all the pistons will need replacing. The area in the piston that the steel center shaft or whatever its called rides in is worn in an egg shape and the pistons are tilting in their bores. Guess the loading isnt even. Is this common as well?

On a side note the accumulator pistons and the housing I need are cheap enough but the part numbers are slightly different. Are they still the same parts?

 

I dont recall there being any difference even in a 4l60, but its always nice to make sure you tell whoever you order from the production date and such.

 

this is a very common problem due to the lack of heat treating by the factory.a permanent fix is to install a 2/3 accumulator spring from a th350 in its place.this spring not only wont break,but will also improve 1/2 ratio change firmness by reducing 2nd gear band accumulation/apply time.

 

I think some of the late model (4l60E?) accumulator pistons are composite plastic ( ).. There are two different accumulator pistons though for 700R4's.. I don't have my ATSG manual handy to give the details, but if you get the later pistons (the ones that you have now are the good ones, 88-up) you'll be in good shape.