th350 piston springs

[stevef]

2 questions please Cliff. I'm using your th350 book while rebuilding two th350's at the same time, and the book covers an amazing amount of detail, and is a great step-by-step. I'm trying to do these things right the first time and there are 2 things I'm not sure about, and would appreciate your expertise.

Question #1: Are all the piston return springs supposed to be the same length in a th350? I opened up my th350 forward drum, V8 piston with spring locator bosses and loose springs. Supposed to have 21 loose springs, but 4 are missing. These springs measure approx 1-7/32" long. I was going to replace the 4 missing springs from my th50 spare parts, but noticed that all the other springs I have are approx 1-16 to 1-3/32 long, So, the ones in my forward drum are about 1/8" longer than the rest of the springs. I don't know the history of this th350, but it looks like it was rebuilt before, and looked fresh inside and out. It probably worked fine, but was wondering about those spring lengths. Logically, since all my other springs, including the ones in cages, are the shorter length, I'd think they all were supposed to be in the 1-16" to 1-3/2" range. But I wanted to get your thoughts about it.

Question #2: Concerning the forward piston I mentioned above that has the spring locating bosses and loose springs. I understand why the loose springs MUST use a piston with bosses. And I've noticed that "caged" spring assemblies are normally used in pistons without bosses, since they don't need them. But, is there a reason I can't use a caged spring assembly on a piston with bosses? I read in the Ron Sessions book not to use loose springs in a flat piston, which is completely understandable. But he also said not to use caged springs with a piston with bosses. And I can't understand why not? I don't see any possibility of binding or limiting piston movement. Considering the clutch pack clearance in the drum is tiny, the piston doesn't have to travel far to compress the clutch pack. I have a caged spring assembly that I'd like to use in that forward piston with bosses. I actually put the caged springs in that piston and mounted it on the oil pump and air checked it, and it worked fine. Wondering if you see any problem with it. Have you done it? Thanks for your help!

[Cliff Ruggles]

Caged springs are fine with a bossed piston if things line up well.

The transmission with loose springs need to be checked closely if someone got there before you to make sure they didn't mix them up.

If you don't know the history then assume they aren't correct and measure the height of all of them and keep them consistent in each drum.  Keep in mind here that the forward drum isn't involved with a shift, but it does impact engagement and why the factory often used waved plates in those drums and full compliment of springs to "soften" the hit slightly as stock converters tend to be pretty efficient at low RPM's.

I'm NOT a fan of tossing out or changing the springs in either drum without specific guidance.  Gil Younger often provided a full set of direct drum spring with some of his higher end shift performance kits (Transgo) and detailed instruction on when and how to use them.

Over the years I've seen "builders" leave out piston return springs in drums, perhaps thinking that this will speed or firm up the shifts, not sure?  I do not recommend this practice.  If you are looking for shorter/firmer shifts and less overlap get a good shift kit or follow SPECIFIC guidance from a professional who has science all that out and had perfect success with it.

We're WAY past simply tossing out most of the check balls and opening up the separate plate hole sizes to HUGE dimensions.  Here I use and prefer Transgo shift kits.  They double feed and provide short/firm shifts without being overly harsh if you follow the directions closely......

[stevef]

Thanks a lot Cliff for such a detailed answer! Thanks for the confirmation that using caged springs with a bossed piston is fine. The only difference is the springs are attached to the lid, versus being not attached to the lid. So, I couldn't see how that would make any difference in operation.

And good to know that leaving out springs is not recommended. It seemed questionable to me when I saw it. So, I wanted to use a full complement of springs, and had this caged set.

I'm building them both back to stock, so not doing any mods for quicker or firmer shifts. If they work as good as new, that's good enough for me :-) .

Thanks for your time! 

[Cliff Ruggles]

Stock is fine for most set-ups.  For heavy duty use and racing I like to use the Transgo kits to firm things up slightly and double feed the direct drum.....