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Discussion Starter · #1 ·
I have done a bit of reading on this, a lot of rebuilders remove two of the four check balls in a Turbo 350 valve body, but don't really say exactly what the effect will be. I did drill out the 1-2 and 2-3 fluid holes in the spacer plate, but put all the check balls back in. I am happy with the way it shifts, but curious what removing the check balls would do for shifting, as well as long-term durability.

Thanks!
 

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1979 Chevrolet Malibu 496-TH400-9" (cruiser). 1992 Chevrolet S10 355-700r4-7.625" (daily driver).
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I can give you my hobbyist opinion on this. I'm more of a shade tree mechanic and less of a transmission guy. If anything I share here is misinformation, hopefully the folks that know better can help. This information is the way I understand it and what I do. If it's wrong I like to learn and I'm certainly not out to discredit anyone doing things differently. I will try for a short version with just the broad strokes.

Generally speaking the check balls either function as open/close or redirecting fluid with apply/release.

In a build like yours, with a modulator, you could get away with just 1 check ball. Without the mandatory one in the modulator circuit the line pressure would be way too low. Leaving out the 2nd of the two check ball set up lets the 1-2 circuit receive fluid from 2 sources instead of 1. This results in a firmer 1-2 shift than having the 2nd of 2 installed....at least that's what I think happens. I think the other 2 work in controlling 1 way flow to their respective accumulators/clutches. Leaving them out does firm up the shifts they help to control.

Personally, I think you did the right thing by installing all of the check balls. We are looking for a firm, quick shift. I think doing the rest of the build correctly provides that. Things like good clearances, good hydraulics and proper feed hole sizing carry massive benefit and less risk.

I think removing check balls helps to create harshness and wear on hard parts without any benefit.
 

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Discussion Starter · #3 ·
My trans is bolted to a stock 350, only street driven. At the time I was assembling the transmission, I didn't know whether to leave the balls out or in, since I didn't know what would happen. Main thing was, I did NOT want to take the valve body back off while under the vehicle if I didn't like how it worked. Just been curious if others had done this trick with the check balls, and were they happy with it. I can definitely say drilling the separator plate holes to 1/8" had a nice result. Firm shift with no bang.
Thanks for the input!
 

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1979 Chevrolet Malibu 496-TH400-9" (cruiser). 1992 Chevrolet S10 355-700r4-7.625" (daily driver).
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Nice! You're welcome. I hope some others chime in, too. I had planned to start a discussion about the exact same thing to get some opinions. There are quite a few people on this forum that really know their stuff. Great timing.

What else did you do on the build? (clutches, steels, other upgrades, etc.) I always like to see what folks are doing and share ideas. Especially when they have a build that works well.
 

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Discussion Starter · #5 ·
I did a lot of searching and video watching before I rebuilt the transmission. There were many recommendations for modification, but without being able to do a mod and drive for myself, there is no way to know what you are getting. I had no desire to do anything twice or pull the trans again, so I felt drilling the separator holes was a safe bet. I bought a Banner kit from Rock auto for about 70 dollars. It included all seals and gaskets, plus clutches, but no steel plates. I reused the original steel plates after buffing them with a paint stripper disc. The kit did not include bushings, but the old ones looked all right. I don't think I have all the correct drivers for those, either.

The transmission is from a 1971 or 72 GMC, and I don't think it had been taken apart since it was new. I had never rebuilt an automatic transmission before, but it didn't look all that difficult, and I felt I had all the necessary tools. After taking it apart, I found some broken clutch return springs. I was able to replace these with used items from Global Transmission Parts. Fortunately, they have some reasonably priced used transmission parts.

I would have been glad to have an experienced person help me with this, but I did not. I'm glad that it worked well after putting it back in the truck, and I would certainly do it again. Beats paying a shop $1k to rebuild your trans.
 

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1979 Chevrolet Malibu 496-TH400-9" (cruiser). 1992 Chevrolet S10 355-700r4-7.625" (daily driver).
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The amount of great information out there makes me wonder why more people don't give it a try. I totally agree with avoiding the cost of a shop doing the work. I think the part where we take things apart and try to figure out "how it works" was what got me into tinkering on cars in the first place.

The first transmission I rebuilt was also a TH350. I had to take it back out twice before I had it working correctly. I forget what the first problem was, but I ended up damaging a lip seal on my 2nd attempt. I got the Ron Sessions TH350 handbook from the library. I always wondered who was cool enough to donate a book like that. I think that was a pretty new book at that time. This was pre-internet 1990. I'm sure an experienced person would have been able to save me some grief. I think it's pretty sweet that we got it accomplished anyway.

My experience is limited to GM TH400, TH350, 700r4 and a few 4L60e. Any information I know is based on that.

With regard to the bushings. I'm sure somewhere in your research you saw a number of folks mention the TH350 as notoriously tough on bushings. It may not apply here but there are a large number of people that don't remove factory bushings if they measure well. The rationale being that the new aftermarket bushing may be a looser tolerance even though it's new. Quite a few use a replacement part with a good used factory bushing rather than put new ones in the part with the bad bushing, if it's available. If you continue on with transmission work consider getting bushings installed at a shop until you have the tools. I don't know what they charge, but it's what I would do.

Plenty of people prep and reuse the steels without any trouble. I haven't done that in a long time. The primary reason is that they are relatively inexpensive. If I needed to use one to get a clearance correct, I would. At this point I have quite a few new ones in various thicknesses from various builds over the years so a used steel is unlikely. I don't think there's anything wrong with the fact that you reused the steels in this build. I've never encountered anything I felt the more expensive Kolene steels. I don't get involved in anything over a 700 to 800 hp TH400. My own car being the exception. Maybe the higher hp stuff benefits from the Kolene, maybe it doesn't. I don't know.

Frictions are Borg-Warner paper or high energy. A large number of people use them in applications that far exceed what I do. It's all I use.

If you can rebuild transmissions, you will find you have friends you didn't realize you had. You could very well get some practice at this.

I always tell everyone I am a hobbyist and a shade tree mechanic. It's the truth. There a many people on this forum that know A LOT more than I do. I just try to explain what I think I know or understand.
 

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Discussion Starter · #7 ·
I have a dead 700R4 I might rebuild in the future. I suppose it's a little more difficult than a 350, but I may give it a shot. This one has a problem for sure, I put it in a truck and it had no forward or reverse. Hopefully, that might be something I can see with the pump removed.

As for the bushings, I never found a specific source for drivers. I guess you just have to figure it out for yourself. I would have to say the most aggravating thing about the 350 rebuild was the lip seals. I didn't know what kind of tool was needed to install these, and I came up with the idea of using a .010 feeler gauge to poke them in. Turns out, it seems that's what most people use.

I have had to pull transmissions more than once to get things right, that's no fun!
 

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Common lip seal tools used with a T-350 is piano wire loop in a tube. End of tube is crushed down on to the wire. ALso the flat tool box slide release tool is used on lip seals. I used these for decades.

Check balls on a T-350: OE style automatic shift T-350 , only 1 check ball is needed, near the modulator valve is location of a check ball. Check balls can be used to redirect oil flow, these are usually in a bathtub shape place. Check ball used for shift speed - feel tune will have a large hole and smaller hole that feed the same passage. Large hole flow starts the shift, the check ball moves, blocks the large hole, the smaller feed hole finishes the shift. You leave the check ball out, you have a large feed hole for shift and a firm shift
 

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Common lip seal tools used with a T-350 is piano wire loop in a tube. End of tube is crushed down on to the wire. ALso the flat tool box slide release tool is used on lip seals. I used these for decades.

Check balls on a T-350: OE style automatic shift T-350 , only 1 check ball is needed, near the modulator valve is location of a check ball. Check balls can be used to redirect oil flow, these are usually in a bathtub shape place. Check ball used for shift speed - feel tune will have a large hole and smaller hole that feed the same passage. Large hole flow starts the shift, the check ball moves, blocks the large hole, the smaller feed hole finishes the shift. You leave the check ball out, you have a large feed hole for shift and a firm shift
Do you have criteria you go by when deciding which check balls to use or are you more likely to run only the required or keep them all in place?

I realize that's a pretty generalized question, but I didn't want to hijack the discussion.
 

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Do you have criteria you go by when deciding which check balls to use or are you more likely to run only the required or keep them all in place?

I realize that's a pretty generalized question, but I didn't want to hijack the discussion.

Street transmissions with automatic shifts.. receive all 4 check balls. To firm up shifts : you can raise main line pressure a bit, open the shift holes for 1-2 & 2-3 shifts and also restrict oil feeds to accumulators
 

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I have a dead 700R4 I might rebuild in the future. I suppose it's a little more difficult than a 350, but I may give it a shot. This one has a problem for sure, I put it in a truck and it had no forward or reverse. Hopefully, that might be something I can see with the pump removed.

As for the bushings, I never found a specific source for drivers. I guess you just have to figure it out for yourself. I would have to say the most aggravating thing about the 350 rebuild was the lip seals. I didn't know what kind of tool was needed to install these, and I came up with the idea of using a .010 feeler gauge to poke them in. Turns out, it seems that's what most people use.

I have had to pull transmissions more than once to get things right, that's no fun!
You might see the problem in that 700r4 just by looking at the pump. Sometimes folks trash them by improper torque converter installation. It could be a fluid level thing or the filter wasn't fully installed and fell out of the hole a bit. It could be a number of other things. The degree of difficulty is a bit higher, as you said. It sounds like you do the kind of research necessary to be able to get this done though.

A google search for a transmission bushing driver set should give you options to consider. Using the handle for a cam bearing tool works pretty well to install rear case bushings. There's a learning curve with all of this. Expect to mangle a few bushings getting a feel for it. Have a look at a TH400 or 4L80e center support bushing...having that pressed in by a shop could save a lot of headaches. That's just an example of what you may encounter going forward. You'll get a sense for what to do with all of this stuff.

Any of the lip seal tools mentioned work well. Your feeler gauge idea is popular. I like the lip wizard too. You're on the right track with your ideas. Best of luck with your future projects!
 

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Discussion Starter · #12 ·
Thanks to Crosley for your explanation of how the check balls work. So it's probably good I put them all back in, since mine is just a street-driven trans.

And thanks, Malibu, I will take a look inside that pump and do a thorough bushing driver search.
 

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I have done a bit of reading on this, a lot of rebuilders remove two of the four check balls in a Turbo 350 valve body, but don't really say exactly what the effect will be. I did drill out the 1-2 and 2-3 fluid holes in the spacer plate, but put all the check balls back in. I am happy with the way it shifts, but curious what removing the check balls would do for shifting, as well as long-term durability.

Thanks!
So u may be able to help some . Drilling the valve body helped 2-3 shift.
that is my pet peeve. The lag upon partial throttle from 2-3.
any more to share?
 

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Discussion Starter · #14 ·
Drilling the spacer plate is all that I have done, so that's all I can make any statements about. After reading the information others gave here, I might try leaving out some check balls to see if further improvements are made.
 

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I have done a bit of reading on this, a lot of rebuilders remove two of the four check balls in a Turbo 350 valve body, but don't really say exactly what the effect will be. I did drill out the 1-2 and 2-3 fluid holes in the spacer plate, but put all the check balls back in. I am happy with the way it shifts, but curious what removing the check balls would do for shifting, as well as long-term durability.

Thanks!
I've installed quite a few B&M shift improver kits in th350's and the instructions say to remove all the check balls except for reverse. This makes the trans shift harder. The check balls make the trans shift smooth for normal family cars.
 
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