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Old 07-23-2013, 07:02 PM
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700R4 lost 3rd gear again

Hi guys, Ive updated my original thread on this issue from last year but I'm thinking that I may get more notice with a new thread. I hope this is okay with the admin.

After losing 3rd gear in my 700R4 last summer, followed by a complete redo using some great heavy duty parts, I am losing 3rd gear again. It seems to be related to cruising in OD on the highway and part throttle forced downshifts to 3rd. All gears were great from the build until I started more highway cruising and using OD more. I had noticed some slipping on these part throttle downshifts from OD to 3rd but I thought it was probably the TC clutch releasing.

Now, 3rd is definitely not as firm as it was and cruising in OD the last day I drove the car, the trans lost drive and I was unable to re-engage 3rd even manually until I stopped the car for a bit. I am thinking maybe pressure loss in OD from a leaking piston seal on the servo or a sticky valvetrain. I know there was one check ball pocket in the trans that was beat up from a steel check ball. Maybe the torlon ball I put in is sticking. I'll have to fix or replace the case. Definitely looking at new 3-4 clutches again. Also possible I've pushed a piston seal on the 3-4 apply piston. I may have also installed the 4th servo piston backward.

Any input is greatly appreciated. I am collecting any and all parts that I may need and plan to tear into the trans over a weekend within the next two months.

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Old 07-23-2013, 08:30 PM
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w as wondering if your using a external cooler, an a 4L60E oil pan, weld or solder some tubing to the inside bottom of the pan to keep the 700r4 filter from falling out, this will give you 2 or 3 more qts. Think of ATF as a coolent not just a lub. Heat is killing your clutch pack. I was going to go the 200R4 route until I happened to get a 2002 4L60E for free, freshly pulled from a Chevy PU,it had a burned up the clutch pack. The only thing you cant use from a 4L60E is the valve body & front half of the pump. I used all the Torrington bearings no thrust washers,overrun clutch hub,forward sprag,3&4 clutch apply plate,reaction carrier shaft & gear, plus a new GM rear 5 pinion. I found this right here so do a search for 700R4 limitations, lots of good info their. I don't work on transmissions an the the only one I know anything about is the 700R4 so Im not going to say whats right an wrong. ATF is a coolent, where is most of the heat generated at, sliping torque convertor,3/4 clutchs,forward sprag? I gota go memes,its late for me.
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Old 07-24-2013, 06:47 AM
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Thanks dogwater for your reply. I've been thinking about heat being an issue. I do have an external auxiliary fluid /air cooler added on top of the stock fluid/coolant cooler. I've been thinking about going to 3/8" lines like used on the heavy duty units to increase cooler flow. I've also done the regulator valve mod suggested by Transgo to increase cooler flow. My TCC has not been working as it should and I bet that the slipping TCC has really heated things up. I will address that. I installed the Smart Tech input housing from Sonnax that maximizes 3-4 clutch capacity. I run 9 frictions with 8 .077 steels. That's more than any other input housing can hold. However, I failed to follow the advice of one 700R4 expert who told me to use the BW high energy frictions instead of the Alto Reds. The high energy hold more fluid for better heat capacity. I won't make mistake this time.

The funky shifting has me concerned though. I swear I was getting a dual apply/binding between 2nd and 3rd a few times this past week. I could feel the drivetrain pull down momentarily through the 2-3 shift. I know that this will destroy the 3-4 clutches super quick. I am trying to understand what was causing this. I'm thinking about just doing the Transgo2-3 shift kit which completely reprograms the VB. I suppose that would solve any shifting issues.
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Old 07-24-2013, 07:01 AM
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A pressure test is a good idea to do. One thing that I haven't been able to find is a list of possible problems when doing a pressure test, such as if the pressure is low or high in any gear, what might be the possible problem. Have you thought about using thicker clutches & steels? The 4l60E forward sprag asy. & reaction carrier shaft & gear have more venting holes in them. One thing I did was drilled divots on top of the 3 & 4 backing plate to create more area for extra cooling. Also I cut 4 slots between the teeth on the reaction sun gear .050 deep to relive oil. These mods might not do anything but I don't think it'll hurt anything.
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Old 07-24-2013, 09:21 AM
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The smart tech housing increases 3-4 clutch capacity even beyond that of the 4L65E, which was the big dog of the 700R4 blood line. It does this by doing away with the snap ring and using a bolt on backing plate, along with a one piece pressure plate. I went with the 9 .062 frictions and .077 steels instead of the 8 frictions with thicker steels option. The .077 steels are thicker than the 9 friction and 8 thin steels sets that we see advertised. The bolt on backing plate eliminates flex in the backing plate that can aggravate warpage and uneven friction wear. We'll find out how well it works when I tear this bad boy down. As far as pressure test results go, I hope to see if there are any cross leaks that might point to a stuck valve train or check ball or failed gasket, or pressure loss in any particular gear that could point to a slipped lip seal or piston failure. I have not been real hard on this unit since my build last winter. The few times I have wound it up between 2 and 3 it shifted like dynamite and the fluid was still nice and fresh afterward. All of the damage seems to have come from cruising in OD.

I have the 29 element BW forward sprag. I do not have the latest style reaction shaft with torrington bearings. Ive seen this combined with the 5 pinion front planet and it looks pretty tough. My 4 pinion front planet looked to be in pretty good shape though. The trans had 22,000 miles from the last rebuild when I took 3rd gear out last summer. What did give me concern was the rear planet and sun gear. While the front planet/sun gear lash was minimal, the rear planet/sun gear lash was probably excessive. I plan on installing GM 5 pinion rear planet with this coming repair.
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Old 07-25-2013, 06:18 AM
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I have another 700r4 torn down an stored away. I drive a 2011 Chevy 2500 van, it my service truck at work,it has the 6 speed auto in it. I really like the 6 speed it makes the 4.8 engine seem larger that it is. I'm having second thoughts on the 700. I like it so much that I would spend the extra cash to put one in my Camaro.
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Old 07-26-2013, 06:24 PM
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I'm thinking now of maybe doing a little modification to the smart tech housing. It's a very pricey piece and I hate to risk screwing it up but I think it may be part of the problem. The OE housing has a snap ring at the backing plate end and fluid can seep out from the 3-4 clutches. The smart tech has a skookum bolt on backing plate that is a machine fit to the housing and leaves no place for fluid to seep out. I'm thinking of drilling small(1/8") holes, maybe 6 or 8 total, around the housing to allow for fluid movement through the 3-4 clutches. It's a thought at least. I think that anything to cool the 3-4 clutches will help.

I took great pains to insure solid quick shifts into 3rd and high apply pressure, all to prevent slipping and burning of the 3-4 clutches. I see now that I didn't do enough. I am far from finished though.
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Old 10-09-2013, 07:37 AM
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Just got my 3,500 stall Edge converter yesterday. I've put these Edge units in customers cars before but never spent the money one one for myself. Very nicely made part. I'm getting so excited and anxious to go on this redo. Just waiting now on the 3-4 clutch pack. My new best friend, Dana at ProBuilt Automatics, misunderstood me when I told him that my input housing(Sonnax Smart Tech) has 1.200" 3-4 clutch capacity(frictions and steels alone). He thought I must mean 1.200" including the apply plate, and sent me a thin stack that would have fit the stock housing. So now he's sending me a new stack with thicker steels and frictions to make up the 1.200" Any day now.

Then it's time to barter with the boss(my awesome sexy wife) for the amount of free time it's actually going to take to first, redo the trans build with the Transgo shift kit and other misc. upgrades, then install new custom hand bent cooler lines, then build my new custom TCC controls. I'm thinking atleast two weekends to really get it all perfect. Since I'm doing the job at the shop this time, it'll mean as much as 4 full days(weekend days) away from the house(time with the other woman). I've given her just a hint but not the whole story just yet. I think she'll be tired enough of dealing with my OCD preparing for the project that she'll be happy to give me all the time I need. I try not to let on that this thing is all I can think about anymore. Every waking minute that I'm not focused on diagnosing an engine control issue on a customer's car, I'm thinking about my beloved red IROC Z28(the other woman) and this transmission build.
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Old 10-21-2013, 09:03 AM
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Got my new 3-4 clutch stack from Dana at Probuilt. With the thicker frictions and steels, this thing looks beefy. It's an 8 friction stack and measures 1.205". I may have to swap one steel thicker or thinner to set clearance but the point is I'm ready now. With my OCD running full tilt at this point, I keep looking for other things to fix or change. That's what happens to me when these projects drag on. I just need to get it done before I spend more money. Looks like I'm clear now to get this thing done next weekend. Once it's done, I'll post how it went and my pressure test and drive test results before and after the repair.
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