'93 4T60E - Same trans, diff prob - Slips in low/reverse now - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 03-26-2007, 12:04 PM   #1
mjw
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Default '93 4T60E - Same trans, diff prob - Slips in low/reverse now

Greetings all,

I finished rebuilding the 4T60E mentioned in an earlier post. Now I have a different problem with this thing. After the rebuild, it slips in low and reverse, unless I disconnect the vacuum modulator line. (valve is not sticking/modulator is new). Up and downshifts are fine, TCC lockup is fine, and it'* not making any noises. There is no slip or shudder in 2nd, 3rd, or 4th and no trouble codes are set (not even an 1870, which is odd).

I was extremely cautious during reassembly, and am positive that I don't have any cut lip seals, damaged clutch pistons, excessive clearances, etc. All seals, sealing rings, clutch pistons, steels & frictions were replaced, as were the vanes in the pump (which was fine, by the way). Everything is torqued, and I air-tested everything during re-assembly and all clutch-packs and servos applied and released properly. Also replaced the TC (and pre-filled it before reinstallation) and flushed the cooler.

As a sanity-check, I took hundreds of 'before-and-after" photos to be able to refer to, just in case something like this happenned. I went though all of them to ensure that I didn't miss something or install something improperly. Everything looks as it should. The correct valve body, spacer plate, and channel-plate gaskets are there, all check-balls are present and accounted for in the proper locations. Made sure I didn't mix early and late parts, etc.

I also completely disassembled, cleaned and lubed the valve body and ensured that all valves moved freely when I finished. Also tested all the solenoids. About 20K miles earlier, I had the valve-body out to replace the 1-2 & 3-4 shift valves, and to install a TCC regulator & isolator kit, TCC clutch-apply kit & modulated line boost valve kit. I never had any valve-body problems after that, but I disassembled everything again because this trans had just ground up a lot of hard parts and I didn't want to chance having any stray metal fragments causing sticky valves.

I'm trying to find somewhere local to purchase a 400psi guage so I can take some readings and not guess at what might be causing this, but in the mean time, I'm trying to gather some information and would appreciate anyone'* feedback that may have had similar problems with a 4T60E, or at least just know a lot more about them than I do. I'm trying to understand what'* in common between low and reverse in this particular transaxle, and at the moment, the only thing I can think of is the reverse boost valve. As I understand it, the reverse-boost valve is responsible for boosting line pressure when in low or reverse. It seems possible to me, that if it sticks, it could be causing slipping in low & reverse. I'm guessing that when I pull the vacuum hose off of the modulator, line pressure increases, and that'* why the slipping stops. Almost like simulating the effect of the reverse-boost valve.

What do you folks think? I know it'* hard to tell without knowing what the actual line pressure is, and that'* why I'm hunting for a guage. But until I find one, I'd really appreciate your feedback as respect your expertise. I'd much rather pull the valve-body than the whole tranny again to fix it. Thanks in advance!

--mike
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Old 03-26-2007, 12:12 PM   #2
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If it doesn't slip with the modulator unplugged, you have low line pressure. Failing pump. An adjustable modulator would be a temporary bandaid at this point. You need to replace the pump (in my opinion).
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Old 03-26-2007, 12:44 PM   #3
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Quote:
Originally Posted by willwren
If it doesn't slip with the modulator unplugged, you have low line pressure. Failing pump. An adjustable modulator would be a temporary bandaid at this point. You need to replace the pump (in my opinion).
Hi,

Actually, I do have an adjustable modulator. I turned the screw almost all the way in (which, pretty much disables it anyway) and reconnected the hose. You're right - same result/workaround. As for the pump, it looked great when I had it out. No scoring, no excessive clearance anywhere and I replaced the vanes, o-rings, slide, etc. - That'* why I'm guessing stuck valve somewhere. Geeze, I really need to find a high-pressure guage.... lol

Of course, if it is the pump, at least I won't have to to pull the valve body to get at it. Probably should anyway though if I have to have it that far apart.
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