OT GM 700R4 Tranny problem

How does it work?

Allan

Allan

The years are starting to get away from me a bit, but that 4L80 was an electronic tranny from the get-go and as I recall takes a separate controller to run it.

An '89 3/4 ton like your van should still be throttle cable controlled if it indeed has the 4L60.

Suppose it certainly could be done, but it would take someone far more adventurous than I to tackle that electrical/PCM/ECM/PROM/wiring swap.

However, that ’89 version of the 4L60 wasn’t all that bad and really, is a pretty darned good transmission. My money says build what you have.

Allan

Remember, we're talking long distance here: :>)

The first thing I would check is that TV cable. As I recall, on a 6.2 it runs up under the intake spider via a transfer rod on the left (driver's) side of the engine.

A. Make sure the black button is hooked to that rod in the back of the manifold and that the front of the rod is also hooked to the injector pump linkage.

B. Make sure the cable isn't pulled out and is returning back again normally at idle position. This cable works opposite the governor pressure in a see/saw manner to control the shift point.

Next, check that governor gear for apple-coreing like the other fella said.

Next pull the pan. You'll see one of three things. Black sootie oil/mud, a pan filled with chopped up iron particles, or just a simply clean, pink oil-filled pan.

If it is black mud, clutches are gone, iron in the pan means hardparts are kaput. If everything looks okay in there, change that filter and add 5 quarts of dextron.

If it still won't come up at that point, it is time for the shop and a pressure gauge. Sounds like a stuck Throttle valve.

Don't wanna scare ya, but the 83s thru the 86s were the worst of the bunch.

Allan

Can't imagine an '83 original still out there. 'Member how they used to puke out that front seal? :>)

Allan

If so, I'm bettin on a cable or filter. Pull your dipstick and see what color of oil we are dealin' with.

Allan

Disclaimer, I think the following is true, not positive.

The 700R4 is not a TH350 with an OD. The early 700R is a 27 spline (small) that could usually be broken without even trying 1982-85?. Then came the 30 spline (Large) 1986 or 87 introduced on the Hi-perf vehicles like the Vette, Trans AM GTA, Z-28 etc.

The 30 spline 700s were a great improvement.

After this came the 4L60 and 4L80. These are the TH350 and 400 with overdrive. 60s for cars and 80s for Light Duty trucks.

2002 or 2003 came the 4L60E and 4L80E with have the full electronic controlled shift, both have a TCM (transmission control module) that has to be swapped with them.

Now I think the 4L65E and 4L80E are the current designations.

To Allans note, I think they even made a TH375 for the 3/4 and 1 ton vans, around 1974. And TH425? cant remember what they put them in.

Again, all this is memory, not sure if it is all correct.

Rick

I didn't mean that GM simply took a 350 and slapped an extra gear in it. What I meant is - the 700R4 uses clutchs with same torque-rating as the 350 - the 700R4 was designed as an equivalent to the TH350 in power-handling capabilities but with and OD and lockup-converter. Same goes for the TH400 (a.k.a. 3L80) and subsequent 4L80E. In regard to the TH400 variants - The original TH400 used a varible-pitch torque-converter that was dropped after 1967. The TH375 used less clutch disks than the standard TH400 and a smaller OD output shaft. Also used a special extension housing so its total length was the same as a TH350. The TH475 was used in heavy trucks, motor homes, school busses etc. and used straight-cut gears in the planetaries instead of helical gears like the standard TH400. I suspect the max. torque ratings are - For the TH350 and 700R4 - 350 lb. ft. For the TH400 - 400 lb. ft. , the TH475 - 475 lb.ft.
I've never found any GM specs that show specific max. ratings for the automatics - but it is listed for all the manual transmssions. GM does state that the newer metric designation of "60", "65", "80", etc. designate the max. torque rating - but in what way, I do not know. Seems the metric "60" equals around 350 lb. ft.

Prior to the advent of the 350 and 400 hitting the bricks in 1968, those old cast iron Dyna-Flows used the "fluid-only" torque converter. That's why the noisey things roared so at launch.

GM started playing with the moveable pitch with both the cast iron Power-Glides and the cast Torque----- (name escapes me) in about 1950.

Every converter since has had a variable pitch stator inserted between the pump and the turbine and still do to this day. It is what gives them their "quick" response.

Allan

Just a bit "beefier" clutch to handle the extra weight.

Allan

So a 3L60 would be a high capacity 3 speer transaxle.

700 after 87 was a stout piece, before that the pump rings would blow.

If you have both direction and the engagement is good (i.e. reverse is not unusually soft or first unusually harsh), look at the TV cable (should have light drag when pulled at the pump with the endinge off and more when running) then I would go after the governer. Plastic gear failure is a known issue.

If governer looks good, try this. Run in D1 up to ~30MPH (no the 6.2 wont be happy) then let off the throttle and shift to D3. It should shift to 3rd. If so you've lost 2nd rear or the 1-2 shift valve is frozen in the valve body. EIther way it's off to the shop.

Numbers are just a strength or "beef" designation. Yep, 4L80 is an overdriven 400. As were the 180-degree 325s vs the 3254Ls (over driven) in those big heavy Eldorados, Riverias and Toronados. Took the power out of the back of the engine and turned around and pushed it forward into the punkin. Just different variations of the old 400 tranny.

GM should have gone with the Allison back in 1929. None of their corporate trannys could tow.

Bless their heart, however. They kept me in beans and sandals for many years. The rougher the country, the more money I made. :>)

Allan