4-3 Downshift issue on 700R4

[argo]

I have a '93 Suburban with a 6.2L diesel and a 700R4 transmission. I originally pulled the transmission from a diesel 1986 C2500 Suburban along with the 6.2. I installed a governor kit to make the transmission upshift sooner shortly after the conversion on my 93 was complete (it upshifted too late and it held the gears too long). After the governor was upgraded, I have had no trouble since until now. Recently I have had an unusual issue with the transmission "neutraling" out on the 4-3 downshift. If I force a downshift with the accelerator, it will rev like I am in neutral. If I let off the throttle it re-engages 4th. If I pull the shifter into drive from overdrive it will immediately drop to 3rd. If I slow down to the automatic 4-3 downshift point (about 35 mph) it will drop to 3rd without a hiccup. The problem is just on a throttle forced downshift, and the transmission doesn't do this all the time, but it seems to be an issue when the trans is warm where sometimes it will work normally, and other times it will act like an imbecile. All other functions are normal, and it upshifts fine. The fluid is cherry red, but I dropped the pan to service the filter anyway, just to be safe. The inside of the trans is clean and there was no evidence of significant wear in the pan. If I use manual drive (manual 3rd) it drives seamlessly. In overdrive it performs normally as well, except for the 4-3 downshift, which is sometimes a 4-neutral downshift. Any trans gurus out there with an idea of what might be wrong?

[dixiepc]

I wish that mine would downshift with my throttle, it never has.

[Robyn]

I suspect there is a sticking valve in the valve body.

These are aluminum bodies and the valves can get a rough spot in the valve bore due to debris circulating in the oil.

The only real fix is going to be to remove the valve body, totally disassemble it and locate the offending valve/bore

First I would drop the pan carefully and see whats in the bottom.

If you find a serious amount of metal crud, then herein lies the issue.

The 700R is picky about having clean oil.

Older boxes like the 400 are more forgiving of dirty oil than the 700R

Hope this helps

Missy

[argo]

I suspect there is a sticking valve in the valve body.

These are aluminum bodies and the valves can get a rough spot in the valve bore due to debris circulating in the oil.

The only real fix is going to be to remove the valve body, totally disassemble it and locate the offending valve/bore

Missy

Yeah, I think that is what I am looking at too. Ugh! I hate messing with automatics. This will probably give me the motivation to get off my ... butt and convert to a long tail TH-350 and 2.73:1 rear end already. I at least understand TH-350s and can rebuild them. I still hate doing it but I'd rather have a trans I can work on without $10,000 in special tools and that are fragile.

First I would drop the pan carefully and see whats in the bottom.

If you find a serious amount of metal crud, then herein lies the issue.

The 700R is picky about having clean oil.

Older boxes like the 400 are more forgiving of dirty oil than the 700R

Hope this helps

I have already been inside (I will of course check it again) and there was no muck in the pan. Just a very light film of material. Actually a lot less than you usually find on a 30K trans service. The fluid was still bright red too. I attribute that to the dual cooler setup I am running (trans fluid to the rad, then from the rad to an 18,000 GVWR auxiliary cooler) and that it nearly always stays locked up in 3rd and 4th gears.This is an aux valvebody 700, so I always have TCC power unless I am on the brake pedal. Thanks as always Missy, and have a Happy New Year!

[john8662]

I had one once that wouldn't a downshift at all once it got warm. Would upshift early and not downshift unless manually shifted to do so.

It was simply the TV cable adjustment. These TV cables need to be tight, you at least need to get one "click" on the self-adjuster when doing a base adjustment to get the right tension.

If you don't, you need to choke up the TV table end until you do.

J

[More Power]

This will probably give me the motivation to get off my ... butt and convert to a long tail TH-350 and 2.73:1 rear end already. I at least understand TH-350s and can rebuild them. I still hate doing it but I'd rather have a trans I can work on without $10,000 in special tools and that are fragile.

I don't think that's a good choice. The 700R4 has a lower 1st gear than the 350. With a higher 1st gear and 2.73 gearing it'll be much harder to get a load moving on a grade and even sometimes when not towing (or even on a grade). Had this happen to me once with a 6.2L diesel, TH350 and 3.42 gearing in the mountains while trying to do a 3-point turn on a spur road. I had to resort to using low-range 4WD on bare ground.

Installation of the 700R4 was the best thing I ever did with that 6.2L diesel pickup. So, I suggest doing what's necessary to get your 700 back to where it was.... Jim

[Robyn]

The 350 is a great tranny, buttttttttttttttttttttttttttttt, as mentioned is a bad choice for your app.

The
3.0 first gear in the 700 is a real plus for getting a load moving.

You don't need a butt load of special tools to do the VB

Get a tranny book that shows the VB break down and your set.

Working with the tranny in the rig, just be sure to take care to capture all the check balls and then get them back where they belong.

The only tools that are special are the seal installers and the spring compression tools, and you are not going to be anywhere near anything that needs these.

Keep your 700R and fix it.

Adjusting the TV cable is a must.

Slide the adjuster towards the firewall, then mash the throttle to the mat, done deal.

Missy

[More Power]

If I use manual drive (manual 3rd) it drives seamlessly. In overdrive it performs normally as well, except for the 4-3 downshift, which is sometimes a 4-neutral downshift.

So... drive in 3rd. With its lockup TC, it'll be just like a lockup 350, but with a lower 1st gear.

[argo]

I am using it that way for now to prevent any damage. However, it's not much fun with 3.73 gears. Also, even if I re-gear the rear end to make overdrive no longer needed, I don't want to push my luck with a half broken transmission that is weak to begin with, even if it is healthy. I am willing to sacrifice a few MPG to have a bullet proof and reliable drivetrain. I'd rather get 24-25 MPG highway with a 2.73 gearset and a TH-350 with a tight converter, or 25-26 MPG with a 2.73 gearset and a TH-350C. I am getting 27-28 now with a 700R4 and 3.73 gears, which works out to a 2.61 final drive. This is for a highway trip in the 55-65 MPH range. I know that a 2.73 ratio will be a bit higher RPM than a 3.73 with overdrive, but I can't see it hurting my mileage that much. Besides, my last trip to my parents house and back (220 miles round trip) using 3rd with 3.73 gears got me 23 MPG. If I can get the revs down with axle gears as opposed to transmission gearing, what is the difference? The key is lower revs (to a point) equals better highway fuel economy.

As for the lower 700R4 1st gear, it doesn't mean much to me because my Suburban pulls well from 5 MPH in 2nd gear so I know that a TH-350 1st gear and 2.73:1 rear end ratio will be OK around town. (3.73 gears with the 700's 1.63:1 2nd gear equals an 6.08:1 overall ratio, whereas a TH-350 and 2.73 gears has a 1st gear overall ratio of 6.88:1) Before anyone gets confused as to why I am comparing the 700's second gear to the 350's first gear please understand that I am comparing them because of their similar ratios and the fact that my 1st gear is up and out very fast, and even at 4-5 MPH rolling my Suburban will be in 2nd gear, and it pulls very strong. I can't get it to stay in 2nd from a dead stop to compare, so 5mph rolling is the best I can do for comparison purposes. Also, I do not tow anything heavier than a 400 lb troybilt log splitter that I share with my brother in law with this Suburban. It is a giant family station wagon. Heavy hauling is reserved for the F-150.

Lastly, I have always been haunted in the back of my mind by the lingering fear of a catastrophic failure while on a long trip with my family because I have not ever liked or trusted this transmission. It has always spooked me. It has always felt flimsy, and I have never driven a 700R4 equipped truck/SUV that hasn't given me that impression. I just trust a TH-350 more. It is a transmission that I actually know and understand, and I can fix myself. That is the other important thing. I do not have a ton of money to sink into a transmission and have it fail again, and I know that a stock Th-350 is stronger than a stock 700 R4, even a mildly built one.

I am not trying to be confrontational about it, I just never liked this unit and I don't trust it. I know many people love it (or at least like it) and have faith in it. That is fine for them, and I don't feel the need to convince them that they are wrong. Also I want to apologize for my last post. I was in a foul and grumpy mood then I posted it, and I feel that I came across as rude and snippy.

[argo]

I have given considerable thought to the situation and I have decided to do the following. I will wait until income tax return time and then I will get a stand alone transmission controller for the 4L60E and put a fresh 4L60E that I have access to into the Sub instead of dealing with the 700. This will allow me to custom program my shift points where I want them, and all I have to do is add on a TPS to the I.P. The controller I am interested in uses the input shaft speed sensor for engine speed reference so I don't even need to put a tach signal generator in the engine. The 4L60E I have access to came from my in-law's 1997 Suburban. It was rebuilt 8,000 miles ago with a 5 pinion planetary, a stronger sun shell and it has a fresh converter with the heavy duty lockup clutch. I think that this will be a good compromise between strength, simplicity (for me because I don't have to rebuild it) and cost. It is nearly new, and the unit made 190,000 miles the first time, without any upgrades. It did so while towing an 8500 lb camper 2x a year, so I (hopefully) will never have issues with it given the relatively light duty it will have in my application. I also intend to use the 3.42:1 axle in the 97 suburban to reduce my cruise RPM a bit. Despite the fact that my 700 likes to kickdown whenever you feather the throttle, this engine really does seem to want lower revs at 65-70 MPH.

Once again, I apologize for my snippy and grumpy outlook earlier. I have not been quite myself lately... I have some other things (not car related) going on that are stressing me out.

[dixiepc]

If you feel like the 700R4 is flimsy, your not helping yourself out with a 4L60E. It's pretty much the same transmission, just with electronic shift.

[Edahall]

If you feel like the 700R4 is flimsy, your not helping yourself out with a 4L60E. It's pretty much the same transmission, just with electronic shift.

His 700R4 is the 1986 version that was known to be pretty weak especially behind a diesel engine. I had one of these and it was nothing but trouble. In around 1987, there were some changes made to the 700R4 that made them a lot more robust.

That said, I've not had any issues once I installed the newer and improved 700R4 into my 1982 6.2L Suburban. It has also been used for some pretty heavy duty towing. However, I'll take the NV5600 6-speed manual in my 1990 Suburban over any automatic transmission.

[JAW14]

Hey first time poster on here.

Real fast just to address the 4-3 downshift issue. I just rebuilt a 700r4 last week and during teardown the 3-4 clutch was cooked and the overrun piston had a blown outer lip seal. Fixed all that restacked the internals and moved to the valvebody. Now just to make sure you know the valve body in all 700R4s (4L60) are cast iron. Notice 4L60. Not 4L60E. The 4L60e replaced the 700. Same internals apart from an aluminum electronically controlled valve body. The 700 used a Throttle valve in order to modulate line psi. It worked with throttle position/ and governor psi to dictate shift points and psi going to clutch or band. Now referring to the downshifting issue you were talking about i had a major stuck 4-3 control valve in the VB I was working on. I was able to remove it and clean the bore but that would cause similar issues. I would if it were mine and I had all of the energy remove the transmission take VB out and pull input drum out and LOOK at the clutch pack and closely examine valve body AND separator plate. Also check the 2-4 servo in the passenger side of the case. Big piston is 2nd gear big spring inside that piston is 3rd accumulator and the top piston is 4th gear.

Good luck!