700R4 downshifting woes

[bmiszuk]

Okay, I've got the IP replaced (finally) and the Suburban is running again. Now I've got a transmission question. When cruising in D (and locked up) on the highway and climbing a hill, when it tries to downshift the transmission often 'misses' 3rd gear and the engine simply revs. Usually tons of black smoke when this occurs on the highway :-) If I back off the throttle it'll go back into 4th just fine. If I manually shift to 3rd while driving, that works fine. Within the past few months I changed the tranny fluid/filter and TV cable.

Is this the beginning of the end for the transmission, or could there be a fix for it short of a full rebuild?

[john8662]

Bob,

TV could still be out of adjustment.

My little 82 pickup will shift from 4th to 2nd gear at 65mph, kinda cool sounding, and well not too good either, but it'll turn 4300RPM's anyways.

For a test, go get up to the same speed but don't have the transmission in OD, keep it pulled down to D, try the same thing, punch it to the floor and see what's happening. If it won't do anything but stay in 3rd, then you know there is something amiss with the internals because the transmission is actually missing a gear when attempting to shift down.

My first impression with your statement is that it could possibly just be going back down to 2nd.

[GregCrabb]

Hey, My 86 does the exact same thing. I didn't know why, but it's always done it since I have owned it, even after the trans rebuild. I've adjusted the TV cable as per instructions found on here, but it still does it. As long as it goes, I don't really care. I don't tow anything or haul anything heavy. It's just my homeowner's truck.

[john8662]

I had a tranny once that had the wrong governor installed after rebuild that did all sorts of funny things. One of the things I didn't like was if I punched it from a stop it wouldn't shift into 2nd until I let off the accelerator a bit. The 6.2 simply couldn't rev high enough to satisfy the transmission. It had a gasser governor in it...

[bmiszuk]

Did a little more experimenting today. Here's a few facts:

1. It does it more right after I start driving. After a few miles it doesn't occur so often. Sometimes it downshifts fine.
2. From D, if I stomp on it and the engine revs up, flipping the shifter to 3rd immediately puts the tranny in 3rd.
3. While the engine is rev'd up, it feels like it's disconnected from the drivetrain. The rpm's run up against the governer and kind of bounce around there until I ease off the pedal and it'll go back to top gear.

Greg, did you ever ask whoever rebuilt your tranny about why it occurs? I'm curious if they had an explanation for it.

Bob

[GregCrabb]

Sorry it took so long for me to answer, worked 5 nights last week at the hospital.
No, I never asked them about it. I just found ways to work around it. I notice mine when climbing a large hill near me (almost a mountain) and it downshifts. If I manually downshift it to 3rd before taking the hill, I can climb it with cruise on and no more shifting. If I let it do it on its own, it "hunts". I'm used to it...just wondered if anyone elses' did it too.

[hoot_223]

i used lucas trasnsmission additive and had great results with my 700r4

[Robyn]

I am thinking that you have one of the sprag units thats not holding and when the tranny tries to shift the sprag lets go and results in the spinup.
The 700 R4 can be a cantacerous little beastie to get to work correctly.
There is enough tech papers on these trannies over the years they were made to fill a shelf 20 feet long. (Ask any good tranny techie)
To properly fix a 700R requires several after market parts and some reeeeeal loving care. I have spent some time on a few that tranny shops had rebuilt and that had failed repeatedly. A 350 can be resealed and clutched and work fairly reliably as can a 400 both of these should have shift kits but can work fairly well stock. Not so with the 700 the TV system is a POS and needs the mods that come with the shift kit. The input shaft and drum assembly are also a weak spot and need to be replaced with the after market unit. These are the large shaft type with a hardened steel ring pressed over the shoulder area above where the input shaft is pressed into the splines. The shell is also weak and breaks at the splined hub. Both the one way clutch in the rear and the front are weak and need the larger units. I have tried several shift kits and I have found that The transgo dash1 dash2 kit is the premium. I am not stumping their products here but this is what I have used and whats in my 700R K case right now.
More tranny shops have lost more money trying to fix 700's than I want to think about.
The issues being discussed here on the 700 are in my opinion not something you can rectify externally.
If you want to have your 700 work right get the large box transgo kit and yank your tranny out. Get a good tech book on the beastie and tear into it.
We all had to learn the first time. The 700 looks like a formidable task but it is simple if you take your time and lay everything out as you go and pay attention to what you are doing.
Their are a few other good publications on line that can guid you through the process of what is needed to really make a good box of a 700R
If yours is toast, look around or watch ebay and get a late 700 "K case" and rebuild it.
Remember its not just about cleaning and resealing and new clutches.
It about replacing poorly designed hard parts that fail.
1-input drum (large shaft with reenforcing ring)
2-heavy duty sun shell
3- Both front and rear sprag units
4- additional clutches in the 3-4
5- heavy duty servo pistons for better band apply
6- shift kit
There are other things to do if you want to build this thing set on kill but this is a great place to start.
The 6.2 is a great engine and needs a great tranny. The 400 is ok but with the taller gears that came with the rigs they were installed in the low gear is too tall and the splits are not quite right. The 3/4 ton subs had 4.10's and a 400 and were fine. The 700 in top form is a wonderful box and will serve you well but you must pay attention to details carefully to get them to perform right. The final piece is setting the tv cable properly.
Install cable and shove the ratchet all the way back to the fire wall and then romp the throttle to the floor. The rachet should pull forward and set itself correctly. The kit explains exactly how to do it.
Once its done and you are ready for a test drive. Go for a very light throttle upshift from 1 into 2 and then mash it hard, the tranny should drop back to 1st gear right now. If it dont you need more Throttle pressure. Poor setting of the TV will result in a 700 going south ABSOLUTELY.
I hope this helps.
I will be happy to coach anyone who wishes to try their hand at a 700R.
It's really not all that hard to do.
After all I did it and mine works and I am not endowed with god like powers.
The tranny repair industry does two things, they try to keep these things as mysterious as possible and wont tell you really what they did to fix it.
Some shops dont have a clue as to what they did other than clean and reseal and reclutch and hope you get far enough away before it quits that you cant find your way back.
Other shops know whats going on but most folks cant afford them as good work comes at a substantial price.
OH BTW just remembered the front pump needs to be replaced with a 13 vane unit. This provides more oil and less noise

Zillions of smiles and millions of miles
Robyn

[Robyn]

I tend to get verbose when I let go on one of the tech problems.
In effect the tranny goes into freewheel when the sprag lets go, The clutches are locked fine but the sprag is holding other components that must be held to allow the particular gear ratio function. (I am not going to explain all the teeny weeny tech here as to what each part is doing) The result though is what you see happening. When you use manual 3rd the sprag is rendered ineffective and all works fine. The sprage works for auto shifts and the manual 3rd give engine braking that you dont have when in OD position.
The rear sprag (One way clutch) I believe in this box is for 1st gear. Manual low applies a clutch for engine braking though.
Look at a good cutaway of the 700 and you will see the sprag up front toward the rear of the input drum. This is the unit thats causing your issue with the cutloose from 4-3

[Robyn]

bmiszuk
This is most likely not the end for your tranny. The 4-3 cutloose as its called in the trade is common. Smell the tranny fluid if its sweet and red and not foul or burnt smelling your fine.
The only real good fix is as I mentioned above.
You can run it manually and get by but there is no magic tricks here.

[ZZ]

Thanks Robyn, I just learned more about the 700R4 from your informative posts than I have from anywhere else. I don't know if it was or someone else who said it best, "some techs & shops who are good at working on the gasser 700R4 have all kids of problems with the diesels" I know I had to order my own new diesel governor for my last rebuild. The shop claimed not to know where to get one.

[Robyn]

functionality on the 700 is the same no matter diesel or gas. The weak spots are the same. The calibration is slightly different to mate the tranny to the torque curve and RPM of the diesel.
All rules apply though as far as rebuild with again slightly different calibration.
Glad to help
Robyn

[bmiszuk]

Thanks Robyn, your answer was not too verbose, in fact very helpful. Since you mentioned it, I'm going to take you up on your offer for more information and help. I'll try to keep most of it out here on the forum so others will benefit also.


Their are a few other good publications on line.
Where? I've found the video from Technical Video http://www.technicalvideos.com/) and the ATSG books available online. I've searched forums here, there and everywhere and assembled a bunch of info about the 700 but it seems everyone has their own opinion... from "this is impossible" to "piece of cake, go for it". What online (or offline) publications do you recommend?


If yours is toast, look around or watch ebay and get a late 700 "K case" and rebuild it.
My fluid looks fine. It's the original '83 tranny that was rebuilt in the mid 90's sometime (before I bought it). You think I can successfully fix this one or is the later case a must?


If you want to have your 700 work right get the large box transgo kit...
Is this the one you're talking about? http://store.summitracing.com/partdetail.asp?autofilter=1&part=TRG%2D700&N=700+400214+115&autoview=sku


Remember its not just about cleaning and resealing and new clutches. It about replacing poorly designed hard parts that fail.
Where do you buy your parts? Do they sell online or mail order?


good work comes at a substantial price
Okay, how much? I do not do serious towing. This is a daily driver that only occasionally tows 2-3,000lbs for short distances.

I'll go a step further. This is a tired 6.2 with blowby. Holding highway speed on hills is a problem without downshifting (which is difficult right now! :-) ). If I can just open the case and fix a $20 widget to fix this problem and keep the tranny alive for a few years, I'll do that. If it's stupid to open it and not replace everything else, then I'll do that. Money IS an object (when isn't it?) but I realize there's a smart way to spend it. I don't want to be penny-wise and pound-foolish but I don't need a $2000 tranny that'll be used to tow 7,000lbs through the Rocky Mountains.

Given these circumstances, what would you do?

Sorry for the verbose answer, but I think the info will be good for many of us! Thanks for your info.

[Robyn]

If your tranny is the original 83 version it will most likely have the small input shaft and other inferior parts.
watch ebay for a "K" case 4x4 700 tranny that is buildable and start gathering parts thenit dont hurt so bad.
As far as the power loss on the hills unless the poor little creature is totally wasted more than likely a pump and nozzles will put the zip back in the little beast.
I have seen late model 6.2's that were so sick they would hardly get the rig away from the curb.
Pump and squirts and off to the races.
Chat more later
Robyn