The Great Smaug

[diesel4me]

You'd have heard siren type noises if the filter plugs up enough to cause slippage..
Your symptoms sound like what I have read in dozens of other 700R4 "death posts" here and elsewhere on the web...they just suck in my opinion..seems like even if you spend a lot to get one souped up or replacing parts known to be weak like the sun shell,doesn't help much sometimes..I don't like the fact the TV cable can mess up and fry one in a few miles...

The 700R4 in my '85 Burb supposedly does the same thing you described ,plus reverse refuses to engage when its been driven 15+ miles,so said the previous owner..but he said they never serviced it ,only after it started acting up did he drop the pan--saw charcoal black fluid that stunk,and he just used a few cans of brake cleaner to spray everything clean again,added a few quarts of fluid and one quart of Lucas,and sold it shortly afterwards to me..
It has always gone in reverse when I go to move it around my yard though,I never have taken it on the road for a "long drive" yet...hate to get far from home and have it not want to move..

You might want to check the govenor and see if the gear is stripped out,or the valve in it might be dirty--usually an automatic wont come out of first gear when the govenor gear fails,but I suppose it might still be trying to spin and it "could" make it act weird..also make sure the TV cable is adjusted and working right..(probably the damage is done already if that proves to be at fault)..

I dont like engines screaming at 3000+ on the highway either,but I still prefer the old 3 speed automatics over the 700R4...everyone defends them saying once they are "built up" they hold up well,but I seem to hear more saying they suck as far as durability...the low first gear and overdrive are nice though--if it holds together..with a TH350 or TH400 you can live with the lack of overdrive by running taller gears..or larger tires..

 

[82355]

What gears and tire size do you have? Were you towing in overdrive?

Martin

 

[campfire]

I dont like engines screaming at 3000+ on the highway either,but I still prefer the old 3 speed automatics over the 700R4...everyone defends them saying once they are "built up" they hold up well,but I seem to hear more saying they suck as far as durability...the low first gear and overdrive are nice though--if it holds together..with a TH350 or TH400 you can live with the lack of overdrive by running taller gears..or larger tires..

I might sound like Martin here, but you can't ever get 5 speeds out of a TH400. And the slushboxes just aren't nearly as handy or durable as a good stick shift. I'd take a good stick over any of them in a heartbeat.


The interesting thing here is that I have all the parts for an NV4500 swap. I hauled up the Blazer planning to put it in that (TH400 isn't shifting, either). I'm not against stick-shift-swapping it, but I wasn't planning to do two at once!

 

[campfire]

What gears and tire size do you have? Were you towing in overdrive?

Martin

This rig has 3.73:1 gears with 31" tires. May wind up going to 32" or 33" eventually, but I don't want to get very large. I would like higher gears, because this is intended to be a road-tripping expedition rig. Drive to Colorado and back. Mild trail riding. No beating on the truck. The NV3500 and NV4500 have 0.73:1 O/D ratios vs. the 0.70:1 that's in there now. So I would be spinning even faster if I did the swap.


On this trip, with trailer behind me, and my one glasspack mysteriously quieting down after hitting that water wall, I found the gearing/engine noise to be alright. I could live with that. Last summer I just wanted to rip it all apart and find some 3.42 gears.

The strange part about this story is that I was finally warming up to the truck after a year of mixed feelings. And that's when it decides to break.

 

[campfire]

What gears and tire size do you have? Were you towing in overdrive?

Martin

Yes, I was towing in O/D. Is there some limitation inside the transmission that makes this a bad idea? Or is it just the constant downshifting that causes problems?

Although this transmission is of completely unknown history, and I was nervous about towing with it, I did not think this trip would be excessively hard on it. Downshifting was relatively rare (though it did happen). I drove it gently (as I typically do to all of my vehicles). What more could it want?

And right when I got to the flat part of the state, where it could have stayed in O/D for the last 4 hours, that's when it conked out.

 

[streetrodchev]

My 700r4 memory is a little rusty, but I don't think they like towing in over drive.

 

[campfire]

My 700r4 memory is a little rusty, but I don't think they like towing in over drive.

My question is whether there's something wrong with towing in 4th gear, or if it's the 4-->3-->4-->3 shifting pattern that causes the tranny to quickly exceed its shifting life expectations.

Since this truck does not often downshift, even with trailer, I was thinking it would not be excessive strain. It's looking like I was wrong.

 

[campfire]

Still don't have any input on what forms of breakage can cause these symptoms...

 

[streetrodchev]

Again memory is rusty on these, but they try to be most efficient when in od and don't flow fluid to the cooler and can over heat when towing in od.

 

[campfire]

Again memory is rusty on these, but they try to be most efficient when in od and don't flow fluid to the cooler and can over heat when towing in od.

That's what I was afraid of.

Would there be any indications of overheating? I don't have discoloration in the fluid. And it seems to be engaging the first 3 gears fine, aside from being slow (hesitant?) on the shifts. Big Blue was terminally stranded within just a few miles. This one didn't do that.

 

[diesel4me]

I wouldn't mind having a manual transmission,I actually prefer them for the same reasons Campfire listed...but GM doesn't seem to have a really "good" one out there either--the SM 465 is OK if you can live with the wide gaps between gears,and the granny low is great,other than not being syncro--the newer 5 speeds aren't perfect either really..they might offer better ratios ,but they seem rather weak if used for towing or hauling heavy loads..

I'm not so sure any manufacturer has a "perfect" manual transmission ,really..they all suck in one way or another..

That said,if it wasn't such a beotch to install a clutch pedal and you didn't have to change everything behind the crankshaft to the rear driveshaft to convert to a manual,I'd have probably converted all my trucks over..

I too do not like the fact an automatic can work great one minute,and refuse to propel the vehicle the next either,all because of a hundred "stupid" things--like a rusted out cooler line letting it go dry,or a rubber seal inside deciding to melt.etc..usually at the worst possible moment ..

My '85 Burb has 3:73's too...I've had 2 other vehicles with those gears and 3 speeds,they aren't that bad,at least you can do 65 without it screaming...I had other trucks with 4:10'a and 4:56's with 31" tires and they wound out at 3500 rpms at 65,that was a bit much!..felt like you were still in second gear..

 

[streetrodchev]

I know atf is sensitive to high temps. It doesn't always change color if it gets hot.

 

[diesel4me]

I recently read about many racers and off roaders now using tractor transmission/hydraulic fluid instead of Dextron in older GM transmissions..they claim it stands up to heat better,has slightly higher viscosity,so the converter feels "tighter" and the stall speed lowers a bit...several users have used it for years and thousands of miles with no issues,so they claim..

Maybe Greg Ducato can chime in on this subject...

I found it quite interesting--and the fact you can use that fluid in many things like power steering ,transfer cases,etc,is tempting,because bought in bulk 5 gallon pails ,its actually cheaper too...

 

[mrk5]

I'm not much help on the diagnosis but if you don't already I would HIGHLY recommend running a big stacked plate trans cooler. Also get a trans temp gauge. I know you said the fluid was nice and red but I'd still wonder if something got overheated.

 

[82355]

and you didn't have to change everything behind the crankshaft to the rear driveshaft to convert to a manual,

You don't. To swap an SM465/NP208 in place of a TH700R4/NP208, you just swap one for the other. Same crossmember, same driveshafts.

Martin

 

[campfire]

You don't. To swap an SM465/NP208 in place of a TH700R4/NP208, you just swap one for the other. Same crossmember, same driveshafts.

Martin

I've read that the NV4500 is also the same length as the SM465. Hoping that is correct, as at least 1 tranny swap is in my near future...

 

[campfire]

I'm not much help on the diagnosis but if you don't already I would HIGHLY recommend running a big stacked plate trans cooler. Also get a trans temp gauge. I know you said the fluid was nice and red but I'd still wonder if something got overheated.

The problem here is that I don't like automatics. I don't want to invest my time upgrading and adding gauges and still be stuck with 2 pedals. If I'm gonna put in very much time, it's getting a stick.

That being said, the professionally-rebuilt 700R4 in Big Blue drives well enough. I'd still prefer an NV3500, but I can live with it as it sits. I was told that he threw a bunch of sturdier parts in it, too, but I didn't know enough about automatics to ask good questions. I probably still don't.

 

[campfire]

I recently read about many racers and off roaders now using tractor transmission/hydraulic fluid instead of Dextron in older GM transmissions..they claim it stands up to heat better,has slightly higher viscosity,so the converter feels "tighter" and the stall speed lowers a bit...several users have used it for years and thousands of miles with no issues,so they claim..

Maybe Greg Ducato can chime in on this subject...

I found it quite interesting--and the fact you can use that fluid in many things like power steering ,transfer cases,etc,is tempting,because bought in bulk 5 gallon pails ,its actually cheaper too...

I've been tempted to do this several times. Never heard how well it worked out...

 

[campfire]

My '85 Burb has 3:73's too...I've had 2 other vehicles with those gears and 3 speeds,they aren't that bad,at least you can do 65 without it screaming...I had other trucks with 4:10'a and 4:56's with 31" tires and they wound out at 3500 rpms at 65,that was a bit much!..felt like you were still in second gear..

3500RPM...with a SBC or with a 6.2 engine? I know there are 6.2 trucks with 4.56:1 gears, but (as I said before), I think that's crazy fast to spin the 6.2 engine. It does not like it.

Was out in Big Blue again yesterday. 1625RPM @ 65MPH = quiet cruiser. It's really nice. If the T/C was locked up, I calculate that the Suburban would be at 1840RPM. Nice power point (noticeable difference between the trucks, power-wise).

3rd in that truck should be a mere 2600RPM. Should be happier than the M1008s out there. But I still think the engine is less happy up there. And this particular truck, with its half-glass-pack exhaust and no headliner, got painfully loud in 3rd. Would have to address that if I planned to spend much time at that engine speed.

 

[campfire]

Drove to town and back today (10 or 12 miles total). The transmission seemed to lock into each gear properly, it just was slow on the shifting. 1st-->2nd took extra time, and 2nd-->3rd floated in neutral for 1/2 a second before finding third. 3rd-->4th shifted normally and stayed locked in normally on my trip into town (55MPH on this section of rural highway).

Coming back from town, it would shift to 4th normally, but immediately downshift if I hit the throttle. Then go back to 4th as soon as I let up.

I don't have a tranny temp gauge, but I expect the tranny was warmer on the return trip, when it was acting up.


Any ideas? Aside from shifting weirdly, the truck is still functional, and still goes from point A to point B. I think the clutches are engaging fully (would surely have found that out after 200 miles, right?).

I've driven several transmissions that were stranger than this one. But I'm still bothered. These symptoms did not occur before this last trip.

Any ideas out there?