700R4 Information Thread

[Itali83]

Buy the Superior Tech governor kit. Should have what you need to adapt your gov for diesel

Just looked that up. That should work. Thank you. Also, do you have a good source for a stock lockup converter to put behind my 6.2 diesel? Thank you. There are few local shops here all with questionable knowledge about older stuff. Thank you

Ben

 

[NickTransmissions]

Just looked that up. That should work. Thank you. Also, do you have a good source for a stock lockup converter to put behind my 6.2 diesel? Thank you. There are few local shops here all with questionable knowledge about older stuff. Thank you

Ben

You're welcome.

Search your area for a converter builder. He will be able to build you exactly what you want...

 

[HotRodPC]

This would be great. I've got mine adjusted pretty good but still not 100% happy with it. I set it up match several articles that said what RPM/Speed it should shift at when at partial throttle but I can't get it to downshift right when I go to full throttle. It's usually not a problem since it's just a cruiser but I sure don't want to kill a good transmission.

Governor is the primary difference. The valve bodies themselves are the same between gas and diesel applications...200-4Rs by contrast, use different governors, valve bodies and 1-2 accumulator housings (in case anyone was wondering, lol).

I'll add a tidbit, the torque converters are also different between gas and diesel. Mainly the stall speed.

 

[NickTransmissions]

I'll add a tidbit, the torque converters are also different between gas and diesel. Mainly the stall speed.

Yep, true. Think they have a 200-300 rpm difference compared to the SBC V8 gas TCs

 

[SirRobyn0]

@NickTransmissions I've got a 700R4 question for you. If it matters the truck in question is a 1984 C20 305 - 700R4 - 3.41 rear end, that one day I'll change to a 4.10 or 4.56. Transmission was rebuilt around 20K ago, it is an original 1984 unit it got the standard heavy duty rebuild, I can get you the list of exactly what was done if it makes a difference, but he knew I tow with it. So today is a perfect example I did job hauling old freezer doors. Trailer weight with the doors was 5K - 5,500lbs. Needed to drive some roads where I'd be at about 45ish, hills and curves so it's not a steady speed. If left in drive it's pretty low RPM under the power band of the engine, so the converter will lock, but it unlocks a fair bit and there is some up and down shifting. But if I run it in 2nd that's about 3K which is great. No shifting and good power in that RPM range. Trans temp stayed right at 150F for the 10 or so miles I was on that road. So my question is, is it harmful to run a 700R4 in second gear for an extended time like that. I'm I over straining second gear somehow, or is it fine to do that?

Thanks,
SRO

 

[NickTransmissions]

@NickTransmissions I've got a 700R4 question for you. If it matters the truck in question is a 1984 C20 305 - 700R4 - 3.41 rear end, that one day I'll change to a 4.10 or 4.56. Transmission was rebuilt around 20K ago, it is an original 1984 unit it got the standard heavy duty rebuild, I can get you the list of exactly what was done if it makes a difference, but he knew I tow with it. So today is a perfect example I did job hauling old freezer doors. Trailer weight with the doors was 5K - 5,500lbs. Needed to drive some roads where I'd be at about 45ish, hills and curves so it's not a steady speed. If left in drive it's pretty low RPM under the power band of the engine, so the converter will lock, but it unlocks a fair bit and there is some up and down shifting. But if I run it in 2nd that's about 3K which is great. No shifting and good power in that RPM range. Trans temp stayed right at 150F for the 10 or so miles I was on that road. So my question is, is it harmful to run a 700R4 in second gear for an extended time like that. I'm I over straining second gear somehow, or is it fine to do that?

Thanks,
SRO

It shouldn't hurt the transmission but wouldn't go too far beyond that as you'll start to feel as though you're in neutral, if so.

 

[SirRobyn0]

It shouldn't hurt the transmission but wouldn't go too far beyond that as you'll start to feel as though you're in neutral, if so.

Thank you. But could you elaborate on the "feel as though you're in neutral" thing. Thanks.

 

[NickTransmissions]

Thank you. But could you elaborate on the "feel as though you're in neutral" thing. Thanks.

You're welcome and sure...Have you ever been in a 700R4 or 4L60E where the 3-4 clutch has burnt up?

If so, when the transmission shifts from 2nd gear to 3rd gear, it will feel like it's in neutral...But it's not actually in neutral - it's simply back in first gear...In third gear on these units, the forward and 3-4 clutch pack is applied..By time you're shifting from 2nd to 3rd, your vehicle speed is at least 20-25 mph, so when mechanically back-shifting to first gear at those speeds with only the forward clutch applied, it will feel like you're in neutral.

The same principle applies to being in 2nd gear at excessive speeds/RPMs but it doesn't start to feel like neutral until you reach higher vehicle speeds/RPMs because 2nd gear is a lot taller than first (1.49 vs 3.06) so you'd have to be traveling proportionately faster. Which, at the speeds you're travelling while towing, aren't at that threshold but you don't want to push too far beyond what you're currently doing in terms of keeping it in second gear.

 

[bucket]

@NickTransmissions I've got a 700R4 question for you. If it matters the truck in question is a 1984 C20 305 - 700R4 - 3.41 rear end, that one day I'll change to a 4.10 or 4.56. Transmission was rebuilt around 20K ago, it is an original 1984 unit it got the standard heavy duty rebuild, I can get you the list of exactly what was done if it makes a difference, but he knew I tow with it. So today is a perfect example I did job hauling old freezer doors. Trailer weight with the doors was 5K - 5,500lbs. Needed to drive some roads where I'd be at about 45ish, hills and curves so it's not a steady speed. If left in drive it's pretty low RPM under the power band of the engine, so the converter will lock, but it unlocks a fair bit and there is some up and down shifting. But if I run it in 2nd that's about 3K which is great. No shifting and good power in that RPM range. Trans temp stayed right at 150F for the 10 or so miles I was on that road. So my question is, is it harmful to run a 700R4 in second gear for an extended time like that. I'm I over straining second gear somehow, or is it fine to do that?

Thanks,
SRO

Holy smokes, 20k already? Seems like it was just last week.

 

[SirRobyn0]

Holy smokes, 20k already? Seems like it was just last week.

I know, it's been a year and 4 months. That's one of the reasons I decided to keep the MDX that was given to me. I'd love to continue to drive the square to work everyday, but I'm got to cut down on the mileage. I still spend plenty of time behind the wheel of the square, just not on my commute as much.

 

[SirRobyn0]

You're welcome and sure...Have you ever been in a 700R4 or 4L60E where the 3-4 clutch has burnt up?

If so, when the transmission shifts from 2nd gear to 3rd gear, it will feel like it's in neutral...But it's not actually in neutral - it's simply back in first gear...In third gear on these units, the forward and 3-4 clutch pack is applied..By time you're shifting from 2nd to 3rd, your vehicle speed is at least 20-25 mph, so when mechanically back-shifting to first gear at those speeds with only the forward clutch applied, it will feel like you're in neutral.

The same principle applies to being in 2nd gear at excessive speeds/RPMs but it doesn't start to feel like neutral until you reach higher vehicle speeds/RPMs because 2nd gear is a lot taller than first (1.49 vs 3.06) so you'd have to be traveling proportionately faster. Which, at the speeds you're travelling while towing, aren't at that threshold but you don't want to push too far beyond what you're currently doing in terms of keeping it in second gear.

Thank you for the explanation. Whilst I'm a mechanic I'm not a transmission guy at all. I've always known someone that did them so I never learned.

 

[mibars]

A friend has a 700R4 in 1992 GMT400 and is experiencing a strange behaviour. At light throttle it quicklys shifts at about 1600-1700 rpm to 2nd and there is a large, like a two step drop of RPM down to about 1000 rpm then it shifts to 3rd about 2000 rpm and also to 4th at about 2000 too (almost 80 km/h or 50 mph). Ther is no distinguishable moment when TC locks.

Is it possible that TC locks at the 1-2 shift and keeps being locked all the time? Is there an easy way to test it? I've heard about a methid with lightly touching brake pedal to disengage TC.

 

[AuroraGirl]

A friend has a 700R4 in 1992 GMT400 and is experiencing a strange behaviour. At light throttle it quicklys shifts at about 1600-1700 rpm to 2nd and there is a large, like a two step drop of RPM down to about 1000 rpm then it shifts to 3rd about 2000 rpm and also to 4th at about 2000 too (almost 80 km/h or 50 mph). Ther is no distinguishable moment when TC locks.

Is it possible that TC locks at the 1-2 shift and keeps being locked all the time? Is there an easy way to test it? I've heard about a methid with lightly touching brake pedal to disengage TC.

if it did lock, its going to accelerate really pigish
but I think some 700r4, i could be wrong, were able to lock the tc in 2nd but it would be under light throttle, but i thought only squarebodies tried that before ditching the idea for 3 and 4 only.

 

[NickTransmissions]

A friend has a 700R4 in 1992 GMT400 and is experiencing a strange behaviour. At light throttle it quicklys shifts at about 1600-1700 rpm to 2nd and there is a large, like a two step drop of RPM down to about 1000 rpm then it shifts to 3rd about 2000 rpm and also to 4th at about 2000 too (almost 80 km/h or 50 mph). Ther is no distinguishable moment when TC locks.

Is it possible that TC locks at the 1-2 shift and keeps being locked all the time? Is there an easy way to test it? I've heard about a methid with lightly touching brake pedal to disengage TC.

What year 700r4?

Only the 1982-E87 in some models had the TC lock up in 2nd gear...Plus the TCC wouldn't drop RPMS that drastically...More than likely, there's a partial tie-up during the 2-3 shift due to the band not releasing completely before the 3-4 clutch pack applies. This happens when either the third accumulator check ball capsule is not completely sealing or the large scarf-cut sealing ring on the very front of the servo assembly is worn out. It can also happen if the band release hole is significantly smaller than the 2-3 feed hole in the spacer plate.

Have you ruled out potential mis-fires or other engine/fuel delivery related causes?

 

[bucket]

What year 700r4?

Only the 1982-E87 in some models had the TC lock up in 2nd gear...Plus the TCC wouldn't drop RPMS that drastically...More than likely, there's a partial tie-up during the 2-3 shift due to the band not releasing completely before the 3-4 clutch pack applies. This happens when either the third accumulator check ball capsule is not completely sealing or the large scarf-cut sealing ring on the very front of the servo assembly is worn out. It can also happen if the band release hole is significantly smaller than the 2-3 feed hole in the spacer plate.

Have you ruled out potential mis-fires or other engine/fuel delivery related causes?

I experienced something very similar with an '86 700r4 in a TPI Camaro that had just been rebuilt by an unknown shop in South Dakota, maybe the same issue that @mibars spoke of.

Under light to moderate throttle, it would run out first gear in a normal fashion, then after shifting to second, the converter would almost immediately lock up, then short shift to 3rd and then also short shift to OD... then lug it's way up to speed. If you applied heavy throttle from a start, it would shift through all the gears as it should, then go into OD and lock the converter when you let off the throttle.

I never did find out why it shifted that way. I bought the car in the winter, then in the springtime, it fragged the reman converter and sent debris all through the trans.