how do the two transmissions compare, besides the fact that the 700r4 has OD. my th400 lost reverse and it is in need of a rebuild, I got a price of $1200 for a shop to rebuild the tranny and remove/install. I dont have many complaints about the th400, but I would really like an OD trans. I am thinking of picking up a good 700r4 and installing it myself, but I dont know how well it will hold up. any input?

You'll need a 700R4 from behind a diesel. Torque converter is different. I remember reading something about the governor being different but i'm no trans mechanic. Also you'll need the bracketry for the TV cable where it hooks to the IP.

Transfer case is different as well from the TH400 to the TH700R4. DIfferent spline count. The TH400 is the 32 spline out. The 700R4 i removed was the 27(i think) spline.

Not sure what else is different. Think your truck would be the NP241 however.

tranny length is also different, the trans crossmember has to be moved back for a 700r4

My SM465 was the exact same length as my 700R4. The crossmember stayed in the exact same place. I even used to old driveshafts from the 700R4/NP208 combo.

For what it's worth the 700 had 27 splines until '84 and then changed to 30.

For what it's worth the 700 had 27 splines until '84 and then changed to 30.

Interesting. My blazer is an 85. I believe that my SM465 is a 32 spline. Worth looking into. :confused:

I read that on wikipedia a few mths ago and I don't trust wiki that much but everything I read about the TH400/th375 turned out to be right

if you find the right guy, he can build a 700r4 pretty stout for $1200, but you also have the added cost of maybe new driveshafts, i dont think the tcase will be a problem if you find the right 700r4, id try to find a case from say 88-91 and then have them put the upgrades in that.

cant say as far as length, all i know is a long shaft th350 is same length as a 700r4 in 2wd versions

For what it's worth the 700 had 27 splines until '84 and then changed to 30.

That's in regards to the input shaft where it goes into the torque converter.....

I've got a 700R4 out of my blazer that was mushy from 1st to 2nd(which really annoyed me), but other than that it was fine.

PM me if your serious about switching to an OD trans. It's not that difficult really. I took oout the 700R4 and swapped in an SM465. The loss of overdrive really didn't hurt me as i'm running 3.08 gears and rarely hit the highway for extended periods with that truck.

my friend rebuilds tranny and he lives in weathersfield. He works for a reputable place. I could ask him he wanted to do it on the side.. Pm me to let me know if your interested,

I've got a 700R4 out of my blazer that was mushy from 1st to 2nd(which really annoyed me), but other than that it was fine.

PM me if your serious about switching to an OD trans. It's not that difficult really. I took oout the 700R4 and swapped in an SM465. The loss of overdrive really didn't hurt me as i'm running 3.08 gears and rarely hit the highway for extended periods with that truck.

Is that all that was wrong?? That could have been fixed in about 15 minutes with a spring change.....or installing the corvette servo.

Is that all that was wrong?? That could have been fixed in about 15 minutes with a spring change.....or installing the corvette servo.

That and there was copious amounts of metal shavings in the pan. I changed the fluid and filter and after maybe 200 miles there was a 1/4 inch or more of clutch material on the pan magnet. The trans needs a rebuild. it's toasted.

That and there was copious amounts of metal shavings in the pan. I changed the fluid and filter and after maybe 200 miles there was a 1/4 inch or more of clutch material on the pan magnet. The trans needs a rebuild. it's toasted.

you said other than that it was fine.......

i guess you meant it was toast LOL

If you snow plow and tow then stay with the 400, it is STRONG! The 700 rocks because it has a low first gear to get loads moving and the OD that locks up, very nice but it takes someone that REALLY knows what they are doing to build it and costs some serious money to do, besides having to change a lot of other things. Have that 400 built right, lots of upgrades to make it bulletproof and last a very long time.

you said other than that it was fine.......

i guess you meant it was toast LOL

It drove fine. Didn't seem to slip at all save for the 1-2. Downshifted fine and everything. the loads of clutch material the second time i dropped the pan is what really made the swap to the SM465 finalized.

i thought i saw on Xtreame4x4 they built up a 700R4 for that scout of theirs and they got a kit from monstertransmission. it put a bunch more clutches in each clutch pack and had alot more beef in that one ring that likes to break off getting rid of your reverse. it was about a grand but it looked like it would take some major SH*T.

Is that all that was wrong?? That could have been fixed in about 15 minutes with a spring change.....or installing the corvette servo.

Not meaning to hijack this thread, but can you tell me more about this? Mine does the exact same thing.

Search for a good th400 from someone who blew the motor or wrecked the vehicle and put it in. If you have to build up the 700r4 to be as strong as the stock 400 you have answered the vs question. Trannys are such a pain in the ass to fix I go with the most robust...plus the ol 3 speed is way less annoying in hills/mountains.

Tjgator, the servo applies the 2-4 band, which is used in second and fourth gears. The band can wear and cause slipping and/or no 2nd or 4th gear. If the T.V cable is mis-adjusted, it can accelerate band and 3-4 clutch wear by lowering line pressure. It can also cause a slip during band application.

The servo is a multiple component unit. The Corvette trans used a different servo for increased surface area. It helped apply the band with a more positive action and additional holding power, due to the larger surface area. The spring pressure was changed as well. This is one modification (among many) to increase life of the transmission.

The servo, when properly assembled, is a fairly trouble free part. The band apply pin length should be checked and if found to be too short or too long, adjustments can be made. The apply pin depth is also used to gauge band wear prior to disassembly. The procedure is covered in the service manual and requires special tools.

Replacing the stock servo with upgraded parts may "tighten up" the band application but most often is added when the transmission is apart for an overhaul. If the band and drum are good and show no abnormal wear, the servo may help a soft band engagement. The critical TV cable adjustment must still be made correctly.

while we are on topics of ways to fix minor problems, can anyone tell me what could be wrong with mine? The transmission drives perfect once it is warmed up, it doesnt shift hard or slip between gears. The problem is when I put it in reverse it almost like slips and doesnt fully engage. if i am on a flat surface it will back up, but if i touch the throttle it will just rev up and not go any faster, almost like its slipping, and when it is on a hill/under a load it wont even move itself. The fluid is bright red and doesnt smell burnt at all. I have been driving the truck like this for about 3 months and besides the reverse problem, the forward gears have been perfect.

Possible reverse band/servo problem. The THM400 uses the direct clutch and the low-reverse band for reverse gear. If the direct clutch were not applying, you would have slipping or no third gear.

The first check is line pressure in reverse, if low, the problem could be in the direct clutch feed circuit. If the pressure is within normal limits, check for engine braking in manual low position. If it has no engine braking, it goes back to a low-reverse band/servo problem.

Did this problem occur just after the installation of the B&M shift kit? If so, a mispositioned or missing low-reverse check ball in the valve body could cause this problem too.

the transmission has engine braking in low gear, and the shift kit hasnt been installed yet due to the problems. 3rd gear is also fine and does not slip

I'd start with a line pressure check, the reverse boost valve may not be boosting the pressure properly. Reverse needs more pressure because of it's design.

The service manual gives pressure ranges (with brakes applied, engine speed of 1000 RPM) as follows: Neutral: 55 - 70 psi, Drive: 60 - 90, Low: 135 - 160 and Reverse: 95 - 150. If low, possible oil leak in direct clutch feed circuit.

what they did on mine after the new rebuild, it still soft shifted 1 to2

all he did was pull the 1-2 solonoid (not really sure what it is, maybe a vavle) pull the spring, add or replace with larger spring = harder shift. This is in or on the valve body and i dont recall that he had to even remove the valve body.

Sounds like a low/rev. band problem
I have never seen the seals blow out of the low /rev servo woren out band yes , Sometimes you may have nice red oil but the material has flaked off of the band .
have you dropped the pan and looked to see what is it . ???

Also you can still have manual low engine breaking but have very pour reverse This is due to the load that it takes to reverse the plantery"s
pressure problem due to stuck valve yes but keep in mind why that may have or is stuck , metal or something has caused it if that is the problem where is the metal coming from .

You should drop the pan on it and have a look see what material is in there the 400 as a rule runs very clean unlike the th350 6 litres of oil and pan gasket then you would have a better idea to what might be happening
also if you do drop the pan look on top of the filter for metal and clutch material . Pull the bolt out of the filtre & suction tube do not tip it over then lay it into a clean pan and turn it over to drain take a light shine it on the oil that drain's out of the filter if she is coming apart you will see it !!!!!!

Sorry to say this but a B-M shift kit is not the best for a 400 may give you harder shifts but cause's alot of overlap between gear's more heat and wear = less life .. Trans-go all the way !!!!!

Sounds like a low/rev. band problem
I have never seen the seals blow out of the low /rev servo woren out band yes , Sometimes you may have nice red oil but the material has flaked off of the band .
have you dropped the pan and looked to see what is it . ???

Also you can still have manual low engine breaking but have very pour reverse This is due to the load that it takes to reverse the plantery"s
pressure problem due to stuck valve yes but keep in mind why that may have or is stuck , metal or something has caused it if that is the problem where is the metal coming from .

You should drop the pan on it and have a look see what material is in there the 400 as a rule runs very clean unlike the th350 6 litres of oil and pan gasket then you would have a better idea to what might be happening
also if you do drop the pan look on top of the filter for metal and clutch material . Pull the bolt out of the filtre & suction tube do not tip it over then lay it into a clean pan and turn it over to drain take a light shine it on the oil that drain's out of the filter if she is coming apart you will see it !!!!!!

Sorry to say this but a B-M shift kit is not the best for a 400 may give you harder shifts but cause's alot of overlap between gear's more heat and wear = less life .. Trans-go all the way !!!!!

Should've seen the metal in my 700R4's filter. :eek:

Some owner before myself beat that trans and hard.

One more You could have a blowen outer lip seal on the 3rd & reverse clutch pack. It only use's half of the piston for 3rd and needs all of it for reverse. Over the years I have seen that before usually a soft and late shift into 3 rd. you have been driving for some time like this so if you drop the pan there should be small pieces of rubber in the pan




Should've seen the metal in my 700R4's filter. :eek:

Some owner before myself beat that trans and hard.

Rode hard and put away wet !!!!!

The 700's are like the 350 they run dirty

Early build 700 was very good for us in the tranny shop's !!!!!

Ferd's first kick at the over drive was even a bigger pile of junk!!!

I've got a couple 700R4's laying around...one's a new unit(well old but never used) and the other is a rebuilt corvette trans(core from a burb, rebuilt as a corvette trans, differential on burb blew shortly after and sealed her fate)