Transmission Rebuild time

[blazerbrad]

The TH700r4 in my Blazer might finally be going out...it's a '90 with about 115k and has been used and abused for years. Never had a bit of trouble with it on the trail but it sat at my parent's place for a year and I think it got driven around the farm fields low on fluid because of a leak. Found it low on fluid and forward gears seem fine now but slips and then "catches" in reverse.

Thought about staying with the 700r4 (worked well for years), or swapping to a TH400 or TH350. Definitely stay with an automatic, and would consider a full manual reverse valve body. Would also like to stay with the NP241 transfer case because of the 2.72:1 low range....yeah, NP205's are bulletproof but have a poor 1.96:1 low range.


Here are the different options I have thought about:

1. Rebuild the 700r4
- bolt in a go, no transfer case or driveshaft mods needed
- retains the low 3.06 first gear (TH400 or TH350 are only about 2.50) = 34:1 crawl ratio
- the overdrive gear is a moot point because of how this truck is used and the axle gears
- most expensive trans to rebuild out of the other options
2. Swap to TH400
- probably cheaper to rebuild, but would have to buy the trans to start with
- super strong
- lose quite a bit of crawl ratio, and sucks up more power = only 28:1
- requires replacing transfer case, or installing new input shaft on existing transfer case
- might require modifying driveshafts to fit
3. Swap to TH350
- probably cheaper to rebuild, but would have to buy the trans to start with
- increase in strength is questionable
- lose quite a bit of crawl ratio
- believe I could get factory parts to mate up to transfer case
- might require driveshaft mods

Let me hear your thoughts and suggestions. If I stay with the 700r4 would be looking for somebody to rebuild it or help me to the work. Any suggestions on this?

If money wasn't an issue would love to have a TH400 with some sort of Doubler or Atlas, but pretty sure the wife would not be very happy with that.....

[humpy]

From my knowledge stock for stock th350 and 700r4 r same strength but 700 has lower first gear and overdrive... Th400 is same $$ to rebuild vs the 700... Last I checked it was bout $1200-$1300 for a 700r rebuild...if its a farm use ride go buy one at a junk yard slap it in and run it another 15-20 years

[93 Krawler]

I would stay with the 700r4. Just find a used one and run it.

[blazerbrad]

Should clarify this is for my trail rig and not some old farm truck (I can see where that could come from on my original post). Not real comfortable with just gettting a junkyard trans and slapping it in, and would hate to get stuck in the middle of a trail because of it. I know several people who have done this and the success rate is not that high on a trans with an unknown history, and have seen a lot of shoddy rebuilds out there also. Considering this trans hasn't come out of the factory in 20 years the chances of getting a really worn out one or one of these rebuilds is fairly high.

[kkoepper]

I just put a newly rebuilt 700r4 into my buggy about a year ago. Local (for me) guy whose been doing it for 25 years. Former GM dealership tranny tech. $450 including a new rebuilt converter. PM me if you want his #. Might be worth the 2 hour drive to Whiteland, IN. I've been betting hard on it for the last year w/o any problems and know a lot of guys with his trannys who swear by him.

[humpy]

Originally Posted by kkoepper

I just put a newly rebuilt 700r4 into my buggy about a year ago. Local (for me) guy whose been doing it for 25 years. Former GM dealership tranny tech. $450 including a new rebuilt converter. PM me if you want his #. Might be worth the 2 hour drive to Whiteland, IN. I've been betting hard on it for the last year w/o any problems and know a lot of guys with his trannys who swear by him.

If this guy does good work id use him.. My guy is a master gm trans guy and it costs 3 times that to get a 700r done... But he's best I have ever seen ... Well worth the $$ if u gonna use it all the time... Hell there's quite a few hundreds of dollars in parts alone in my th350 with reverse valve body

[93 Krawler]

I do my own stuff, so I don't know any good shops. I rebuilt the 4l65e in my dd van and the 700r4 in my rig.

Sent from my Radar 4G using Board Express

[blazerbrad]

Originally Posted by 93 Krawler

I do my own stuff, so I don't know any good shops. I rebuilt the 4l65e in my dd van and the 700r4 in my rig.

Sent from my Radar 4G using Board Express

I hate taking stuff to a shop...both for the price and I just hate not doing it myself. Just never been into an auto trans before.

[93 Krawler]

Originally Posted by blazerbrad

I hate taking stuff to a shop...both for the price and I just hate not doing it myself. Just never been into an auto trans before.

Same here. The first transmission I rebuilt was a 350. I bought a rebuild book and borrowed the tools from a friend. I was around 26 then, now 44. I have all the tools now. If you want to try it yourself, I will let you borrow the tools and give you some pointers. Patience and cleanliness is important. The 700 is the hardest one I've done, but easily doable is you take your time and lay everything out on a clean bench as it comes out of the case. There are a few seals that can suck, and one c clip in the bottom of the case that I always fight with. That's where the Patience comes in. If you want it built with a bunch extra stuff, then you might want to take it to a shop. That take skill from experienced builders. If you want it freshened up like new on the cheap, then do it yourself. The 700 in my rig is stock except I put a shift kit in for firm shifts. That's great in 2H, but in 4L it rips your neck off with 538 gears. I put the lightest shift feel in it too.

[blazerbrad]

I don't need any high zoot parts in it. Haven't researched much yet but figured some decent clutches and maybe a good sunshell? The biggest thing I was considering is a reverse manual valve body. Anybody have experience with them? I like the idea of being able to lock it into 2nd gear while in low range.

[humpy]

Originally Posted by blazerbrad

I don't need any high zoot parts in it. Haven't researched much yet but figured some decent clutches and maybe a good sunshell? The biggest thing I was considering is a reverse manual valve body. Anybody have experience with them? I like the idea of being able to lock it into 2nd gear while in low range.

U do know that a reverse valve body switches the shift pattern right?

Instead of. PRN321 it becomes PRN123

U can get a full manual valve body and retain stock pattern if u want


Main reason for reverse is so u can jam from 1st gear to reverse when hill climbing or when front if rig pops up

[93 Krawler]

Originally Posted by blazerbrad

I don't need any high zoot parts in it. Haven't researched much yet but figured some decent clutches and maybe a good sunshell? The biggest thing I was considering is a reverse manual valve body. Anybody have experience with them? I like the idea of being able to lock it into 2nd gear while in low range.

Upgrading the sun shell, clutches, 2-4 band, servos, sprags etc are a good idea. It all adds up quick.
If all you want to do is hold it in gear, then you should use a shift kit. http://www.summitracing.com/parts/tr...make/chevrolet

[JeffK5]

Originally Posted by blazerbrad

I don't need any high zoot parts in it. Haven't researched much yet but figured some decent clutches and maybe a good sunshell? The biggest thing I was considering is a reverse manual valve body. Anybody have experience with them? I like the idea of being able to lock it into 2nd gear while in low range.

I've owned two RMVB , one with compression braking and one without. The body with no braking is more suited to hauling ass (free wheels off the gas) but can be scary in the steep stuff.

[blazerbrad]

Yep, know it changes the shift pattern hence the "reverse " part of the name;) Wouldn't do a manual valvebody without it since this puts 1st and R close together. But I guess the question is what is the difference between the $300 RVMB and the $80 kit if it does basically the same thing? Just so people know where I'm coming from, the 700r4 will always take of in 1st gear unlike some other auto trans that will take off in 2nd if you place the gear selector in 2 (the 4L80E in my tow rig, wife's Odyssey, buddies C6, etc...). Once you do get it into 2nd gear (like climbing a slick hill) it will want to downshift back into 1st if you give it too much throttle.

[blazerbrad]

Talked to a friend who spent some time as a transmission tech and he thinks it might just be a sticky valvebody. Recommend changing the fluid and filter along with some additive to help clean it out. I don't believe in the "rebuild in a can" but sometimes additives or cleaners can fix problems.

Fluid was dirty but still was fairly red. Bottom of the pan had a thin layer of the blackish clutch material but what I would expect. Didn't get to test drive because it was getting late but just cycling between D and R it felt like it was engaging in reverse and would move backwards when you took your foot off the brake.

[93 Krawler]

Originally Posted by blazerbrad

Talked to a friend who spent some time as a transmission tech and he thinks it might just be a sticky valvebody. Recommend changing the fluid and filter along with some additive to help clean it out. I don't believe in the "rebuild in a can" but sometimes additives or cleaners can fix problems.

Fluid was dirty but still was fairly red. Bottom of the pan had a thin layer of the blackish clutch material but what I would expect. Didn't get to test drive because it was getting late but just cycling between D and R it felt like it was engaging in reverse and would move backwards when you took your foot off the brake.

Changing the fluid in the pan really isn't effective. You can do your own flush with the help of a friend. I do the filter change, add 7-8 quarts, take the trans return line off the radiator "Usually the top line" and put a fitting in the radiator. Attach a hose to the fitting and drop it in a bucket. While your friend is moving the trans in different gears, keep adding fluid so it doesn't run dry. I usually run 15 quarts through and stop. I have done this to a lot of cars and it works great. It gets rid of all the old fluid.

[blazerbrad]

Originally Posted by 93 Krawler

Changing the fluid in the pan really isn't effective. You can do your own flush with the help of a friend. I do the filter change, add 7-8 quarts, take the trans return line off the radiator "Usually the top line" and put a fitting in the radiator. Attach a hose to the fitting and drop it in a bucket. While your friend is moving the trans in different gears, keep adding fluid so it doesn't run dry. I usually run 15 quarts through and stop. I have done this to a lot of cars and it works great. It gets rid of all the old fluid.

Good point. Probably only got about 4-5 quarts out by dropping the pan and it probably holds at least 10 quarts total (converter, cooler and lines, etc...).

[93 Krawler]

Originally Posted by blazerbrad

Good point. Probably only got about 4-5 quarts out by dropping the pan and it probably holds at least 10 quarts total (converter, cooler and lines, etc...).

I'd say closer to 12qts. If you really want to do it right, put Dex 6 back in it. This replaces all previous Dexrons. It's the only one that GM actually approves of and checks on. From what I read, any brand as long as it's Dex6, has been approved by GM. Wal-mart's house brand has Dex6 at a good price. I've used it to flush out several cars.

[blazerbrad]

Short test drive tonight and it feels normal again in the driveway, but no big loads on it. It will chirp the tires on the garage floor in reverse now but still need to get it bound up and make sure it's applying enough power.