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700R4 blown, Now what?

firemedicsafd

firemedicsafd

Professional Murphy magnet
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I have a 88k5 with 1 ton axles geared to 4.56, stock 305 motor, stock transfer case. This tranny blew due to long term lack of use. I want to get frankenblazer back on the road asap. But i also want strength and reliability. I plan on replacing the motor in the future but won't as long as this one runs good. Should i stay with 700r or start a manual trans swap process. Or do a complete gen 3 swap? If i swap to manual, which should i go with and what kind of costs should i expect. I plan on spending about a grand on a better tranny. Any help would be appreciated. thank you!
 
It all depends on where you want your truck to end up. Determine your goal and apply your money towards the trans that will best take you there, you don't want to have to spend money twice. If you are looking for opinion, then mine is to go back with a well built 700R4, the truck is already set up for it and the advantages of this trans are many if properly built and maintained.
 
I hate automatics. My vote is manual. But, as Greg points out, the 700 has a lot of pro's vs the 465, which is the only viable manual trans that will hold up and is easily found.

A well built 700 will hold up. Regardless if it's still got a million more parts to fail lol.
 
Ok then, now for diagnostic help. I just went and started it up to keep the motor lubed up and all. I tried to move it and...it moved! Reverse then back to drive several times. Granted I only went about 10 feet each way but it felt normal. Do I have another issue like drive shaft too short? Does hot fluid cause problems? I know I'm prob gonna have to rebuild it again but I'm hoping I don't have to do it RIGHT NOW! Thanks for all the help.
 
lots of guys here over the years had good luck with bowtie overdrives .

look there web site up .

I have had both stick and auto for dd / work / play . stick nice for pullin loads / long hills in 1 gear holding power .


but auto setup correct and keep cool with a gauge also I like best .
 
"Long term lack of use"....well,maybe it hasn't "failed"...it might have just failed to engage due to the pump not priming right away, or a stuck valve body spool ,pressure regulator valve was hung up.etc...

A lot of "good used transmissions" we sold at the junkyard that either sat in the vehicle for 10+ years or on a pallet in a truck body "shed" didn't always work perfectly the first time the new owner installed them and went to drive the vehicle..
Some had water get in them from condensation,or the fluid leaked out over time and seals shrunk--more than a few came back to life after a full fill of fresh fluid and some additive like "trans-kleen" or similar product was added to the fluid..some took a long time to finally go into forward gears or reverse,but eventually freed up and worked OK...water cant pass thru the paper filter in an automatic or the hydraulics as easily as oil can..

What I'm saying is dont give up on it too hastily..it may surprise you...I've added a pint of brake fluid to a TH350 that had hardened lip seals on the forward clutch piston,and it did help it to go into forward gears faster--without it I had to wait a good 5 minutes ,especially in cold weather...
 
That depends on how much time and money your willing to spend on what might turn out to be a futile attempt--I would say changing the filter & fluid wouldn't hurt it any,and dropping the pan will let you see if its all rusty inside,if it is,it might be best to forgo spending the 40 bucks on fluid and filter and just pull it out instead...

One thing a guy who rebuilds automatics told us,was its best to jack the vehicle up and run it in the gears with no load on the tires at first,to help the fluid get to all the passages and valve body and apply the clutches fully,to avoid burning them up on the first "awakening"...he reccomends doing that on a freshly rebuilt tranny also..

More than a few TH350's and TH400's we sold took awhile after installation to shift right and go into gear right away...the customers were advised to change the fluid after a week or so again,and to add some tranny fluid conditioner like K&W or Trans-Kleen, (not "stop leak" type stuff)...usually doing that and replacing the vacuum modulator (that a 700R4 does not have,they use a TV cable instead)--most of them panned out well in the end..
 
Good advice Diesel. Yep fluid and filter change is a fairly inexpensive check. Also disconnect the fluid lines on both ends and blow them out. They make a flush spray in an aerosol can that my tranny guy uses. If you have a cooler then flush it out also.

Vacuum modulator is also fairly inexpensive to replace and check the vacuum hose is not cracked rotted and hooked up properly.
 
But even not hooked up or failing, it will still shift, unlike a mal-adjusted TV.

May shift hard, may shift a bit late, but it will shift. Many seem to think the modulator is what controls the shift vs. providing the trans some idea of the load the engine is under, which is the modulators purpose.

I only managed a 5MPH+/- difference in shift timing with an adjustable modulator or even no vacuum input.
 
We are drifting off topic here,but while we're on the subject of modulator valves--

When I had a bad modulator,or the vacuum hose came off one or no vacuum was getting to it, on TH350's and TH400's,the transmission would upshift harsh and very late,(like first to second at 35-45 mph!)--and when you let off the throttle, there is no "engine braking" effect...never understood why it feels like "neutral" when you let off the throttle,when there wasn't any vacuum supply...

My TH400 in my diesel pickup acts that way in second gear sometimes,it "freewheels" when I let off the throttle--the vacuum regulator valve on the injector pump is NG on it, so I ran direct vacuum to the modulator from the vacuum pump,and screwed the modulator adjustment screw in all the way,then backed it out 1/2 a turn,as suggested by a local transmission guy I knew and trusted..it's plowed a lot of snow and hasn't burnt the clutches up so far..

Its seemed to work OK since 12 years ago that way,(only 5000 miles though!)--but it does shift a bit weird at times--sometimes it seems to upshift into third "early" and other times it takes its time upshifting into third...

I considered getting a cable operated modulator like they use on supercharged engines,but it was way too much for my budget..
 
When running it with the wheels off the ground, should I get it up to highway speeds or just let it idle along? Is there a place I can read up on the 700r4?
 
The procedure the guy I know reccomends is to jack both wheels off the ground and make sure it cant slip off the stands,then put the transmission in 1st gear and let the wheels spin a few minutes,then gently accelerate until it gets up to about 20 mph,then shift into second gear,let the wheels spin a few minutes,then accelerate and get it up to 30 mph and shift it into third and let the wheels spin for a few minutes--then get it up to 65 mph and see if there is any unusual vibrations or shaking going on,that might indicate a drive
shaft or u-joint troubles..then stop the wheels,put it in reverse and let them spin a few minutes..then stop the wheels,put it in park,and check the fluid level,making sure its in the right range on the dipstick..

Whether this is something that "must" be done,or is just a hocus-pocus quirk of his I cant say,but I know if he rebuilds a transmission for someone and they fail to do this after its installed before driving the vehicle,he wont warranty his work...and he has had very few transmissions come back to bite him..and most of the ones that did had case porosity or crack problems,it wasn't his work at fault..
 
I had a TH700R4 in my truck behind a stock 305 and when it went out, I found a TH400 and rebuilt it and put it in there and I like it waaayyyy better than the 700, but that's just me. I don't think I would go back. Not in this truck at least. It wasn't that much work, if you're wanting to get you Blazer back to driving again pretty quick.
 
ok, she is blown. i jacked it up and went thru the process. Once it FINALLY shifted into 4th, it made lots of noise and lost all power. 3rd went to 55 but at very high rpm. so ill pull it and rebuild.

What things do i want on the inside to make it stronger and better? i heard stuff like carbon/ kevlar clutches, billet sunshell. i found a place that said all that stuff for around 800. is that reasonable? thank you folks for all your help!
 
Are they saying they'll rebuild it for $800 with all the goodies or sell you all the stuff for $800? If you can get it rebuilt/beefed up for $800, I'd say that was pretty good as long as it's a reputable shop.
 
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