700-R4 tranny problems....

[mlmtrujillo]

ive got an '88 astro 4.3L w/700-R4 trans. this is the 3rd time that its lost 2nd and 4th gears. does anyone know the cure??? the first time, i just swapped out with a rebuilt tranny. second time this happened i got it rebuilt at a shop, they put in - master baner kit, torque converter, o/d drum, o/d sprag, servo piston, some kind of bushing kit, sunshel, filter, fluid. im new to transmissions so i don't know what alot of this stuff is just yet but anyway, this is the third time this has happened. ive read about problems with the throttle valve sticking, or the 2-4 gasket burnt etc. etc. is there any way of knowing whats happening and a way to prevent it from happening again? the series of events seems to be - it runs fine for months, then it starts shifting late, then after a few weeks it will slip out of gear if i punch the gas, then eventually i lose 2nd and 4th all together. its been a great van besides that so im hoping i wont have to decide to get rid of the thing... any help or info is appreciated.

[troy1]

Your buring up the band which is 2nd and 4th. I would make sure the kickdown cable is adjusted correctly. the 2nd tranny was a completely different transmission right? If it not I would check the servo area for wear when they fix it again. The servo in question is the one on the outside near the front of the trans on the passenger side. The cover is roughly about the size of a oil filter. Also do you pull anything heavy or does the van shift in and out of overdrive alot?

[mlmtrujillo]

first off thanks for the reply and info. i do use the van to haul drums and percussion equipment to gigs alot, usually to distant places on the highways. i don't think the stuff is too heavy, not more than a small boat and trailer weighs. anyway, do you think thats the problem? is there a way to modify the tranny to handle the wieght and long hauls? or maybe a stronger model trans. all together? thanks again for the help and ill check that servo out too....

[Blue Bowtie]

Instead of the band, you might want to check the 2-4 servo, accumulator, and if you dig into it, replace the reaction sun shell. The splined hubs in the factory units tend to rip out easily.

The TH700-R4 should easily be able to handle towing and hauling. I had an '88 that I used for towing a boat, two snowmobiles, and very frequent hauling - and a lot more weight than a few instruments. Usually, the trips were from the house to the cottage - 351 miles door-to-door. All I ever did with the trans was change fluid and filter regularly, and allow it to warm up sufficiently before driving. Most people don't, and pay the price. It had 186K miles on it when it was traded in on a new one.

[troy1]

all the failures were not on the same tranny right? you have the oringial one exchanged for a unit they had built. correct?

[mlmtrujillo]

thanks for the response blue bowtie, ill check everything i can on this thing... and yes, the original trans. was swapped for this "rebuilt one" hehe when it went out, and now this is the second time for this to happen on this one. ive discovered that 2nd isn't completely gone, its there if i stand on the gas, but if i drive normal it either slips out back to first or skips it all together. sooo, are we having fun yet???? anyway, thanks for the replies and lets see what i can discover.....

[Blue Bowtie]

Well, now we're getting somewhere. That sounds more like higher oil pressure is able to clamp the band and make it to 2nd range. Since there are many, many possible reasons, it might be good to perform a line pressure test before proceeding. There is a good chance that the hard parts are intact, and you may be able to repair the problem with the trans in the vehicle.

An easy thing to do is manually place the trans in 2nd range and see if the gear engages properly and moves the vehicle or still slips.

Another easy check is to take troy1's advice, and temporarily disconnect the TV cable. If the automatic shifting to 2nd improves, the cable and/or governor may be at fault.

If you connect a 0-300 PSI pressure gauge to the upper test port on the left side of the trans, just behind the bellhousing, you can possibly isolate the problem even further. At 1,000 engine RPM you should read a minimum of 65 PSIG from this port. In manually selected 2nd range, the pressure should increase to at least 165 PSIG.

[MT-2500]

Are you using silcone sealer on the pan gasket?
MT