700r4 help

[matt69olds]

I just finish a overhaul on a friends 86 (no aux valve body) 700r4 trans. It was rebuilt with new input sprag, 10 vane pump kit, Corvette servo and stock replacement frictions and band. The problem is it wont move with the trans in overdrive range, drop the shifter in 3rd gear all is good. Once the truck is moving occasionally you can get a 3-4 upshift, however, ususally 3rd gear is the highest gear you can get it to shift. I also have no engine braking in 1st gear. According to my range reference charts the only difference between d4 and d3 is the application of the overrun clutches. Shift points are normal (according to the owner) reverse is good and everything air checked good during assembly. I'm scratching my head on this, any ideas?

 

[matt94z]

kinda sounds like the Detent cable is too tight. My 2004r did that after a rebuild. I loosened the cable like 3-4 clicks and it shifts perfectly.

 

[GNeric]

Did you check the outer seal groove on the forward piston and make sure it isn't cracked? This will cause the no movement until you put into the Drive range instead of OD range. Pressure is bleeding off. Classic symptom. Your engine braking should apply the low clutches. Do you have any pressure readings? Pressure in L1 and L2 should be higher than Drive position. Is the Low/Rev piston sealing up well when hot? Air pressure cold can fool you and when hot fluid behind it may blow open any crack. I used to have a lot of cracked pistons to show people what happens but threw them out a few years back otherwise I would show you what I am trying to describe.

 

[WE4]

Your problem could be...

One of two things.....

First.... The L/R sprag may have an issue. It is the only thing on (holding) when the forward clutch is on, in OD only.
Second: Ck the over run clutch and sealing rings. See in 1-2-3 the over run clutch assists the sprag in holding. Once the trans is in OD the over run clutch releases. Something funny there.

I would be looking at the sprag and over run piston and clutch, in the input drum. (Just cause it is new means nothing) Remeber there were several changes to that sprag during those years.

Will it move forward from a stop in OD? At all? If not, a sprag or over run clutch is going to be your culprit.

Also, ck to make sure you have the ck balls in the vb correct. 86-87-88 are slightly different and the plate and gaskets can be confusing sometimes.

Gneric is correct as well. But you got more symptoms than just that. But He is correct.

Contact me if you and when you can and I can give you some more things to try once I ask you some questions so we can figure this thing out.

Hope this helps.

Bruce
We4
PTS XTREME
916-739-0510
If machine comes on leave message. I will get back to you asap.

 

[matt69olds]

With some tech advice from Bruce, I solved my 700r4 issue! I replaced the reverse input drum due to damage from a smoked band, the drum I used had a aluminum piston. According to the ATSG book, the aluminum piston drums require a specific pump. I swapped in a pump from the same core, didn't realize the pump had a aux valve body. The trans I was rebuilding didn't have a aux valve body, which left the hole for the transfer tube in the pump open (no forward clutch apply). When the shifter is in a manual position the reverse boost valve kicks line pressure up enough to apply the clutch. With some careful measuring, I was able to drill a access hole in the case and tap the pump for a setscrew to block of the port for the transfer tube. I would like to thank Bruce, he was a big help! I didn't buy any of the parts from him, and he still took the time out of his day to help me. Everyone takes the time to bitch and complain, few people write to offer thanks!

 

[WE4]

Yea baby!!!!!!!!

Well Matt, Called that one, eh? I told you I thought you could plug that in the car and it would work. So you ended up leaving the 732 in there and just cut off the feed right? All working cool now? Man, that was right after surgery and I was looped. Wow. ROFL!!! Call me as I would like to know some more about this.
How come with these problems we can usually solve other peoples issues but cannot seem to solve our own? LOL I find that funny sometimes but I am a whack job anyway. I just like everybody to have fun as frustrating as it can be, and believe me, with what has happened to me in the last few years my faith has been tested through and through.
Man, dude, I am so glad you got it handled. You didn't have to pull the SOB again, cool! How much crap was in the pan if any? Did we catch it before any damage was done?
Anyway, give me a shout, or better yet, email me your phone number and I will call you from the house.
Another lesson learned, as the money, time or pain syndrome comes true again!!!
Good job Matt,
I know you can't wait to see the tailights going away down the street and home with the customer after that week of fun....:smile:

Bruce
WE4

 

[GNeric]

That is Bruce. That is probably the main reason I like him. Could call at any time and he is willing to help. Hell, I talked with him for almost 2 hours one night when he was out near the end of his property messing with his horses and he still wanted to talk transmissions. Great guy in my book.

With some tech advice from Bruce, .... I would like to thank Bruce, he was a big help! I didn't buy any of the parts from him, and he still took the time out of his day to help me. Everyone takes the time to bitch and complain, few people write to offer thanks!