This isn't necessarily a third gen question but I know there are a lot of transmission experts on this board. I've built a 700r4 for my play truck and I use it for sled pulling on occasions. The last few times ive pulled I've lost fluid out the vent tube. Enough to release the clutch packs and over rev the engine. Its about 450-500 HP and I typically turn about 7k when hooked to the sled. The trans has 2300 12" lockup with balloon plate. New pump 10 vane.500 boost valve, superior shift kit, hi rev clutch springs , beast shell, gm 5 pinion planets, z pack, superior servos , wide band, HD sprag and new roller clutch, deep pan and large cooler. I'm wondering why I'm blowing fluid. Too high rpm for the pump? Extreme pressure? Relief valve issue? I'm completely lost with this.

 

I'm trying to research this and I'm really not finding much other than. Too much heat and/ or too much rpm. I read a post that explained that at rpm above 5500 the cintrifugal force can push fluid up through the vent. Input on this?

 

You're building up heat and pressure in the case. A th400 or th340 has a vent/ overflow on the top. If you over fill these trannies you will spew fluid at high rpm, I've seen it. The usual cause is over filling.

I'm not too familiar with the 700R4 but I'd have to say its a restriction in the VB somewhere. You might have to open up the pump feed hole to allow more flow into the pump and less restriction.

 

It wasn't overfilled but that's not to say the level diddnt rise too high with heat. I can't see the trans being too hot though as the engine only got to about 170-180. I'm thinking its more an rpm/ pressure issue that's a bit over my head. I've been trying to get ahold of Dana at pro built but it seems he's hard to reach the last couple days

 

I guess no one experiences this? I'm wondering if I run the vent to the fill tube and put a tee in it and run up above the trans. It'll still vent but when it blows out it will go back into the trans. Input?

 

Let me ask my buddy. He's a master trans tech for Ford and actually teaches local mechanics on trans issues.

You'd be amazed at how much your trans will heat up, especially with a trans brake and high stall converter. My buddy was just at the strip on test n tune the other night. 60* night. The car was running 180* but the trans got up to 220* at the line on the converter.

For my street/ strip Camaro I will be running a thermostatically controll fan just for the trans cooler.

 

Using the early pump to case gasket is most likely the culprit. The later gasket has a large area of the gasket covering the hole that can cause this. Why the early pump gasket is still in the rebuild kits I do not know, as the later gasket will retrofit.

 

Thanks guys. I will check the gasket. I'm always pretty sure to use the new style gasket but I'll check it out. What exactly causes it to blow out. Even with the old style gasket? Is there a drain back hole that should be oversized or something?

 

I took the truck out today to do some testing since it hasn't moved since the last pull. The transmission holds great till I get to about 6500 and then it more less neutrals itself and revs to the moon. What is going on? Pump pressure dropping off? Why? Help please! I have 2 weeks to try and fix it

 

The pump must be setup correctly to keep the oil volume up at hi-rpm. The stock pump starts to lose pressure above 5,500 rpm in stock form. And as the pressure goes down, the holding pressure of the clutches drops. If you get a lot of air in the oil (known as aeration), that can also cause this even if the pump is set up correctly. TransGo offers a Hi-rpm priming spring and steels rings (known as a NoYoYo setup) to keep the oil volume and pressure up to 7,800 rpm. I put these in all my rebuild kits that will see over 5,500 rpm.

 

OK it looks like I'll have to do that. Pretty sure I'll need new clutches now too

 

Thanks dana

 

Well.. I pulled the pump apart to find the rotor split in half! Why does that happen? Never seen that before

 

Put in a th400 with brake. It'll hold up!

 

I'm really trying to avoid that. I have a th350 and a th400 I can put in it. I'll probably build the 350 and put in it.

 

The 400 has a TON of clutches n steels inside. I'm just a big fan of the th400. I don't like the fact that the th350 only has a clipped in center support as apposed to the th400's bolt in.

 

Very Interesting...I also have the same issue going on. I have 700R-4 professionally built and upgraded parts. I'll be honest, I'm no trany expert, but I'm learning quickly. First time I burned up the 2-4 band (carbon band) and damaged the drum(trans lasted about year- street/strip car). Had it rebuilt again tried using the red alto eagle band - had the trany over rev on the 2-3 shift (out on the street), sprayed oil out the vent tube and the up dip stick tube. Pulled the pan, nothing in the pan but the oil is burnt, looks like motor oil and smells burnt. this time the trany lasted 4 passes at the dragstrip and handfull of trips around town and done. So rather than driving it further just pulled the transmission and going to take it to a different trans shop (racing trans shop-not joe blow out of his garage) in chicago. This is 2nd time i've blown the trany up so I'm going to get a 2nd option from someone else. I'm guessing i'm some where between 650 and 700 hp @ 15 pounds of boost with my procharger set up.

Any thoughts? Thanks.