A little different beast - TH425

[fog]

Started to build the trans again, since the roller bearings arrived, and we got the friends GN to start up. So busy times are gone for now.

I have now gone trough the whole valve body and the th400 kind of "stage right" will not work.

The problem is, that the manual valve is operated from the other end opposed to th400 and therefore a new shaft that will block the reverse->exhaust flow at 1st is not simple to do.

The shaft could be lengthened to have the desired effect, but then it would want to go trough the oil pan at park.

For feeding, there is a double acting check ball before the rear servo release that allows pressure there either from lo or from reverse. That check-ball seat could be tampered to get it to flow from lo to servo release and reverse and from reverse to servo release.

But this feed is trough the modulator, so it will see lower pressure, so in worst case, I would have to ditch the modulator altogether. Not a big problem for a strip car only.

Am I way off the path with this thing?

 

[fog]

Well, just used some common sense, and made it...

Reverse side exhaust blocked:

Reverse side exhaust routed to Lo side exhaust:

I just hope it will do the trick.

OEM:

park:
line goes nowhere
servo and reverse exhausts in reverse side
3rd, 2nd and 1st exhausts in 1st side

Reverse:
Line goes to servo and reverse.
3rd, 2nd and 1st exhausts in 1st side

neutral:
Line goes to servo.
Reverse exhausts in reverse side.
3rd, 2nd and 1st exhausts in 1st side

3rd:
Line goes to servo and 3rd.
Reverse exhausts in reverse side.
2nd and 1st exhausts in 1st side

2nd:
Line goes to 3rd and 2nd.
Reverse and servo exhausts in reverse side.
1st exhausts in 1st side

1st:
Line goes to 3rd, 2nd and 1st.
Reverse and servo exhausts in reverse side.

--------------------------------------------------------
Now:

Since I connected 1st and reverse side exhaust, in Park, Reverse, Neutral, 3rd, 2nd: 1st is exhausted, so is exhausted also all as before.

In 1st:
Line is applied as above, plus Reverse and servo.

Is there anything I should address more? I know there is a 1-2 issue while in manual 1st in th400. Should I mod that also?

 

[fog]

Finally got the car running, and having a strange issue with the brake.
I cant get off the brake.
The shift valve gets hydro-locked to 1st since reverse circuit is pressurized and it is in the "end" of the valve, rather between tho full diameter dishes.

How to solve that?

 

[KL Mallender]

Best of luck with your efforts, there is a simpler way of acheiving your goals, but seeing other ideas brings humor, always fun in my book these days.


Kevin.

 

[fog]

Best of luck with your efforts, there is a simpler way of acheiving your goals, but seeing other ideas brings humor, always fun in my book these days.


Kevin.

Sorry, but I did it this way since no product is available, and you did not want to get crossed in a possible problem. And now it is "fun". From my point of view, it is not, since first event is May 21 and I have no tbrake.
If you have a solution for me, please PM me with price. Be it either $ for telling me what to do or $ for a VB that you would ship to me. I'm all ears.

 

[fog]

Anyone? Vendors?

Be it either automatic or full manual or reverse manual, electric or "stage right" style brake?

 

[dartguy340]

You are VERY unlikely to snap the chain in a TH425, been a long time since being inside one(I had 2 '67 Toros many moons ago) you may twist a shaft out of the sprockets(maybe) but you aren't gonna phase that chain assembly.
Will take far more than the stub shafts can, that I'm sure of.
Good luck with your project, should be one hell of a ride.

Kevin.





ps: If you are sure you want a "simple" transbrake, I might be able to help you out, provided someone has a spare VB lying around.

Back in 1975 or 1976 I remember I put a chain in a cadillac or a toronado front wheel drive but, I can remember if it was the chain that broke or the sprockets had their teeth worn off of it. The chain was about 3 inches wide I think! I didn't think at the time that it was a very good setup.

 

[fog]

Well, I almost broke the chain Actually, the bearing block that carries the driven sprocket. I'll just make a stronger new one, no worries there.

Anyhow, Is there a transmission specialist who could make me a full manual VB with an electric transbrake for the TH425?

I just bought a spare trans, so I could ship over a virgin VB if needed.

I really need help with this one, 10.4 is pathetic for the combo.

Please PM me if anyone is willing to work with this.

 

[jakeshoe]

I may have a solution for you. Do you have a picture of the manual valve?

 

[fog]

I may have a solution for you. Do you have a picture of the manual valve?

Not at the moment, but it is identical to TH400 one less the actuator rod that is on the other end. So the actuator rod is connected near the LO not near the Reverse as in TH400.

Right now I have:
plugged reverse side exhaust(in th400 the reverse exhaust is to the pan trough the manual valve sleeve, but in 425, it is separate groove in VB).
Connected the now "dead end" reverse exhaust to LO.
This made me a brake, but the brake did not dis-engage. Since the fluid pressure was between a end-plug and manual valve end.
Then I made a longer manual valve on lathe, that had an extra disc, so the transbrake pressure was held between the rod discs.
This has worked, but the downsides are slow release and governor dictated 1-2 shift.

 

[fog]

Here's the picture. Cleaned the garage today and found the original manual valve.

 

[fog]

So, I have now drilled a new spacer plate and modified the VB for full manual reverse pattern and brake, but do have some concerns.

1) I fed the rear band from manual valve servo cirquit, so rear band is applied in neutral, will it be a problem?
2) The rear band is applied trough the 1st gear and force-released on 1-2 change. But will it release fast enough?
3) There is a small pinhole in the bottom of the modulator valve, but this cavity gets filled with line pressure in reverse and transbrake. Will it start to release the brake if brake is used for long time?

Other issues should be taken care of, no line pressure modifiers(boost valve), 3rd and tb is fed together trough a two-way checkball that used to feed the rear band. And a lot of the other check-balls have been retained for controlled orifice apply and fast release. 1-2 and 2-3 are both .118 feeds.

 

[jakeshoe]

The band on in neutral is fine.
Yes it will release fine, you can increase the spring tension if you feel the need.
This is the same way a TCI and Hipster and many other transbrakes work for a TH400.

I'm not sure exactly what you have going with the modulator. Plug the pinhole. You should have line trying to force the mod "off" to speed brake release.

 

[fog]

Then it should be okay, the pinhole provides the pressure towards brake release.

Now I just need to get the solenoid and springed modulator valve. Chris has both, but haven't gotten back to me for some days.

It is getting below zero outside, but I want to test the valve body out before I tear the car apart for winter.

 

[Bigblockfiero]

 

[Bigblockfiero]

View attachment 261933

My third broken chain.

 

[34blazer]

There's a guy on PFF with a Caddy 500/425 combo, that you?

 

[Bigblockfiero]

There's a guy on PFF with a Caddy 500/425 combo, that you?

Yes I was on pff ten years ago but got banned. I believe mine was the first big block fiero that is fully functional. i've seen some pretty neat ones since.