[Malibu Vette]

I finally got the new motor and trans in the car and went for the first test drive. The transmission is a JW TH400 with reverse pattern trans brake valve body. When we took it it out I noticed that no matter what gear I put the shifter in the trans started in first. When I throttled the car and shifted, the 1-2 shift was good, but when I pulled into 3rd nothing happened. When I let off the gas it stayed in second but did not compression brake. I have never had a problem like this. I know somebody out there can give me some advice.

 

[Oldani Motorsports]

Hmm, was this a complete trans from JW? With nearly all transbrake valve bodies also you have no engine braking since they eliminate the intermediate band. You also need to be very careful about lifting with a 3-speed/neutralling a 3-speed/etc. as you'll have a nasty explosion if you are not careful!

 

[charbilly2001]

Hmm, was this a complete trans from JW? With nearly all transbrake valve bodies also you have no engine braking since they eliminate the intermediate band. You also need to be very careful about lifting with a 3-speed/neutralling a 3-speed/etc. as you'll have a nasty explosion if you are not careful!

I, for one, would like to hear more about this explosion business. What explodes and why?

 

[Sandy]

Should wait for the experts to respond to this one, but.....

My understanding of manual valve body tranny brake turbo 400 is that it is NOT idiot proof.

Two things to remember:

1) do NOT push tranny brake button when going down the track

2) do NOT downshift or go to neutral at the end of a quarter mile pass.

 

[Trans1226]

Check external linkage if that's ok check the internal linkage where the rooster cone bolts onto shaft.

 

[charbilly2001]

Should wait for the experts to respond to this one, but.....

My understanding of manual valve body tranny brake turbo 400 is that it is NOT idiot proof.

Two things to remember:

1) do NOT push tranny brake button when going down the track

2) do NOT downshift or go to neutral at the end of a quarter mile pass.

I got #1. Thats obvious. You get two gears at once. The least that would happen is that your rear wheels would instantly stop rotating. Ugly!


I further understand that you shouldn't downshift at the top end of the quarter mile. I wouldn't like what would happen to my transmission if I did that in its stock form much less with a manual valve body.

What I want to know is why specifically, in the case of a manual valve body, is it more harmful to down shift at the top end of the quarter mile OR shift into neutral?

 

[Guest]

Manual VB or not you do not want to ever shift to neutral at speed.

Simple explanation is, the planetary gears that produce gear reduction in 1st and 2nd gear, when shifted to neutral are no longer "driven" by the forward drum. They begin to "drive" the direct drum if there are no clutches engaged.
When this happens, they overdrive the direct drum. Gear reduction backwards is gear overdrive.
So if you are doing 120 at the end of the 1/4 mile and let off at 7000 rpm, you start overdriving the direct drum it may see well over 10,000 rpm.
It is a cast iron component and it can centrifugally explode.

You really shouldn't downshift either.
A downshift from 3rd to 2nd causes the direct drum to go from engine rpm to a complete stop. This happens on a 1-2 shift anyway (albeit from 84% of engine rpm) BUT, it is slightly less harsh because the clutches engage to make it happen. There is some slip of the clutches as they engage that let the drum "spin down".
In 3rd gear the intermediate or 2nd gear clutches are already engaged, so the directs release and you are back in 2nd.

It goes back to the direct clutch being driven by the planets. A 3-2 downshift under acceleration isn't nearly as much shock as a 3-2 under deceleration.