4.2 kickdown lever

-

Brooks James

VET, CPT, Huey Medevac Pilot
FABO Gold Member
Joined
Dec 12, 2020
Messages
4,817
Reaction score
3,155
Location
Fruitland Park Fl
I have a spare small block 904 that i Want to use behind a 408 i Want to build. When i look for high quality rebuild parts i often see 4.2 kick down levers as well. I thought that with a reverse manual valve body it isnt necessary. What exactly does it do ??
 
Puts more leverage on the band when actuated.
 
it holds the drum with greater force by changing the distance from the band strap seat to the pivot point. Iirc hemi trans had a 5.1 or so. reverse or forward or manual shift didnt matter as this piece is always used.
 
Available through most places like A&A, etc.
 
We use the 5.0 lever in our 904s.....got 5 of them in use....4 of them with Transbrakes.
 
I have a spare small block 904 that i Want to use behind a 408 i Want to build. When i look for high quality rebuild parts i often see 4.2 kick down levers as well. I thought that with a reverse manual valve body it isnt necessary. What exactly does it do ??
With a performance valve body with increased line pressure, the 4.2 is the most commonly recommended leaver. Along with the noted
Increased leverage compared to numerically lower number levers, the 4.2 gives the least amount of shift overlap. The multiple spring
Clutch piston kit installed in the front drum also helps with overlap.
The 904 with its factory coiled spring, really messes up the shift timing. Overlap is the amount of time that the front clutch is applied before the band has fully released. This can be very noticeable on the 2-3 shift with 904.
 
the 24 spring kit will help elminate the shift overlap....or cheaper ATi has a correctly wound spring for sale 29 dollars i think or mrrandy who list tranny parts for 904/727 over at Moparts...30 dollars......He has alot of billet pieces for sale...
 
the 24 spring kit will help elminate the shift overlap....or cheaper ATi has a correctly wound spring for sale 29 dollars i think or mrrandy who list tranny parts for 904/727 over at Moparts...30 dollars......He has alot of billet pieces for sale...
Agreed, but afaik a lower numbered lever further improves the timing. 3.8 or 4.2 was recommended in the instructions with my tranzact brake. I have gone to 3.8 but I have a lightweight drum
and sunshell.
 
It does give more holding power, but the biggest thing it does is speed up the band actuation.
 
It does give more holding power, but the biggest thing it does is speed up the band actuation.
Increased line pressure does that too. Again it depends on the valve body and what you are trying to accomplish. 170 psi pressure or higher which is what most transbrake operate at, speeds up everything. The trend with these kinds of pressure is to decrease
The lever ratio because of overlap.
 
Increased line pressure does that too. Again it depends on the valve body and what you are trying to accomplish. 170 psi pressure or higher which is what most transbrake operate at, speeds up everything. The trend with these kinds of pressure is to decrease
The lever ratio because of overlap.
Sorta. As long as you use a wide band, the 5.0 lever is a big plus. Otherwise, it really doesn't do much. No 904 ever came with the 5.0. That was a Hemi only option and they used a wider band than all the rest of the 727s. That's why you need the widest 904 band you can fit in if you use the 5.0 lever. I believe the widest that will fit is 2" wide in the 904.
 
Sorta. As long as you use a wide band, the 5.0 lever is a big plus. Otherwise, it really doesn't do much. No 904 ever came with the 5.0. That was a Hemi only option and they used a wider band than all the rest of the 727s. That's why you need the widest 904 band you can fit in if you use the 5.0 lever. I believe the widest that will fit is 2" wide in the 904.
Well I can tell you that my Tranzact pro nitro brake was set at 170 psi for use with a 904. The instructions clearly recommend either a 3.8 or a 4.2 . The line pressures are set higher for a 904 because it has less clutch surface than a 727. That increased line pressure speeds up the application of the front drum aggravating the shift overlap.
Increasing the spring pressure and plate clearance in the front drum
Is done to slow down the piston application and give the band more time to release.
Paul Forte of Turbo action sets his brake at 190 psi and he recommends a 3.8 lever. The band width has nothing to do with it.
I have the widest band made for a 904. This band is not usually recommended any more because the apply lugs are not centered
and causes uneven wear. At these kinds of pressures clamping force
Is not an issue for the bands. Harshness and speed of apply/release
Is the problem. Afaik
 
Well I can tell you that my Tranzact pro nitro brake was set at 170 psi for use with a 904. The instructions clearly recommend either a 3.8 or a 4.2 the line pressures are set higher for a 904 because it has less clutch surface than a 727. That increased line pressure speeds up the application of the front drum aggravating the shift overlap.
Increasing the spring pressure and plate clearance in the front drum
Is done to slow down the piston application and give the band more time to release.
Paul Forte of Turbo action sets his brake at 190 psi and he recommends a 3.8 lever. The band width has nothing to do with it.
I have the widest band made for a 904. This band is not usually recommended any more because the apply lugs are not centered
and causes uneven wear. At these kinds of pressures clamping force
Is not an issue for the bands. Harshness and speed of apply/release
Is the problem. Afaik
Therein is the difference in the discussion. I'm not talking about a transbrake.
 
Therein is the difference in the discussion. I'm not talking about a transbrake.
The op asked why he sees the 4.2 lever recommended for a reverse manual valve body. I am saying that it is the most recommended
Because of shift timing issues. Most performance valve bodies
Will have increased line pressures over stock.
 
-
Back
Top