Just a dumb transmission question

Timmayy

FBBO Gold Member
FBBO Gold Member
Local time
3:21 PM
Joined
Dec 16, 2015
Messages
1,573
Reaction score
4,557
Location
Tiverton RI
Reading through all the posts about trans kickdowns I saw a post about not driving without one. In all my years I've never been told this. Will it hurt the tranny? I've always had them myself but what about the guys running various aftermarket shifters? I had a friend back in the 80s that would just downshift manually. I believe he had a B&M auto shifter. Just curious is all.
 

Gus chiggins

Well-Known Member
Local time
3:21 PM
Joined
Jan 14, 2021
Messages
895
Reaction score
894
Location
State of diminished reality
Reading through all the posts about trans kickdowns I saw a post about not driving without one. In all my years I've never been told this. Will it hurt the tranny? I've always had them myself but what about the guys running various aftermarket shifters? I had a friend back in the 80s that would just downshift manually. I believe he had a B&M auto shifter. Just curious is all.
No kickdown, burned transmission.
 

bolson6333

FBBO Gold Member
FBBO Gold Member
Local time
1:21 PM
Joined
Feb 15, 2016
Messages
216
Reaction score
301
Location
lewistown,mt.
put in manual shift valve body to eliminate kickdown with no harm to transmission
 

R413

Well-Known Member
Local time
12:21 PM
Joined
Feb 4, 2019
Messages
3,871
Reaction score
7,889
Location
NW USA
An aftermarket shifter doesn’t affect the kick down linkage.

Manual valve body doesn’t need linkage.

you will get about 300 miles out of your trans without KD linkage.
 

Fran Blacker

1 of 27
FBBO Gold Member
Local time
3:21 PM
Joined
Sep 23, 2016
Messages
13,852
Reaction score
14,605
Location
Connecticut
No kickdown is how I learned how to dig into a trans. Calling it kickdown covers up what it really does. It's throttle pressure control linkage.
 

Jerry Hall

FBBO Gold Member
FBBO Gold Member
Local time
2:21 PM
Joined
Mar 26, 2018
Messages
8,871
Reaction score
15,279
Location
Alabama
Without kick down linkage, first you lose drive, then 2nd, until you end up with just park an neutral. Ofcourse it has to be adjusted for proper pressure or you are still in trouble.
 

Timmayy

FBBO Gold Member
FBBO Gold Member
Local time
3:21 PM
Joined
Dec 16, 2015
Messages
1,573
Reaction score
4,557
Location
Tiverton RI
I honestly never knew that. Thanks for clearing it up.
 

Dave6T4

Well-Known Member
Local time
3:21 PM
Joined
Dec 31, 2020
Messages
4,353
Reaction score
8,461
Location
Ontario, Canada
Years ago, I rebuilt a 727 for a friend to install in a '73 'Cuda he intended to race. I made sure it had the good stuff in it (4.2 lever, 4 pinion planeteries,, 5 clutch discs in front drum, shift kit). what I did not realize, was that he had no kickdown linkage, and wired the lever back when he installed the transmission. He raced it for a couple of seasons. The next Spring, he called to say that it would not back out of his enclosed car trailer that he used for winter storage. He said it drove in OK the previous Fall. I told him he would have to pull the trans, and drop it off to me. This is when I discovered he had the lever wired back. I pulled the oil pan and discovered that the rear servo had pretty well exploded. The sheet metal spring retainer was distorted, and had been forced through the retainer snap ring, and was hanging on the band apply lever, along with the spring. The band apply strut had been folded over and broke, with the pieces laying in the pan, along with shrapnel from the servo piston. Fortunately, the servo bore was not damaged, so the 727 was still repairable with replacement parts. Tying the kickdown lever back replicates what happens inside a transmission if the gas pedal is at the floor with all linkage installed, with all hydraulic circuits in the trans experiencing full pressure. In reverse, this can be 300 pounds. After seeing the damage, my friend acquired the proper linkage for his car.
 

Kern Dog

Life is full of turns. Build your car to handle.
FBBO Gold Member
Local time
12:21 PM
Joined
Apr 13, 2012
Messages
30,433
Reaction score
99,904
Location
Granite Bay CA
No kickdown, burned transmission.
This has been stated numerous times yet I have driven cars that I bought that had the linkage disconnected and the transmissions were fine.
I think many people repeat this warning without actually experiencing transmission failure from it.
I wouldn't tempt fate by removing it but It isn't like Russian Roulette where you face instant death from it.
 

R413

Well-Known Member
Local time
12:21 PM
Joined
Feb 4, 2019
Messages
3,871
Reaction score
7,889
Location
NW USA
Ok you first! LOL. if you are going to refresh a trans anyway, then just remove the linkage and let us know how long it lasts.

1F802895-27F6-4597-B040-AB6786624406.png


F116A9CF-804E-4038-95BA-C744BB4313D2.png
 
Last edited:

turbine68rt

Turbine Bronze Member
FBBO Gold Member
Local time
3:21 PM
Joined
Dec 1, 2019
Messages
2,414
Reaction score
4,025
Location
SE PA
In 3rd and reverse the front clutch is applied. Without sufficient clamping force provided by the throttle valve (line pressure +/-) the front clutch will slip under load. Subjecting it to the same conditions repeatedly, it's not hard to figure out what will eventually happen to that clutch pack. I rebuilt a '65 904 for a customer that complained of intermittent 3rd gear engagement. First thing I noticed was that the throttle linkage was adjusted that it only started moving about half-throttle. Second thing was that the friction material in the front clutch pack was almost gone. The linkage adjustment is one of the most important things that should be checked on these transmissions.
 

Kern Dog

Life is full of turns. Build your car to handle.
FBBO Gold Member
Local time
12:21 PM
Joined
Apr 13, 2012
Messages
30,433
Reaction score
99,904
Location
Granite Bay CA
I agree that it needs to be in place and adjusted properly.
I'm just stating that the warnings that "immediate destruction will occur" are an exaggeration. I had the Bouchillon cable come off of the carburetor of my Charger. I drove 40 miles before I noticed it and that transmission is still going strong in my other car.
Warnings that are based on scare tactics are silly. Smart people will see right through them.
 

R413

Well-Known Member
Local time
12:21 PM
Joined
Feb 4, 2019
Messages
3,871
Reaction score
7,889
Location
NW USA
40 miles is not going to kill it.

300 miles is fairly accurate. I have seen it plenty.
Yes it depends on how deep foot is on the throttle. Flat ground steady speed will last longer. The big problem is the upshifts to 3rd gear with a heavy foot. It slips before it grabs and eats clutches up.

I’m not a construction guy so I don’t try to see right through your excellent advice on that subject, I just accept it as good advice.

I‘m and ASE master tech and former trans builder. The **** will burn up. No scare tactics, just facts.

67667880-6887-470E-967B-4D0B2A0BFD52.png
 
Last edited:

dvw

Well-Known Member
Local time
3:21 PM
Joined
Feb 16, 2010
Messages
7,185
Reaction score
11,717
Location
waterford mi
It’s not kick down linkage. It’s actually throttle pressure linkage. More throttle, more transmission fluid pressure. Thus greater hydraulic clamping force of the clutches and bands. Light throttle doesn’t need as much clamping load. Drive it easy? No short term issue. Run it hard without linkage? You can answer your own question. This linkage also modifies shift points. But that’s another discussion.
Doug
 

Kern Dog

Life is full of turns. Build your car to handle.
FBBO Gold Member
Local time
12:21 PM
Joined
Apr 13, 2012
Messages
30,433
Reaction score
99,904
Location
Granite Bay CA
It’s not kick down linkage. It’s actually throttle pressure linkage. More throttle, more transmission fluid pressure. Thus greater hydraulic clamping force of the clutches and bands. Light throttle doesn’t need as much clamping load. Drive it easy? No short term issue. Run it hard without linkage? You can answer your own question. This linkage also modifies shift points. But that’s another discussion.
Doug
Excellent clarification. Thank you.
 

Dave6T4

Well-Known Member
Local time
3:21 PM
Joined
Dec 31, 2020
Messages
4,353
Reaction score
8,461
Location
Ontario, Canada
I
Have a picture of that hanging on my shop wall. I told all my transmission rebuild customers that if their 727 ended up looking like that, there would be no warranty. It clearly had fluid in it, and I told my friends that their transmission was fully warranted UNTIL they put fluid in it! LOL
 
Top