1975 Performance
Thread Starter
Safety Car
Joined: Feb 2006
Posts: 3,557
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From: Ridgeway VA
1975 Performance
I have a '75 and have completely redone the interior, used a clay
bar on the exterior and the engine is clean. However, I am still
learning about better performance. The first thing I did was get
a 3-inch air filter and new converter - a noticable difference. The
second thing, just recently, is - a complete tune-up including replacing
fuel lines, filter. But, the most important was replacing the modulator
valve on the tranny - as I understand it this valve reacts to the
vacuum and changes shift points vs the throttle. Plus adjusted
throttle linkage to allow throttle to open more. And replaced the
passing gears downshift switch. NOW - this '75 goes like a rocket -
it "roars" in passing gear. ( I understand the modulator can actually
cause tranny fluid burn out the pipes if not in good condition.)
PS- I would be interested the experts on the board to explain the
relationship between the carb/timing & tranny - I really haven't seen
this explained. Thanks!
bar on the exterior and the engine is clean. However, I am still
learning about better performance. The first thing I did was get
a 3-inch air filter and new converter - a noticable difference. The
second thing, just recently, is - a complete tune-up including replacing
fuel lines, filter. But, the most important was replacing the modulator
valve on the tranny - as I understand it this valve reacts to the
vacuum and changes shift points vs the throttle. Plus adjusted
throttle linkage to allow throttle to open more. And replaced the
passing gears downshift switch. NOW - this '75 goes like a rocket -
it "roars" in passing gear. ( I understand the modulator can actually
cause tranny fluid burn out the pipes if not in good condition.)
PS- I would be interested the experts on the board to explain the
relationship between the carb/timing & tranny - I really haven't seen
this explained. Thanks!
Burning Brakes
Joined: Feb 2005
Posts: 1,235
Likes: 0
From: Mesa AZ
carb and timing don't have an effect on the tranny as far as shifting. the trans has the kickdown switch on the accelerator pedal, and the modulator will shift the trans depending on how much vacuum it is getting determined by the amount of load on the engine.
Pro
Joined: Dec 2004
Posts: 570
Likes: 0
From: glace bay nova scotia
a quick power boost is a distributor spring advance kit. leave all parts intact with the exception of one spring.remove one spring and replace it with the lightest spring in the kit.this will give you full vaccum advance at about 2800 rpm.
don't change the weights as they are not as good quality as the original.
on my 75 i replaced the th400 tranny with a th350.steeper first gear plus you free up some h.p.(been told anywhere from 15 to 25 h.p.) your th350 converter will fit the 400
don't change the weights as they are not as good quality as the original.
on my 75 i replaced the th400 tranny with a th350.steeper first gear plus you free up some h.p.(been told anywhere from 15 to 25 h.p.) your th350 converter will fit the 400
Le Mans Master
Joined: Sep 2003
Posts: 8,812
Likes: 2,029
From: eastern NC
Originally Posted by PETKAH
I have a '75 and have completely redone the interior, used a clay bar on the exterior and the engine is clean. ...But, the most important was replacing the modulator valve on the tranny - as I understand it this valve reacts to the vacuum and changes shift points vs the throttle. ... ( I understand the modulator can actually
cause tranny fluid burn out the pipes if not in good condition.)
PS- I would be interested the experts on the board to explain the
relationship between the carb/timing & tranny - I really haven't seen
this explained. Thanks!
cause tranny fluid burn out the pipes if not in good condition.)
PS- I would be interested the experts on the board to explain the
relationship between the carb/timing & tranny - I really haven't seen
this explained. Thanks!
It's not an bad idea when doing a tuneup to pull the vacuum line (from the modulator) off the intake and check for evidence of transmission fluid. If there's a problem, you will see it very clearly as fluid will drain out. More importantly, there will be indications of a problem as the transmission will not want to up-shift smoothly.
Good move on replacing the converter. These things came with the "pancake" style that was relatively inefficient compared to the newer hi-flow cats and prone to blockage as they aged.
Good luck with the '75. IMHO they're sleepers in value and can be real gems when cared for, all for relatively little money... GUSTO
