A little history, 71 Cuda, 340 4 Speed. I installed a new clutch and flywheel (both McLeod) earlier this summer. I also replaced the pilot bushing and throw-out bearing. Before the clutch replacement, I would get a loud screeching sound when releasing the clutch pedal only. I traced this back to the chewed up (dry) pilot bushing. I also had issues downshifting into 1st at speed. I drained the ATF and filled the transmission with Lucas 90w gear oil and have driven the car a few hundred miles since. Shifting has been very smooth, great pedal feel, no strange sounds etc.

This Saturday (so far the hottest day this summer, 90*) I took the car out and after a few miles, when coming to a stop, I was not able to downshift into 1st at speed, only grinding. Downshifting into 3 and 2 was smooth and quite. I was able to downshift into 1st while moving less than 5mph.

Do I contribute this to the heat or do I have another issue? Could be 1st gear synchro be going out? I also adjusted the clutch and have about an inch of travel.

That would be something other than ambient temperature.

Yes, most likely.

Personally I do not think you have an issue at all here.. Granted I am sure your tranny is older and worn some, but this was the norm back when these were fairly new...

Why would you want a first gear downshift for anything but coming to a stop at a sign or redlight to be prepared ( in first gear) for proceeding after stopping????

Again, I don't remember 4 speeds being really friendly about going into first at much speed....

What speed? There is a limit to the speed you can safely downshift....a lot depends on the axle ratio.

X 2

1" of free travel, this means nothing, you need to know what the airgap clearance is on the clutch, 1st and reverse engagement or lack of it can usually be attributed to the airgap being too small for complete engine/drive line disengagement until the rpms are extremely low enough to allow you to forcefully engage a gear, esp 1st

A diaphram clutch spec is approx .030
A Borg/Beck aprox .050


IMHO, the prior use of ATF may also lead to the untimely demise of your 4 spd also

Your clutch mfg should have a specific air gap requirement

10mph and over I would say. Excuse my ignorance, but this is the first old-school manual I have owned. It sounds like I need to do just what you guys are mentioning, downshift to 3 and 2 and then wait until almost stopped to drop into 1. I appreciate all the help guys, I just wanted to make sure I was not having another issue.

I will also measure the clearance between the clutch and flywheel, we checked for clearance when we installed the clutch but did not measure.

What is the GL rating of the Lucas oil , you need something that is GL4 , if the lucas is Gl 5 equivalent then you need to change it out , Castrol Syncromesh is made for transmissions with brass syncros.

The Lucas 80W-90 that I used exceeds service level API GL-5.

Don't use it again. As stated, find a GL-4. GL-5 has extreme pressure additives that are required for ring & pinions but are not compatible with brass (synchros) long term.

Redline makes several GL-4s

Thanks guys, I was under the impression that as long as the fluid exceeded GL-4 and GL-5, it would be safe to use. I have some Red Line MT-90 75W90 coming today that I will fill the transmission with.

It sounds like to me that the clucth disc has worn enough now to not allow full disengagment due to noraml wear, try adjusting it again and see if that fixes the down shifting problems I've onw and used a bunch of Mopar 4 speed NP833 that had ATF in them from Ma Mopar and never had a issue with wear or destructions, that was in the Mojave Desert in SO CA with ambient outside air temps above 100 F most of the days in the spring, summer and part of fall

Not the way I remember them. There was many times I'd be rolling along in 4rth with my 833. Simutaniously floor the clutch, floor the throttle as Im jammed the shifter from 4rth to 1st for a roll race.

Anyways there is 2 definate ways to engage a gear. One is with light pressure on the shifter. This gives the synchronizer time to slowly spin the speed gear to the same rpm, once its matched it easily slides in. Like stepping lightly on the brakes.
Next method is a strong forceful engagement, like described above. This gives the synchronizer less time to match speed but since there is so much pressure on the it will quicky match speed and go in. Again, like braking hard.

Either method will not grind the gears in a proper functioning transmission.

Wow, that's how you do it.... LOL

Seems to me if you try to power down to 1st from 4th, you will get thrown into the dash, if your lucky. Must have been spinning the motor above 8 grand or better in the short time it takes to engage 1st. I can just hear the clutch or tranny explosion from here.

We would run around town in third and drop to second for a "rolling start" race.

Of course I lived in town and cruising Villard ave. or Highway 100 4th wasn't even used, as the speed limit was 35 at max.

I always only engage 1st when almost at a complete stop. Just before the motor starts to lug.

Absolutely Minivan. I was in my teen years when we were abusing these cars. Downshifting into 1st, powershifting without releasing the throttle, launching with slicks from redline, driving off the pavement and jumping like a scene from Bullit.

Had some clutch linkage issues, shifter handles coming loose but never broke anything inside an 833.