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Gearbox Issues

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pakiwi

pakiwi

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I have a 1973 Midget 1275. The previous owner barely drove it and after the clutch seized on him, he got it fixed and decided to sell it. The car has 19,000 miles on it and everything is in excellent condition, except for the Gearbox.
Changing from 2nd to 3rd is fine on start up, but as fluid warms up, it does not change easily. Also from 4th to 3rd, there is a noise as it goes into 3rd gear. Rather than cause further damage, I change from 4th to 2nd most of the time. I have changed the fluids, with no difference. I have read about the clutch bleeding problems and wonder if this could be it or if synchro has been damaged.
I also have difficulty changing from 1st gear sometimes, but just move into second, then back to first.
Thanks,
Allan
 
Without knowing the history of the troubles, it is difficult to diagnose the problem. If you can raise the vehicle on a lift, and have one person press the clutch fully and another person observe the clutch lever. It should move a good 3/4". If not, a bleeding of the clutch system would be my first task. Other than that, the gearbox would have to be removed and repaired.
Scott in CA
 
Agree, might also think about Red Line MTL oil. Check it on their web site.
 
pakiwi said:
I have changed the fluids, with no difference.
Click to expand...

Allan,

You say you have changed fluids, but don't say what you've used as replacement.

You should be using straight 30 weight non-detergent motor oil. NOT gear lube. Some people make that mistake and that could damage the transmission and/or cause the problems you mention.

The other thing that comes to mind is that 1275's have a flex line to the slave cylinder. Perhaps the line is collapsed internally and limiting your flow volume. When the problem occurs, have someone observe how much travel you have on the clutch fork/pushrod. The difficulty you describe sounds like not enough release.

If you are using the correct oil and the rest checks out, try adding 25% to 50% MMO and see if it improves shifting. If none of that works, try bleeding the clutch to see if that helps.
 
I agree the clutch is the place to start.
Most tranny problems are really clutch issues.
As for clutch travel, you will get a clean disengage with a pushrod movement of 7/16". I personally have never seen 3/4" movement in a 1275, even with all rebuilt parts.
If you don't know the age of the clutch flex line, replace it.
As for fluid, I always use 30 wt non-detergent. There are studies on foaming which will convince you this is best. Yes, it will shift better with some other stuff, but will not last very long.

YMMV.

Paul
 
Thanks for the feedback. I will get access underneath and take a look at clutch travel. I did change the oil with a 30 weight motor oil and the state of the Clutch flex line.
Thanks for the feedback.
Allan
 
I've seen a few gearboxes over the past 30+ years where moisture condensation/oil interaction has set up a deposit on the syncronizer cones in the gearboxes and actually caused the syncro rings to stick on the gear cones. Kind of like the ivory colored oil froth that sometimes shows up on the underside of the valve cover cap. This was usually present in gearboxes from cars that set for a long period of time. Driving the car and fresh motor oil in the gearbox should clean these deposits off the syncronizer cone/mainshaft gear.

If gear oil had been used in the gearbox previously, and the car set for a long period of time, gear oil does thicken a good bit as the aromatics evaporate and the syncros could be sticky from this as well.

First gear is non-syncromesh. If the clutch is dragging any and spinning the laygear, 1st gear will be hard to engage. Moving to second gear first helps by using the syncronizer arrangement in 2nd gear to stop the gearbox internals from spinning and permits the straight cut 1st gear teeth to mesh on both the 1st gear hub and the laygear.

If all the above discussed actions don't result in improvement in operation, then removal and a teardown, inspection, cleaning and re-assembly/build are the likely next steps.

HTH,
Mike Miller
 
I did the easy thing first and replaced with MTL oil. Nothing metallic came out with the old oil, though it was only 80 percent full. I did take it for a test drive and the noise was still apparent betwen 3rd and 4th, though if I am slow to engage between these changes, it goes into gear with out issue. Is there any sort of gate that could be warn.
Once I have an assistant, I will check clutch movement.
Thanks,
Allan
 
If this is a 1275 you should be running SAE 20W-50W not SAE 30. You also want an oil with plenty of ZDP in it. Valvoline VR1 20W-50 Racing is clains to have high levels of ZDP Additive which our Flat Tappet Cams love and need.

PS it doesn't take 5 quarts either, more like 3.5
 
For the tranny, a bit less than a full quart, like maybe 80 to 90% will be fine.

Use what ever you are running in the engine. You can not overfill. Excess will run out.
 
Just got back from a 50 mile run and a local club meeting. By the time I got back, things seem to be better from second to third gear, though very little change from forth to third. Next I will check be checking the cluth, otherwise I guess it will be a removal of the engine to work on gearbox.
Allan
 
If you have to remove the gearbox and tear down, be sure to check the condition of the small caged needle bearing in the back of the input shaft. A bearing problem in this area can make shifts between 3rd and 4th a bit difficult. Also make sure the bearing surface on the main shaft has not erroded and is out of round.

Clean and inspect everything. Let me know if you need any of the small NLA stuff. I've collected a goodly number of these bits and pieces over the years.

HTH,
Mike
 
Ok just got some time and checked the clutch. There was 3/8" of movement at the slave cylinder. I sort or remember it should be 3/4 - 7/8 so I am guessing I need to bleed the clutch and if that fails rebuild master and slave.
Allan
 
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