Downshifting from 3rd to 2nd

[Jersey]

I have no problem shifting from 4th to 3rd, but shifting from 3rd to 2nd is met with a grinding sound generally. Even when I match engine rpms with a double clutch I stll am about 50% successful.

Does anyone know if there is a explanation for this? I am guessing I need to replace the synchro rings and possible rebuild the tranny.

Jersey

 

[Randy Forbes]

Second gear synchromesh ring is toast.

Very good chance that the layshaft also has a groove worn in it, allowing the laygear to move too far away from the mainshaft gears.

Sounds like you have a winter project on your hands! Don't feel bad, I'm planning on rebuilding my side-shift trans to go back in my car too (replacing the MGC trans I put in about 20 years ago).

 

[healeynut]

Jersey, mate -

Do not downshift any BN2 or 6 cyl healey from 3rd to 2nd. It's a pointless exercise and all you will do is wear out the teeth on your second gear.

It is much cheaper and easier to ride your brakes a little more - when your brakes wear out it's just a matter of replacing pads.

If you keep downshifting to second gear from third, you will crap out your gearbox and have to pay to rebuild your gearbox.

By the way, the BN1 gearbox synchros are better and the three speed downshifts from 2 to 1 pretty easy, but as a matter of practice I don't do that either.

:thumbsup:

 

[anthony7777]

healeynut, isnt downshifting a three speed box from second to first the same as shifting a four speed box from third to second? is the bn1 trans. realy a four speed with first gear blocked off? or is it just another trans. all together?, what makes its syncros "better"? not looking for an argument here just trying to understand something, thanks.

 

[zblu]

Maybe a session on a square cut cog box with no synchros might enable a better understanding of ratio/rev matching

 

[tahoe healey]

I'm not sure which Healey you have, Jersey, but on my BJ8 I have no toruble shifting into 2nd if the speed/RPM is appropriate. I don't do it often, just in traffic if I need to creep. I'm seldom in traffic up here and I get out of 2nd as soon as possible. I think it is better than riding the clutch. I often start the car in second instead of first if I'm on flat or down hill. I believe these are pretty hardy gear boxes. You may have something wrong with the inside. Thats my two cents, which is worth less in todays economy.

 

[Randy Forbes]

healeynut, isnt downshifting a three speed box from second to first the same as shifting a four speed box from third to second? is the bn1 trans. realy a four speed with first gear blocked off? or is it just another trans. all together?, what makes its syncros "better"? not looking for an argument here just trying to understand something, thanks.

The BN1 is indeed a four (4) forward speed gearbox; there is a blanking plate under the side cover that prevents engagement of 1st gear.

As anyone that's ever removed the blanking plate knows, 1st gear really is useless (you'd have to upshift before you make the middle of the intersection). Remember that the long-stroke four (4) cylinder engine doesn't have a very high redline.

From a rebuilder's standpoint, the BN2 through BJ8 synchromesh rings are far easier to replace; the BN1 type being fitted and then sized to the gear(s), whereas the later type are drop in.
That's certainly not to say that a BN1 box in good condition wouldn't shift better than a BN2 (& onwards) in poor condition. At this point in the car's lives, a comparison of the two is virtually pointless. A comparison when both were new and fresh is another story...

 

[nevets]

Jersey
Are you sure you're not pulling the lever over into reverse territory? Can happen on some cars.