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MG MGA - Grinding in 3rd gear??!!

I just bled the brakes and clutch and it went very well. The car stops much better.

However, I am still grinding 3rd gear and I have only been able to downshift from 4th to 3rd. Is this the performance I should expect or am I doing something wrong?
gerard hutchinson

Gerard - definitely not something you should expect as normal.

By "grinding 3rd gear and have only been able to downshift from 4th to 3rd" do you mean the grind is only on the upshift? If so, it sounds like you are hitting a bit of 1st gear on your move to 3rd. I'm not sure of the actual cause, but try to make the move with a definite push to the right as you go up and see if it makes a difference.
- Ken
Ken Doris

What was it like B4 you did this?
Art Pearse

Gerard, I am presuming that you are getting the grinding when changing from 3rd to 2nd, this shouldn't happen, but is quite a common fault with MGA's. There are three possibilities as far as I can see. The worst is wear in the synchromesh, which will entail removal and ovehaul of the gearbox (unless you want to learn how to double de-clutch properly!),but before you rip the engine and gearbox out there are two other things to consider. First, make sure that you have ordinary engine oil in your gearbox. If someone has put hypoid oil in the gearbox, you will have similar symptoms. The cure is drain and refill with 20/50 or similar. Second, you could still have air in the clutch hydraulics, causing the clutch not to free-off completely. MGA clutch slaves are notoriously hard to bleed the conventional way. I 'back-bleed' by removing the slave cylinder push rod clevis pin from the clutch lever and pushing the slave cylinder piston fully back into the cylinder gently by hand and allowing it to restore naturally. Repeat this two or three times and then re-connect the push rod. Hope this helps.
Lindsay Sampford

I think what he means is, it grinds on an up shift from 2nd to 3rd, but not on a down shift from 4th to 3rd. Grinding gears in only one gear, 2nd, 3rd or 4th, is about 99% chance of worn synchronizer ring. This requires removal and disassembly of the gearbox to replace the part. See picture.


Barney Gaylord

It might be worth checking to see that you have bled the clutch sufficiently - it is a bear!

I finally got it by bleeding from the bottom with a syringe full of brake fluid connected to the bleed nipple.

JIM in NH
AJ Mail

During the test drive today I did not grind any gears on the way up and was able to downshift from 4th to 3rd. However I can not downshift from 3rd to 2nd.

The synchronizer rings are brand new.
gerard hutchinson

How about 1st to 2nd?
Art Pearse

Gerard, what oil do you have in your gearbox? See my previous post.
Lindsay Sampford

Art,
1st to 2nd improved greatly after bleeding the system!
gerard hutchinson

Lindsay, I'm not sure what oil I put in. That realization seems to suggest that I should empty the oil and replace it with 20/50!!!
gerard hutchinson

I had filled my box and had some trouble - even using the 20/50.

Later I discovered that it was still a bit under-full - guess I had some trouble reading the dip stick.

Filled all the way up, it was much better!

JIM in NH
AJ Mail

Gerard, hypoid oil has a real smell to it! Pull the gearbox dipstick and give it a sniff. If it just smells oily, you are OK, but if it has got a strong smell like the oil in your rear axle, it is hypoid, and should be drained and the box re-filled with ordinary engine oil.
I have mentioned it before on here, but when I first got my A, the synchro when shifting from 3rd to 2nd didn't work at all. It was obvious to me, when the gearbox got warm, that it had been filled with hypoid gear oil because of the horrible smell that filled the cockpit. I drained the box and refilled with the correct oil and the synchro started to work, and over the next couple of weeks got better and better. After about 500 miles I drained and refilled the gearbox again to get rid of the last traces of hypoid oil. Twelve thousand miles later the synchro works fine. I think there is some stuff on Barney's site about hypoid oil destroying the bronze synchronizers in MGA gearboxes.
Lindsay Sampford

During the test drive today I did not grind any gears on the way up and was able to downshift from 4th to 3rd. However I can not downshift from 3rd to 2nd.

The synchronizer rings are brand new.
gerard hutchinson

Gerard, I assume you have just rebuilt the box as you say the sync rings (baulk rings?) are new. My memory is struggling here as it is about 4 years since I rebuilt a 3 speed box and made two mistakes.

First mistake was fitting a brass baulk ring to a box that should have had the steel type. The symptom of that mistake was generally hard to shift into second and as time went on the harder it got. I was also experiencing grinding changes from 4th to 3rd. I only found my mistake with the baulk ring when I stripped the box down to fix the 4th/3rd problem. The brass "dust" in the oil gave that one away.

Second one is a bit harder to remember. I managed (by lack of care!) to put the sliding coupling, which I think is usually referred to as the dog,on the 3rd motion shaft offset by one spline. This restricted the movement of the baulk ring and caused mis-alignment of the dog and the synchroniser thus causing the grinding changes.

If you have recently re-built the box then it is worth considering if you have done one of the above. Surely nobody else could be as silly as me and make two mistakes on the same job!

Tony
Tony Oliver

This thread was discussed between 22/10/2011 and 25/10/2011

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