Transmission trouble

[Pete3000]

Hello all. Looking for some much needed advice while transmission is again apart. BT7 Mk2 Centershift w/OD. Recently had tranny at a local guy's shop who was recommended by a friend. 1st gear excessive noise. He disassembled and inspected all and was not able to "see" anything wrong. He was impressed with which the fine condition of all components and we decided to put back together only replacing seals. Still has same loud grindy first gear. Then the next problem occured.. 100 miles from the reinstall, the transmission has developed a loud whine and vibration. I did a little troubleshooting and here is what I came up with. It starts to howl/vibrate around 15 to 20mph. Louder if I go faster. Does not matter what gear I am in. I can throw it in neutral, still there. I can shut of the engine, still there. I thought that because the wheels/driveshaft were still spinning at say 20mph that it might be them but I removed the driveshaft and while spinning through gears , noise is still there. Appears to be something that is on the output side as this is the only thing turning when both the car is in neutral and motor is shut off. I removed it and returned it to the tranny shop and once again, he cannot "see" anything wrong. What could he be missing and what would be the most likely culprit for both the first gear noise on a first gear that looks very good and second on the whine/vibration when coasting past 20mph. Any help or guidance would be greatly appreciated. Thanks.

 

[nevets]

seek a 2nd opinion?

 

[Randy Forbes]

The needle rollers on the layshaft, in my opinion, are the first to go (especially at the 1st gear end). However, the laygear in "connected" to the engine any time the clutch is out, so shouldn't have been making noise when the engine was off. The main bearing on the 3rd motion shaft would be the next candidate, or the bearings in the overdrive unit, though less likely in my mind.

Quite honestly, I've never opened up a Healey gearbox and not seen something that was wrong/worn/chipped.

My money is on the layshaft...

 

[tahoe healey]

Were the detent balls and spring present (69 and 70 in Moss cataloge)? They are frequently omitted on rebuilds and allow the shafts to move.
TH

 

[Pete3000]

Thanks guys. The balls and springs were present. Did you mean that the laygear is not spinning when in neutral with engine off? So what, in the gearbox is still spinning say rolling down a steep hill, in neutral with engine off? This is where I'm confused to what actually is spinning, causing such a noise.

 

[Legal Bill]

What do you mean when you say your first gear is grindy? Please explain this issue in more detail. The first gear is the loudest gear in the car even when it is perfect.

 

[Randy Forbes]

First gear (and reverse) are straight-cut teeth and noisier by design than the helical-cut (at an angle) gears. First gear always howls, but should be a consistent sound, and not "grindy", just growling.

With the engine off and the clutch out (engaged) the laygear should be stationary__assuming the xmsn is in neutral__while coasting down the hill. The 3rd motion (or output) shaft would be spinning; its bearing is at the back of the main gearbox (ahead of the overdrive). The forward end of the 3rd motion shaft rides on needle rollers inside the 1st motion shaft, and that is another possibility for your noise.

You'll have to tear down the gearbox to isolate those two (2) bearings.

 

[Pete3000]

First gear is a consistent growl, more than a grind , however it definitely is excessive and louder than normal. I am aware that it is a straight cut as is reverse but first is louder and really seems excessive, although it does not jump out of gear and looks to be in good condition. I found a guy that has rebuilt many healey trannys and am going to bring it to him.

 

[Healey 100]

Pete:

Your well thought out diagnostic tests tell me the problem is confined to the main shaft. The only main shaft bearings moving for all the situations you describe are the rear main transmission bearing and the OD output shaft bearing. It makes the noise in every gear, with or without the engine running, and with the car in neutral, this eliminates most other bearings. And it does it even with the driveshaft out (this eliminates the rear axle as the source).

Did the OD work after the rebuild? Attaching the OD to the gearbox is tricky, making a mistake in there could produce noise in the main shaft. How about the OD oil pump, it could be not properly engaged with the cam on the main shaft. This would also produce noise for all the conditions you describe.

If it was quiet before being taken apart, there is a problem with the reassembly, and it needs to come apart to find out why. If it was always noisy, I would replace the mainshaft output bearings on the tranny and OD even if they look OK.

Noise in first gear? Get used to it, this is a Healey. Most of them are loud. Start it in second! Seriously, the needle bearings on the layshaft need to all be there or it will not align properly and be noisy. If you dismantle, check to make sure there is no side or end play on the layshaft.

Bill.

 

[Pete3000]

Thanks Bill. Yes the O/D worked, but the noise began after driving about 75 miles @ 60mph, while engaged in O/D. It was not fun as I was still 120 miles from home. Still may be a reassembly problem at the O/D to tranny. I'll be sure to check that layshaft. Especially with what looks like a good first gear assy.

 

[BUNDYRUM]

Hello pete3000,

Not sure what I can add here but there is something I've noticed missing in the replies.

The design of the transmission is such that while ever the input shaft is turning the laygear turns as well. They are directly connected, one cannot turn without the other not turning.

With regard the "grindy 1st gear noise". Yes some of the reason it is because the teeth on the 1st and reverse gear are straight cut and not helical cut like on the other gears. The main reason for the noise is that the gears were case hardened after they are manufactured(this is not a bad thing by the way) and over a period of time the hard case (which is like a skin)tends to wear off and pull away from the gear material. The teeth look as though they have a bad case of acne. Now you have a mating surface that is not smooth and when it runs against the mating gear it tends to tear at the surface of that gear (still with me?).

If the O/D worked as you said then there shouldn't be a problem with it. The oil pump must be lined up correctly otherwise there wouldn't be oil pressure and thus a working O/D. The ball bearings inside the O/D are usually very long lasting and I mean very long lasting so if it was working before then there is no reason it shouldn't work now.

Drain the oil from the transmission and look to see if there are any metal pieces in there. You may see some brass/bronze colored but your looking for steel colored pieces. Drag a magnet through the oil and see if it picks anything up.

The problem would most likely be the needle roller bearings on the layshaft as well as the layshaft itself. Once again the needle roller bearings and the shaft are case hardened when manufactured and the same applies as I said earlier. Yes it could be the needle rollers that the 2nd gear and the 3rd gear run on but more likely the layshaft.

The internals of the transmission will have to dismantled to get to the laygear/laysghaft.

If you are taking it to another mechanic that sounds like a good thing as the first guy sound as though he has no idea. Find someone who can recommend a mechanic because of their experiences.

These transmissions are not difficult to take apart and put back together again. Even the "Haynes" workshop manual does a good job of explaining the process together with good illustrations and descriptions.

Yes, I am mechanically inclined so it's a little easier for me but this job is not beyond the scope of the beginner especially.

Sorry to go on for so long.

Keep us informed how you get on because then someone else can benefit from your experience.

Best regards,

bundyrum.

 

[zblu]

Sometimes, if the cogs are not meshed tooth to tooth as they came apart this can contribute to noise as they have already bedded in to the tooth they were originally aligned with

 

[Johnny]

Here's what you don't want to see;

 

[Pete3000]

Ok all, its been 3 months but the gearbox is fixed. Gearbox was disassembled completely by a more experienced mechanic this time. Since he never was able to hear the problem , he could only go by his detailed visual inspection. First gear noise was caused by a chewed laygear. First gear was not bad but I opted to replace it anyway. Noise in first gear has never been quieter. As far as the main loud howl that was developed, He could not find anything that really jumped out at him however the Thrust washer on the first gear side of the laygear was badly shaved. He also replaced 2 bearings, 1 in the main gearbox and one in the O/D as they were inexpensive enough, although they did not feel at all worn or bound. I also had a worn synchro but would not have caused the noise. So, I do not know for sure if the thrust washer was the culprit but the noise is not there. She shifts smooth and O/D engages great. 1 reconditioned laygear, 1 first gear assy, all 3 synchros (brass), 1 thrust washer, 1 bearing in gearbox, 1 bearing in O/D, all new springs and balls, gaskets and seals = $1500. Not bad...

 

[Johnny]

Thanks Bill. Yes the O/D worked, but the noise began after driving about 75 miles @ 60mph, while engaged in O/D. It was not fun as I was still 120 miles from home. Still may be a reassembly problem at the O/D to tranny. I'll be sure to check that layshaft. Especially with what looks like a good first gear assy.

Let me state the ovious that I'm sure you checked. One, is there oil in the transmission, two did you replace the spigot bearing in the flywheel?