A Type Overdrive "Refresh"

[TRDejaVu]

A Type Overdrive "Refresh"

I broke this away from the other current overdrive thread so as not to hijack it. Over the years I have overhauled most major components on these cars (engines, brakes, suspension etc etc.), but never a transmission. I consider this work as therapy so I am having a go at rebuilding an early TR6 O/D gearbox before replacing the existing unit in my non O/D TR4. The data plate shows that this O/D unit had been previously rebuilt.

I have it almost completely apart; the key word being "almost". As I don't have access to Mr. Churchill and his special tools I need to make up a rubber expansion tool to pull out the accumulator piston (small version without threaded insert). I am also trying to remove the 2 operating pistons but they are putting up a good fight. I have a couple of the online tip documents, but am open to all ideas; unfortunately I don't have a compressor.

When I removed the OD clutch housing I found a thrust washer broken into 8 pieces. Other than that, first impressions are that this is still in good condition. I am trying to find out what the wear limits are for the clutch material - anyone know?

 

[jjbunn]

Re: A Type Overdrive "Refresh"

Is it as weird as it looks that the thrust washer broke into eight identical pieces? What's happened to do that?

 

[2wrench]

Re: A Type Overdrive "Refresh"

In my mind's eye, I seem to remember seeing, somewhere,
a washer similar in nature with "scores" in it that
could well replicate a destruction of this nature.
I just don't know where. Certainly not from the
inside of an overdrive, it seems.
Does look a little strange.

 

[TheSearcherMan]

Re: A Type Overdrive "Refresh"

Clutch wear is not the only issue. They come apart probably as a result of age. It's a gamble not to replace it during a rebuild.

 

[TR3driver]

Re: A Type Overdrive "Refresh"

Yup, it's scored like that, in an A-type OD. 4 on one side and 4 on the other, evenly spaced for 8 weak spots total. I don't recall which one offhand, maybe the one between the sprag clutch and the annulus, or the one inside the planetary gear assembly. In fact, now that I think about it, maybe there is more than one of them.

The scores are for oil circulation. Never seen one break all the way into 8 pieces, but I've seen 4 or 5. My theory is that when things get a bit loose, the clutch carrier bangs around at every shift and eventually breaks the washers.

I've never seen a clutch thickness spec, either new or wear limit. AFAIK it's like the main clutch, it's not worn out until the rivet heads are about to be exposed. And from your photo, it looks like there is plenty of material left.

I've always just grabbed the center post of the pistons with pliers or vice grips; don't recall ever having to resort to air pressure. Wiggle them around a bit, they should come out.

 

[DougF]

Re: A Type Overdrive "Refresh"

Be sure to check the mating surfaces to that washer. Mine went and cut into the surface of the annulus. It will be going to Quantum for resurfacing.

 

[TRDejaVu]

Re: A Type Overdrive "Refresh"

I've always just grabbed the center post of the pistons with pliers or vice grips; don't recall ever having to resort to air pressure. Wiggle them around a bit, they should come out.

The accumulator piston is now out, but the 2 operating pistons are not moving; in/out or rotating. I am going the PB Blaster route at this time.

 

[TRDejaVu]

Re: A Type Overdrive "Refresh"

Well, the 2 operating pistons really didn't want to come out. I finally got to meet angelfj and we tried to coax the blighters out with his air supply (and some beer); but they weren't falling for that old trick. 2 more days of soaking (this time with Gibbs) as well as various heat/freeze combinations and then they started to move. They fought me all the way, but I finally out them out.

Looked for all the damage that must have been preventing them from moving and found nothing. There are some very minor little marks that I plan on cleaning with crocus paper and that is all.

These look like they will be a fight to get back in so I will have to make up a smaller version of a piston ring compressor and use plenty of lube. How "snug" should the piston be in the bore (without the o-ring)?

 

[angelfj1]

Re: A Type Overdrive "Refresh"

Ian: Oh, so that is the early type with the metal piston rings rather than the O-rings after all? What condition are the rings in?

Frank

 

[TR3driver]

Re: A Type Overdrive "Refresh"

Don't know a spec for the clearance, but mine would slip easily in & out if you didn't get them cocked in the bore. Even with lube, though, it was easy to get them cocked, so it wasn't something I played with much.

A worm-type hose clamp makes an adequate (barely) ring compressor, if you do have the early version with the metal rings. The O-rings shouldn't need a compressor.

Last time I looked, you could buy a pair of O-ring type pistons for about the same price as a set of metal piston rings. If the rings need to be replaced, I'd change the pistons instead.

 

[TRDejaVu]

Re: A Type Overdrive "Refresh"

I may not have explained it properly, but the pistons had the single (rubber?) o-ring, not the metal rings.

As to fit, these pistons are extremely "snug". When you say easily slip in and out, do you mean that if you temporarily fitted them WITHOUT the o-ring they would fall under their own weight, or would there be resistance due to the restriction of the displaced air only being able to escape through the oil-way? I hope that question came out clear.

 

[TR3driver]

Re: A Type Overdrive "Refresh"

What I meant was that, with the rings removed (either metal or rubber, I have both), the pistons slip into the bores with only finger pressure. But that's entirely friction between the piston & bore, I didn't try blocking off the passageway to look for air resistance. And they wouldn't fall of their own weight.

Sounds like your OD may be less worn than mine were; so I'm not sure I'd try to relieve the bores or pistons any. Maybe polish them just a bit if there are rough spots.