A couple of Overdrive questions

[jasper]

Hi All, Overdrive experts one step forward please!

 

As we are now into the minus centigrade numbers here I decided it was time to set about getting the promised winter work done, opening the gearbox up to sort the second gear jumping out problem. Whilst stripping that and waiting for parts I braved a look inside the Overdrive and found a thrust washer staring out me, broken possibly in four pieces (I only found 3 bits), so I decided to delve further.....

The (next) thrust washer which sits under the sun wheel in a recess in the Planet cage is also broken, although this is "halved, both pieces in situ and due to the make up of Bronze, the ragged edges "key" with each other, stopping it from coming out, the planet gears overlap the edge of the washer by about a 1/16" and I will need to break it completly to remove. The new replacement which I have is chamfered around the edge, I assume to aid fitting without removing the gears.

Is my assumption correct? If I break the old washer there is no going back. At the moment I could rebuild with the broken washer in place, but as it is all apart it makes sense to replace it if poss.

 

The second question, I also removed the operating pistons to clean the sludge and old oil out, thereby relieving the pressure behind them. I started rebuilding the accumulator area and I have replaced the solenoid bracket and after tightening the 2 red painted screws up have found the smaller (inner) Accumulator spring sits very loose inside the larger outer spring which is held under pressure by the bracket.

 

Is this normal? Will it be tensioned once the pressure is built up? Or have I knackered something for which I will pay for dearly very soon?

For any replies well and truly grateful!

Cheers

Jasper

[Colin Fairhurst]

Hi Jasper,

 

I think there are very few people who will claim to be an expert on overdrive units even when they may have some experience.

I am not an expert but I have found the TR register "TECHNICALITIES" CD very helpful and also a download of the "Greasy Hands Garage Guide To Rebuilding The Triumph A-Type Overdrive" in which he lists the complete procedure step by step.

In the latter he states that the overdrive manual calls for an end float for the sun gear to rotate freely of 0.014 to 0.020 thou' whereas the later Haynes and Bentley manuals specify 0.008 to 0.014. He says "So I tend to believe the 0.008 to 0.014 spec. in the later manuals.Perhaps a large clearance contributes to the problem of broken planet carrier washers".

I think he may have something there because it is a common problem and may have a common cause.

I don't know if you can replace that broken thrust washer without dissmantleing further. I think that you should definitely replace the thrust washers and check the end float. The broken thrust washer will eventualy brake up completely.

I would dismantle the unit and check the other components and where possible get the uprated version of any parts that you replace.

Hope that helps.

 

Regards, Colin.

[Don Elliott]

I believe that the thrust washers are available in different thicknesses and you may need to measure the thickness you need to get that clearance you want.

 

Here are some links that may help

 

http://www.buckeyetriumphs.org/technical/AOD/AOD1/AOD1.htm

 

http://www.buckeyetriumphs.org/technical/AOD/AOD4/AOD4.htm

[RandallD]

No, unfortunately you will need to remove one of the planetary gears to replace that lower thrust washer. The chamfer is there to avoid interference with the gears after it is installed.

[jasper]

Hi all,

thanks for the comments, I think I have a possible reason for the broken washer this evening, on a search I found the very good info on the Buckeye triumph website as Don suggests, reading this gave me the courage to remove a planet gear and in fitting the washers I have found that the ID's of 2 were too small to fit on the main shaft from the g'box, and, as with the new replacement second gear bush (probable cause of it jumping out of gear), a quick hone on the lathe has sorted them out. Can well imagine that brute force was used to force the g'box and OD together last rebuild (all looks pretty clean in there for it's age so it has been apart at least once before).

Yes, I have been checking the thicknesses with a micrometer and the new washers either side of the sun wheel are both 5 thou thicker compared to the old ones. The one under the clutch is a thou thicker. The steel washer sitting on top of the sun wheel seems to be the only part that you can get in different thicknesses. Need to investigate that further, but it does make sense.

 

The greasy hands link from Colin is also good, hadn't seen that one.

 

The other question about the 2 springs is still open. Seeing as they quote almost 1/2 ton pressure on those springs when all is pumped up, it could well be that the smaller of the 2 will "take up the slack" once running. I haven't yet found anything that says how long those springs should be and/or the tolerances allowed. There is a comment in part 4 of the info on the Buckeye site made by a moss employee that the smaller spring is there just to keep the larger one straight! Can't see it managing that, but fair enough. Seems to come down to checking the pressure and adding spacers to suit. the OD worked before so they can't be that far out.

 

Again, thanks for the pointers, they have helped a lot.

 

cheers

jasper

[dingle]

Jasper-The spring lengths are in part 4 of the Buckeye articles. He really beats the subject of accumulator springs to death.

Berry

[jasper]

Jasper-The spring lengths are in part 4 of the Buckeye articles. He really beats the subject of accumulator springs to death.

Berry

 

 

Hi Dingle,

you are right, but I read it as "his" findings and not what they should be. I have a copy of the Service instruction manual from Triumph now and I have ordered a new set

 

Cheers

Jasper

[dingle]

Jasper-I was disappointed in the service instruction manual and found that the Buckeye articles much more usefull. Nelson Riedel (the author) was very carefull to document his sources. The comment about the inner accumulator spring having little effect on the pressure and was used to support the outer spring came from Overdrive Repair Services. I believe they are pretty much the authority on OD rebuilding and supplier of parts. When I rebuilt my OD, I used the original accumulator springs and was able to get 370 lbs. pressure with one .020" shim. I did replace the clutch return springs which cured a slow to release problem. Be sure to check the amount of lining on the clutch sliding member. I think that they were .100" new and should be replaced when less than .060.

Berry

[scotland]

Hi Jasper,

 

1/ I'm not sure I really get which washer you're dealing with. There's some washer to adjust the sun axial clearance. You should find the expected clearance in the overdrive tech documentation. Tell me if you dont'. When I was rebuilding my overdrive, I've made this adjusting washer from an old bush, which I cut to keep only a washer, and I adjusted the tickness to get the correct clearance.

 

You can try a quick look on my blog where I put some pictures :

http://tr3.photoscotland.org/?q=en/node/14

 

About the second question. I agree that he inside spring is probably useless. Anyway the A type overdrive is know to be brutal, and it can be considered as a kind of improvement to have less force in the spring, to make it engage smoother. I wouldn't change anything.