[Fot] A-Type Overdrive Dilemma

[Larry Young]

I don't think the unidirectional (overrun) clutch can slip. It can only 
break and you would know it. I'd guess it is just slipping. 350 is about 
right for a large accumulator model, but you need about 450 for a small 
accumulator. Low pressure is usually just spring fatigue. That can be 
fixed by shimming the spring with a couple of hardware store washers. 
I'd get the pressure up to spec first before anything else. I suppose 
the type of oil might cause slipping too.
  - Larry Young

On 8/1/2018 12:02 PM, Glenn Franco via Fot wrote:
> Looking for some help from the wisdom of the FOT List.
>
> I have rebuilt a number of Triumph A-type overdrive transmissions in 
> the last few months but have one that is giving me problems.
>
> The overdrive functions OK when applied and will go into overdrive at 
> a steady cruising speed.
>
> The problem is when under load accelerating up a hill or to pick up 
> speed it softly drops out. When you lift throttle it will go back in.
>
> We put a 500 psi gauge on the operating valve thinking we were losing 
> oil pressure when it drops out of overdrive. Gauge reading shows a 
> pretty steady 340 psi reading. When it drops out the gauge doesn't 
> drop out but remains steady.
>
> 340 psi is lower than the expected 400 - 500psi. Does that indicate 
> oil pump replacement is necessary? The engine rpm was approximately 
> 2500-3000 rpm.
>
> Since it softly drops out of overdrive I'm thinking a slipping 
> overrunning clutch??
>
> Any advice would be greatly appreciated.
>
> Thanks in advance
>
> Glenn Franco
>
> 74 TR6 , TR250, MG TC, BMW e10 2002
>
>
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