I normally shim them with plan hardware store washers that are about
1/16". These old springs always seem to be a little week, but I have
never had to use more than two to get an OD back to spec. I checked
several manuals (but not the TR4 workshop manual) when we wrote the
articles. There were often discrepancies between different sources. I
think the accepted spec for a large accumulator is about 360 psi and 450
for a small accumulator. The change to the small accumulator was made
to give a more gentle engagement for the IRS cars. I can't remember
exactly what I did to get my large accumulator to 525. Since the inner
spring doesn't do much, I may have used a small accumulator spring as
the inner spring or used a plug to shim the inner spring more than the
outer spring. Sam and I should revise the article, if it only takes 1/4
inch to reach coil bind one must be very careful.
Larry
On 7/31/2013 9:55 AM, Randall wrote:
> I'm sorry, Larry, I don't recall the thickness of washers. Maybe
> around 3/16". It was a large accumulator, and I had shimmed it from
> around 300 (no shims) to around 450 psi (original TR4 workshop manual
> says that 490-510 "is required" even though the Bentley gives
> 380-400)). At 300, the OD wouldn't always grab in 2nd gear, so I knew
> that was too low. After the damage was discovered, I loaded the main
> spring (which I believe was original to the unit, but with a whole
> lotta miles on it) into a hydraulic press and measured the length with
> it compressed solid. Combined with all the other measurements, I
> believe that the spring was reaching coil bind with the ports
> uncovered only about 1/4 of the way. The relief ports were definitely
> opening enough to flow some oil during bench testing, but as I'm sure
> you are aware, the pump output volume is a direct function of shaft
> rpm and they were apparently not able to open far enough to handle the
> entire pump output at higher rpm. I was also using cheap motor oil
> during bench testing (saving the MT-90 for the road) so it's possible
> the oil change had some impact as well. Nelson also wrote about
> finding coil bind, but he found it on the bench with around 1/4" of
> shims. It just hadn't occurred to me that it was possible for the vent
> holes to be only partially uncovered when the spring bound. I'm pretty
> sure that "root cause" is that my spring was old and sagged from it's
> original dimensions. Unfortunately, I didn't have a new one on hand to
> compare against (or I would have just installed the new one). At the
> time, they were backordered at all US vendors (and the one I ordered
> from the UK didn't come in for over a month). (Moss actually changed
> the part number and doubled the price, so I'm guessing that a new
> manufacturer had to be found.) -- Randall
_______________________________________________
fot@autox.team.net
http://www.fot-racing.com
Archive: http://www.team.net/archive
|