[Healeys] Transmission / Overdrive or Clutch slippage
gradea1 at charter.net
gradea1 at charter.net
Thu May 20 21:22:43 MDT 2021
Rafael-a few comments about your issues. I coming from a different
place by assuming that the cone clutch is ok.
First, what oil is in the gearbox and transmission?-only use 30W NON
detergent-all others will foam...especially with the addition of heat.
When the OD was rebuilt- there are two sets of springs of the 8...4
are 4-1/4" and 4 are 4-1/2" the longer springs must go to the outside
and the shorter to the inside of the cone structure. If the springs
are coil bound from misuse-replace them. If they are reversed the
pressure to hold the clutch in direct drive is not sufficient.
The overdrive must achieve at least 400lbs of pressure at all times in
use. The low numbers indicate an accumulator issue. O-rings or piston
rings worn or misplaced.
It is exteamely important that the car never goes into reverse with
the overdrive engaged. Make sure the lockout switch is working.
Be sure the two check balls are in proper place 1/4" and 5/16" do not
mix them up with each other.
Has your OD rebuilder done other Laycock overdrives? Hank
-----------------------------------------From: "Rafael Abugattas via
To: "healeys at autox.team.net"
Sent: Thursday May 20 2021 2:47:20PM
Subject: [Healeys] Transmission / Overdrive or Clutch slippage
Last year I requested your help regarding a strange overdrive or
slippage problem I have in my 1962 Tricarb BT7.
I received very valuable comments and suggestions but sadly the
problem persists: Overdrive would not activate under any circumstances
and when the engine / transmission is warm and we engage reverse, the
engine revs but the car won´t move.
There is slippage somewhere in the transmission / clutch or
overdrive. When the car is cold, reverse engages without any issues.
This only happens in reverse gear after the car has been driven a few
miles and the engine and transmission are warm. Forward gears engage
all the time without any issues.
The car has been recently restored. Before the restoration the
overdrive was operational. Now it’s not.
The transmission and overdrive have been taken apart and assembled
twice looking for something visually wrong. Everything seemed to be
The clutch and plate were also removed for inspection. The clutch was
recently redone, adjusted and tested.
A friend suggested we should verify the oil pressure on the
overdrive. On this link you will find a couple of videos of a test we
have recently done with a manometer installed on the overdrive to
check the oil pressure at different RPM´s.
The pressure on 3rd and 4th gears goes up to 400 psi and drops as it
goes to lower gears. At idle is between 150 to 200 psi
In forward gears the car runs fine; the problem that we need to solve
is that the overdrive would not activate(even though it is connected
and everything seems visually OK) and the slippage we have when
engaging reverse (the car won´t move) when the engine / transmission
We are located in Lima – Peru and as you may imagine, there are not
many experts in this particular area of expertise.
Any thoughts or suggestions from you collective knowledge and wisdom
on how to proceed will be much appreciated.
Thanks in advance!
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