[Healeys] Transmission / Overdrive or Clutch slippage

Bob Spidell bspidell at comcast.net
Thu May 20 16:44:11 MDT 2021

Strange case indeed. My guess--and it's only a guess--is that the cone 
clutch in the O/D is worn and slipping when the oil is hot. The cone 
clutch is a 'wet' type, and AFAIK new ones aren't available (DWM sells 
relined ones, with a core of course). When the O/D is not engaged, eight 
very strong springs hold the cone clutch together as a 'solid' unit, 
when you engage the O/D oil pressure--yours appears to be 
adequate--pushes a couple pistons that force the cone clutch apart and 
locks the sun gear, which starts overrunning of the output gearing 
(hence 'overdrive'). Since new clutches aren't available, yours may be 
original and not have sufficient material to fully engage the outer part 
(FWIW, I went through my BJ8's O/D and it still had sufficient material 
at 205K miles; I attribute this to my superior O/D operating technique ;)).

The other thing is the springs; I read somewhere--possibly in the shop 
manual--that these springs should ALWAYS be replaced when going through 
the O/D and, even though mine looked fine I bit the bullet and bought a 
new set. It's possible the springs weaken over time and become unable to 
keep the cone clutch engaged in all conditions (e.g. hot, slippery oil).

Again, this is just a semi-informed guess, but maybe someone can expand 
on it.


On 5/20/2021 2:41 PM, Rafael Abugattas via Healeys wrote:
> Hi all,
> 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 OK.
> 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.
> https://www.dropbox.com/sh/t5p8kqz6v6yduyt/AADizyVMyBKPozy284B-udA4a?dl=0 
> <https://www.dropbox.com/sh/t5p8kqz6v6yduyt/AADizyVMyBKPozy284B-udA4a?dl=0>
> 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 
> is warm.
> 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!
> Rafael
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