Reverse Piston Failure - time to crack open the tool chest!

DMGRS · 28th April 2021, 11:05

It's no secret that I've been rather excited about the very early 75 Tourer I picked up a couple of months ago - sadly our Rear Upper Arm project and some other bits and pieces and home got in the way of getting her back on the road...
...until now!

I finally found a couple of hours to delve into the mysterious world of automatic gearboxes - they're very much a dark art to me, but I've always been a little fascinated by how they work.

I'll do a full write-up for the How To section at a later date - I'll keep this as brief as possible so I don't put the rest of you to sleep.

Stuff you'll need to remove for the job - undertray, arch liner on the nearside, access panel on the side of the gearbox facing the nearside wheel, battery box, FBH (if fitted), fuel pump / filter (diesel only), airbox etc (petrol only)
Tools you'll need - standard socket set, spanners, Torx bits to remove the battery tray, some clamps to squeeze the drum removed to separate the reverse piston, circlip pliers

Not a bad job so far - just a bit fiddly in places.
I removed the battery box, fuel filter and pump etc to allow access to the gearbox mount bolts - you'll need to lower the gearbox down to get the cover off and remove it.

Once the gearbox was dropped down a little I removed the wheelarch liner and then all the bolts holding the cover in place - if you've not emptied the gearbox of oil, it'll escape at this point. It might need a little pry to break the seal (instant gasket-type stuff).

To remove the cover completely I had to drop the subframe a couple of inches - it wouldn't quite fit through the gap between inner arch and subframe.
Once removed you can pull the full drum assembly from the gearbox... and then the fun begins!

Getting the drum assembly to release the reverse piston itself was pretty fun - you need to remove the clutch packs a step at a time by releasing the circlips as you go, be sure to inspect the clutches as the High Clutch Assembly in this was absolutely knackered (there's 5 clutch plates, all 5 were damaged very badly).
Finally, you'll need to apply some compression to the last part in order to split it - there's a retaining ring holding a spring between the reverse piston and drum itself, so you need to compress this to release the retaining ring.

I'll go into more detail in the write up - I'm now waiting for the clutch plates to arrive (along with some other bits and pieces).
And now for the pictures!

The crack is circled in blue; took me a while to spot but oh boy is she a beauty.

cb750chris · 28th April 2021, 12:17

Looking good

What were the symptoms of the reverse piston failing?
I was asked to look at an auto that I suspect may have a dodgy reverse piston, but I have not stripped the box to look yet, as I want to limit the work to only the repairs necessary.
see my other thread for the symptoms I have got

Regards Chris

mh007 · 28th April 2021, 21:47

Quote:

Originally Posted by cb750chris

Looking good

What were the symptoms of the reverse piston failing?
I was asked to look at an auto that I suspect may have a dodgy reverse piston, but I have not stripped the box to look yet, as I want to limit the work to only the repairs necessary.
see my other thread for the symptoms I have got

Regards Chris

In my experience, reverse starts to lose drive (almost like a slipping clutch) & eventually completely fails, losing all drive.

DMGRS · 29th April 2021, 13:05

Quote:

Originally Posted by cb750chris

Looking good

What were the symptoms of the reverse piston failing?
I was asked to look at an auto that I suspect may have a dodgy reverse piston, but I have not stripped the box to look yet, as I want to limit the work to only the repairs necessary.
see my other thread for the symptoms I have got

Regards Chris

Exactly as mh007 says Chris - it'll slip and lose drive altogether (but in this instance it was the upper gears that failed I believe).
The problem is if you drive it slipping, you'll need to do the clutch pack(s) too in all likelihood - but given the low mileage of this gearbox and history of the car I figured it was worth the effort

28th April 2021, 11:05	#1
DMGRS Discount MG Rover Spares Rover 75 CDTi, 2x MG ZS180 Join Date: Jun 2011 Location: Hythe, Southampton Posts: 11,320 Thanks: 456 Thanked 3,377 Times in 2,027 Posts	Reverse Piston Failure - time to crack open the tool chest! It's no secret that I've been rather excited about the very early 75 Tourer I picked up a couple of months ago - sadly our Rear Upper Arm project and some other bits and pieces and home got in the way of getting her back on the road... ...until now! I finally found a couple of hours to delve into the mysterious world of automatic gearboxes - they're very much a dark art to me, but I've always been a little fascinated by how they work. I'll do a full write-up for the How To section at a later date - I'll keep this as brief as possible so I don't put the rest of you to sleep. Stuff you'll need to remove for the job - undertray, arch liner on the nearside, access panel on the side of the gearbox facing the nearside wheel, battery box, FBH (if fitted), fuel pump / filter (diesel only), airbox etc (petrol only) Tools you'll need - standard socket set, spanners, Torx bits to remove the battery tray, some clamps to squeeze the drum removed to separate the reverse piston, circlip pliers Not a bad job so far - just a bit fiddly in places. I removed the battery box, fuel filter and pump etc to allow access to the gearbox mount bolts - you'll need to lower the gearbox down to get the cover off and remove it. Once the gearbox was dropped down a little I removed the wheelarch liner and then all the bolts holding the cover in place - if you've not emptied the gearbox of oil, it'll escape at this point. It might need a little pry to break the seal (instant gasket-type stuff). To remove the cover completely I had to drop the subframe a couple of inches - it wouldn't quite fit through the gap between inner arch and subframe. Once removed you can pull the full drum assembly from the gearbox... and then the fun begins! Getting the drum assembly to release the reverse piston itself was pretty fun - you need to remove the clutch packs a step at a time by releasing the circlips as you go, be sure to inspect the clutches as the High Clutch Assembly in this was absolutely knackered (there's 5 clutch plates, all 5 were damaged very badly). Finally, you'll need to apply some compression to the last part in order to split it - there's a retaining ring holding a spring between the reverse piston and drum itself, so you need to compress this to release the retaining ring. I'll go into more detail in the write up - I'm now waiting for the clutch plates to arrive (along with some other bits and pieces). And now for the pictures! The crack is circled in blue; took me a while to spot but oh boy is she a beauty. __________________ Your trusted MG Rover specialist! Tel: 02380 001133 / Email: [email protected] We now have a 'chat' function on our site for even quicker replies. Give it a try! Remember - discount code FORUM5 for 5% off

28th April 2021, 12:17	#2
cb750chris Trader Rover 75 Tourer Join Date: Apr 2011 Location: Portsmouth Posts: 849 Thanks: 201 Thanked 292 Times in 200 Posts	Looking good What were the symptoms of the reverse piston failing? I was asked to look at an auto that I suspect may have a dodgy reverse piston, but I have not stripped the box to look yet, as I want to limit the work to only the repairs necessary. see my other thread for the symptoms I have got Regards Chris __________________ Now offering T4 services in the Fareham area Replacement keys programmed / supplied / cut Diesel 135 upgrade available IPK virginisation and T4 matching available Sorry, due to a big change in home circumstances, I am unable to do any large jobs at present, but can still offer evening time diagnostics.