slips when in 3rd(auto)

[sliver]

r75 2.5 v6, hi everyone, gearbox fluid changed a couple of weeks ago checked level again last week. when in drive or manual shift it slips in third gear when the power increases, just drove it again in manual shift only just to prove thats whats happening. as i have read else where on the forum could this be a loss of oil pressure and could someone explain what this reverse piston is. many thanks to one and all once this is fixed i'll be cruising.

[xsport]

What fluid did you use for the fluid change ? Also did you use the official mgrover proceedure , flat surface/ worked through the gears and up to temperature ? ...

[sliver]

Thanks for your response much appreciated, followed procedure on the forum, but weren't sure how to monitor the temperature, waited until the gear box felt reasonably warm, only had the car a couple of months. Dropped oil first time only got 2ltrs out instead of 4,put just over 4 back in and have put another ltr in recently to do a level check. Resistance readings for solenoids all in range, may drop half oil out again but will read up on how to monitor temperature, not sure how to do it with engine running.

[daveo138]

Was the problem there before the fluid change, or did it occur after?

Does it slip constantly, or is it a brief slip?

[SD1too]

Originally Posted by sliver

... will read up on how to monitor temperature, not sure how to do it with engine running.

That's a very good point Steve which I don't think anyone has raised before.
Clearly you wouldn't want to run the engine with automatic gearbox sensors and solenoid valves disconnected.

On the face of it the answer would appear to be to stop your warm engine before separating connector C0243 then take a resistance reading to reveal the fluid temperature. Although somewhat "hit and miss" I can't think of a better way at the moment. I don't believe that absolute precision is necessary since before the advent of on-board diagnostics, correct fluid level was successfully achieved using a gearbox "at normal operating temperature" and a dipstick.

Simon

[sliver]

morning all, thanks for your replies, it never slipped it's gears before being run on low gearbox oil, EP fault showed up, had to be recovered, would imagine it got quite hot.In respect of temperature for oil change think i'll stick to old school method. Did have it plugged in while having MOT but no codes showing, ask garage if they had T4 diagnostics, don't think they had it don't know if it makes a difference, he did have £4000 worth of equipment. Thanks Steve.

[xsport]

Your car is a 99 model and these were the earlier versions of box that gave rise to the reverse piston issues. They were later upgraded with a stronger reverse piston. A few of these cars had problems in the early days but by no means all of them. I think the loss of reverse gear and eventually others followed with this fault , which yours does not seem to be. You have not said which fluid you have used ,this is very important, and there is a list of compatible oils on here if you do a search using the search bar at the top.

[sliver]

Thanks xsport, missed that off, N402, going to drop another 4ltrs tomorrow make sure its accurate, will let you know, sorry to here the bad news, hope your both ok.

[sliver]

Hi,r75 2.5 v6 1999 auto, update, checked oil levels and test run car before stripping gearbox, 3rd gear slipping out at 3,000 revs. Now got reverse piston on bench looks mint, no cracks, no signs of burning on anything/clutch plates etc. One rubber o ring seal had a piece broken out don't think i did it because i could see the tail end of it sticking out before pulling apart, piece was still with the unit. should i just replace the o ring seals and damaged circlip or do i need to go further. mot station said it may be a replacement gearbox because of the grey primer on it, also where is the best place to buy replacement parts for the gearbox. Thanks Steve.

[SD1too]

Originally Posted by sliver

... where is the best place to buy replacement parts for the gearbox. Thanks Steve.

J.P. Automatic Transmissions south of Bristol Steve.

Simon