Transgo 5HP25 PR Valve
 

In an attempt to avoid the common A drum failures on my 5HP24 gearbox, I decided to replace the ZF pressure regulating valve with the TRANSGO 5HP24 PR kit.

I ordered the valve and a new filter from the American Transmission Warehouse and was impressed with their prompt service. P&P is a bit hefty to the UK but it still worked out cheaper than any alternative I could find.

Two of the pan bolts were seized so that added a couple of hours to the job but they came out eventually. The front valve body was hung up on the locating pin and would not drop. In the end I looped a cable tie around the small cylindrical section that protrudes out of the front of the valve body and that allowed me to apply some downward force to free up the body. Worked a treat. Don't be tempted to use a pry bar in case it scratches the castings.

I can confirm there are no small balls, springs or other bits and pieces that come flying out if you are just dropping the front valve body (much to my relief).

The only other tips I can pass on are to use some cable ties to help with the closure of the retaining plate as you compress the valve springs on reassembly. Also, fasten the hand pump used for filling the gearbox onto a convenient strut with some cable ties (I like cable ties!). It made the job a lot easier. I am pretty sure I picked up that last tip from someone else on the forum so kudos to them.

The TRANSGO instructions are very clear and its all pretty straight forward. I reused my oil as it was replaced less than 10k miles ago according to the service record but I did have to top up with another 2 litres to get the correct fill. I noticed I have a slight leak around the output unit so I guess I will need to replace its oil seal at some point.

I have only done a few miles since the work, but all is well and I do think the gear changes are slightly smoother, not that they were bad before - probably the extra oil helped but who knows.

Hope that's helpful for someone.

Does anyone have any information on improvements to the 5HP24 through the production run? This valve problem was known and documented for several years before the end of production of this model transmission.

Just wishing my '02 had been upgraded at some point in the production cycle.

I thought the valve was upgraded in '01 and the A drum in '02. How many failures have been reported in the '02? I don't recall any.

It is probably best to put a note in this post, that if the trans is already banging, on take off, it is useless to replace the PR valve, or valve body. Just use that money and put it towards another trans. Even if it does seem to work, it will probably only buy you 6 months or less, before bad things happen again......The voice of experience....Mike

I think it is also worth noting that the ZF gearbox company (ZF Friedrichshafen AG) was founded by none other than Ferdinand von Zeppelin who also founded the Zeppelin Airship company (Luftschiffbau Zeppelin GmbH), who rather famously manufactured the Hindenburg.

You have been warned :D

Transgo ZF5HP24 Upgraded Valve body
 

I recently posted about this kit.

You can call up ZF in Chicago and get official info on the transmissions, very useful. Phone number in that thread.

BTW, they suggested changing the regulator and the valve body, not the A drum, a rebuild, or let it grenade.

I hope to tackle the pressure regulator in my car next. Not sure if I'll use the TransGo or the Sonnax kit. I would prefer a kit directly from ZF but I haven't found one, only complete valve bodies. Any recommendations?

Thanks everyone.

I believe the 02 model had the updated ZF pressure valve. I replaced the one in my 97 with the updated version and saw that the difference was a shorter open section near the inboard end. I no longer have the part #, but it should be easy enough to source from a ZF parts supplier.

I believe RJ is right:- ZF did update both the 'A' drum and the pressure valve, but I'm not sure when. You may already have the updated parts fitted - ZF would most likely tell you based on the trans serial #.

ZF recommends replacing the valve body and not just the pressure valve. I've attached a TSB (courtesy of jagrepair.com) which concerns the broken 'A' drum. It offers an explanation of the issue and includes the updated ZF part numbers.

I believe that the Sonnax part requires the valve body to be reamed to fit?

FWIW, I used the TransGo valve. Easy to do while you have the pan off during a filter & fluid change.

Yes, the Sonnax part requires some machining. I can't recall the source, but found a transmission shop online that sent me a rebuilt valve body with the Sonnax kit already installed and I sent the old one back afterwards for a refund of the core charge. The thing is that what actually wears out is the aluminum bore in the valve body itself, not the piston/valve. I could feel the distinct ridge that had worn in the bore after I disassembled the old valve body so I probably caught it just in time. The other kits get around that wear by changing the length of the land on the valve to avoid the worn ridge and ride on an undisturbed part of the bore plus teflon seals on the piston end that expand when warm to make up for the larger worn bore diameter.

Help me out... The way I understood this was,,,, that the banging and rough up and down 1-2 shift had to do with the bad valve and NOT the drum,,, yet. That the roughness in shifting had to do with wear in the valve body (maybe) and bad leaking valve allowing a strange or harsh shift in the a drum due to surging pressures, bad valve.

Importantly,,, that if left untreated, in time, the a drum FAILS. And if it fails, at that point, major surgery is needed...

So, changing the valve does work - before failure...correct?

Thanks, Phil.
There was no discernable wear/scratching on the valve, or ridge in the valve bore when I had things apart (possibly the relatively low mileage), so I was happy to re-use the valve body and just fit the TransGo valve. I had no previous rough-shift history and everything is working as it should. Caveat here is that CovID has meant that I've only done minimal mileage since the filter/fluid change :(

@Jay:- note this is for the 5HP24 not the 6HP26 which doesn't appear to suffer from this particular malady.

There is some discussion about whether the original 'A' drum was too weak, or the failure totally attributable to a malfunctioning main pressure valve, which may also be implicated in cases where the valve body cracks in a (now) predictable place. The original valve is certainly suspect, as ZF recognised. See the TSB I attached earlier.

TransGo doesn't promise that its product will eliminate the risk of an 'A' drum failure, just that it will reduce its likelihood. It made sense to me (with some impetus from RJ237) to do as PM while I had the pan off during the trans service. BobRoy and DonB have contributed a superb how-to that makes it really easy.

Hi Michael...
​​​​​​I got ya... I have an XK8 with the 5hp as well as the xkr with the 6hp... I've installed 2 of the transgo valves in the the XK8. One on the trans that had 212k miles a year or so ago, maybe more, and one in this newer trans that came with swapping the engine with 36k miles. In both cases I got a noticable change in low gear shifting. I didn't need a new transmission...

The instructions, or I read somewhere, says to check for wear in the VB. Then, to see how it feels when you place the new valve. If there is no clear wear and the new valve feels snug, go for it. In some places that I had read, the problem had to do with, after thousands of hot cold cycles, and them being different parts within the body, that expansion and blah blah blah... The new valve has soft rings on it which makes up for the change in tolerances...

All I was saying is that the harsh shifts don't mean it's a wrap and one would need to go a drop cash on a while new tranny+labor++++...

Apologies for the lecture - I forgot you have two XKs :)

Nah Man,,, it's all good :)
I didn't take it that way at all...

Honestly, I don't and didn't mean to go on and on...

Often, I'm afraid/hesitant to offer suggestions and advise here - cuz I'm no expert. It's quite possible I'm wrong about this. Completely open to being corrected. But if what I'm saying is even remotely accurate,,, well, I hope it saves someone from spending 3, 4 grand on a transmission. Or feel defeated. Or to give up on one of these amazing cars.

I had also thought I felt a little harshness at times, but it was barely perceptible. What really set me off was a several second delay going from park into reverse followed by a significant clunk as it engaged. I remember it happening very noticeably one time as I was reversing out of a parking spot after a visit to the zoo. I drove home, but then quit driving the car till I could research it (I am lucky that I have other cars and I can DIY my own repairs but I know most people often have to just take their chance for a while till they can get in to see their mechanic). Later I read somewhere on here that was also a symptom of an impending main pressure valve problem. As many A-drum stories as I'd seen on here, I didn't mess about. I just ordered the stuff and did it as soon as I could. That was nearly a decade and 45K miles ago so I'm fairly well convinced that its a good preventative maintenance step.

Whether the A-drum should have actually been made stronger, I don't know. I'll leave that to the engineers. But I've operated a manual jack and a press. If it reaches the end of its travel or the object is too heavy, I can't pump the handle anymore and I stop. If a hydraulic valve gets stuck inside the tranny, that V8 engine isn't going to stop and wonder why its feeling excess resistance. I figure its going to bust something, if not the A-drum, then something else. So either way you look at it, its still a good thing to upgrade that valve before it gets too many miles of wear on it.

Gents,

I have heard stories of transmission people modifying/welding up the A-Drum of the ZF5HP24 to strengthen it, and I'm pretty sure someone/somewhere a tranny mechanic will have compared the ZF upgraded A Drum with the old stock part and decided this is the best/cheapest way to go.

Still, I'm with Phil, and I installed the Transgo PR valve simply as a preventative measure when I did my ATF & filter change. The valve is a cheap part (relatively) and with the great guidance here on this Forum, not beyond the skills of a humble home DIY mechanic. Obviously if the tranny is too far gone ie broken, it's not going to help.

Per another Jag forum, improved input shaft/A drum started Nov 2000. Trans serial # 355863. Haven't confirmed this so best double check.
I was hoping my 2000 had the upgrade. It doesn't. It shifts smoothly altho a little slowly. With the fluid change (77k), best to do drain and fill or flush and fill? Am inclined to do a drain and fill + filter change and drive. Maybe the Transgo. I've heard the argument that a flush stirs up debris and can make shifting worse. I've done with w/ 2 other cars (Lexus and Honda) and it worked well. Also the torque convertor holds quite a bit of ETF. How do you get a full change of fluid?

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