Daft question, but just how interchangeable are classic / p38 bellhousings & Torque Convertors? if I had for talking sakes acquired a 4.6 gearbox bellhousing & torque convertor, ignoring the electronic controls for this conversation, would the gearbox bolt up to a 3.5 / 3.9 v8? Or does the diameter of the bellhousing & thus the circular bolt pattern, increase in diameter with the torque convertor size?
Henry_b
Think outside, no box required.
You can swap the bellhousings.
The diameter of the bellhousing does not change with the size of the torque converter the only thing I recall is a spacer behind the flexplate as they're different thicknesses for both the 4.0 "3.9" and 4.6 converters. your biggest issue will/would be the electronic side of things a 4hp24EH will not work without the ECUs
You could rebuild the original hp22 with 24 internals, keeps everything simple.
The diameter of the bellhousing does not change with the size of the torque converter the only thing I recall is a spacer behind the flexplate as they're different thicknesses for both the 4.0 "3.9" and 4.6 converters. your biggest issue will/would be the electronic side of things a 4hp24EH will not work without the ECUs
You could rebuild the original hp22 with 24 internals, keeps everything simple.
Thanks Henry. I've got a 6.2 diesel which lunched on the clutch packs for the 3.9efi autobox I had it married to, I was trying to see if it would be feasible to buy a 4.6 box, take out the electric valve block, flush and fit my 3.9efi valveblock, and also get the 4.6's more efficient torque convertor which locks up earlier. Sounds like that could be made to work, but I might need to do some jiggery pokery with the shimming on the flexplate, but at least its the same bolt pattern for the bellhousings. Cheers /Jay
PS - might be doing something similar to a 300tdi.
PS - might be doing something similar to a 300tdi.
norseman
Well-Known Member
I found this comment interesting as I had always assumed that the gearbox controlled the TC lock-up point. My '87 will lock at 40mph at all but a heavy throttle application, whereas the 3.9 I had years ago wouldn't do so until until the car reached 50. Back in those days a mate had his 3.9 reset (?) so that the lock-up took place at 45.
I have read that, should my own ZF ever need replacing, it would be a good idea to have the factory fitted TC replaced by a larger unit.
Datatek
Well-Known Member
The torque convertor lock up is controlled by the ECU on the P38. The 4.6 has a larger diameter torque convertor than the diesel and thus has a larger bell housing. The HP24e box is, in later versions, exactly the same as the HP22e in terms of casing dimensions.
Sorry, I misspoke, you are correct that the transmission valve block, electric or hydraulic controls the torque converter lock-up clutch, while the larger torque convertors "stall" at lower RPM than a smaller one. To me semantically the effect is the same, the reason for that is that "stalling" in the context of a torque converter refers to the point at which the torque converter fluidic elements stop "slipping" relative to each other, they move as one, and thus can be perceived as locked up.
So, now I've clarified that the larger converter doesn't lock up earlier, but instead stalls earlier, I'd better explain why this is something I perceive as desirable... When the impeller and turbine are "slipping", transmission fluid temperatures rise because the fluid is being put under pressure without doing any useful work, and that energy has to go somewhere. Because smaller torque converters stall later, and are thus spending more time slipping, this will result in higher ATF temperatures for the same workloads than you would see with a larger converter. Because less of the energy from the engine that's being put into the fluid via the impeller is being converted into propulsion and instead that energy is going into waste heat, you should also see (slightly) better mpg with a bigger converter than you would when using a smaller conversion.
The driving characteristics of an automatic box are as equally dependent on the converter as they are the ratios... You know how automatics were derided as "slushboxes" because of their horrible nature of accelerating out of a junction. In that situation, the initial 1500rpm above tickover doesn't really result in much propulsion, but you keep on the loud pedal up to say 40mph for this example. As the speed increases the box shifts up, so by the time you are at speed, you're up a couple of gears and the revs have dropped accordingly, lets call it 3rd gear at 3000rpm, when you lift off to coast, the torque convertor goes into its sloshy mode and engine revs drop to 1500rpm, and you can now play tunes on the loud pedal between 1500rpm and 3000rpm, without affecting vehicle speed. Whereas a modern say 6 or 8 speed auto, hell, even a decent 5 speed auto like the one in the hippo, once the fluid is warm, will be very closely tied between engine RPM in coast and engine speed when accelerating at that road speed.
Going with a bigger torque convertor reduces the size of the disparity of engine vs transmission revs, so in that case, with a larger torque convertor, the revs might fall to 2250rpm, and be offering some propulsion between that speed and the 3000rpm engine to road speed. I know that's a lot of words, but it's a difficult thing to describe, but if you something more visual, compare these two videos you'll see how little the later 4.6 compared to the earlier range rover:
Timestamp: 13:46
Timestpamp 03:27
You'll also find that the smaller the torque convertor is, the smaller and less capable it's lock-up clutch is, and from what I've read, the smaller stock torque clutches seem to struggle with standard loads, never mind tuned engines / larger displacements. Apart from the lost efficiency of an overwhelmed and thus slipping torque convertor clutch, and the detriment to the driving experience this creates, the slipping TC clutch also contaminates the fluid, the debris of which then attack other clutches and or band brakes within the gearbox, hastening it's demise.
So, in summary, the benefits of going with a large torque convertor would be less transmission sloshing about resulting in a more relaxed driving style, because the vehicle will "pick up" at lower engine RPMs. It will do so with less energy being converted into waste heat, ergo lower transmission fluid temperatures and a slight increase in fuel efficiency. The larger TC also has more capacity for the transmission of torque from the engine into the gearbox. That increased torque transmission capability also means the TC clutch is less stressed ergo less likely to slip and fail, so the bigger TC has reliability advantages as well.
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Hi Jon, I wasn't aware of that one, I genuinely thought the P38 transfer case was interchangeable with the earlier ones, well certainly as far as the mounting flange, obviously the P38 runs it's props on the wrong side of the vehicle...
The HP24 tail housing needs changing for the hp22 so the BW or LT will bolt up.
The output shaft on the 24 is too long and doesn’t have the hole in to bolt the adapter shaft on.
Either change for the 22 shaft (both gearbox’s apart to do this) or cut and drill the 24s shaft.
As you have both boxes you will be able to compare.
J
AND thanks to your valuable contribution, I now know what to look for
AND thanks to your valuable contribution, I now know what to look for
Also remember that the earlier 24s were 15mm longer. Can’t remember the serial numbers of top of me head.
61 and 65 rings a bell though.
good luck and let us know how it goes
.J
I'm going to be a while before I get onto these builds, we've spoke in PM's about the RRC build that is head of the queue, and that's just one of many projects. But I've got a 300tdi engine currently set up for manual and sitting beside an r380, but I've also got the back plate, flexplate etc so it could go Auto. I've also got the 6.2 diesel, that might go into an ultra-4 type racer, but I might import another engine instead, in which case the 6.2 might find itself going into my D1?
These other builds will be a long ways down the line by the time I've finished the RRC, so there's plenty of time for me to change my mind plenty of times by then :joy
These other builds will be a long ways down the line by the time I've finished the RRC, so there's plenty of time for me to change my mind plenty of times by then :joy
Datatek
Well-Known Member
The 65 is the later HP24 fitted into the HP22 casing. On the P38 there is a spacer fitted at the end of the HP22 box and the model 65 HP24 so with the spacer fitted the shaft length is the same on early and late HP24's and all HP22'sAlso remember that the earlier 24s were 15mm longer. Can’t remember the serial numbers of top of me head.
61 and 65 rings a bell though.
good luck and let us know how it goes
J
norseman
Well-Known Member
In addition for thanking you JR for a most informative post (#7) I will add that the day when my ZF needs replacing may not be far away.
Although my RRC has only covered 60k from new (I possess virtually all the MOT's to back that statement up) unless the ATF was changed within the first 40k prior to my ownership 14 years ago it's never been changed & the car is now 35 years old
But the old girl trundles along nicely & the 'box appears to function as it should in respect of smooth changes, kick-down & lock-up/stall, so I think the old adage of 'if it ain't broke don't fix it' is probably the best policy.
nb: Not sure where Kingsley got their 0-60 in 16.6secs, applicable to the standard V8 engine fitment ... diesel version perhaps?
Although my RRC has only covered 60k from new (I possess virtually all the MOT's to back that statement up) unless the ATF was changed within the first 40k prior to my ownership 14 years ago it's never been changed & the car is now 35 years old
But the old girl trundles along nicely & the 'box appears to function as it should in respect of smooth changes, kick-down & lock-up/stall, so I think the old adage of 'if it ain't broke don't fix it' is probably the best policy.
nb: Not sure where Kingsley got their 0-60 in 16.6secs, applicable to the standard V8 engine fitment ... diesel version perhaps?
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If it's driving nicely, why are you anticipating it's demise? As for the 0-60 times Kingsley state, I'm going to give them the benefit of the doubt and guess they did a GPS run on Draggy or something similar. However, I suspect benchmarked an old worn 3.5 with a slipping auto box prior to restoration and upgrades, which would have had the hopefully unintentional consequence of making their upgraded restomodded vehicle look better by having a bigger delta vis a vis the "original" 0-60?
Again, I'll give them the benefit of the doubt that they did this not to mislead their customers, but to give "real world" "before and after" metrics. Put it this way, if you took your RRC to Kingsley just now, given the lack of maintenance you've alluded to on the gearbox, I suspect it will be transmitting less torque from flywheel to diff crown-wheel than it would have done back in the mid eighties, where it was measured by autocar magazine as having a 10.8-11.7 0-60 depending on whether it was a 3.5 or 3.9, and the current 0-60 would be closer to their 16.6 figure than the figures on this pages table:
https://www.autozine.org/Archive/Rover/classic/Range_Rover.html
Edit: just had another thought, wonder if their 0-60 time was for a diesel model, 2.5VM / 200tdi / 300tdi? 300tdi was 17.2 according to google [shrugs]
Again, I'll give them the benefit of the doubt that they did this not to mislead their customers, but to give "real world" "before and after" metrics. Put it this way, if you took your RRC to Kingsley just now, given the lack of maintenance you've alluded to on the gearbox, I suspect it will be transmitting less torque from flywheel to diff crown-wheel than it would have done back in the mid eighties, where it was measured by autocar magazine as having a 10.8-11.7 0-60 depending on whether it was a 3.5 or 3.9, and the current 0-60 would be closer to their 16.6 figure than the figures on this pages table:
https://www.autozine.org/Archive/Rover/classic/Range_Rover.html
Edit: just had another thought, wonder if their 0-60 time was for a diesel model, 2.5VM / 200tdi / 300tdi? 300tdi was 17.2 according to google [shrugs]
norseman
Well-Known Member
I'm sure you are correct in your estimate of the reduction in efficiency due to 35yo fluid. Ashcrofts advised me not to mess with it at such an age & that was 4/5 years ago.
It does drive nicely & doesn't lose fluid, so maybe at my age it will outlast me
@zed put a 6.2 in a Classic. If any of his old threads are still about they're worth a read. He was doing something about getting the gearbox setup right in one of them.
