Choosing gearbox shims & preload without factory specs - sanity check.

[Boxman]

Apologies up front that this thread is not specifically about a DSM transmission, however when googling for forums that seemed knowledgeable on gearbox shimming, bearing preloads etc, this forum seemed to have a lot of knowledgeable people, so I'm hoping I'm allowed to ask my question here regardless, since it's in general terms about the principles of gearbox preloads and shimming. I'd like to get a sanity check on my reasoning, since this is the first time I'm rebuilding a transmission myself. So here we go!

I'm trying to determine adequate preload settings now that I'm rebuilding a Volvo M56H FWD gearbox for my trusty Volvo 850 - or well, 'rebuilding'... There are no rebuild kits nor any specs, so I basically bought 2 donor boxes and rebuilt it with the best looking parts amongst them, new seals and new bearings all round. The thing has three shafts of differing length and an internal differential which I upgraded to a Quaife LSD. On to the fun part: setting preload and shimming.

In the absence of any factory specs, and in seeing so many different specs in different gearboxes, I'd like to hear from some experts if I'm on the right track. I did a lot of research into tapered roller bearings, bearing life vs preload, benefits of preload vs endplay etc... From what I found, is that too much preload is something to avoid while maximum bearing life occurs at 0.000" end play. So I'm trying to settle on getting it to hover around 0.000" clearance at operating temperature (max 90 degrees C in my case). Consider this question 1) - Is there any point for additional preload @ operating temp on a gearbox that is 99% of the time just a daily driver (albeit somewhat sporty at times) but other than that will not be raced except for maybe a track day?

For the second part, my line of reasoning is that I need to apply preload at room temp (20 deg C) due to thermal expansion of the different parts. My gearbox has an aluminum housing and uses steel shafts, so the box will expand more than the shafts. Without preload, this would result in endplay when everything is heated up. So, I measured each shaft length from bearing-to-bearing (215, 250, 165 mm for the shafts, 145 mm for the diff). Then I calculated how much the aluminum box would expand in that linear direction (using the thermal expansion coefficient of general aluminum), followed by calculating the expansion of the shaft (using the thermal expansion coefficient of 1040 steel). The difference between these two then gives me the end-play at operating temp. Question 2) - Am I correct in assuming that this difference is the amount of preload I should set with shims at room temp? So that the pre-load would compensate for the expansion? And am I correct in assuming extra preload is not necessary or desired?

The numbers I obtained through this method are (I'll convert to imperial, since this is a USA based forum if I'm correct):

Shaft 1 - 215mm (8.465") requires 0.17mm (~0.006") preload
Shaft 2 - 250mm (9.843") requires 0.21mm (~0.008") preload
Shaft 3 - 165mm (6.50") requires 0.14mm (~0.005") preload
Diff - 145mm (5.709") requires 0.12mm (~0.005") preload

Any thoughts? Any insights in how gearbox manufacturers determine preload? I've also seen numbers flying around for VW gearboxes that desire 0.4mm preload on the diff, and then somewhere else I saw a race engineer that always put a few thou endplay on their diffs. Lots of new information to take in, so if anyone would be willing to share their knowledge on what affects these considerations, that would be amazing.

Cheers from the Netherlands!

 

[1990TSIAWDTALON]

Now first off, I am NOT the gearbox expert but I do some of my own work. I believe that you will need a specific size of solder and then measure how much it is compressed after mock up. Let's get a couple of my friends tagged. @pauleyman , @twicks69 ,can you guys give any assistance to this new member?

 

[Boxman]

That exact thread is how I got to this forum, haha! Cheers, @1990TSIAWDTALON !

I did indeed as per that thread use tiny bits of solder to measure (and re-measure and then re-measure once again for good measure) the clearance, which is between 0.83 and 1.39mm for those shafts. So the shims I'll be selecting are that + the cold preload setting. Indeed hoping some experts can chime in on my thought process, I'd rather not overload those bearings (or end up with tons of play, for that matter).

Also, I did also attempt to reverse-engineer factory settings by measuring the clearances and shims that came with the donor boxes, but I'm assuming since they were used boxes too that the numbers were all over the place. In both boxes, some shafts had ~0.1mm preload while others had similar amounts of endplay. So unfortunately that was of no use to me.

 

[1990TSIAWDTALON]

And here is one thing that was TERRIBLE a couple years back. One of our MAIN transmission man's shop burned to the ground with literally a million $ in inventory, customers transmission's/parts and obsolete stuff, including the shims. It happened to Tim Zimmer (twicks69) and took out all kinds of things we need now. I do think he is trying to reproduce some of the important stuff, so I hope he chimes in.
Here is a link to his web page:

Home

www.tmzperformance.com

Marty

 

[Boxman]

Such horrible thing to hear! I managed to find the thread and gofundme, and made a small donation. I know it's not much and just a very small drop on the plate, but losing your entire shop and suffering burns at the same time is horrible. Haven't been able to figure out if his business made it back on his feet entirely, regardless I hope it helps a tiny bit, but in any case the lost inventory can never be recovered.

 

[twicks69]

To the OP, is your box using tapered roller bearings for all shafts and the differential?

The bearing preload values estimation you posted look fairly good for the application with tapered roller bearings; what kind of power levels is the vehicle making?

Do you have the bearing race part number or dimensions or shim dimensions so we can find a shim that may work with your application? Not sure if there is any access to these parts from your manufacturer anymore, but we can at least get a consensus of what you have and then find a solution.

What are the thicknesses of the shims in each location (ID/OD as well)? You will then use a solder thickness close enough to that of the shim, using two evenly sized pieces curved and placed in the case evenly across from each other with an assembly gel or petroleum jelly, then slide in the bearing race without the shim, for all locations, install trans case and assemble to torque specs (If you don't have those specs, just use a standardized number like (25NM = 18ft/lbs for a M8 fastener, 38NM = 29ft/lbs for a M10 fastener if they are grade 8.8). Let the case sit assembled for a bit of time, ideally in 18-23 degrees celcius with rosin core solder. Pull off the case, remove the bearing races and measure both pieces of solder for each location, the values should be fairly close to each other so then take your average value to get your zero preload value and then we can see how close the existing shims are.

Example:
Shaft description /// Bearing race ID/OD /// Shim ID/OD /// Shim thickness /// Solder measurement average /// endplay or preload value --> preload value goal --> Shim thickness needed to reach goal

Input shaft /// 49mm x 59mm /// 50mm x 58mm /// 1.39mm thick shim /// 1.485mm solder average /// = 0.095mm endplay --> 0.178mm preload goal --> 1.663mm shim thickness to reach goal

Then we can look for either shims that can be stacked with your existing shim, or find a shim that actually matches the thickness and dimensions needed for each location.

 

[Boxman]

Lets goo! Hold on, I'll grab my notebook and give the relevant info, since I made notes of basically everything I did so far.

My gearbox uses tapered roller bearings everywhere, two bearings on each shaft. I think I must've read one of your posts regarding the solder method, as that is exactly what I did last week My rebuilt engine makes about 400HP, nothing too shocking. Stock was 225. I'll list all the numbers I obtained below.

Preface on the shims: I've so far had an incredibly hard time on finding any shims in the dimensions of my box period, especially in the Netherlands - let alone in the correct thickness. So I'm kind of improvising here and have an idea that I'd like to hear your opinion on, but more on that later.
Regarding parts: zero parts available so far. Volvo made these boxes in-house in a Swedish company that has since been sold - I've contacted them, but no reply yet. The Volvo 850 community has forever been trying to find replacement parts as simple as synchro's, but nothing was ever found. No matter, I'm relatively happy with the parts I found in the donor boxes, lots of synchro clearance etc, but if I ever find a manufacturer that can manufacture gears and rings for these boxes, I could make a fortune by offering rebuild kits haha.
All I was able to do, is take the numbers of the original bearings (which was a mix of SKF, Koyo and Timken, same mix in all three boxes for that matter) and find new Koyo / SKF replacements.

Anyway, this is the setup:

• Input shaft: 215mm (+- 5mm) bearing-to-bearing length // Upper bearing: Koyo 32007JR-2YD // Lower bearing: Koyo 32005JR-N
• 'Large' layshaft: 250mm (+- 5mm) bearing-to-bearing // Upper bearing: SKF 32006X/QCLNVA // Lower bearing: Koyo 30206JR
• 'Small' layshaft: 165mm (+- 5mm) bearing-to-bearing // Upper bearing: Koyo 32005JR-N // Lower bearing: SKF 32006X/QCLNVA
• Differential: 145mm (+- 5mm) bearing-to-bearing // Upper bearing: Timken Y-32008X // Lower bearing: Timken Y-32008X

The shims are all in the upper housing, here's what I have. (Note, the two solder pieces never differed more than 0.015mm):

• Input shaft: Shim ID/OD 54.3mm/62.7mm // Solder avg: (1.15 +- 0.01) mm // Preload goal: 0.177mm --> Shim goal: 1.327 mm // Available thicknesses: 1.080 / 1.105 / 1.065 mm
• 'Large" layshaft: Shim ID/OD 48.3mm/54.7mm // Solder avg: (0.83 +- 0.01) mm // Preload goal: 0.207mm --> Shim goal: 1.037 mm // Available thicknesses: 0.970 / 0.910 / 0.875 mm
• 'Small' layshaft: Shim ID/OD 40.3mm/46.7mm // Solder avg: (0.93 +- 0.01) mm // Preload goal: 0.136mm --> Shim goal: 1.066 mm // Available thicknesses: 0.970 / 1.055 / [broken shim]
• Differential: Shim ID/OD 60.4mm/67.7mm // Solder avg: (1.43 +- 0.01) mm // Preload goal: 0.120mm --> Shim goal: 1.550 mm // Available thicknesses: 1.280 / 1.390 / 1.070 mm

Preload goal / shim goal is calculated purely based on the difference in thermal expansion of housing vs shaft, which differs for different shaft lengths. As you can see, except for the 'small' layshaft i have no shims that come close to the goal.

Since I have two full sets of shims available, would it be an option to have a shop grind two shims down to exactly half the desired shim thickness, and stack them?

This is also the reason why I'm meticulously double-checking everything with you guys, before I grind down the shims. I want to get it right, because I'm not convinced I can find replacement shims if I get it wrong.

Any and all comments on my thought processes /reasoning is very much welcomed And thanks a bunch already for your informative reply @twicks69 ! Extremely appreciated.

Edit: Adding some pictures of the box as it sits now (no forks installed yet, was measuring), for some visual reference:

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[Boxman]

I made some progress, feeling more confident in the numbers after twicks69's post, I went to a local transmission shop who was very helpful - they were able to get some similar shimrings out of their stash that fit my cups, and were kind enough to grind them to my exact specifications! Re-measured them at home with my own gauges and fine-tuned it (i make it a habit to use measurements from the same tool, other people's tools might be calibrated differently) to within 0.01mm of target. Installed & lubed everything with gear oil, torqued down the box and tried my luck:

It spins! I can rotate the input shaft by hand in neutral, 1st, 2nd and 3rd gear, all in slightly increasing resistance. 4th gear gives me trouble and 5th gear can't be rotated by hand. So for 4th and 5th gear I put the clutch plate on the input shaft and used that to spin the gears round a few times with relative ease to settle the bearings. It feels tight, but unfortunately I just don't have the experience & muscle memory to gauge if it is too tight or not. Nothing is grinding, and I don't feel like i need to use excessive force.

I did measure the backlash of each gear while I was at it, by marking out 10 degrees on the bellhousing and using the clutch plate as a reference. Not accurate by any stretch, but an indication:

1st gear: 3-4 degrees
2nd gear: 2-3 degrees
3rd gear: 2-3 degrees
4th gear: 1-2 degrees
5th gear: 1-2 degrees
Reverse: ~5 degrees

Seems about right?

It feels a lot more solid than before the rebuild, I can tell you that.

 

[twicks69]

So for shims, yes, you can always toss them on a mag base surface grinder and grind them down and then stack them to your desired preload shim value.

just compiling notes -
bearing --- shim dim -- bearing race dim ID/OD
32005 - 40.3 x 46.7mm -- 40x47mm -- I have 40x46 shims in stock - look for 0.042" (1.066)
32006 - 48.3 x 54.7mm -- 48x55mm -- look for or make 0.041" (1.037mm)
32007 - 54.3 x 61.7mm -- 54x62mm -- look for or make 0.052" (1.327mm)
32008 - 60.4mm x 67.7mm -- 60x68mm -- look for or make 0.061"(1.550mm)

 

[twicks69]

For the 32005 bearing -
The 40x46mm shim is the same as a DSM transfer case pinion preload shim, which I have in stock.
Small ones that I have in stock are (sae): (you need 0.042", so stacking a 0.012" and 0.031" shim would work)
0.012" (magnus)
0.015" (tmz)
0.025" (tmz)
0.031" (Magnus)
0.040" (tmz)
0.0469 (OEM) - MD726172

Magnus Motorsports sells this shim as well with 0.012" and 0.031" increments - MMCDRV9116 or MMCDRV9117, they charge $22 each + s/h

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For the 32006 bearing needing a 48x55mm shim
They can be custom made - https://us.misumi-ec.com/vona2/detail/221004991334/?list=PageCategory&Tab=wysiwyg_area_0&curSearch={"field":"@search","seriesCode":"221004991334","innerCode":"","sort":1,"specSortFlag":0,"allSpecFlag":0,"page":1,"pageSize":"60","jp000113868":"mig00000000457798","jp000113869":"mig00000000452539","jp000113870":"mig00000000479353"}

Above is not cheap this way, but doable. 47mm x 55mm

I can get a 47mm x 55mm shim made out of 0.040" 5052 aluminum, which would be cheaper and small batch custom order.

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So for the 32007 bearing -

I have 54mm x 62mm shims in the following:
0.5mm-1.05mm range with 0.5mm increments -- taken out of a Mopar automatic transaxle spacer kit
These are 55mm x 62mm dimensionally.
ebay link (shims on right side of case)- https://www.ebay.com/itm/403329722597?_nkw=mopar+automatic+transaxle+spacer+kit&itmmeta=01J7EA1SXRN59P9CH7EA13J4D8&hash=item5de85328e5:g:h6MAAOSwB9Rhp7Lq&itmprp=enc:AQAJAAABAHoV3kP08IDx+KZ9MfhVJKn4q+wObimx4MJ05cg/A4mNZkJznhuxna2JaCMPVDl786e3H0Ut3Pc6kElOcQdrayiI0Os/6E/F+1XuHwzLClQhZMXBcNR/NA3o79zapaHakMDjTnVF5A3QNFP1YhYvFZD59opK/uQ2up9f1nJieLbyX4O3ixVIS8/zeJjsOZeH8Q+PQj+vsQhC3DKjzW/wC2Vb4SWTWseZl6tw+JMVkdR9cBXFx/Ik3CU7iyiJN3ePKMx5zz9hsqWe7LoaBMjxXL0etZDQRnURHrrttfjLjoeElwfYt6xvRWy8jtscznkt5THCNeXLWaY3oTdpHPArmQk=|tkp:Bk9SR4yfh8q7ZA

I also have 52mm x 62mm shims in stock in 0.1, 0.2, 0.3, 0.5, 1.0mm sizing, so I could do either 1.3 or 1.4mm sizing. These are the same as a DSM intermediate shaft on a W5M33 / F5M33 gearbox.

I also have 50mm x 62mm shims in stock in 0.1, 0.2, 0.3, 0.5, 1.0, 1.5mm sizing, so I could do either 1.3 or 1.4mm sizing. These are the same as a DSM intermediate shaft on a W5M33 / F5M33 gearbox.

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For the 32008 bearing - 60 x 68mm

I have 55mm x 68mm shim in the following sizes: (McMaster-Carr)
0.1mm
0.15mm
0.2mm
0.3mm
0.5mm
1.0mm
1.5mm
I have 57mm x 67mm shims made
My shims are the following sizes -
0.048" = 1.22mm
0.059" = 1.52mm

These are the same as DSM W5M33 center differential shims from OEM.

Just stack the one with the smaller ID further away from the bearing into the case first, then put in the one that fits the bearing race better and will allow the bearing not to contact the smaller ID shim.

 

[Boxman]

@twicks69 Holy moly, I appreciate that a lot! Such a warm welcome and it's honestly kind of special to see someone on the other side of the globe put such effort in helping me out finding the right shims!

I almost feel kind of bad for saying that in the meantime I've gotten my hands on some fitting shims locally...

However, this is an amazing resource, and when all is said and done (and if my box is confirmed operating properly) I plan to make a detailed post / guide on this particular gearbox for the M56H gearbox to put on the Volvo forums. I have gained a lot of knowledge on the incremental changes on this box up to the 2000 model, regarding what is and isn't interchangeable, and what does and doesn't benefit. This information on shimming is the literal cherry on the cake - I have seen many hobby-rebuilders mention they don't bother with shims and just use the old ones regardless. I will make sure to include this information so it may help others, and direct them to you for the ones you have in stock! There are plenty of Volvo folks eager to rebuild their old gearboxes, but many opted not to do it in absence of good reliable information.

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That said, I have gotten fitting shims, and thank you for the tip of putting the largest ID's furthest to the back!

Basically, I went to transmission rebuilder #1 locally with my old shims, they turned me away saying "we have no shims" (i doubt it but ok) and directed me to an industrial parts store.
> Industrial parts store did their best to help me, but didn't have anything fitting, but directed me to a local engine rebuild shop that could maybe mill down my original shims.
>> The local engine rebuild shop told me he didn't dare put it in his machine, for if it might fly off and ruin the shim altogether - but he did direct me to transmission rebuilder #2 just 15 minutes away, telling me that if I mentioned his name they'd be very willing to help.
>> So I went to transmission rebuilder #2, showed him my shims, and off he trodded - 5 minutes later he came back with a handful of similarly sized shims, and started measuring them out. For the diff he had a shim 0.1 mm too thick, so off he trodded again and came back with a shim of exactly 1.550mm. Amazing. I thanked him and then he just walked off to wash his hands.. And then he went for lunch I had to stop him in his tracks to ask "How much do I owe you", so he asked his boss to go see what I should pay. Boss said "just do a tenner for the effort" so I gave him 15 and asked him to give the fiver to the guy that helped me 10 minutes into his own lunch break.


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Long story short, I've inserted the shims and put the case together and torqued it down. Cold, I can turn the input shaft by hand in 1st, 2nd, 3rd and reverse. 4th takes quite some effort and for 5th I need two hands and straining. To double-check my reasoning, I heated up the case with my hot air gun for 10 minutes, and I don't think I ever got it over 40 C (which is like 104F) but that did enable me to turn the input shaft by hand also in 4th and 5th. Not effortlessly, but I think it's a good sign.

Again, a million times thanks for your effort in helping me out, it's so appreciated! I will make sure the research you did in sourcing these shims will be spread to Volvo community, since there are a lot of enthusiasts in the USA too.

The one question that remains, is if you would be able to comment on the effort it takes me to turn the input shaft, and the backlash measurements I did a few posts back? If that all checks out, I'm gonna install all seals, silicone and appendages and get this thing back on the road

 

[twicks69]

You are all good, the turning feel will increase in difficulty the taller the ratio, and the backlash values look good!

If people need to get a hold of me for shims, my email is [email protected], or copy a link to this thread on DSMTuners and I am happy to help!

Thanks,
TMZ