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  1. #1
    Edward G
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    10 Mar 2011
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    Victoria Australia
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    Saab(s)
    T5.5 84 900T8
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    Post All things c900 5spd

    I thought it would be a good idea to create one major 5 speed thread that connects a number of really good threads made by others. A place where people can ask questions and read threads to learn more about the c900 5spd. For those considering it in the future here are a number of threads that will help you understand more. Definitely a couple of hours reading here. Most are from SC where I am very active. I thought this site could benefit with another additional thread compiling information. Feel free to ask any questions I will do my best to answer.

    5 Speed Rebuild Nutcase style
    C900 5 Speed Gearbox Rebuild - Nutcase Style - SaabCentral Forums

    DIY 5 speed rebuild how to MMOE
    DIY 5-speed Transmission Rebuild How-to - SaabCentral Forums

    Pinion bearing install with no Press MMOE
    Pinion bearing install with no press. - SaabCentral Forums

    The definitive Gearbox thread
    The Definitive Gearbox - SaabCentral Forums

    Australian saab 5 speed transmission bearing discussion
    good/cheap sources for bearings - SaabCentral Forums

    900 Gearbox tool debate
    C900 Gearbox tool debate - SaabCentral Forums

    Li arc's project thread
    C900 5 Speed Gearbox Rebuild - Nutcase Style - SaabCentral Forums

    Jim M's words on checking gearbox for pinion wear
    SaabCentral Forums - View Single Post - primary case? or what?

    Transmission info page - compatibility and part numbers
    http://www.fixmysaab.com/900_repair/...on/tranny_info

    Fixmysaab quick tranny teardown
    FixMySaab: C900 Transmission Rebuild - Introduction

    Townsend's reverse gear fix
    REVERSE GEAR MODIFICATION IN 900 5 SPEED TRANS

    Jim Ellis Saab site with his unofficial EPC - very useful for checking gearbox parts, and getting numbers to check with your dealer if still available - very handy if you don't have an EPC.
    Gear box, 5-speed, Shafts, gears Manual. Fits: 1989 Saab 900 | Jim Ellis Saab Parts

    (Saab manuals - including transmission rebuild guide and transmission training guide)
    The Saab Register • View topic - SAAB 900 [ Old Generation ]

    Transmission rebuild manual (not written by Saab)

    www.saabrally.com/downloads/trnsm900_90.pdf

    Check out the SC workshop FAQ for other threads on c900 trannys I didn't bother reposting them.

    900 Workshop FAQ - updated 17rd July 2009 - SaabCentral Forums

    Let's make the c900 transmission less daunting for enthusiasts

    NB: You don't need to become a member to view any of these threads and I shouldn't be breaking any rules because I am not passing the information off as my own. Happy reading.

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  2. #2
    Saab Fan
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    08 May 2011
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    Quote Originally Posted by s900t8v View Post
    I thought it would be a good idea to create one major 5 speed thread that connects a number of really good threads made by others. A place where people can ask questions and read threads to learn more about the c900 5spd. For those considering it in the future here are a number of threads that will help you understand more. Definitely a couple of hours reading here. Most are from SC where I am very active. I thought this site could benefit with another additional thread compiling information. Feel free to ask any questions I will do my best to answer.

    5 Speed Rebuild Nutcase style
    C900 5 Speed Gearbox Rebuild - Nutcase Style - SaabCentral Forums

    Hoping to finish that thread soon - just waiting on delivery of the primaries

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  3. #3
    Edward G
    Saab Enthusiast
    Join Date
    10 Mar 2011
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    Victoria Australia
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    121
    Saab(s)
    T5.5 84 900T8
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    Just thought I'd update this thread with the list of tools that are critical to a gearbox rebuild & how to get around them with cheap DIY tools.

    First some tools you can't get around (unless you have friends or pay someone) I'm listing the either expensive/unusual type ones that not everyone will have. You pretty much need a decent toolkit/shed!

    - (recommended no less than - has been done with 6t) 10 tonne press
    - heavy duty vice well secured to workbench (or you can use press as a vice as long as the press is bolted down )
    - 47mm spanner - pinion nut
    - 32mm socket - sprocket nut
    - 27mm socket - pinion end nut
    - inch pound torque wrench (light duty) - differential bearing preload
    - heavy duty torque wrench (for sprocket nuts etc) - torquing nuts
    - drill with various bits to drill out stakes on nuts
    - heat gun can be useful or blowtorch for neutralising loctite
    - various other sockets 12,13mm etc
    - circlip pliers etc - for upper sprocket circlip
    - large torx drivers

    - Pinion bearing preload - this is achieved by crushing the metal collar between the pinion bearings when torquing the pinion nut. It is measured by immobilising the pinion shaft and using a spring scale with string around the housing. The required preload is 4.7-7kgf.

    Tool required: spring scale - you can get digital spring scales off ebay for $10.

    - Pinion bearing depth - This determines how shallow or deeply the pinion gear rides on the crown wheel (differential) - I thought my way through a number of options for this and if you don't have access to the proper tool here a couple of cheap and reasonably accurate ways of measuring the depth.

    This is the proper tool

    And how it works in situ

    Tools required: There are a number of cheaper alternatives. Because the premise set by knowledgeable people on the forums, it is not acceptable to measure the pinion depth on disassembly and match it on reassembly, but to return the ring/pinion to the depth that was determined at the factory (stamped on the crown wheel/pinion gear). I've devised a couple of cheap ways

    - Get a 30-45mm diameter round bar, have an engineer throw it in a cylindrical grinder to ensure it is true (in Aus round bar comes out pretty true already, but to do it properly get it ground - a good engineer can ensure it is infact true).

    There are a few options from here
    - Get the engineer to make up a 14.8mm long 10mm wide and 10mm high gauge block. You then sit it on the pinion gear ensure the gearbox is lying level - slide the bar through the driver housings, let it roll to the lower point use feeler gauges to measure between the lowest point of the bar and the gauge block. Record your measurement and ensure it is reproducible.

    - The variation of this just involves using 2 sets of feeler gauges (separate them from their packs and make up one set to 14.8mm and use the others to do your actual measurements. (you may want to ensure your feeler gauges are accurate they are made from shim stock so generally as accurate as you're going to get)

    - the other variation (not tested) involves drilling a hole for a dial indicator through the round bar (you want a big 35-45mm bar so it doesn't roll around too much, you might have to get it shaved in half so you don't need a long dial gauge. You will have to rotate it with the dial indicator in situ carefully (as not to bend/damage the gauge) to find the highest reading - (the hole you drill must be a snug fit so there is no lateral play to throw out the measurement). You then use a 15mm gauge block to 0 the gauge. After that you can take your measurements as +/- 0
    NOTE: If you do it this way you must remember the gauge will show the opposite, so if the gauge shows +5 on the dial it actually refers to -5 (or whatever is scribed on the pinion) and vise versa.

    So how do these all work!?

    Measurement Info
    For the first 2 - you use 15mm as your 0 reference. (14.8mm from gauge block or feeler gauge 'block' + your ACTUAL measurements)

    The pinion gear theoretical ideal depth is 60mm, which we will also call 0. The number on the pinion indicates whether the depth in reality is more or less than that number. For example a pinion gear stamp of -5 means 59.95mm and + 8 means 60.08mm
    The lower (more negative) the number the closer the ring and pinion are and thus the greater the pinion depth and vise versa

    To increase the pinion depth you add shims (making the number <0 or negative)
    To decrease the pinion depth you remove shims (making the number >0 or positive)

    So for example if your feeler gauges record 0.10mm you know that the depth total is 14.8+0.10 = 14.90. The 0 reference is 15mm here so we have a reading of -10. Compare this to the reading on the pinion gear, we know we are 0.05mm too deep, so we need to remove 0.5mm worth of shims! It's that simple!

    People say this measurement is crucial, hence all the fuss, tolerance is 0.05mm as a guess (guess only) I'd say unless it is SEVERELY out say >0.1mm you shouldn't cause too much harm. Most are out by 0.1-0.15mm if not more with worn pinion bearings. I have had a go with the feeler gauge method and it seems to work well and based on the fact the round bar is ground and the feeler gauges are meant to be precision tools it should be accurate! I will try and compare it to a genuine tool (which my mechanic has) if he ever gets free time to go find it in his workshop!

    - Crown wheel (ring gear) backlash, this is a measurement to determine how much play or lash there is between the crown wheel and pinion gear - it has also been agreed to reset this to new measurement which is 0.17mm +/-0.05mm and is reduced by adding shims to left side or increased by adding shims to right side (under driver housing)


    Tools required: a magnetic stand ($10) and a dial indicator with 0.01mm resolution (and little more error) you can get cheap indicators which are probably up to 0.1mm out ($10-$20), if you can borrow one do so, it's a good idea to get it as accurate as possible as it's useful in many areas during the rebuild

    Differential (carrier) bearing preload - This involves using an (inch pound) torque wrench to determine the carrier bearing preload, which is 16-24 INCH pounds.



    Tools required: This one can be done quite simply, get some 25mm round bar (hollow might be good but original tool is solid), about 180mm long, weld a socket that will fit your torque wrench to one end, and on the other cut a section out to look like this, IIRC it's about 22mm wide and about 25mm deep. I will confirm these when I have some more time


    A simpler way to do this (if you don't have welder etc) is to use 25mm dowel, and get a 27mm socket - bang it onto one end of the dowel, it will fit snugly, and then cut the tooth out of the other end. then use 1 or two of the very thin CV style banding clamps with a banding tool to reinforce the dowel at the other end (to prevent it breaking under load). This works very well. You may want to take into account a tiny amount of flex in the wood when measuring torque, if there is any at all - something to consider when going wood style.

    Stack height - This measurement is used to ensure that the gear stack on the pinion shaft lines up with the cluster gear, if you get this wrong (195mm-195.1mm) I believe you will cause excessive wear of the gear faces and may experience a premature transmission failure, you may also have shifting issues (as a guess) and all sorts of other problems (that I'm not aware of)

    Tools required: stack height gauge or accurate depth gauge (0.01m resolution) If you can find someone with reliable accurate gauges then get onto it! Try an engineer sometimes they let you (under their supervision) use their tools for a small fee. I have not had to look into making one of these as I have the proper tool, ideas welcome, I did at one stage think about getting a T piece precision machined up (to mimic the stack height gauge) A cheap depth gauge really isn't good enough for this IMO, it's critical, more so than pinion depth if you ask me (pinion depth can just cause accelerated wear if too shallow or deep as well as horrible drivetrain noise :S)




    Input bearing housing play - This is to ensure when installing the input bearings between the housing that there is no rolling resistance and no axial play in the setup. To check this you press the input bearings together with a couple more shims than they were disassembled with (to give axial play on purpose) you then set up the magnetic stand arm through a bolt hole on the housing and rock the housing watching the amount of play on the dial gauge. (whilst the press is delivering a couple of tonnes to the bearings to ensure the shims are squashed as they should be etc) You then press the bearings off and remove the thickness of shims equal to the play you read on the dial gauge, recheck to ensure there is no rolling resistance and no play


    Tools required - Dial gauge and magnetic stand - There are 3 potential uses for a dial gauge in a gearbox rebuild so it could definitely be worth your while getting one with minimal measurement error. As dial gauges are used to make 'relative' not absolute measurements they are easier to build decently for less $, (unlike a proper depth gauge which relies on precision ground stems which if bent are completely useless etc) if you were going to splurge I'd get a Mitutoyo they're around $60-$100 and have 0.01 resolution and 0.01-0.02mm error

    Well that's the major measurements required in a c900 gearbox rebuild! I will upload some photos of the devices in action to help give a better understanding of how they're made and how useful they are! I haven't included ALL the specifics of these jobs, refer to the c900 transmission rebuild manual PDF which can be found floating about the interwebs

    I will also update with some DIY tools & methods that are cheap to make and make the job possible/easier soon!

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    Last edited by s900t8v; 18 June 2012 at 13:58.

  4. #4
    Sam Carlson
    Tutorial Bot euromobile900's Avatar
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    '90 900 LPT with a flat-nose conversion
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    I've been collecting tools to do the transmission rebuild myself. I believe there are several shortcuts you can take, if you don't have access to the proper tools.

    First shortcut is with the input bearing. I've seen the input shaft bearing shimmed without a press, simply by tightening and torquing down the input shaft nut and checking for play or resistance. Since I figure the press is supposed to simulate the pressure on the bearings that the input shaft nut provides, why not just use the nut itself and a spare input sprocket? The nut is not not self-locking, and only must be thrown away if it comes off after having been peened.

    Next shortcut is with the differential bearing preload. You can eliminate the need for a precision low-values torque wrench and a welder by using the hollow or solid metal bar the way s900t8v has described, only then add a bend in the middle, and drill a hole on the end, exactly six inches away from the bend. Then you can attach a spring scale (the type commonly used by fishermen to weigh their catches) to the tool, and divide the value by 6 to get the inch-pound reading.

    I'm still working on the shortcut for the stack-height tool, since I, too, think this measurement is neglected. I think I may figure out something with a cheaply-available digital micrometer caliper that can be zeroed at any value. Most of them are 200mm long, so they have a chance of working. If I could zero it on something sturdy and flat spanning the end of the 'box and then somehow drop it down, I think I could accurately and precisely measure stack height. But I'll have to test it to make sure it works the way I think it will.

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    Last edited by euromobile900; 20 June 2012 at 22:47.
    Ask me a question about your c900! I promise I either can answer it or know someone who can

  5. #5
    Edward G
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    Yeah great ideas euromobile, I thought about the depth gauge as well before I got the proper tool. I came to the opinion that you could buy any cheap 20 dollar depth gauge, visit a machinist, get them to either make you up a 195mm gauge block using their precision tools and then use that to zero your depth gauge OR just use their tools The biggest problem with cheap depth gauges is that they have short bases and the bases aren't honed to be accurate. To accurately measure you need a 130mm wide base at the minimum. This could be overcome by getting a T bar made by a machinist, a flat bar across the top and then a long bar 195mm long, with the surfaces precision ground it should be accurate, then use feeler gauges to measure the gap.

    You're exactly right about the input shaft bearing shimming step. I believe the manual even states a force of 3t must be applied to accurately simulate the input shaft nut when torqued.

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