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Thread: Gaskets and clearances

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  1. #1
    Yoda
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    Gaskets and clearances

    You may remember the saga of my BJ8 jumping out of 4th gear after an engine rebuild. While sorting out the issues in the gearbox and OD I've been pondering why the car would start doing this after an engine rebuild when it hadn't done it for over 100K miles before. Thanks to people on the List and the Forum, I've noted some possible culprits:

    1) weak detent springs on the shifting forks

    2) weak or worn springs or balls in the shifting hubs

    3) excessive end play

    4) other/all of the above

    I don't think it's the shifting forks' job to hold a gear, but it's been noted that especially stiff shift lever boots could command an unwanted shift, but I don't think that' the issue as my shifting forks, springs, etc. are in fairly good shape, and I could feel the shifter fight to release from gear when I held it. #2 is very likely a contributor (I'm replacing mine as the small gears that mesh with the synchro are worn). #3 is certainly a possible cause, as Dave P and others have pointed out, but I think it's a combination of things, and one that just dawned on me. A poster--I believe it was Steve Gerow--has been alerting owners to a problem caused by too thick paper gaskets on the rear axle hubs. There's a spacer in there, whose job it is to clamp the outer race on the bearing to keep it from turning, but the new gaskets are too thick and prevent the axle disk from clamping down on the spacer sufficiently to apply the necessary pressure to the spacer, and spun bearings can ensue (I heard of a shop doing a pretty steady business fixing rear axle hubs with spun bearings).

    Similarly, there are thin shims at both the front and rear of the gearbox that are there to apply pressure to the gearbox front and rear bearings. Magnus K notes in his (excellent) video that these are critical to minimize end float in the input and main shafts, which can cause the jumping out of gear. When I split the adapter from my OD I noted that the original--AFAIK--gasket was very thin; paper thin to be exact (unfortunately, I split the bellhousing and gearbox and didn't save the gasket, which was installed at the last rebuild about 130K miles ago). The new gaskets that Moss, and probably others, provide are much thicker than this. The front shims for the gearbox are either 0.002" or 0.004", and the rear are 'A/R' and none are available (at least from Moss). A random gasket I pulled from the set--which, I believe, are also for some MG and/or TR cars--measured 0.019", a lot more than the width of available spacers.

    Obviously, I can't prove any one cause conclusively, but if the shims are for a setup with, say, a 0.002" gasket, then a 0.019" gasket is going to eliminate the pressure that should be applied to the bearing outer races. This also fits with the behavior of the box, which had jumped out of gear a few times after a previous engine rebuild, but had settled in and not jumped for over 100K miles. And now, the problem is, where do I get an 'original style' gasket, which is probably only a thou or two thick? It is not practical to 'roll your own' as these are complex gaskets and there are many openings that need to line up. Note these are smooth, machined, non-porous surfaces which should not require a thick gasket to fill imperfections like, say, a thermostat housing (yet the gaskets appear to be made out of the same thick material). I could use a silicone or other sealant, but I am more comfortable with a gasket with a bit of sealant spread on it ('belt and suspenders' as it were).

    Anyone else seen this problem? Oh, and I've got 2 gaskets sets minus the front and top gaskets for a centre shift gearbox available to a good home for postage.

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    Re: Gaskets and clearances

    Agree with #2 as possible culprit but also consider gear lever bush and correct gear stick locating bolt (image from DWR). Oh, how about trans pilot bush. Good luck, GONZO

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    Re: Gaskets and clearances

    Well Bob, it could be coincidental that one of the failures you have mentioned could have occurred at the same time that you had the engine rebuilt. But I must tell you quite factually that in the only two times I have had my transmission cover off in the last 5 years, each time after a prolonged period of inactivity, I would then reinstall the trans cover and start driving only to find that all of a sudden my trans would jump out of 4th gear. Having done no work to the transmission my 1st thought was "oh great now I have trans trouble'. Then reviewing the situation I would discover that in my effort to "get it all right" I had installed the rubber shifter boot with the nipple facing down as all the restoration guides illustrate. And each time it was installed this way, the trans would not stay in 4th gear. So I turned the boot upside down with the nipple facing up and all is well and trans works perfectly. My boot is at least 30 years old. Maybe a little stiff. I also had to keep it unclipped from the perimeter of the tunnel opening. So take the boot off the shifter and go for a ride and see what it does.
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    Yoda
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    Re: Gaskets and clearances

    Thanks, but the gearbox and OD are on the bench in pieces. One of the thrust washers in the OD was in pretty bad shape and the accumulator was showing wear, so all-in-all it was time to go through them. When I was driving in conditions that caused jumping out of 4th, I tried a few times to hold it in gear but it felt like the box was really fighting to jump out; I didn't resist too much as I was afraid I could snap a shifting fork. But, I DID install the shift boot with the nipple down; first time in many years, so you are probably on to something. With only one exception, it only jumped out of gear when decelerating sharply or engine braking going downhill.

    What I'm going to do, thanks to your suggestion, is to install the boot nipple down and see if I've actually cured the problem or not.

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    Re: Gaskets and clearances

    Bob, I believe when it wants to jump out of gear for any reason, it will fight you. I'm not an expert on transmissions but each time I have had a car which jumped out of gear it was found difficult to hold it in. I believe in some cases that the wanting to jump out of gear is because it wasn't engaged completely to begin with. This scenario with the Healey is just that kind of scenario. The rubber shift boot is keeping it from going all the way in. Also as I mentioned, I had to keep my boot from being clipped or fastened to the perimeter of the tunnel opening. Probably because of the age of the boot. Also in my case I noticed that the opening in the tunnel is not exactly centered around the pivot point of the shifter. The lower edge of the opening encroaches on the "H" pattern of the shifter. It is easy to see that a stiff boot has no where to go when shifting into 4th. Good Luck with it. You obviously have alot of confidence when tearing into this sort of thing.
    About TV Shows-
    "...you really can't restore a car in 10 days. I don't want to watch a race where people have to restore it in a week. It's not going to drive, and those cars never work. In real life, it takes years to get it right. " Jay Leno.

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    Yoda
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    Re: Gaskets and clearances

    Quote Originally Posted by vette View Post
    ... You obviously have alot of confidence when tearing into this sort of thing.
    I didn't, until I got some encouragement from Randy F and Tom Monaco, who both generously offered to help with advice, and Magnus Karlsson's videos, which are very informative (and entertaining). I'm actually more confident about getting the OD back together correctly; once you understand the principle of operation and see the parts it makes sense. The gearbox has a lot of fiddly bits that have to be 'just so' to avoid problems, but we've gone through it before and it worked for over 100K miles. I got a lot of feedback on the jumping out of gear problem; it appears to be fairly common as DWR sells shifting hubs--on backorder--that they claim helps solve the problem. The problem appears to be due to one or more possible culprits:

    - alignment of the bellhousing to the rear engine plate. Although I installed the second, previously missing dowel bolt my input shaft (heh) is worn a bit at the tip, which could contribute to this.

    - end play. There is a distance piece with a collar that was worn; apparently this serves as a thrust washer as well. New on order from DWR.

    - stiff/improperly installed shift boot. If, after all the repairs and improvements, it still jumps out of gear I'll reverse the boot; I want to install nipple down first to see if I've totally fixed the problem

    - a couple of knowledgeable people have cited 'end play,' which led me to the too thick gasket possibility. I'll be paying close attention to this aspect.

    My synchros were worn, maybe 70-80%, and the layshaft and its bearings and the OD accumulator and thrust bearing were showing wear as well, so overall it'll be a good thing to have a fresh gearbox and OD to go with the 'new' engine. I'm 64, so if I can get another 30 years/150K miles out of this car I'll be happy

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