TH400 Trans bellhousing bolts

[Corvette1974]

Hello.


I looked under my 1986 M1028 today and noticed that two of the trans to engine bellhousing bolts are missing. I need to replace them.

What size/type are they, and what is the torque spec for them? Do I need any form of washer for them?

Will

 

[hndrsonj]

Pull out one of the bolts that's still in there, measure it and replace with the same size grade 8 bolt. I've never "torqued" one, just get it tight. I'd put a lock washer on it.

 

[rlwm211]

Take one out of the ones that are left and go to a hardware store. Be sure to use at leastr grade 5 or better. A lock washer would be recommended as well.

 

[Corvette1974]

Pull out one of the bolts that's still in there, measure it and replace with the same size grade 8 bolt. I've never "torqued" one, just get it tight. I'd put a lock washer on it.

Take one out of the ones that are left and go to a hardware store. Be sure to use at leastr grade 5 or better. A lock washer would be recommended as well.

Alright, I'll go pull one out and get a few new grade 8 bolts and lock washers. I'll replace all of the ones I can easily get to.


Thanks,
Will

 

[Matt65]

The top passenger side bolt was the most difficult for me to get to. I had 1 in bad shape I replaced by going to AutoZone.

 

[Corvette1974]

Pull out one of the bolts that's still in there, measure it and replace with the same size grade 8 bolt. I've never "torqued" one, just get it tight. I'd put a lock washer on it.

Take one out of the ones that are left and go to a hardware store. Be sure to use at leastr grade 5 or better. A lock washer would be recommended as well.

The top passenger side bolt was the most difficult for me to get to. I had 1 in bad shape I replaced by going to AutoZone.

Luckily that one is still there, I'm just going to tighten it. I got the bottom passenger side one out for the example. A 14mm socket fit it perfectly, but when I got it out it has three dashes on it. This indicates that is is a grade 5, SAE bolt, not metric (correct?). I read that these trucks are metric, but they definitely seem to be the standard 80's SAE/metric mix. Which is correct and what parts on the truck are metric vs SAE?

Either way, it seems I need three new grade 8 SAE bolts with lock washers and maybe some blue loctite, and I'll be good to go.

Will

 

[rlwm211]

As I recall, 3/8 SAE coarse and 1-1/2 inches long but I am not absolutely sure so I recommended to match to one that is already there.

Here in my shop I probably have a couple of dozen of these from all the years I was building and rebuilding cars and trucks

 

[Corvette1974]

As I recall, 3/8 SAE coarse and 1-1/2 inches long but I am not absolutely sure so I recommended to match to one that is already there.

Here in my shop I probably have a couple of dozen of these from all the years I was building and rebuilding cars and trucks

Yeah, you're right on the size, that's what it seems to be to me. I'll get some new bolts tomorrow, throw them in and tighten all of the existing bolts.

This is kind of unrelated, but should I retorque my starter bolts and brace bolts? The truck came with the starter/brace, I havent touched it. Is it the standard 30 Ft/Lbs?

Will

 

[spicergear]

14mm fits as they're 9/16. A lot of times people cheat and don't put the top two in because they're hard to get to. Good way to crack the transmission bell on the 400's. A buddy had that happen on a truck her bought, had to pull the 400 to get it welded. Have run across it a couple other times too.

 

[Corvette1974]

14mm fits as they're 9/16. A lot of times people cheat and don't put the top two in because they're hard to get to. Good way to crack the transmission bell on the 400's. A buddy had that happen on a truck her bought, had to pull the 400 to get it welded. Have run across it a couple other times too.

Yeah, the top ones seem fine. What is the best way to access the top top ones, from the engine bay or underneath? I just have to tighten them.

Will

 

[Gunfreak25]

Yep, they are 3/8 coarse thread 1 1/2". They don't have to be fancy partially threaded bolts or anything. The dowel pins are what take all the load, the bolts are just there to keep things clamped together. I torque mine to 35 lbs.

 

[mudman]

12" extension and a universal joint gets the top ones tight!!

 

[bearboley]

Yes, a very long extension and a swivel socket is your friend.

 

[Matt1031]

Yeah, the top ones seem fine. What is the best way to access the top top ones, from the engine bay or underneath? I just have to tighten them.

Will

I use a "transmission extension" from underneath. It's 1/2" drive and fat so it doesn't flex/twist and lose torque like long or multiple 3/8 extensions would, but it has a 3/8 male end that's well suited for smaller sized impact swivels. Mine's from Cornwall, but a few different tool companies make them. Looks like this:
1/2"F-3/8"M Drive, transmission extension Adapter 35'' OAL- SK-Tools-Air Compressors & Air Tools-Impact Socket Accessories

If you R&R transmissions on a regular basis, it's the only way to fly.

 

[chevyCUCV]

Yeah, the top ones seem fine. What is the best way to access the top top ones, from the engine bay or underneath? I just have to tighten them.

Will

I climb on top of the engine and get them with a socket on a ratchet with the flexible head, or a wrench.

 

[camogriz]

Use a really long extension and a swivel on the socket. It is no problem to just tighten the very top bolts from the bottom. As far as the bolts being standard and not metric thread, all the American carmakers used both types of bolts on their vehicles during the 1980's. It seemed to be a transition period from standard to metric thread. All CUCV's have both standard and metric thread bolts throughout the vehicle.

 

[Corvette1974]

Alright sounds good. I'll go at it with a swivel socket and some extensions (which when combined with other extensions my friends and I call the "Alaskan Pipeline"!)

I'll let you know hoe I make out with it.

Will

 

[Corvette1974]

Ok so I have a problem. I bought three new bolts. The one that I took the example bolt out of, I tried to install and tighten it, and the threads in the hole seem to be stripped. It tightens then loosens. The other two holes on the driver side dont seem to want to accept the bolt. The bottom one "threads" but gets pretty hard to thread in, and the top one doesnt even want to start. What should I do about this?

Will

 

[Bob H]

1. Verify that you have the correct length 3/8-16 bolts.
2. Rather than chance a broken tap in the block, take a new bolt and cut a cleaning groove or two length wise up the thread. Srew the bolt into the holes, backing it out often. Don't force it.
If you can get bolts secure in all but the one stripped hole, you should be ok.
If not, well it's time to drop the trans or pull the engine and repair the threads in the block.

 

[Corvette1974]

1. Verify that you have the correct length 3/8-16 bolts.
2. Rather than chance a broken tap in the block, take a new bolt and cut a cleaning groove or two length wise up the thread. Srew the bolt into the holes, backing it out often. Don't force it.
If you can get bolts secure in all but the one stripped hole, you should be ok.
If not, well it's time to drop the trans or pull the engine and repair the threads in the block.

The bolt is a 3/8-16 and it's 1 1/2 inches long. It is actually a tad larger than the one I took out. I'm going to go take another look at it and see If I can see any problems in the thread/hole.

Will