View Full Version : rear-end woes

08-13-2000, 12:27 AM
Hope somebody can help me here.
I've got my '69 GMC upgraded to a 350. Now I have lots of power, very fun, all that.
Problem... I still have 6 cylinder gearing.
This thing is geared like a tractor. I didn't notice it so much when it was a six (maybe because I could never keep it running long enough) but now I need another gear or three. I don't think a different trans is going to cut it so I'm thinking new rear end.
I've noticed some of you guys bragging about speeds up to 120 mph. If I did over 60 the engine would jump out of the dog-house and slap me! What are you guys running for gears? I've also spotted somebody talking about a factory 4:11 posi in these cool old boxes. How can you tell? Can anyone point me to a rearend that would work better, from another type of vehicle even? Can anyone tell me how I'd recognize what rearend a van like these has if I find one?
Help me? Please?

08-13-2000, 12:51 PM
I'm the guy doin 120 mph....but that was with a 350 that was built to rev to 6000rpm. The stock rear end ratios were 3.23, 3.73 and 4.11. Remember, in the 60's these were work vehicles and needed low end grunt to get the payload rollin. Posi (limited slip in GM speak) was an option on all models. Any rear end shop can install nearly any ratio available, since these are GM 10 bolt or 12 bolt rears. By the way, did you upgrade to a V8 radiator or get at least a 4 row core installed on your six banger tanks? Do it now, before you destroy that 350, I have a $4000 lump on an engine stand cuz I didn't.......

[This message has been edited by Vanner68 (edited August 13, 2000).]

08-13-2000, 04:44 PM
Congrats on that speed, Vanner68! You are a braver man than I. I've gone that fast before (once!) but in a van?(shudder)
Thanks for the heads up on the radiator. I had noticed the topic coming up on the bulletin board often & had resolved to save up for a re-core, but it's good to know people care. So far the van is running a little on the warm side of where I like it, but nothing too bad...and actually cooler than the old 6. I'm keeping a close eye on the temp guage and sticking to short trips for now.
Do you have any idea how to tell what gearing I have? Or any reccomendation on a good gear ratio to look for?
Thanks again

08-14-2000, 08:13 PM
If you don't still have the build sticker in the right side wall above the wheelwell, there may be a metal tag under one of the cover bolts on the rear end. Car Craft sept. issue has a formula to figure it out from tire size, speed and rpm's, but I can't find my issue right now.
3.23's aren't a bad choice, will keep the rpm's down to about 3000 at hiway speeds, and with a 350 you'll still have some pulling power. 3.73's are better if you plan to tow a trailer. 4.11's are good for bragging, or yanking those pesky tree stumps out of the yard! http://www.vcvc.org/ubb/biggrin.gif

08-15-2000, 08:09 AM
No sticker, no tag on the rear-end. I suppose I'll have to take a guess at it. Or dig up a Sept Car Craft and a tach. If the 4:11 is a stump-puller though, I suspect that's what I've got. If I could get the tires to stick to the ground I think I could drag about anthing.
What a dilemma...do I keep the legendary 4:11 posi and go looking for a drag strip? Or do I swap it out for better highway driving? Well, I've got enough other things to do to the van, I can think about it for awhile.
Thanks for all the help and info. It definitely gives me a place to start from.

08-16-2000, 03:30 PM
well, you could always put in a TH700-R4 overdrive trans, there is a big debate on this with a lot of info somewhere on this message board......

08-16-2000, 06:40 PM
Yeah, I saw something on that. I'll have to take a closer look. It might make sense to go that route. I'm pretty sure I can find a used transmission cheaper than I can get the rear re-geared. It would be worth trying before I take more drastic measures. Thanks.

08-16-2000, 07:31 PM
By the way...
I went down to the local radiator shop to price a re-core. They said its a piece of cake. They also reccomended adding a spacer behind the fan to push it closer to the radiator (its sits a good 8" back now because of the shorter V8). Seems like a good idea so I thought I'd share.
They also told me about another option. It seems they have available a racing grade product that would make the radiator effectively a five row core and (if I remember right) triples the fins per inch. They use this stuff in monster-horse race engines and swear that it will cool ANYTHING!
Its pricey, would push my $235 re-core up to about $400, but if heat is a big issue in these vans it might be worth consideration.
Any thoughts?

08-18-2000, 08:17 PM
It's unnecessary with a stock 350, but if you are even considering performance mods, it's well worth it! Also, run a fan shroud, it helps to "seal" the airflow from the fan. An added benefit is it keeps your hands out of the fan! http://www.vcvc.org/ubb/biggrin.gif

08-20-2000, 05:33 PM
Since my 350 is a mild rebuild, I'll probably stick with the standard re-core for now. It seems to have worked well for others (judging from the message board) and it will be some time to come before I'm likely to do anything strange to the engine. Too many other things to tackle first. (Bodywork, interior, suspension, etc., etc.)
I can appreciate what you mean about the fan shroud keeping the fingers out of trouble though! A few days ago, I snapped the cobbed-up throttle cable I was using and had to drive home working the throttle by hand. Those spinning fan blades were far to close for my comfort!
By the way, I want you to know that all the advice and suggestions are greatly appreciated. Thanks!

08-26-2000, 11:13 PM
How about a 4;56 http://www.vcvc.org/ubb/smile.gif

Thats what I;m running behind my 350!

It's a bit revy at 3200 rpm at 60 MPH but I'm getting almost 13 Miles per Gallon so thats not too bad! considering

I may leave the gears in I plan to set up a big trailer to tow and I haul a TON (literally) if stuff around sometimes.....the van wieghs over 5000 GVW all the time

The rear end I used is 14 bolt out of a mid seventies one ton pick up.

At least the 4:56's make speeding tickets less likely


08-28-2000, 06:50 AM
Isn't that even lower geared?
I really don't need towing power, but the 13 mpg sounds good for a 350. I couldn't get anywhere near that with the old straight six. The thing was the biggest gas-hog I've ever seen.
Did the truck rear-end need to be modified? Or was it a simple bolt-in?
I would have thought the trucks were wider.

09-07-2000, 01:19 AM
i'm going to put a 4 spd tranny in mine im going to hook it up so my colum shifs my forward gears and im fabracating a second lever for reverse

09-07-2000, 08:18 PM
Second lever for reverse...

09-07-2000, 11:07 PM
Mad elf.....yep that's`even lower......I was thinking when you heard that you might keep the gears you have?

The truck rear end is about 2 1/2" wider......but the spring pads actually needed to be moved farther apart.....shock mounts had to be moved too and I have too narrow the spring saddles to suit the 2" wide springs.....and get new U bolts made up.

While I had it out a put a Detroit Locker in and all new bearings an seals.

I did some calculateing since I posted last and its reveing at 3500 RPM at 60 MPH....but still gets 12 MPG at that speed with the stock Q jet......our gallons are a bit bigger though that would only be about 10 MPG US.

So the tires stick out past the fenders about an inch.....looks pretty good actually http://www.vcvc.org/ubb/smile.gif

09-07-2000, 11:17 PM
there is only linkage for three gears so i have to put a new lever and linkage for the reverse or have no reverse. has any one ever herd of some one puting a big block in their early chevy van because i have a 427 i and i was con sidering puting it in my 67 panel because the inline six just dosent cut it for the power i want and i like some suguestions if some one has done it

09-08-2000, 10:55 AM
Yeah, I get the linkage thing, but wouldn't it be easier to put in an aftermarket floor shifter? Or, if you're fabricating a linkage for reverse, why not fab one for all of them? Plus how would you get the linkage for the forward gears to an "out-of-gear" position to engage the reverse linkage. I'm not knocking what you're trying to do. If you can make it work more power to you. I guess I just can't visualize it.

I'm going to keep my current gearing for now since it is tolerable, marginally, but I'll be doing something about it eventually. I know it could be worse, but I tend to drive a lot & I don't like my new engine winding out quite as much as it is. (I don't have a tach so I couldn't tell you what exactly what rpm I'm running, but I'm used to driving cars, like my AMX that would do 70 at about 1500, so the van seems high revving, even much higher than my pickup was.)
I think I'm liking the idea of the overdrive transmissions as an option, giving me the snap on take-off still, but getting the cruising rpms down. If I can find one, it sounds like an easier swap than the rear-end too. If I go for a new rear-end, maybe one that's a litter narrower from a car would be good, then I could tub the wheel wells & put some fatter tires on it. (Too many ideas, too little time & money!)
When you swapped the rear, did you have any trouble with the offset I've been hearing about on the van drive train?

09-09-2000, 03:50 PM

I put a 396/375 with a turbo 400 into a '69 108" Panel many, many years ago. I never got around to swapping out the original 6 cyl. rear end, but it was great for burnouts. I moved the engine back about 1.5 feet. Open the side doors, there's the doghouse (I made a new one). The driveshaft was about 18" long as I recall. All that weight right in the middle of the van made for great handbrake turns, even with the leaf springs. It was a low-budget project and I was a stupid kid, but what a great ride... a real sleeper.

09-09-2000, 08:26 PM
Wow! I would love to get the doghouse out from between the seats. Unfortunately, my van being a 90", I don't think I could move the engine back unless I to the driveshaft out & just welded the universal joints together.
But maybe... Hmmm... ((Insane cackle)) Can we say torque? Sure we can!

09-10-2000, 02:51 PM
to put in reverse you shift the forwad gears into reverse my dad did it in a bel-air he is the one who told me ho to do it. jtclark i have a 67 90 pannel do you think i could iput a 427 in it with out moving the dog house

09-10-2000, 02:54 PM
oops should have read that last one thrugh to put it in reverse you shift the forward gears into nutral

09-11-2000, 11:01 PM
Mad Elf:

That's funny you metioned the offset....I never knew about it untill a few weeks ago reading here......Even after the engin tranny rearend swap I never knew there WAS an offset......so no it was no problem.....I used the stock top tranny mount to line up the engine/tranny assembly so I still retained the offest without knowing it.....the drive shaft is about 20" long and the offset does not bother it....incedently I made the drive shaft myself...Remember the tranny is from a 79 Capris and the rear end from 76 chev 1 ton...I had both drive shafts (Capris and 1 ton) and just cut them both with a pipe cutter......I then stuck the Capris one inside the 1 ton (it was jst the right size) and welded them up....works great!!

If you want a good shop can make up a full drive shaft only 6 inches long too.

The over drive is a good idea....I want to get one but they are just way too much money.......I was reviewing TH700R trannys and now think (if rebuilt properly) they would be fine......bearing that in mind a gear swap to one set slower and the 700R would make the first gear ratio the same (the 700R has real low first) and the over drive just right for hiway.

I rebuilt the TH350 I have myself and hate to change it so I will explore the over drive some more

09-12-2000, 01:21 PM
6" driveshaft you say?
That means I could slide the engine back about a foot. If a got an electric fan to take up less room & slid the radiator back too, still keeping an air slot between the seats...
It could be narrower than the V8 doghouse...
I could move the seats inward a couple of inches to fit my fat butt in without being mashed up against the door...
All right...where's my tape measure?