Driveline vibrations, '76 Cosworth, Saginaw + 4.10

Moderator: Moderators

Driveline vibrations, '76 Cosworth, Saginaw + 4.10

Postby stembridge » Wed Aug 08, 2018 6:14 pm

I recently purchased 1976 Cosworth Vega #2196, which has its original Saginaw 4-speed but with 4.10 posi gears swapped in by the PO for autox. I'm looking for a set of 3.73 gears to make it a little less frantic driving on the highway.

I'm getting a lot of drivetrain vibration that peaks between 50-70 mph (indicated, the speedo reads about 17% fast due to the 4.10 gearing). I have a lot of end play in the driver-side rear axle (not measured, but feels close to 1mm). The pass. side is a lot tighter. The input shaft also has some play. U-joints were pretty dry when I greased them while doing my first engine oil change, but not sloppy loose.

The tires that came with the car were 18 years old and have been replaced with new T/A Radials, machine balanced (my rural tire shop can't do road force balancing). Wheels appear to be straight and true as observed running at idle in 4th gear while on jack stands.

So before I start chasing things at random, does anyone have suggestions on what to look at first? Would the end play be suspect? I'll plan to fix that when I swap the gears, of course.

Oh, the car has dual Webers, and I have yet to sync them as it runs great as-is - I've been told they can set up some engine vibration if not in sync.

Since this is my second post here, for background, my first car (high school) was a '71 notchback that got a sleeved engine with tube headers and a GT cam - could chirp second gear all day long with the Opel 4-speed. In college, I swapped in a Buick 3.8l and automatic. My brothers had a pair of Kammbacks ('72, '73), and I had a '73 hatch for parts. Those are all long gone, of course.

Anyway, thanks for any suggestions before I dig into it.

es

Image
2018 Buick TourX
2015 RAM 2500 4x4
1963 Volkswagen Type I
1962 Volkswagen Type I Sunroof
User avatar
stembridge
 
Posts: 13
Joined: Sun Jul 15, 2018 3:56 pm
Location: The Middle South


Re: Driveline vibrations, '76 Cosworth, Saginaw + 4.10

Postby dindin » Thu Aug 09, 2018 9:12 am

Hi, My 75 Cos Vega had vibrations at about 50 MPH also, turned out to be loose bolts on the rear sway bar, for some reason at about 50 MPH or so it made the whole car vibrate like a son of a gun..

Al
dindin
 
Posts: 550
Joined: Wed May 21, 2014 10:01 am

Re: Driveline vibrations, '76 Cosworth, Saginaw + 4.10

Postby cjbiagi » Thu Aug 09, 2018 9:24 am

Vibrations can be tricky. Obviously wheel and tire balance are first to check. Can you tell if it seems to be coming from the front or rear of the car? Sometimes swapping wheels front to back can help diagnosing a problem. It could also be worn shocks, suspension control arm bushings, worn steering components, out of balance driveshaft, worn output bushing on the trans, worn u joints. .....yeah, you get the idea, it could be a lot of things. I would also look at the condition of the rubber engine and trans mounts. It's frustrating trying to find the source sometimes but if you can take a close inspection under the car for worn or loose components that would be my best suggestion at this point. If the rubber components on the car have never been replaced you need to take a real close look at those. You may also want to check the front wheel bearing adjustment, too loose could cause a wobble but don't overtighten either. There is a normal amount of endplay in the axles with a C clip design, it can seem excessive but I doubt that is your vibration issue.
Clyde.........75 Monza 2+2
User avatar
cjbiagi
 
Posts: 8608
Joined: Sun Jun 25, 2006 2:37 pm
Location: Glenwood, Illinois

1975 Chevrolet Monza

Re: Driveline vibrations, '76 Cosworth, Saginaw + 4.10

Postby stembridge » Thu Aug 09, 2018 1:24 pm

Good input... I'm pretty sure I can rule out wheels/tires, as I have two sets and both act the same way at the same speeds. I have the new T/As on right now, the other set has sticky autox tires mounted.

The PO did a bare shell resto in 1999 (including engine rebuild), and only put about 6,000 miles on it until I bought it a couple months ago. Rubber components are probably hard, but shouldn't have appreciable wear unless he used the originals when it was rebuilt. Looks like I need to start and the front and work my way back and see how worn everything looks or if I have anything that needs a tighten.

Thanks,

es
2018 Buick TourX
2015 RAM 2500 4x4
1963 Volkswagen Type I
1962 Volkswagen Type I Sunroof
User avatar
stembridge
 
Posts: 13
Joined: Sun Jul 15, 2018 3:56 pm
Location: The Middle South

Re: Driveline vibrations, '76 Cosworth, Saginaw + 4.10

Postby cjbiagi » Thu Aug 09, 2018 1:42 pm

Yeah, it's process to narrow it down. It seems like others have had vibration issues so please keep us posted with your findings, it may help someone else down the line. You never know what a previous owner may or may not have done. If you can rule out wheels that's good but now it points to shocks, driveshaft, worn rubber mounts, u joints etc. Good luck.........
Clyde.........75 Monza 2+2
User avatar
cjbiagi
 
Posts: 8608
Joined: Sun Jun 25, 2006 2:37 pm
Location: Glenwood, Illinois

1975 Chevrolet Monza

Re: Driveline vibrations, '76 Cosworth, Saginaw + 4.10

Postby Bullet » Tue Aug 14, 2018 2:32 pm

Don't forget some technology, a GoPro camera mounted at different angles under the car may help pinpoint the location of the vibration to close in on the problem. My son uses one quite a bit while autocrossing to help make adjustments.
User avatar
Bullet
 
Posts: 162
Joined: Fri May 25, 2012 10:46 am
Location: Bristol TN just 2 miles from Thunder Valley

Re: Driveline vibrations, '76 Cosworth, Saginaw + 4.10

Postby stembridge » Tue Aug 14, 2018 3:07 pm

Bullet wrote:Don't forget some technology, a GoPro camera mounted at different angles under the car may help pinpoint the location of the vibration to close in on the problem. My son uses one quite a bit while autocrossing to help make adjustments.

Great idea... thanks!

es
2018 Buick TourX
2015 RAM 2500 4x4
1963 Volkswagen Type I
1962 Volkswagen Type I Sunroof
User avatar
stembridge
 
Posts: 13
Joined: Sun Jul 15, 2018 3:56 pm
Location: The Middle South

Re: Driveline vibrations, '76 Cosworth, Saginaw + 4.10

Postby cosvega76 » Wed Aug 15, 2018 8:29 am

Here's an alternative to changing the rear gears:

https://www.ebay.com/itm/Chevrolet-Cosw ... 6000&rt=nc


Chuck
cosvega76
 
Posts: 2739
Joined: Mon Jul 03, 2006 8:36 am
Location: Moscow Mills, MO

1973 Chevrolet Vega GT

Re: Driveline vibrations, '76 Cosworth, Saginaw + 4.10

Postby stembridge » Wed Aug 15, 2018 10:21 am

cosvega76 wrote:Here's an alternative to changing the rear gears: ....

Chuck


Saw that last month, actually. Decided that the dog-leg 1st and other known issues with the T-50 strike it from my list. The guy selling that one went to a T-5 instead, which says something in and of itself!

es
2018 Buick TourX
2015 RAM 2500 4x4
1963 Volkswagen Type I
1962 Volkswagen Type I Sunroof
User avatar
stembridge
 
Posts: 13
Joined: Sun Jul 15, 2018 3:56 pm
Location: The Middle South

Re: Driveline vibrations, '76 Cosworth, Saginaw + 4.10

Postby dindin » Wed Aug 15, 2018 12:26 pm

I drove a Ferrari that had first gear like , kinda felt weird but got used to it pretty quickly.. :lol:
I read it has issues that caused it to sieze or something, but it can be fixed.., I also read it makes a big difference in the way a cosworth moves along..

Al
dindin
 
Posts: 550
Joined: Wed May 21, 2014 10:01 am

Re: Driveline vibrations, '76 Cosworth, Saginaw + 4.10

Postby cosvega76 » Thu Aug 16, 2018 8:18 am

stembridge wrote:
cosvega76 wrote:Here's an alternative to changing the rear gears: ....

Chuck


Saw that last month, actually. Decided that the dog-leg 1st and other known issues with the T-50 strike it from my list. The guy selling that one went to a T-5 instead, which says something in and of itself!

es


I found a parts car and put a T-50 in the Cosworth I had. Mine was a 4-speed with a 3.73 gear. I really liked the T-50 better since I didn't have to slip the clutch so much to get going from a stop. It wasn't that bad getting used to the shift pattern, and it was useful when I was high-speed autocrossing the car, as it was a straight shot between 2nd and 3rd where I spent most of my time.

Comparing the gear ratios between the CV with the T-50 and 3.73 and my Miata, I would have considered going to the 4.10 because that would have complemented the power band of the CV better, and still have the overdrive for highway cruising.


Chuck
cosvega76
 
Posts: 2739
Joined: Mon Jul 03, 2006 8:36 am
Location: Moscow Mills, MO

1973 Chevrolet Vega GT

Re: Driveline vibrations, '76 Cosworth, Saginaw + 4.10

Postby stembridge » Sun Aug 19, 2018 4:49 pm

So I learned from the PO yesterday that #2196 was factory ordered with the Saginaw and 4.10 posi - I had misunderstood him when I bought the car. Apparently it wasn't that rare for CVs to be ordered that way.

es
2018 Buick TourX
2015 RAM 2500 4x4
1963 Volkswagen Type I
1962 Volkswagen Type I Sunroof
User avatar
stembridge
 
Posts: 13
Joined: Sun Jul 15, 2018 3:56 pm
Location: The Middle South

Re: Driveline vibrations, '76 Cosworth, Saginaw + 4.10

Postby hammerdown7 » Sun Aug 19, 2018 7:56 pm

I don't believe that was an option. I'll see if I can confirm that.
Dick

By the way, being a CV owner of a number of the cars for the past 40 years and an active CVOA member I have only seen two Cosworths running the 4-speed with a 4.10, both were autocross cars that were changed by their owners. Also there have been 5 or 6 cars that were raced in either SCCA and/or IMSA that the owners switched rear axles between the 3.73 and 4.10's depending on the road courses where they were raced.
User avatar
hammerdown7
 
Posts: 3805
Joined: Mon Jun 26, 2006 7:53 pm
Location: Clawson, MI

1976 Chevrolet Vega Cosworth

Re: Driveline vibrations, '76 Cosworth, Saginaw + 4.10

Postby stembridge » Mon Aug 20, 2018 7:29 am

I'd appreciate it if you could confirm... I could be misremembering, but I thought the PO told me (when I picked the car up) he had swapped the rear gears to 4.10 posi (for autox), and was unable to find the right speedo gear to compensate - which jives with my speedo reading about 16% fast.

But when I asked him a couple days ago if he had kept the 3.73 gears , that's when he said the car came with the Saginaw/4.10 posi... so either he's misremembering, or I am.

Either way, it would be nice to know which scenario was/is more likely. I'm leaning toward putting 3.73s back in since I only autox once or twice a year, but will be cruising to C&C or car shows much more frequently. 4K RPM @ 60MPH is pretty frantic!

es
2018 Buick TourX
2015 RAM 2500 4x4
1963 Volkswagen Type I
1962 Volkswagen Type I Sunroof
User avatar
stembridge
 
Posts: 13
Joined: Sun Jul 15, 2018 3:56 pm
Location: The Middle South

Re: Driveline vibrations, '76 Cosworth, Saginaw + 4.10

Postby hammerdown7 » Mon Aug 20, 2018 7:58 am

My records on the car says that it was a bare shell restoration in 2000 and Joe is a standup guy. I would say when he got the car it already had the 4.10 when he bought it.

Dick
User avatar
hammerdown7
 
Posts: 3805
Joined: Mon Jun 26, 2006 7:53 pm
Location: Clawson, MI

1976 Chevrolet Vega Cosworth

Next

Return to Transmission and Driveline Tech

Who is online

Users browsing this forum: No registered users and 12 guests

cron