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35 P-8 rear end gear change


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Yes, a 1935 Eight would normally be 4.55. 4.89 "mountain gears" and 4.11 "plains gears" were also offered by Pontiac.

 

Your options are limited. This is not an economical change. I am in the midst of building a taller 1936 axle with a 3.82 ring and pinion. 1936 is either almost identical to yours, or identical if you happen to have a late 1935 car. The design of the axle is like Chevrolet Master and the same and ring and pinion interchange for late 1935-1936 Pontiac, late 1935-36 Chevrolet Master, and late 1935-39 Chevrolet 1/2 ton. Early 1935 is the same too, except for the pinion and rear pinion bearing. The pinion must stay with the ring gear it came with.

 

This implies that the ring and pinion and some internal parts interchange between all of the above. The axle assemblies and torque tube length and drive shaft length and diameter vary so whole assemblies do not interchange. Also do not confuse Chevrolet Standard with the above list. Nothing from Chevrolet Standard fits. Always check the part numbers.

 

Extant ratios are 4.89, 4.55. 4.44, 4.11, 3.82 (hard to find), 3.36 (aftermarket, only a handful made, expensive, and nearly impossible to find).

 

I can go on about this at length if you like, I have explored this rabbit hole as deep as it goes, and will have more time later tonight when I get home.

 

Here is some quick advice if you want to make a change as economically as possible. The default Chevrolet ratio is 4.11, and that is the same as a Pontiac "Plains" gear set. Buy up multiple used 1935-36 Master and 1935-39 1/2 ton rear axles that have been discarded by street rodders until you have a good ring and pinion set (it will be 4.11), and the pinion is still solidly riveted to a good usable differential case. You read that right, the ring gear is cold riveted on, and no one will rivet it for you. Make sure the rivets are not loose. If they are, keep looking.

 

I think your housing and torque tube assembly will work no matter what, but I am unsure on that point. If your ring and pinion are late 35-39, and your car is early 35, you may need a late 1935-36 Pontiac housing and torque tube assembly. Use new bearings. All are discontinued except one, but can be found on Ebay and elsewhere as new old stock. Use tapered roller bearings on the carrier where it meets the case. Those are also discontinued, but easier to find and cheaper than the original balls, and they have a less catastrophic failure mode.

 

Welcome to the forum!

 

Edited by Bloo (see edit history)
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Bloo

Thanks for the info. My car is A 2011 #33385 so I would expect it may be a late one as the P8 was 1001 to 42561 in my Pontiac book. It doesn't show part #s for 1935 so I had no idea what to look for. I have a Chevrolet book that lists the 37-39 GC,HC,JC 42-11 set 602477 and guess I will look for that in hopes it will fit. 

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Hi David.

 

Chevrolet 602477 is indeed the part number for the 3.82 ring and pinion set for late 1935-36 Chevrolet Master and late 1935-39 1/2 ton. 4.11 is Chevrolet 602476. 602477 are a bit hard to find, as they were an unusual Chevrolet gas mileage option and rare even when they were a current product. I heard of a set in the Netherlands from an old VCCA forum thread, where a member had opted not to buy it because the price was rather high, and the shipping would have been high as well. I contacted that poster asking for the information about the guy in the Netherlands. The poster told me he had acquired a 3.82 set on ebay, decided not to use them, and would sell them. I bought that set from him and never found out about the set in the Netherlands. My set is definitely not GM parts, they are aftermarket of some kind and have had the maker's mark ground off.

 

Pontiac offered 4.89 (Mountain option), 4.55 (eights), 4.44 (sixes), and 4.11 (plains option). Chevrolet offered 4.11 (99+% of everything they made) and 3.82 (economy option).

 

The difference between early and late 35 is the rear pinion bearing. Early 1935 use a ball bearing. Later versions use a Hyatt roller bearing. According to my parts manual the change was made at rear axle number 1452022 on eights and axle 1451985 on sixes.

 

There is one more complication for 3.82, at least if you have a late 1935. Because Pontiac never offered the ratio, no speedometer gears ever existed for it. You can use an external speedometer gearbox for correction, but not if you want the conversion completely invisible. My speedometer gears are some custom modified Chevrolet gears for who knows what from the postwar era, and have not been tried yet. Both gears must change. Pontiac changed the transmission in late 35, and the speedometer gears are unique, not similar to any other GM cars. They fit through 1936 and then change again.

 

If you have an early 1935 transmission, that one is based on a Chevrolet design and it is possible that some Chevrolet gears might fit it, I don't know about that. The transmission design changed to a more Buick-like one at engine number 8-27163 (eights) and number 6-46474 (sixes).

 

Get the 35-36 Pontiac shop manual if you don't have it. There seem to be many of them out there on ebay, etc., both original and reprint. I suggest getting an original as I suspect the pictures will be more useful. A 36 (or maybe 35) Chevrolet manual would also be useful. On the oldcarmanualproject Chevrolet page, there is a 1934 manual and a 1938 manual. These are quite useful if you understand that the 1934 Master axle is the same as design as yours except for the weird 1934 pinion attachment, and in 1938 ONLY the 1/2 ton axle is like yours. There are parts books over there as well.

 

http://chevy.oldcarmanualproject.com/

 

P.S. I have been fumbling around with this 3.82 project for nearly 4(!) years now and it isn't done. It probably will be this spring. I have spent at least as much as an overdrive costs. If I had looked for and found a Chevrolet 4.11 with the ring gear already riveted on, this could have been done and on the road a long time ago.

 

P.P.S. You might find this thread interesting, it is about making a custom axle for a 1936 1/2 ton with 3.55. The idea is to take a 1937 Chevrolet Car rear axle, which is the new for 1937 axle design, move the hinge points where the axle meet the springs to the correct spacing, then use a 1953-54 center section from a Powerglide equipped Chevrolet, after cutting the torque tube and driveshaft to the correct length and splicing, using the 1937 spline up at the front so the u-joint will connect. Since it was done for a 1936 1/2 ton, it does not address how to get the much better Pontiac (Bendix) brakes mounted, but I assume it is possible. Later on the thread morphed into a thread about my 3.82 project.

 

https://vccachat.org/ubbthreads.php/topics/395256/1.html

 

 

 

Edited by Bloo (see edit history)
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So my car is the late transmission. I'll probably keep looking and go for a 411 if one comes up. It would be a lot better than 455. Checked with a couple places and they have no 382 sets. Maybe by next winter I can find something. Going to drive it some this summer, guess ill just go 50 this year.

 

A shot of my car from my son's engagement pics.

 

Thanks

 

20201107_163217b.jpg

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57 minutes ago, David Osier said:

I don't have extra any very good ones. I've seen a few nos on ebay and never won one yet. The last used set I saw brought $250.

I'll post a pic if I can find the box they are in.

David, the last decent one i saw on ebay was probably 4yr ago, i missed it, $95, maybe i`m looking in the wrong place. I did see a couple not long ago with severe curb rash, i don`t know why the seller would even list them.  Thank you

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